Overexpression of oncogenic STK15/BTAK/Aurora A kinase in human pancreatic cancer.

PURPOSE: Multiple chromosome abnormalities, including gain of chromosome20q, have been detected frequently in human pancreatic cancers. Overexpression of the STK15/BTAK/Aurora A gene located on chromosome 20q13, which encodes a centrosome-associated serine/threonine kinase, has been shown to induce chromosomal instability, leading to aneuploidy and cell transformation in multiple in vitro experimental systems. The purpose of this study was to investigate the expression and copy number alteration of STK15 in pancreatic cancer. EXPERIMENTAL DESIGN: STK15 expression at both the mRNA and protein levels together with the copy number of STK15 gene was measured in nine pancreatic carcinoma cell lines: (a) HPAF-II; (b) Aspc-1; (c) Panc-1; (d) Panc-3; (e) Panc-28; (f) Panc-48; (g) HS766T; (h) MIAPaCa-2; and (i) BxPc3. STK15 protein expression was also examined in normal pancreatic tissues and tumors by Western blotting and immunohistochemistry. RESULTS: STK15 was overexpressed in all of the nine cell lines examined, but gene amplification was infrequent. Western Blot analysis of primary tumor tissues revealed 2-10 times overexpression of STK15 protein compared with normal adjacent tissues from pancreatic cancer patients. Concurrent overexpression of cdc20, an STK15-associated protein, and reduced expression of cdc25, a mitosis-activating protein phosphatase, were detected in the same tumor samples. Elevated STK15 protein expression was detected in 22 of 38 tumor sections (58%) from pancreatic cancer patients. The extent of STK15 expression was not significantly correlated with the size, degree of differentiation, and metastasis status of the tumors. CONCLUSIONS: These results show that STK15 is overexpressed in pancreatic tumors and carcinoma cell lines and suggest that overexpression of STK15 may play a role in pancreatic carcinogenesis.     

Biological characteristics in bladder cancer depend on the type of genetic instability.

PURPOSE: Malignant tumors show an inherent genetic instability that can be classified as microsatellite instability (MSI) or chromosomal instability (CIN). To elucidate the differences in biological characteristics of bladder cancer between the two types of genetic instability, the expression of the mismatch repair (MMR) proteins, Aurora-A and p53 proteins, the number of centrosomes, numerical aberrations of chromosomes and 20q13, and DNA ploidy were examined in 100 human urothelial carcinomas of the bladder. EXPERIMENTAL DESIGN: Expressions of the MLH1, MSH2, Aurora-A, and p53 proteins and the numbers of centrosomes were immunohistochemically assessed. Numerical aberrations of chromosomes 7, 9, 17, and 20q13 spots were evaluated by fluorescence in situ hybridization, and DNA ploidy was assessed by laser scanning cytometry. RESULTS: The expression levels of the MMR related-proteins decreased in 9 of 100 tumors. Tumors with low MLH1 or MSH2 expression (designated as MSI cancers) were not linked with centrosome amplification, Aurora-A overexpression, increased p53 immunoreactivity, 20q13 gain, DNA aneuploidy, and disease progression. MSI cancers showed a favorable prognosis. CIN cancers (49 cases), defined as tumors with a large intercellular variation in centromere copy numbers, were associated more frequently with centrosome amplification, Aurora-A overexpression, increased p53 immunoreactivity, and 20q13 gain than the others (51 cases). Tumors with disease progression were included in the CIN cancer group. CONCLUSIONS: The present observations suggest that there are differences in the biological characteristics of the two types of genetic instability.     

Frequent overexpression of STK15/Aurora-A/BTAK and chromosomal instability in tumorigenic cell cultures derived from human ovarian cancer

