Alterations in Wnt–β‐catenin and Pten signalling play distinct roles in endometrial cancer initiation and progression

Endometrioid endometrial cancer arises through a gradual series of histological changes, each accompanied by specific alterations in gene expression and activity. Activation of the Wnt–β‐catenin pathway and loss of PTEN activity are frequently observed in endometrial cancers. However, the specific roles played by alterations in these pathways in the initiation and progression of endometrial cancer are currently unclear. Here, we investigated the effects of loss of Pten and Apc gene function in the mouse endometrium by employing tissue‐specific and inducible mutant alleles, followed by immunohistochemical (IHC) and loss of heterozygosity (LOH) analysis of their corresponding cancerous lesions. Loss of the Apc function in the endometrium leads to cytoplasmic and nuclear β‐catenin accumulation in association with uterine hyperplasia and squamous cell metaplasia, but without malignant transformation. Loss of Pten function also resulted in squamous metaplasia but, in contrast to loss of Apc function, it initiates endometrial cancer. On the other hand, loss of Apc function in the endometrium accelerates Pten‐driven endometrial tumourigenesis. Analysis of compound heterozygous mice confirmed that somatic loss of the wild‐type Pten allele represents the rate‐limiting initiation step in endometrial cancer. Simultaneous loss of Pten and Apc resulted in endometrial cancer characterized by earlier onset and a more aggressive malignant behaviour. These observations are indicative of the synergistic action between the Wnt–β‐catenin and Pten signalling pathways in endometrial cancer onset and progression. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Genome‐wide mutation analysis in precancerous lesions of endometrial carcinoma

Clinicopathological evidence supports endometrial atypical hyperplasia (AH) or endometrial intraepithelial neoplasia as the precursor of uterine endometrioid carcinoma (EC), the most common gynecologic malignancy. However, the pathogenic progression from AH to EC remains unclear. Here, we employed whole‐exome sequencing to identify somatic mutations and copy number changes in micro‐dissected lesions from 30 pairs of newly diagnosed AH and EC. We found that all but one pair of AHs shared the same DNA mismatch repair status as their corresponding ECs. The percentage of common mutations between AH lesions and corresponding ECs varied significantly, ranging from 0.1% to 82%. Microsatellite stable AHs had fewer cancer driver mutations than ECs (5 versus 7, p = 0.017), but among microsatellite unstable AHs and ECs there was no difference in mutational numbers (36 versus 38, p = 0.65). As compared to AH specimens, 19 (79%) of 24 microsatellite stable EC tumors gained new cancer driver mutations, most of which involved PTEN, ARID1A, PIK3CA, CTNNB1, or CHD4. Our results suggest that some AH lesions are the immediate precursor of ECs, and progression depends on acquisition of additional cancer driver mutations. However, a complex clonal relationship between AH and EC can also be appreciated, as in some cases both lesions diverge very early or arise independently, thus co‐developing with distinct genetic trajectories. Our genome‐wide profile of mutations in AH and EC shines new light on the molecular landscape of tumor progression. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Measurement of telomere length in cells from pleural effusion: Asbestos exposure causes telomere shortening in pleural mesothelial cells

We estimated the telomere lengths of neoplastic and non‐neoplastic mesothelial cells and examined their correlation with asbestos exposure and the expression of markers of mesothelial malignancy. Cell blocks of pleural effusion obtained from 35 cases of non‐neoplastic disease (NN), 12 cases of malignant mesothelioma (MM) and 12 cases of carcinomatous effusion due to lung adenocarcinoma (LA) were examined. Fifteen of the 35 NN cases had pleural plaques (NNpp+) suggestive of asbestos exposure, and the other 20 cases had no pleural plaques (NNpp‐). Telomere length was measured using the tissue quantitative fluorescence in situ hybridization method, and expressed as normalized telomere‐to‐centromere ratio. NN cases had significantly longer telomeres than MM (P < 0.001) and LA (P < 0.001) cases. Telomeres in NNpp+ cases were slightly shorter than those of NNpp‐ cases (P = 0.047). MM and LA showed almost the same telomere length. NN cases with shorter telomeres tended to show aberrant expression of epithelial membrane antigen (EMA), CD146, glucose transporter 1 (GLUT1) and IGF‐II messenger RNA‐binding protein 3 (IMP3). These results suggest that telomere shortening and subsequent genetic instability play an important role in the development of MM. Measurement of telomere length of cells in pleural effusion might be helpful for earlier detection of MM.     

