PTEN signaling through RAF1 proto-oncogene serine/threonine kinase (RAF1)/ERK in the epididymis is essential for male fertility

Without a fully developed initial segment, the most proximal region of the epididymis, male infertility results. Therefore, it is important to understand the development and regulation of this crucial region. In addition to distinctively high activity levels of the components of the ERK pathway, which are essential for initial-segment differentiation, the initial segment exhibits high protein and activity levels of phosphatase and tensin homolog (PTEN). To understand the role of PTEN in the regulation of the initial segment, we generated a mouse model with a conditional deletion of Pten from the epithelial cells of the proximal epididymis from postnatal day 17 (P17) onward. Shortly after Pten deletion, hypertrophy of the proximal epididymis became evident. Loss of Pten resulted in activation of the AKT (protein kinase B) pathway components from P28 onward, which in turn gradually suppressed RAF1 proto-oncogene serine/threonine kinase (RAF1)/ERK signaling through the interaction between AKT and RAF1. Consistent with progressive changes in RAF1/ERK signaling, loss of Pten progressively altered cell shape, size, organization, proliferation, and survival in the initial-segment epithelium and resulted in dedifferentiation and extensive epithelial folding. Most importantly, knockout males progressively lost fertility and became infertile from 6 to 12 mo. Spermatozoa from older knockout mice showed a lower percentage of motility and a higher percentage of flagellar angulation compared with controls, suggesting compromised sperm maturation. Therefore, under normal physiological conditions, PTEN suppresses AKT activity to maintain activation of the RAF1/ERK signaling pathway, which in turn maintains normal function of the initial segment and therefore, normal sperm maturation.Spermatozoa enter the epididymis from the testes as immotile cells that are incapable of fertilization. During epididymal transit, a complex process called sperm maturation allows for conversion of spermatozoa into motile and fertilization-competent cells. The long, convoluted epididymal duct—which is ∼6 m long in humans and 1 m in mice (1)—provides a luminal fluid microenvironment that is necessary for sperm maturation (2).It is apparent that the most proximal region of the epididymis, the initial segment, plays an important role in sperm maturation. C-ros oncogene 1 (Ros1) knockout male mice that lacked prepubertal differentiation of the epididymal initial segment were healthy but infertile (3). Spermatozoa from Ros1 knockouts showed flagellar angulation, a defect in sperm maturation (4). Therefore, it is important to examine the mechanisms by which the initial segment develops, functions normally, and contributes to normal sperm maturation.The initial segment exhibits high activity levels of the ERK pathway components. The ERK pathway [also known as the RAF (RAF proto-oncogene serine/threonine kinases)/MEK/ERK pathway] is an intracellular protein kinase cascade containing at least MAPK3 and/or MAPK1 (commonly known as ERK1 and ERK2), a MAPKK (commonly known as MEK), and a MAP3K (including RAF1). The kinases in each tier phosphorylate and activate the kinases in the downstream tier to transmit a signal within a cell. During prepubertal development, the first wave of testicular luminal fluid enters the epididymis and activates the ERK pathway components in the initial-segment epithelium. The activated ERK pathway then promotes initial-segment differentiation (5), which is demonstrated by tall, columnar principal cells and long projections of basal cells (6, 7). Efferent duct ligation prevents luminal fluid from entering the epididymis and abolishes the high activity levels of the ERK pathway components in the initial segment (5, 8). Such abolishment results in the arrest of ongoing initial-segment differentiation in juvenile mice (5). Therefore, the high activity levels of the ERK pathway components are essential for differentiation of the initial-segment epithelium.In addition to higher activity levels of the ERK pathway components, the initial segment exhibits higher protein and activity levels of phosphatase and tensin homolog (PTEN) compared with other epididymal regions (5). It is known that PTEN dephosphorylates PIP₃ and negatively regulates AKT (protein kinase B) activity. However, the significance of PTEN-regulated AKT signaling in the initial segment is unclear. To examine the role of PTEN in the initial segment, we generated a mouse model with a conditional deletion of Pten from epithelial cells of the proximal epididymis from postnatal day 17 (P17) onward. Results from our studies show that PTEN plays an essential role in maintaining normal initial-segment differentiation and function and, therefore, male fertility.     