The STK15 (also known as Aurora-A/BTAK) gene localized on chromosome 20q13 and encoding a centrosome-associated serine/threonine kinase is amplified and overexpressed in multiple human tumor cell types. Overexpression of this gene is involved in tumorigenic transformation, induction of centrosome duplication-distribution abnormalities, and aneuploidy in mammalian cells. To examine the potential role of STK15 in ovarian tumorigenesis, its mRNA and protein expression status were examined in cells grown in culture from 15 ovarian cancer specimens using semiquantitative RT-PCR and Western blot analysis. Normal ovarian surface tissues and the near diploid nontumorigenic breast epithelial cell line MCF10 were used as controls. The status of STK15 correlated with transformation-associated cellular phenotypes including tumorigenicity in nude mice, p53 expression level, and chromosomal ploidy. For chromosome ploidy analyses, FISH was carried out with direct fluorescence-labeled a-satellite probes for chromosome 3 and 17. STK15 mRNA was found overexpressed in 10 of the 15 ovarian cancer cell cultures. Five of these cell cultures revealed a truncated form of the STK15 protein with a molecular mass of 36 kDa. When tested for tumorigenicity in nude mice, 9 of the 10 cell cultures that overexpressed STK15 mRNA formed tumors in nude mice, while only one of the five cell cultures with no overexpression did. Cells overexpressing STK15 mRNA showed significant correlation with chromosome 3 polysomy. Six of the 13 (46%) cell cultures analyzed for p53 expression revealed overexpression of p53 and five of these six (83%) also overexpressed STK15. Four of the remaining seven cultures (57%) with overexpression of STK15 revealed minimal or no expression of p53. These results demonstrate that overexpression of STK15 significantly correlates with nude mice tumorigenicity and chromosomal aneuploidy in human ovarian cancer cells grown in vitro. Additionally, cells overexpressing STK15 also revealed frequent coordinate loss of wild-type p53 function manifested either as highly expressed intense staining reflective of a mutant form of p53 or almost complete absence of p53 staining. Overexpression of STK15 with coordinate loss of wild-type p53 function thus appears to play an important role in ovarian tumorigenesis and offers a novel molecular target in designing effective therapy of human ovarian cancer.     

Centrosome hyperamplification predicts progression and tumor recurrence in bladder cancer.

PURPOSE: Recent studies have reported that centrosome hyperamplification (CH) is closely related to chromosomal instability in bladder cancer. In this study, we investigated whether CH could be used as a prognostic biomarker for patients with bladder cancer. EXPERIMENTAL DESIGN: CH was evaluated by immunohistochemistry in 50 bladder cancers (< or =pT1: 43; > or =pT2: 7). In addition, numerical aberrations of chromosomes 7, 9, and 17 and gain of 20q13, on which the Aurora-A gene is located, were evaluated by fluorescence in situ hybridization, and DNA ploidy was assessed. Preliminary experiments on eight bladder cancer cell lines found that six had over 5% of CH cells associated with a gain of 20q13 and overexpression of Aurora-A; therefore, CH-positive cases (CH+) were defined as those having over 5% of cells with > or =3 centrosomes per cell. RESULTS: CH+, 20q13 gain, chromosomal instability, and DNA aneuploidy were detected in 30 (60%), 18 (36%), 22 (44%), and 19 (38%) patients, respectively. There were significant differences in tumor number, grade, recurrence, and progression between the CH+ and CH- groups. The later had significantly higher recurrence-free and progression-free survivals than the former (P = 0.0028 and P = 0.0070, respectively, log-rank test). Multivariate analysis revealed that CH+ was the strongest predictor for tumor recurrence in nonmuscle invasive (pTa and pT1) bladder cancer (hazard ratio, 1.882; 95% confidence interval, 1.161-3.325; P = 0.0094). CONCLUSIONS: Detection of CH may provide crucial prognostic information about tumor recurrence in bladder cancer.     

Amplification/overexpression of a mitotic kinase gene in human bladder cancer

BACKGROUND: The mitotic kinase-encoding gene STK15/BTAK/ AuroraA is associated with aneuploidy and transformation when overexpressed in mammalian cells. STK15 overexpression activates an unknown oncogenic pathway that involves centrosome amplification and results in missegregation of chromosomes. Because clinical prognosis and tumor aneuploidy are tightly linked in human bladder cancer, we examined whether increased STK15 copy number and protein levels are linked to aneuploidy in bladder cancers. METHODS: STK15 protein was visualized by immunohistochemistry in 205 formalin-fixed, paraffin-embedded human bladder tumors. STK15 gene copy number was evaluated in 61 tumors by Southern blot hybridization and in 21 of these 61 tumors by fluorescence in situ hybridization (FISH). Copy numbers of chromosomes 3, 17, 20, and 21 were evaluated by FISH with chromosome-specific probes. STK15 expression levels were related to histologic grade, stage, and DNA ploidy of the tumors and to the patients' follow-up data. The chi-square test for association was used to analyze the relationship between STK15 expression and pathologic features. All statistical tests were two-sided. RESULTS: Tumors with low levels of STK15 amplification (3-4 copies) showed minimal deviation in their chromosome copy number and diploid or near-diploid total nuclear DNA content. Tumors with higher levels of STK15 amplification (>4 copies) had a major increase of chromosome copy number and of their total nuclear DNA content, i.e., exhibited pronounced aneuploidy. Elevated expression of STK15 was strongly associated with parameters of clinical aggressiveness including high histologic grade (P<.001), invasion (P<.001), increased rate of metastasis (P<.001), and decreased metastasis-free (P<.001) and overall (P<.001) survival of patients with bladder cancer. CONCLUSION: STK15 gene amplification and associated increased expression of the mitotic kinase it encodes are associated with aneuploidy and aggressive clinical behavior in human bladder cancer.     