Thiopurine‐induced mitotic catastrophe in Rad51d‐deficient mammalian cells

Thiopurines are part of a clinical regimen used for the treatment of autoimmune disorders and childhood acute lymphoblastic leukemia. However, despite these successes, there are also unintended consequences such as therapy‐induced cancer in long‐term survivors. Therefore, a better understanding of cellular responses to thiopurines will lead to improved and personalized treatment strategies. RAD51D is an important component of homologous recombination (HR), and our previous work established that mammalian cells defective for RAD51D are more sensitive to the thiopurine 6‐thioguanine (6TG) and have dramatically increased numbers of multinucleated cells and chromosome instability. 6TG is capable of being incorporated into telomeres, and interestingly, RAD51D contributes to telomere maintenance, although the precise function of RAD51D at the telomeres remains unclear. We sought here to investigate: (1) the activity of RAD51D at telomeres, (2) the contribution of RAD51D to protect against 6TG‐induced telomere damage, and (3) the fates of Rad51d‐deficient cells following 6TG treatment. These results demonstrate that RAD51D is required for maintaining the telomeric 3′ overhangs. As measured by γ‐H2AX induction and foci formation, 6TG induced DNA damage in Rad51d‐proficient and Rad51d‐deficient cells. However, the extent of γ‐H2AX telomere localization following 6TG treatment was higher in Rad51d‐deficient cells than in Rad51d‐proficient cells. Using live‐cell imaging of 6TG‐treated Rad51d‐deficient cells, two predominant forms of mitotic catastrophe were found to contribute to the formation of multinucleated cells, failed division and restitution. Collectively, these findings provide a unique window into the role of the RAD51D HR protein during thiopurine induction of mitotic catastrophe. Environ. Mol. Mutagen. 59:38–48, 2018. © 2017 Wiley Periodicals, Inc.     

Nuclear remodeling of telomeres in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a hematologic cancer characterized by the proliferation of myeloid cells and the translocation between chromosomes 9 and 22, [t(9;22)(q34.1;q11.2)]. At the chronic phase (CP), CML cells present longer telomeres than at the other clinical phases, display arm‐specific maintenance of individual telomere lengths, and are chromosomally stable. We asked whether an alteration of nuclear organization of telomeres, which is associated with genomic instability, occurs in CML cells at the CP. We used fluorescent in situ hybridization of telomeres combined with three‐dimensional (3D) quantification to study the nuclear telomeric architecture of CML cells at the CP. We found that cells can exhibit high telomere numbers, different telomere distributions, and alterations in peripheral or central nuclear location of telomeres. Also, we show that CML cells can be categorized in two groups according to the number of their telomere aggregates (TAs). We propose that the presence of high TAs in some samples is associated with the increased genomic instability and could be an indication of the clinical transitional phase. Also, alterations of nuclear organization of telomeres at the CP confirm that nuclear remodeling of telomeres can occur at an early clinical stage of a cancer. © 2013 Wiley Periodicals, Inc.     