Cyclosporine attenuates cardiomyocyte hypertrophy induced by RAF1 mutants in Noonan and LEOPARD syndromes

RAS activation is implicated in physiologic and pathologic cardiac hypertrophy. Cross-talk between the Ras and calcineurin pathways, the latter also having been implicated in cardiac hypertrophy, has been suspected for pathologic hypertrophy. Our recent discovery that germ-line mutations in RAF1, which encodes a downstream RAS effector, cause Noonan and LEOPARD syndromes with a high prevalence of hypertrophic cardiomyopathy provided an opportunity to elaborate the role of RAF1 in cardiomyocyte biology. Here, we characterize the role of RAF1 signaling in cardiomyocyte hypertrophy with an aim of identifying potential therapeutic targets. We modeled hypertrophic cardiomyopathy by infecting neonatal and adult rat cardiomyocytes (NRCMs and ARCMs, respectively) with adenoviruses encoding wild-type RAF1 and three Noonan/LEOPARD syndrome-associated RAF1 mutants (S257L, D486N or L613V). These RAF1 proteins, except D486N, engendered cardiomyocyte hypertrophy. Surprisingly, these effects were independent and dependent of mitogen activated protein kinases in NRCMs and ARCMs, respectively. Inhibiting Mek1/2 in RAF1 overexpressing cells blocked hypertrophy in ARCMs but not in NRCMs. Further, we found that endogenous and heterologously expressed RAF1 complexed with calcineurin, and RAF1 mutants causing hypertrophy signaled via nuclear factor of activated T cells (Nfat) in both cell types. The involvement of calcineurin was also reflected by down regulation of Serca2a and dysregulation of calcium signaling in NRCMs. Furthermore, treatment with the calcineurin inhibitor cyclosporine blocked hypertrophy in NRCMs and ARCMs overexpressing RAF1. Thus, we have identified calcineurin as a novel interaction partner for RAF1 and established a mechanistic link and possible therapeutic target for pathological cardiomyocyte hypertrophy induced by mutant RAF1. This article is part of a Special Issue entitled ‘Possible Editorial’.     

CNK and HYP form a discrete dimer by their SAM domains to mediate RAF kinase signaling

RAF kinase functions in the mitogen-activated protein kinase (MAPK) pathway to transmit growth signals to the downstream kinases MEK and ERK. Activation of RAF catalytic activity is facilitated by a regulatory complex comprising the proteins CNK (Connector enhancer of KSR), HYP (Hyphen), and KSR (Kinase Suppressor of Ras). The sterile alpha-motif (SAM) domain found in both CNK and HYP plays an essential role in complex formation. Here, we have determined the x-ray crystal structure of the SAM domain of CNK in complex with the SAM domain of HYP. The structure reveals a single-junction SAM domain dimer of 1:1 stoichiometry in which the binding mode is a variation of polymeric SAM domain interactions. Through in vitro and in vivo mutational analyses, we show that the specific mode of dimerization revealed by the crystal structure is essential for RAF signaling and facilitates the recruitment of KSR to form the CNK/HYP/KSR regulatory complex. We present two docking-site models to account for how SAM domain dimerization might influence the formation of a higher-order CNK/HYP/KSR complex.     