Overexpression of aurora kinase A in mouse mammary epithelium induces genetic instability preceding mammary tumor formation

Aurora-A/STK15/BTAK, which encodes a centrosome-associated kinase, is amplified and overexpressed in multiple types of human tumors, including breast cancer. However, the causal relationship between overexpression of Aurora-A and tumorigenesis has not been fully established due to contradictory data obtained from different experimental systems. To investigate this, we generated a mouse strain that carries an MMTV-Aurora-A transgene. We showed that all the MMTV-Aurora-A mice displayed enhanced branch morphogenesis in the mammary gland and about 40% developed mammary tumors at 20 months of age. The tumor incidence was significantly increased in a p53(+/-) mutation background with about 70% MMTV-Aurora-A;p53(+/-) animals developed tumors at 18 months of age. Of note, overexpression of Aurora-A led to genetic instability, characterized by centrosome amplification, chromosome tetraploidization and premature sister chromatid segregation, at stages prior to tumor formation. Most notably, the severe chromosomal abnormality did not cause cell death owing to the activation of AKT pathway, including elevated levels of phosphorylated AKT and mammalian target of rapamycin, and nuclear accumulation of cyclin D1, which enabled continuous proliferation of the tetraploid cells. These data establish Aurora-A as an oncogene that causes malignant transformation through inducing genetic instability and activating oncogenic pathways such as AKT and its downstream signaling.     

Overexpression of Aurora-A contributes to malignant development of human esophageal squamous cell carcinoma.

PURPOSE: Aurora-A/STK15/BTAK, a centrosome-associated oncogenic protein, is implicated in the control of mitosis. Overexpression of Aurora-A has been shown to result in chromosomal aberration and genomic instability. Multiple lines of evidence indicate that Aurora-A induces cell malignant transformation. In the current study, we are interested in investigating the expression of Aurora-A in human esophageal squamous cell carcinoma (ESCC) and characterizing the association of Aurora-A with ESCCmalignant progression. EXPERIMENTAL DESIGN: Aurora-A protein expression was examined in 84 ESCC tissues and 81 paired normal adjacent tissues by either immunohistochemistry or Western blot analysis. In addition, a gene-knockdown small interfering RNA technique was used in ESCC cells to investigate whether Aurora-A contributes to the ability of a tumor to grow invasively. RESULTS: The amount of Aurora-A protein in ESCC was considerably higher than that in normal adjacent tissues. Overexpression of Aurora-A was observed in 57 of 84 (67.5%) ESCC samples. In contrast, <2% of normal adjacent tissue displayed high expression of Aurora-A. Interestingly, overexpression of Aurora-A seemed to correlate with the invasive malignancy of ESCC. Disruption of endogenous Aurora-A using small interfering RNA technique substantially suppressed cell migrating ability. CONCLUSION: The findings presented in this report show that Aurora-A expression is elevated in human esophageal squamous cell carcinoma and is possibly associated with tumor invasion, indicating that overexpression of Aurora-A may contribute to ESCC occurrence and progression.     

STK15 gene overexpression, centrosomal amplification, and chromosomal instability in the absence of STK15 mutations in laryngeal carcinoma

Centrosomes regulate cell division by forming bipolar mitotic spindles and, thus, play an essential role in the maintenance of chromosomal stability. Centrosomal amplification has been found commonly among tumor cells. Previous studies have suggested that a STK15 (serine/threonine kinase 15) gene can induce centrosomal amplification, chromosomal instability, and cell transformation. To investigate the role of STK15 gene abnormalities in the occurrence of centrosomal amplification and chromosomal instability, a combinatory approach has been taken to investigate the expression level and point mutations of the STK15 and centrosomal/chromosomal aberrations among 72 cases of laryngeal squamous cell carcinoma and a representative Hep-2 cell line. Although no mutation was detected within its exons 6 or 7, overexpression of STK15 has been found in 47 cases (65 percent) as well as in the Hep-2 cell line; for the latter apparent centrosomal amplification also has been noted, with the number of centrosomes within a single cell varying between 1 and 7 and the proportion of cells with amplified centrosomes reaching 11∼ 23 percent. Karyotype analysis of Hep-2 cell line has suggested common occurrence of chromosomal aberrations, with the number of chromosomes ranging between 43 and 84, modal number between 69 and 74, and structural aberrations, represented by 13 marker chromosomes, including translocations, deletions, and isochromosomes found in various subclones. Our results suggest that in Hep-2 cell line overexpression of STK15 gene may cause centrosomal amplification thereby result in chromosomal instability through abnormal mitosis. Detection of STK15 overexpression in laryngeal carcinoma has led us to propose that the above may be one of the mechanisms underlying laryngeal carcinogenesis.     