Q‐FISH analysis of telomere and chromosome instability in the oesophagus with and without squamous cell carcinoma in situ

Chromosomal and genomic instability due to telomere dysfunction is known to play an important role in carcinogenesis. To study telomere dysfunction in the surrounding background epithelium of squamous cell carcinoma in situ (CIS) of the oesophagus, we measured telomere lengths of basal and parabasal cells of epithelia with and without CIS using quantitative fluorescence in situ hybridization (Q‐FISH) and our original software, Tissue Telo. Additionally, we assessed histological inflammation and the anaphase bridge index. In non‐cancerous epithelium, telomeres in basal cells were significantly longer than those in parabasal cells, whereas CIS showed a homogeneous telomere pattern in the basal and parabasal cells. Telomeres in basal and parabasal cells were significantly shorter in the background with CIS than in epithelium from age‐matched normal controls. Significant negative correlation was observed between the normalized telomere : centromere ratio (reflected telomere length) and the anaphase bridge index in non‐cancerous epithelia from both normal controls and the CIS background with no histological inflammation. These findings indicate that tissue stem cells may be located among basal cells, and that telomere length distribution in component cell types differs between CIS and non‐cancerous epithelium. We have demonstrated conclusively that oesophageal CIS arises from epithelium with short telomeres and chromosomal instability in the absence of histological inflammation. Copyright © 2010 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

The very long telomeres in <Emphasis Type="Italic">Sorex granarius</Emphasis> (Soricidae,Eulipothyphla) contain ribosomal DNA

Two closely related shrew species, Sorex granarius and Sorex araneus, in which Robertsonian rearrangements have played a primary role in karyotype evolution, present very distinct telomere length patterns. S. granarius displays hyperlong telomeres specifically associated with the short arms of acrocentrics, whereas telomere lengths in S. araneus are rather short and homogenous. Using a combined approach of chromosome and fibre FISH, modified Q-FISH, 3D-FISH, Ag-NOR staining and TRF analysis, we carried out a comparative analysis of telomeric repeats and rDNA distribution on chromosome ends of Sorex granarius. Our results show that rDNA sequences forming active nuclear organizing regions are interspersed with the long telomere tracts of all short arms of acrocentrics. These observations suggest that the major rearrangements that gave rise to today’s karyotype in S. granarius were accompanied by a profound reorganization of chromosome ends, which comprised extensive amplification of telomeric and rDNA repeats on the short arms of acrocentrics and finally contributed to the stabilization of telomeres. This is the first time that such telomeric structures have been observed in any mammalian species.     

Heterozygous mutations in the PALB2 hereditary breast cancer predisposition gene impact on the three‐dimensional nuclear organization of patient‐derived cell lines

PALB2/FANCN is a BRCA1‐ and BRCA2‐interacting Fanconi Anemia (FA) protein crucial for key BRCA2 genome caretaker functions. Heterozygous germline mutations in PALB2 predispose to breast cancer and biallelic mutations cause FA. FA proteins play a critical role in the telomere maintenance pathway, with telomeric shortening observed in FA cells. Less is known about telomere maintenance in the heterozygous state. Here, we investigate the roles of PALB2 heterozygous mutations in genomic instability, an important carcinogenesis precursor. Patient‐derived lymphoblastoid (LCL) and fibroblast (FCL) cell lines with monoallelic truncating PALB2 mutations were investigated using a combination of molecular imaging techniques including centromeric FISH, telomeric Q‐FISH and spectral karyotyping (SKY). Mitomycin C and Cisplatin sensitivity was assayed via cellular metabolism of WST‐1. The PALB2 c.229delT FCL showed increases in telomere counts associated with increased mean intensity compared with two wild‐type FCLs generated from first‐degree relatives (P =1.04E‐10 and P =9.68E‐15) and it showed evidence of chromosomal rearrangements. Significant differences in centromere distribution were observed in one of three PALB2 heterozygous FCLs analyzed when compared with PALB2 wild‐type, BRCA1 and BRCA2 heterozygous FCLs. No significant consistently increased sensitivity to Mitomycin C or Cisplatin was observed in LCLs. Our results are suggestive of an altered centromere distribution profile and a telomere instability phenotype. Together, these may indicate critical nuclear organization defects associated with the predisposition to transformation and early stage development of PALB2‐related cancers. © 2013 Wiley Periodicals, Inc.     