5-氟尿嘧啶对肝癌细胞株PLC/RAF/5生物学特性及耐药机制的影响

目的研究化疗药物5-氟尿嘧啶(5-Fu)反复作用肝癌细胞株PLC/RAF/5后生物学特性的变化,探讨耐药肝癌细胞与肝癌干细胞之间的相关性。方法用低浓度的5-Fu(1μg/ml)反复多次作用于人肝癌细胞株PLC/RAF/5后建立PLC/RAF/5/5-Fu细胞株,观察两种细胞的形态学差异。用CCK-8法检测不同浓度的5-Fu(0、0.25、0.5、1、1.5、2μg/ml)对两种细胞增殖的抑制作用;在不同浓度的5-Fu(0.5、1、2μg/ml)作用48 h后,流式细胞仪分析不同浓度下两种细胞的凋亡情况;检测两种细胞中侧群细胞的比例;平板克隆集落实验比较两种细胞的克隆形成能力;Western Blot检测两种细胞中Bax、Bcl-2、ABCG2和Fox M1蛋白的表达情况。计量资料组间比较采用t检验。结果用化疗药物5-Fu成功建立PLC/RAF/5/5-Fu细胞株。PLC/RAF/5/5-Fu细胞比PLC/RAF/5细胞体积大,突起减少,呈长梭形改变,折光性增强。与亲本细胞相比,PLC/RAF/5/5-Fu细胞对5-Fu增殖抑制作用的敏感性降低,细胞周期G0/G1期比例降低,而S期和G2/M期比例上升;抗凋亡能力增加;侧群细胞比例增加;增殖能力增强,上述差异均具有统计学意义(P值均0.05)。Western Blot检测表明PLC/RAF/5/5-Fu细胞Bcl-2、Fox M1、ABCG2蛋白表达增强,而PLC/RAF/5细胞的Bax蛋白表达增强,差异具有统计学意义(P值均0.01)。结论细胞株PLC/RAF/5/5-Fu中肝癌干细胞可能是其耐药的根源;低浓度的5-Fu(1μg/ml)可以富集肝癌干细胞样细胞。     

Synergistic antileukemic interactions between 17-AAG and UCN-01 involve interruption of RAF/MEK- and AKT-related pathways

Interactions between the protein kinase C (PKC) and Chk1 inhibitor UCN-01 and the heat shock protein 90 (Hsp90) antagonist 17-AAG have been examined in human leukemia cells in relation to effects on signal transduction pathways and apoptosis. Simultaneous exposure (30 hours) of U937 monocytic leukemia cells to minimally toxic concentrations of 17-AAG (eg, 400 nM) and UCN-01 (eg, 75 nM) triggered a pronounced increase in mitochondrial injury (ie, loss of mitochondrial membrane potential [Deltapsim]; cytosolic release of cytochrome c), caspase activation, and apoptosis. Synergistic induction of apoptosis was also observed in other human leukemia cell types (eg, Jurkat, NB4). Coexposure of human leukemia cells to 17-AAG and the PKC inhibitor bisindolylmaleimide (GFX) did not result in enhanced lethality, arguing against the possibility that the PKC inhibitory actions of UCN-01 are responsible for synergistic interactions. The enhanced cytotoxicity of this combination was associated with diminished Akt activation and marked down-regulation of Raf-1, MEK1/2, and mitogen-activated protein kinase (MAPK). Coadministration of 17-AAG and UCN-01 did not modify expression of Hsp90, Hsp27, phospho-JNK, or phospho-p38 MAPK, but was associated with further p34cdc2 dephosphorylation and diminished expression of Bcl-2, Mcl-1, and XIAP. In addition, inducible expression of both a constitutively active MEK1/2 or myristolated Akt construct, which overcame inhibition of ERK and Akt activation, respectively, significantly attenuated 17-AAG/UCN-01-mediated lethality. Together, these findings indicate that the Hsp90 antagonist 17-AAG potentiates UCN-01 cytotoxicity in a variety of human leukemia cell types and suggest that interference with both the Akt and Raf-1/MEK/MAP kinase cytoprotective signaling pathways contribute to this phenomenon.     

Complex formation between RAS and RAF and other protein kinases.

We used a Saccharomyces cerevisiae genetic system to detect the physical interaction of RAS and RAF oncoproteins. We also observed interaction between RAS and byr2, a protein kinase implicated as a mediator of the Schizosaccharomyces pombe ras1 protein. Interaction with RAS required only the N-terminal domains of RAF or byr2 and was disrupted by mutations in either the guanine nucleotide-binding or effector-loop domains of RAS. We observed interaction between MEK (a kinase that phosphorylates mitogen-activated protein kinases) and the catalytic domain of RAF. RAS and MEK also interacted but only when RAF was overexpressed.     