Loss of aurora A/STK15/BTAK overexpression correlates with transition of in situ to invasive ductal carcinoma of the breast.

The biological mechanisms involved in the progression of ductal carcinoma in situ (DCIS) to invasive breast cancer are not fully understood. We previously have shown that the putative oncogene Aurora-A/STK15/BTAK, encoding a centrosome-associated kinase that regulates centrosomes and chromosome segregation, is amplified in human breast cancer. In this study, 37 archival breast tissue specimens of histologically confirmed DCIS lesions with adjacent invasive carcinoma and morphologically nonmalignant mammary ducts were analyzed immunohistochemically for expression of STK15. Statistically significant differences in overexpression of STK15 was found between invasive cancer and either nonmalignant mammary ducts (P < 0.0001) or DCIS lesions (P < 0.0005). Abnormalities in centrosome size and number was detected in the samples analyzed and 56% (14 of 25) of the cases also showed aneuploidy reflected in >2 signals of chromosome 3 and 17. Our data demonstrate that STK15 overexpression correlates with centrosome anomaly and aneuploidy in DCIS, and loss of STK15 overexpression is associated with progression of in situ to ductal invasive breast carcinoma.     

Aneuploidy of human testicular germ cell tumors is associated with amplification of centrosomes

Testicular germ cell tumors occur in three age groups. Seminomas and nonseminomas of adults, including mature teratomas, and the precursor carcinoma in situ (CIS) are aneuploid. This also holds true for yolk sac tumors of newborn and infants, while the mature teratomas of this age are diploid. In contrast, spermatocytic seminomas occurring in the elderly contain both diploid and polyploid cells. Aneuploidy has been associated with centrosome aberrations, sometimes related to overexpression of STK15. Aneuploidy of non-neoplastic germ cells has been demonstrated in the context of male infertility, a risk factor for the development of seminoma/nonseminoma. We investigated aneuploidy, centrosome aberrations and the role of STK15 in different types of testicular germ cell tumors as well as in normal and disturbed spermatogenesis. The aneuploid seminomas and nonseminomas tumors (including CIS) showed increased numbers of centrosomes, without STK15 amplification or overexpression. Four out of six infantile teratomas had normal centrosomes, the remaining two and an infantile yolk sac tumor showed a heterogeneous pattern of cells with normal or amplified centrosomes. Spermatocytic seminomas had two, four or eight centrosomes. Germ cells in seminiferous tubules with disturbed spermatogenesis shared both aneuploidy and centrosome abnormalities with seminomas/nonseminomas and showed a more intense STK15 staining than those with normal spermatogenesis and CIS. Therefore, aneuploidy of testicular germ cell tumors is associated with amplified centrosomes probably unrelated to STK15.     

The putative serine/threonine kinase gene STK15 on chromosome 20q13.2 is amplified in human gliomas

Searching for amplifications in low grade and high grade gliomas we observed an interesting correlation between the recurrence and progression of astrocytic low grade gliomas and the amplification of the STK15 gene located in the chromosomal region 20q13. Chromosome copy gains in this region have been reported previously in astrocytic gliomas and glioma cell lines and in many cancer types including breast, colorectal and ovarian cancers. The putative serine/threonine kinase STK15 has been reported to be amplified and overexpressed in breast cancer cell lines and colorectal cancer. Another candidate gene located in this region is PTPN1, a protein tyrosine phosphatase non-receptor type 1 that might play a role in cell cycle control. We used comparative PCR for quantitative DNA analysis to search for STK15 and PTPN1 amplification in gliomas previously characterized by CGH. Five out of 16 tumors (31%) of different WHO grade (1x grade II, 1x grade III, 3x grade IV) showed DNA amplification of STK15 whereas we did not detect amplification of PTPN1. We hypothesize that amplification of the STK15 gene may be a non-random genetic alteration in human gliomas playing a role in the genetic pathways of tumorigenesis.     