PTEN loss and activation of K‐RAS and β‐catenin cooperate to accelerate prostate tumourigenesis

Aberrant phosphoinositide 3‐kinase (PI3K), mitogen‐activated protein kinase (MAPK) and WNT signalling are emerging as key events in the multistep nature of prostate tumourigenesis and progression. Here, we report a compound prostate cancer murine model in which these signalling pathways cooperate to produce a more aggressive prostate cancer phenotype. Using Cre‐LoxP technology and the probasin promoter, we combined the loss of Pten (Pten^fl/fl), to activate the PI3K signalling pathway, with either dominant stabilized β‐catenin [Catnb^+/lox(ex3)] or activated K‐RAS (K‐Ras^+/V12) to aberrantly activate WNT and MAPK signalling, respectively. Synchronous activation of all three pathways (triple mutants) significantly reduced survival (median 96 days) as compared with double mutants [median: 140 days for Catnb^+/lox(ex3)Pten^fl/fl; 182 days for Catnb^+/lox(ex3)K‐Ras^+/V12; 238 days for Pten^fl/flK‐Ras^+/V12], and single mutants [median: 383 days for Catnb^+/lox(ex3); 407 days for Pten^fl/fl], reflecting the accelerated tumourigenesis. Tumours followed a stepwise progression from mouse prostate intraepithelial neoplasia to invasive adenocarcinoma, similar to that seen in human disease. There was significantly elevated cellular proliferation, tumour growth and percentage of invasive adenocarcinoma in triple mutants as compared with double mutants and single mutants. Triple mutants showed not only activated AKT, extracellular‐signal regulated kinase 1/2, and nuclear β‐catenin, but also significantly elevated signalling through mechanistic target of rapamycin complex 1 (mTORC1). In summary, we show that combined deregulation of the PI3K, MAPK and WNT signalling pathways drives rapid progression of prostate tumourigenesis, and that deregulation of all three pathways results in tumours showing aberrant mTORC1 signalling. As mTORC1 signalling is emerging as a key driver of androgen deprivation therapy resistance, our findings are important for understanding the biology of therapy‐resistant prostate cancer and identifying potential approaches to overcome this. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Impact of oviductal versus ovarian epithelial cell of origin on ovarian endometrioid carcinoma phenotype in the mouse

Endometrioid carcinoma (EC) is a relatively indolent ovarian carcinoma subtype that is nonetheless deadly if detected late. Existing genetically engineered mouse models (GEMMs) of the disease, based on transformation of the ovarian surface epithelium (OSE), take advantage of known ovarian EC driver gene lesions, but do not fully recapitulate the disease features seen in patients. An EC model in which the Apc and Pten tumour suppressor genes are conditionally deleted in murine OSE yields tumours that are biologically more aggressive and significantly less differentiated than human ECs. Importantly, OSE is not currently thought to be the tissue of origin of most ovarian cancers, including ECs, suggesting that tumour initiation in Müllerian epithelium may produce tumours that more closely resemble their human tumour counterparts. We have developed Ovgp1‐iCreER^T2 mice in which the Ovgp1 promoter controls expression of tamoxifen (TAM)‐regulated Cre recombinase in oviductal epithelium – the murine equivalent of human Fallopian tube epithelium. Ovgp1‐iCreER^T2;Apc^fl/fl;Pten^fl/fl mice treated with TAM or injected with adenovirus expressing Cre into the ovarian bursa uniformly develop oviductal or ovarian ECs, respectively. On the basis of their morphology and global gene expression profiles, the oviduct‐derived tumours more closely resemble human ovarian ECs than do OSE‐derived tumours. Furthermore, mice with oviductal tumours survive much longer than their counterparts with ovarian tumours. The slow progression and late metastasis of oviductal tumours resembles the relatively indolent behaviour characteristic of so‐called Type I ovarian carcinomas in humans, for which EC is a prototype. Our studies demonstrate the utility of Ovgp1‐iCreER^T2 mice for manipulating genes of interest specifically in the oviductal epithelium, and establish that the cell of origin is an important consideration in mouse ovarian cancer GEMMs. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Telomere shortening and chromosomal instability in myelodysplastic syndromes