High-throughput mutation profiling of CTCL samples reveals KRAS and NRAS mutations sensitizing tumors toward inhibition of the RAS/RAF/MEK signaling cascade

Cutaneous T-cell lymphomas (CTCLs) are malignancies of skin-homing lymphoid cells, which have so far not been investigated thoroughly for common oncogenic mutations. We screened 90 biopsy specimens from CTCL patients (41 mycosis fungoides, 36 Sézary syndrome, and 13 non-mycosis fungoides/Sézary syndrome CTCL) for somatic mutations using OncoMap technology. We detected oncogenic mutations for the RAS pathway in 4 of 90 samples. One mycosis fungoides and one pleomorphic CTCL harbored a KRAS(G13D) mutation; one Sézary syndrome and one CD30(+) CTCL harbored a NRAS(Q61K) amino acid change. All mutations were found in stage IV patients (4 of 42) who showed significantly decreased overall survival compared with stage IV patients without mutations (P = .04). In addition, we detected a NRAS(Q61K) mutation in the CTCL cell line Hut78. Knockdown of NRAS by siRNA induced apoptosis in mutant Hut78 cells but not in CTCL cell lines lacking RAS mutations. The NRAS(Q61K) mutation sensitized Hut78 cells toward growth inhibition by the MEK inhibitors U0126, AZD6244, and PD0325901. Furthermore, we found that MEK inhibitors exclusively induce apoptosis in Hut78 cells. Taken together, we conclude that RAS mutations are rare events at a late stage of CTCL, and our preclinical results suggest that such late-stage patients profit from MEK inhibitors.     

Single-molecule superresolution imaging allows quantitative analysis of RAF multimer formation and signaling

The RAF serine/threonine kinases regulate cell growth through the MAPK pathway, and are targeted by small-molecule RAF inhibitors (RAFis) in human cancer. It is now apparent that protein multimers play an important role in RAF activation and tumor response to RAFis. However, the exact stoichiometry and cellular location of these multimers remain unclear because of the lack of technologies to visualize them. In the present work, we demonstrate that photoactivated localization microscopy (PALM), in combination with quantitative spatial analysis, provides sufficient resolution to directly visualize protein multimers in cells. Quantitative PALM imaging showed that CRAF exists predominantly as cytoplasmic monomers under resting conditions but forms dimers as well as trimers and tetramers at the cell membrane in the presence of active RAS. In contrast, N-terminal truncated CRAF (CatC) lacking autoinhibitory domains forms constitutive dimers and occasional tetramers in the cytoplasm, whereas a CatC mutant with a disrupted CRAF–CRAF dimer interface does not. Finally, artificially forcing CRAF to the membrane by fusion to a RAS CAAX motif induces multimer formation but activates RAF/MAPK only if the dimer interface is intact. Together, these quantitative results directly confirm the existence of RAF dimers and potentially higher-order multimers and their involvement in cell signaling, and showed that RAF multimer formation can result from multiple mechanisms and is a critical but not sufficient step for RAF activation.The RAF serine/threonine protein kinase is a component of the three-tiered MAPK signaling pathway that regulates cell growth and many other essential biological processes (1, 2). In normal cells, extracellular mitogenic stimuli are transmitted to the nucleus via the receptor–RAS–RAF–MAPK cascade (2). Abnormal activation of this pathway is a central event in many human cancers and results from activating mutations in BRAF itself or in upstream factors (such as the RAS genes) (3, 4). As the RAS proteins so far are intractable pharmacologic targets (5), attention has shifted to development of small-molecule RAF inhibitors (RAFis) as antitumor therapeutic agents (6). To date, RAFi clinical efficacy has been demonstrated only for BRAF^V600E melanoma (6–8). In tumors with WT BRAF or mutant RAS, most RAFis paradoxically promote growth, at times malignant in nature (6). Moreover, BRAF mutant melanomas that are initially sensitive to RAFi rapidly become resistant by using a variety of compensatory mechanisms including RAF isoform switching and activation of other pathways including RTKs, RAS, or PI3K (9). In addition, some RAFis (e.g., vemurafenib) accelerate the occurrence of secondary squamous cell carcinomas (10).Several lines of investigation suggest that multimer formation plays an important role in RAF activation and tumor responses to RAFi (11–16). RAF dimerization-mediated signaling was first suggested by the observation that artificial dimerization activates RAF (17, 18). Next, immunoprecipitation (IP) suggested that formation of homo- and heterotypic RAF “dimers” is associated with active RAS (15, 16, 19). X-ray crystallography of the BRAF catalytic domain (CatB) identified critical residues postulated to enable CatB–CatB dimer formation (11). Mutations of these residues (e.g., R509H in BRAF and, equivalently, R401H in CRAF) profoundly diminished dimerization and kinase activity of RAF (11–13). Recently, dimerization also was implicated in RAFi-mediated activation of RAF in BRAF^WT tumors (12, 13), in acquired resistance of BRAF^V600E tumors to RAFi (14), and in the development of RAFi-induced secondary squamous carcinomas (10).Although these studies implicate RAF multimer formation in the regulation of signaling in some circumstances, they do not provide direct characterization of the nature of these multimers, nor the information about their intracellular locations. This is in a large part because of the lack of techniques with sufficient spatial and stoichiometric (protein counting) resolution to visualize RAF multimers inside an intact cell. For example, X-ray crystallography studies used purified and truncated RAF proteins (11, 20). IP measures protein–protein interactions but does not provide stoichiometric or cellular localization information of the protein complexes (12, 13).The foregoing studies underscore the need for better tools to study the RAF complexes involved in cell signaling. In the present work, we show that recently introduced single-molecule superresolution imaging techniques such as photoactivated localization microscopy (PALM) (21, 22) can be used for direct, quantitative analysis of RAF multimer formation inside an intact mammalian cell. We first demonstrate that PALM provides sufficient spatial and stoichiometric resolution to distinguish artificial protein dimers and higher-order multimers from monomers when using a suitable fluorescent probe and combined with quantitative spatial analysis. We then apply the quantitative PALM imaging approach to study CRAF multimerization under resting and various activating conditions, including the presence of active mutant RAS, N-terminal truncation, and artificial membrane localization. Our results clearly indicate the formation and significance of RAF dimers in cell signaling. The biological and therapeutic implications of these results are discussed.     