Aurora-A regulation of nuclear factor-kappaB signaling by phosphorylation of IkappaBalpha

The Aurora-A/STK15 gene encodes a kinase that is frequently amplified in cancer. Overexpression of Aurora-A in mammalian cells leads to centrosome amplification, genetic instability, and transformation. In this study, we show that Aurora-A activates nuclear factor-kappaB (NF-kappaB) via IkappaBalpha phosphorylation. Inhibition of endogenous Aurora-A reduces tumor necrosis factor alpha (TNFalpha)-induced IkappaBalpha degradation. We analyzed primary human breast cancers, and 13.6% of samples showed Aurora-A gene amplification, all of which exhibited nuclear localization of NF-kappaB. We propose that this subgroup of patients with breast cancer might benefit from inhibiting Aurora-A. We also show that down-regulation of NF-kappaB via Aurora-A depletion can enhance cisplatin-dependent apoptosis. These data define a new role for Aurora-A in regulating IkappaBalpha that is critical for the activation of NF-kappaB-directed gene expression and may be partially responsible for the oncogenic effect of Aurora-A when the gene is amplified and overexpressed in human tumors.     

Overexpression and amplification of STK15 in human gliomas

The serine/threonine kinase 15 (STK15) at chromosome 20q13.2 is frequently shown to be amplified and overexpressed in several human cancers. STK15 has been reported to act as a cell cycle regulator and its overexpression induces centrosome amplification and aneuploidy. Recently we showed that STK15 even plays a role in human malignant brain tumours and we described an amplification of the gene in 31% of the investigated gliomas. In this study we scrutinized the correlation of increased STK15 on DNA and mRNA levels in gliomas of different histological grades. Southern blotting confirmed the amplification frequency of the STK15 gene, which had been previously detected by comparative PCR. In total, DNA gains were found in 26% of the investigated gliomas. Interestingly, we detected overexpression of STK15 mRNA in 60% of the analyzed brain tumours. The elevated expression does not strongly correlate with gains on DNA level, but all cases with an amplification of the STK15 gene display overexpression. Gains of the STK15 gene seem to occur irrespectively of the histological grades of the tumours, so that STK15 probably is not a progression associated factor. Amplification and overexpression of the kinase rather represent a primary alteration in human gliomas, which could play an important role as an early event in all glioma subtypes.     

Overexpression of Cdc20 leads to impairment of the spindle assembly checkpoint and aneuploidization in oral cancer

Defects in the spindle assembly checkpoint are thought to be responsible for an increased rate of aneuploidization during tumorigenesis. Despite a plethora of information on the correlation between BUB-MAD gene expression levels and defects in the spindle checkpoint, very little is known about alteration of another important spindle checkpoint protein, Cdc20, in human cancer and its role in tumor aneuploidy. We observed overexpression of CDC20 in several oral squamous cell carcinoma (OSCC) cell lines and primary head and neck tumors and provide evidence that such overexpression of CDC20 is associated with premature anaphase promotion, resulting in mitotic abnormalities in OSCC cell lines. We also reconstituted the chromosomal instability phenotype in a chromosomally stable OSCC cell line by overexpressing CDC20. Thus, abnormalities in the cellular level of Cdc20 may deregulate the timing of anaphase promoting complex (APC/C) in promoting premature anaphase, which often results in aneuploidy in the tumor cells.     

Cre-loxP-controlled periodic Aurora-A overexpression induces mitotic abnormalities and hyperplasia in mammary glands of mouse models

Aurora-A, a serine/threonine mitotic kinase, was reported to be overexpressed in various human cancers, and its overexpression induces aneuploidy, centrosome amplification and tumorigenic transformation in cultured human and rodent cells. However, the underlying mechanisms and pathological settings by which Aurora-A promotes tumorigenesis are largely unknown. Here, we created a transgenic mouse model to investigate the involvement of Aurora-A overexpression in the development of mammary glands and tumorigenesis using a Cre-loxP system. The conditional expression of Aurora-A resulted in significantly increased binucleated cell formation and apoptosis in the mammary epithelium. The surviving mammary epithelial cells composed hyperplastic areas after a short latency. Induction of Aurora-A overexpression in mouse embryonic fibroblasts prepared from the transgenic mice also led to aberrant mitosis and binucleated cell formation followed by apoptosis. The levels of p53 protein were remarkably increased in these Aurora-A-overexpressing cells, and the apoptosis was significantly suppressed by deletion of p53. Given that no malignant tumor formation was found in the Aurora-A-overexpressing mouse model after a long latency, additional factors, such as p53 inactivation, are required for the tumorigenesis of Aurora-A-overexpressing mammary epithelium. Our findings indicated that this mouse model is a useful system to study the physiological roles of Aurora-A and the genetic pathways of Aurora-A-induced carcinogenesis.