Telomere shortening and chromosomal instability are believed to play an important role in the development of myeloid neoplasia. So far, published data are only available on the average telomere length in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), but not on the telomere length of individual chromosomes. We used a new technique, telomere/centromere‐fluorescence in situ hybridization (T/C‐FISH), which combines fluorescence R‐banding and FISH using a probe against the telomere repeats to measure the telomere length of each chromosome arm in 78 patients with MDS. In line with the previous results, patients with MDS showed significantly shorter telomeres than those of healthy controls. Telomere lengths did not differ significantly between distinct morphological subtypes of MDS. However, there was a significant difference in telomere length between patients with an isolated monosomy 7 and patients with a normal karyotype (P < 0.05). Notably, patients with an isolated monosomy 7 showed significantly longer telomeres than patients with a normal karyotype in many chromosome arms, among them 7p and 7q. Neo‐telomeres were found in two patients with a complex karyotype, in one case at the fusion site of a dic(14;20). Normal and aberrant metaphases of the same patient did not differ in telomere length, thus indicating to telomere shortening as a basic mechanism affecting all hematopoietic cells in patients with MDS. In some MDS subtypes, like MDS with isolated monosomy 7, telomeres may be stabilized and even increase in length because of the activation of telomerase or alternative mechanisms. © 2009 Wiley‐Liss, Inc.     

Conditional Pten knock‐out mice: a model for metastatic phaeochromocytoma

Phaeochromocytomas (PCCs) are neuro‐endocrine tumours of the adrenal medulla that are usually benign, but approximately 10% of patients develop metastases. Malignant PCCs can only be diagnosed with certainty if metastases are present. Here we describe adrenal tumours generated in a Pten conditional knock‐out (KO) mouse model. We characterized the molecular alterations in these tumours and compared them with human PCC. Thirty‐two of 41 (78%) male Psa‐Cre;Pten‐loxP/loxP mice presented adrenal tumours that were shown to be PCC by histology and by immunohistochemical staining for enzymes in the catecholamine biosynthetic pathway. In 6 of 17 investigated mice, histological and immunohistochemical evidence was obtained for the presence of PCC lung metastases. Array comparative genomic hybridization (CGH) analysis of the primary tumours showed loss of chromosomes 6 and 19, which are syntenic to human 3p and 11q. Another frequent alteration found was gain of chromosome 15, which is syntenic to human chromosome 5. The molecular aberrations in the mouse model corresponded to the alterations found in a subtype of human PCC, suggesting that the PCC of the Pten KO mice might be representative of human PCC. The mouse model should allow further studies into the pathogenesis of human malignant PCCs and into therapeutic strategies for these tumours. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

A Reduction in Pten Tumor Suppressor Activity Promotes ErbB-2-Induced Mouse Prostate Adenocarcinoma Formation through the Activation of Signaling Cascades Downstream of PDK1