Role of next-generation genomic sequencing in targeted agents repositioning for pancreaticoduodenal cancer patients

BackgroundPancreaticoduodenal cancer (PDC) is a group of malignant tumors arising in the ampullary region, which lack approved targeted therapies for their treatment.MethodsThis retrospective, observational study is based on Secondary Data Use (SDU) previously collected during a multicenter collaboration, which were subsequently entered into a predefined database and analyzed. FoundationOne CDx or Liquid, a next-generation DNA sequencing (NGS) service, was used to identify genomic alterations of patients who failed standard treatments. Detected alterations were described according to ESMO Scale of Clinical Actionability for molecular Targets (ESCAT).ResultsNGS analysis was performed in 68 patients affected by PDC. At least one alteration ranking tier I, II, III, or IV according to ESCAT classification was detected in 8, 1, 9, and 12 patients respectively (44.1%). Ten of them (33.3%) received a matched therapy. Patients with ESCAT tier I to IV were generally younger than the overall population (median = 54, range = 26–71 years), had an EGOG performance status score = 0 (83.3%), and an uncommon histological or clinical presentation. The most common mutations with clinical evidence of actionability (ESCAT tier I-III) involved genes of the RAF (10.3%), BRCA (5.9%) or FGFR pathways (5.9%). We present the activity of the RAF kinases inhibitor sorafenib in patients with RAF-mutated advanced PDC.ConclusionsIn advanced PDC, NGS is a feasible and valuable method for enabling precision oncology. This genomic profiling method might be considered after standard treatments failure, especially in young patients maintaining a good performance status, in order to detect potentially actionable mutations and offer molecularly targeted therapeutic approaches.     

Roles of genetic variants in the PI3K and RAS/RAF pathways in susceptibility to endometrial cancer and clinical outcomes

Purpose

The phosphatidylinositol 3-kinase (PI3K)/PTEN/AKT/mTOR and Ras/Raf/MEK/ERK pathways have been implicated in endometrial tumorigenesis. In this candidate pathway analysis, we investigated associations between genetic variations in these two pathways and both risk and clinical outcomes of endometrial cancer.

Methods

We genotyped a total of 48 potentially functional SNPs in 11 key genes (AKT1, AKT2, AKT3, BRAF, FRAP1, KRAS, PDPK1, PIK3CA, PIK3CB, PIK3R1, and PTEN) with the Sequenom genotyping platform in 115 endometrial cancer patients and 230 cancer-free women to evaluate their associations with risk, survival, and recurrence of endometrial cancer.

Results

We found the following: (1) PIK3CA rs6443624 and rs9838411 variants either borderline or significantly decreased risk of endometrial cancer in a dominant model (adjusted odds ratio [OR], 0.62; 95% CI, 0.39?C1.00 and 0.59; 95% CI, 0.36?C0.95, respectively). Furthermore, there was a statistically significant multiplicative interaction (P _int?=?0.036) between these two loci in risk of endometrial cancer. In contrast, the AKT1 rs2498801 genotype significantly increased risk of endometrial cancer (adjusted OR, 1.94; 95% CI, 1.02?C3.67 in a recessive model). (2) In Cox regression analyses, three SNPs (PIK3R1 rs1862162, AKT2 rs892119, and PIK3CA rs2699887) showed significant associations with survival of endometrial cancer patients. (3) KRAS rs7312175 and PIK3CA rs6443624 had significant effects on recurrence of endometrial cancer individually and combined in a locus?Cdosage manner (adjusted P _trend?=?0.003).

Conclusion

These results suggest that common genetic variations in these pathways may modulate risk and clinical outcomes of endometrial cancer. Further replication and functional studies are needed to confirm these findings.     

Sorafenib inhibits MAPK‐mediated proliferation in a Barrett's esophageal adenocarcinoma cell line

SUMMARY. Esophageal adenocarcinoma continues to rise in incidence. Despite recognition of Barrett's metaplasia as the histological precursor, prognosis remains poor. The mitogen‐activated protein kinases (MAPK) pathway is activated in Barrett's‐associated dysplasia and adenocarcinoma and this activation is, in part, due to acid and bile acid reflux. We investigated the effects of sorafenib, an orally active Raf‐inhibitor, on acid and bile acid‐stimulated growth and signaling in SEG‐1 cells, derived from a Barrett's esophageal cancer. SEG‐1 cells were pretreated with sorafenib or vehicle and subsequently stimulated with acid or bile acid. MAPK signals, including phospho‐ERK and phospho‐p38, as well as cyclin D1 expression were assessed by Western blotting. Cell proliferation was measured by WST‐1 colorimetric assay. Acid (pH 3.0–4.0) and bile acid (taurocholate 50–100 µmol/L) activated ERK and p38. Acid and bile acid exposure also increased levels of cyclin D1, a G1 to S cell cycle regulator. Furthermore, acid and taurocholate exposure increased cell proliferation. Sorafenib abrogated MAPK activation and cyclin D1 up‐regulation and significantly inhibited cell growth. In summary, sorafenib inhibits acid or bile acid‐stimulated Barrett's esophageal cancer cell proliferation by a mechanism involving the MAPK pathway. Our results suggest that sorafenib might be useful in the management of Barrett's‐associated dysplasia and adenocarcinoma. These findings provide a foundation for in vivo studies to assess the efficacy of sorafenib in Barrett's‐related neoplasia.     

H9N2亚型禽流感病毒A/Chicken/Gansu/2/99株基因组的分子特征

目的测定H9N2亚型禽流感病毒A/Chicken/Gansu/2/99(CK/GS/2/99)分离株的基因组序列并与参考毒株进行同源性分析,阐明该毒株的遗传变异及分子特征。方法采集发病鸡泄殖腔样品,经鸡胚尿囊腔接种分离病毒,采用RT-PCR方法对CK/GS/2/99株的8个分节段基因进行扩增,分别将其克隆到pGEM-T easy载体后进行序列测定与同源性分析。结果CK/GS/2/99株PB2、PB1、PA、HA、NP、NA、M、NS基因的开放阅读框分别由2280、2274、2151、1683、1497、1401、759、864个碱基组成,分别编码759、757、716、560、498、466、252/97、231/122个氨基酸残基。该毒株HA上HA1和HA2裂解位点序列为PARSSR↓GLF,具有典型的低致病性禽流感病毒的特征。同源性分析显示,CK/GS/2/99株与1998-2002年间大部分中国大陆分离株遗传关系较近,尤其与CK/NX/4/99和CK/HB/31/00株遗传关系密切。结论CK/GS/2/99与大部分流行于中国内陆的H9N2亚型毒株均来源于共同的祖先毒株CK/BJ/1/94,这为了解中国H9N2亚型禽流感病毒的分子流行病学提供了资料。