Loss of function at the Pten tumor-suppressor locus is a common genetic modification found in human prostate cancer. While recent in vivo and in vitro data support an important role of aberrant ErbB-2 signaling to clinically relevant prostate target genes, such as cyclin D1, the role of Pten in ErbB-2-induced prostate epithelial proliferation is not well understood. In the Pten-deficient prostate cancer cell line, LNCaP, restoration of Pten was able to inhibit ErbB-2- and heregulin-induced cell cycle progression, as well as cyclin D1 protein levels and promoter activity. Previously, we established that probasin-driven ErbB-2 transgenic mice presented with high-grade prostate intraepithelial neoplasia and increased nuclear cyclin D1 levels. We show that mono-allelic loss of pten in the probasin-driven-ErbB-2 model resulted in increased nuclear cyclin D1 and proliferating cell nuclear antigen levels and decreased disease latency compared to either individual genetic model and, unlike the probasin-driven-ErbB-2 mice, progression to adenocarcinoma. Activated 3-phosphoinositide-dependent protein kinase-1 was observed during cancer initiation combined with the activation of p70S6K (phospho-T389) and inactivation of the 4E-binding protein-1 (phosphorylated on T37/46) and was primarily restricted to those cases of prostate cancer that had progressed to adenocarcinoma. Activation of mTOR was not seen. Our data demonstrates that Pten functions downstream of ErbB-2 to restrict prostate epithelial transformation by blocking full activation of the PDK1 signaling cascade.The proto-oncogene ErbB-2 (Neu or HER2) is an 185-kDa receptor tyrosine kinase with no known ligand and is the preferential dimerization partner for all members of the epidermal growth factor receptor family. Enhanced ErbB-2 signaling has been demonstrated in a number of cancers, including those of the breast, head and neck, pancreas, and colon, and recently, increased ErbB-2 levels in the absence of gene amplification was shown to correlate with poor prognosis in prostate cancer (PCa) patients with progressive disease.^1,2 In previous studies, we established that increased ErbB-2 membrane expression correlated with increased nuclear cyclin D1 staining in clinical PCa specimens.³ We also established in human PCa cell lines that ErbB-2 induced both cell cycle proliferation and cyclin D1, and that small interfering RNA targeting cyclin D1 blocked a significant proportion of the ErbB-2 or heregulin-induced cell cycle progression. Furthermore, we established that probasin-driven ErbB-2 transgene mice (PB-ErbB-2) presented with high-grade prostate intraepithelial neoplasia, (PIN), a localized adenoma, and induced epithelial cyclin D1 expression; transformation to adenocarcinoma was not observed.³The phosphatidylinositol-3-kinase (PI3K) signaling pathway is a major mediator of receptor tyrosine kinase signaling and plays an important role in controlling cell proliferation and cell survival. Pten is a lipid phosphatase that catalyzes the dephosphorylation of phosphatidylinositol-3,4,5-tri-phosphate and phosphatidylinositol-3,4-bis-phosphate, thereby inhibiting PI3K signaling. Modifications at the pten locus are frequently found in human diseases, and pten is one of the most frequently mutated genes identified in human PCa.⁴ Pten levels were reduced in as many as 50% of the tumors examined,⁵ and haploinsufficiency of pten was associated with early stage PCa.⁶ Additionally, loss of heterozygosity at the pten locus (and thereby loss of Pten expression) has been associated with increased Gleason score and poor clinical outcome.⁷ Mutations in pten may also serve as a molecular marker for metastatic PCa progression in humans,⁸ further supporting the hypothesis that pten is a clinically important PCa tumor suppressor gene.In preclinical models of prostate disease, prostate intraepithelial neoplasia has been observed in mice deleted of candidate tumor suppressor genes, and combinatorial genetic manipulations allow for the accurate modeling of known human genetic lesions in vivo (reviewed in⁹). Mice harboring heterozygous deficiency at the pten locus (pten^+/−) displayed intermittent PIN with long latency.¹⁰ In some models where genetic modification induced PIN, but not adenocarcinoma, the extent of glandular involvement and PCa progression could be induced through the combination of pten haploinsufficiency and alterations in the function of key cell regulatory genes, such as p27Kip1¹⁰ or nkx3.1.¹¹ Pten haploinsufficiency has recently been shown to interact cooperatively with the overexpression of the mTOR regulatory protein Rheb, to induce PCa.¹² Additionally, the targeted homozygous ablation of pten induced latent PCa, which was dependent on the p110β catalytic subunit of PI3K,^13,14 Pten ablation in a p53 knockout background resulted in the induction of early invasive PCa and the loss of cellular senescence,¹⁵ while modeling studies have further established that in FGF8b transgenic × pten^+/− mice where prostate cancer is seen, the expression from both pten alleles was lost.¹⁶To better understand the role of Pten in regulating ErbB-2-induced tumorigenesis in the prostate epithelium, we analyzed the effect of alterations in Pten levels on ErbB-2 signaling both in vitro and in vivo. Herein, we demonstrate that the heterozygous loss of pten when integrated into the PB-ErbB-2 mouse model (PB-ErbB-2 × Pten^+/−) resulted in increased cyclin D1 and proliferating cell nuclear antigen (PCNA) nuclear positivity and decreased disease latency compared with either singly modified genetic model. Notably, the PB-ErbB-2 × Pten^+/−mice also developed prostate adenocarcinomas while retaining Pten expression. Pten re-expression in the Pten-deficient prostate cancer cell line LNCaP inhibited ErbB-2-induced cyclin D1 promoter activity. Mechanistically, modest activation of phosphoinositide-dependent kinase (PDK)1 (phosphorylated at S241) was observed in PIN lesions, and which was further increased in adenocarcinomas. In contrast, the combined activation of 70S6K (phosphorylated at T389) and inactivation of the eIF4E-binding protein-1 (4E-BP1, phosphorylated at pT37/46) was primarily restricted to those glands that had progressed to adenocarcinoma, interestingly however, activation of mTOR was not observed.Collectively, these data indicate a role for Pten in the suppression of ErbB-2-induced prostate epithelial transformation through an inhibition of proteins that function downstream of PDK-1 that are involved in the regulation of cell proliferation and protein biosynthesis.     

Mutations of the RTEL1 Helicase in a Hoyeraal‐Hreidarsson Syndrome Patient Highlight the Importance of the ARCH Domain

The DNA helicase RTEL1 participates in telomere maintenance and genome stability. Biallelic mutations in the RTEL1 gene account for the severe telomere biology disorder characteristic of the Hoyeraal‐Hreidarsson syndrome (HH). Here, we report a HH patient (P4) carrying two novel compound heterozygous mutations in RTEL1: a premature stop codon (c.949A>T, p.Lys317*) and an intronic deletion leading to an exon skipping and an in‐frame deletion of 25 amino‐acids (p.Ile398_Lys422). P4's cells exhibit short and dysfunctional telomeres similarly to other RTEL1‐deficient patients. 3D structure predictions indicated that the p.Ile398_Lys422 deletion affects a part of the helicase ARCH domain, which lines the pore formed with the core HD and the iron–sulfur cluster domains and is highly specific of sequences from the eukaryotic XPD family members.     

Organization of the macronuclear gene-sized pieces of stichotrichous ciliates into a higher order structure via telomere–matrix interactions

Macronuclear DNA of stichotrichous ciliates occurs in small ‘gene-sized’ molecules with sizes of about 0.5 to 40 kb. Each of these molecules is terminated by telomeric sequences of defined length. A single macronucleus contains up to 10⁸ DNA molecules; due to the high concentration of telomeric sequences in this nucleus it is an attractive model to study telomere behaviour. We recently provided evidence that macronuclear telomeres are attached to the nuclear matrix and that this interaction is mediated by the telomere binding protein (TeBP). Using various experimental approaches, we now demonstrate that telomeres as well as both subunits of the telomere binding protein are associated with the nuclear matrix. However, there is no direct binding of telomeric DNA to the matrix but telomere matrix interaction is exclusively mediated by the TeBP. In addition, we show that telomeric sequences adopt in vivo the antiparallel G-quartet structure when bound to the nuclear matrix. These data not only allow us to propose a model for macronuclear architecture but may also be relevant for further analysis of telomere–matrix interactions in higher eukaryotes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Jumping translocations: Short telomeres or pathogenic TP53 variants as underlying mechanism in acute myeloid leukemia and myelodysplastic syndrome?

Chromosomal rearrangements involving one donor chromosome and two or more recipient chromosomes are called jumping translocations. To date only few cases of acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) with jumping translocations have been described and the underlying mechanisms remain unclear. Here, we analyzed 11 AML and 5 MDS cases with jumping translocations. The cases were analyzed by karyotyping, FISH, telomere length measurement, and next‐generation sequencing with an AML/MDS gene panel. Cases with jumping translocations showed significantly (P < .01) shorter telomeres in comparison to healthy age‐matched controls. Additional neo‐telomeres were found in two cases. In total, eight cases showed recipient chromosomes with a breakpoint in the centromeric region all of them harboring a pathogenic variant in the TP53 gene (n = 6) and/or a loss of TP53 (n = 5). By contrast, no pathogenic variant or loss of TP53 was identified in the six cases showing recipient chromosomes with a breakpoint in the telomeric region. In conclusion, our results divide the cohort of AML and MDS cases with jumping translocations into two groups: the first group with a telomeric breakpoint of the recipient chromosome is characterized by short telomeres and a possibly telomere‐based mechanism of chromosomal instability formation. The second group with a centromeric breakpoint of the recipient chromosome is defined by mutation and/or loss of TP53. We, therefore, assume that both critically short telomeres as well as pathogenic variants of TP53 influence jumping translocation formation.     

<Emphasis Type="BoldItalic">Drosophila</Emphasis> telomeres: the non-telomerase alternative

In most eukaryotes, telomeres are composed of simple repetitive sequences renewable by telomerase. By contrast, Drosophila telomeres comprise arrays of non-LTR retrotransposons HeT-A, TART, and TAHRE belonging to three different families. However, closer inspection reveals that the two quite different telomere systems share quite a few components and regulatory circuits. Here we present the current knowledge on Drosophila telomeres and discuss the possible mechanisms of telomere length control.     

PTEN loss and KRAS activation leads to the formation of serrated adenomas and metastatic carcinoma in the mouse intestine

Mutation or loss of the genes PTEN and KRAS have been implicated in human colorectal cancer (CRC), and have been shown to co‐occur despite both playing a role in the PI3' kinase (PI3'K) pathway. We investigated the role of these genes in intestinal tumour progression in vivo, using genetically engineered mouse models, with the aim of generating more representative models of human CRC. Intestinal‐specific deletion of Pten and activation of an oncogenic allele of Kras was induced in wild‐type (WT) mice and mice with a predisposition to adenoma development (Apc^fl/+). The animals were euthanized when they became symptomatic of a high tumour burden. Histopathological examination of the tissues was carried out, and immunohistochemistry used to characterize signalling pathway activation. Mutation of Pten and Kras resulted in a significant life‐span reduction of mice predisposed to adenomas. Invasive adenocarcinoma was observed in these animals, with evidence of activation of the PI3'K pathway but no metastasis. However, mutation of Pten and Kras in WT animals not predisposed to adenomas led to perturbed homeostasis of the intestinal epithelium and the development of hyperplastic polyps, dysplastic sessile serrated adenomas and metastasizing adenocarcinomas with serrated features. These studies demonstrate synergism between Pten and Kras mutations in intestinal tumour progression, in an autochthonous and immunocompetent murine model, with potential application to preclinical drug testing. In particular, they show that Pten and Kras mutations alone predispose mice to the spectrum of serrated lesions that reflect the serrated pathway of CRC progression in humans. Published by John Wiley & Sons, Ltd. www.pathsoc.org.uk     

Analysis of alternative lengthening of telomere markers in BRCA1 defective cells

Telomeres are specialized structures responsible for the chromosome end protection. Previous studies have revealed that defective BRCA1 may lead to elevated telomere fusions and accelerated telomere shortening. In addition, BRCA1 associates with promyelocytic leukemia (PML) bodies in alternative lengthening of telomeres (ALTs) positive cells. We report here elevated recombination rates at telomeres in cells from human BRCA1 mutation carriers and in mouse embryonic stem cells lacking both copies of functional Brca1. An increased recombination rate at telomeres is one of the signs of ALT. To investigate this possibility further we employed the C‐circle assay that identifies ALT unequivocally. Our results revealed elevated levels of ALT activity in Brca1 defective mouse cells. Similar results were obtained when the same cells were assayed for the presence of another ALT marker, namely the frequency of PML bodies. These results suggest that BRCA1 may act as a repressor of ALT. © 2016 The Authors Genes, Chromosomes & Cancer Published by Wiley Periodicals, Inc.