Patricia A. Kruk

Deacetylation of cortactin by SIRT1 promotes cell migration.

Cortactin binds F-actin and promotes cell migration. We showed earlier that cortactin is acetylated. Here, we identify SIRT1 (a class III histone deacetylase) as a cortactin deacetylase and p300 as a cortactin acetylase. We show that SIRT1 deacetylates cortactin in vivo and in vitro and that the SIRT1 inhibitor EX-527 increases amounts of acetylated cortactin in ovarian cancer cells. We also show that p300 acetylates cortactin in vivo and that cells lacking or depleted of p300 express less-acetylated cortactin than do control cells. Deletion analysis mapped the SIRT1-binding domain of cortactin to its repeat region, which also binds F-actin. Mouse embryo fibroblasts (MEFs) lacking sir2α (the mouse homolog of SIRT1) migrated more slowly than did wild-type cells. The expression of SIRT1 in sir2α-null cells restored migratory capacity, as did expression of a deacetylation-mimetic mutant of cortactin. SIRT1 and cortactin were more abundant in breast tumor tissue than in their normal counterparts, whereas SIRT1 expression inversely correlates with the ratio of acetylation cortactin versus total cortactin. These data suggest that deacetylation of cortactin is associated with high levels of SIRT1 and tumorigenesis. Finally, breast and ovarian cancer cell lines expressing an acetylation mimetic mutant of cortactin are less motile than that of control cells, whereas cells expressing the deacetylation mimetic mutant of cortactin migrate faster than that of control cells in Transwell migration assays. In summary, our results suggest that cortactin is a novel substrate for SIRT1 and p300 and, for the first time, a possible role for SIRT1 in cell motility through deacetylation of cortactin.

Aurora-A induces cell survival and chemoresistance by activation of Akt through a p53-dependent manner in ovarian cancer cells

Aurora‐A is frequently altered in epithelial malignancies. Overexpressing Aurora‐A induces centrosome amplification and G2/M cell cycle progression. We have previously shown elevated level of Aurora‐A in ovarian cancer and activation of telomerase by Aurora‐A in human mammary and ovarian epithelia. Here we report that Aurora‐A protects ovarian cancer cells from apoptosis induced by chemotherapeutic agent and activates Akt pathway in a p53‐dependent manner. Ectopic expression of Aurora‐A renders cells resistant to cisplatin (CDDP), etoposide and paclitaxel‐induced apoptosis and stimulates Akt1 and Akt2 activity in wild‐type p53 but not p53‐null ovarian cancer cells. Aurora‐A inhibits cytochrome C release and Bax conformational change induced by CDDP. Knockdown of Aurora‐A by RNAi sensitizes cells to CDDP‐induced apoptosis and decreases phospho‐Akt level in wild‐type p53 cells. Reintroduction of p53 decreases Akt1 and Akt2 activation and restores CDDP sensitivity in p53‐null but not p53‐null‐Aurora‐A cells. Inhibition of Akt by small molecule inhibitor, API‐2, overcomes the effects of Aurora‐A‐on cell survival and Bax mitochondrial translocation. Taken collectively, these data indicate that Aurora‐A activates Akt and induces chemoresistance in a p53‐dependent manner and that inhibition of Akt may be an effective means of overcoming Aurora‐A‐associated chemoresistance in ovarian cancer cells expressing wild‐type p53.

Aurora-A Kinase Regulates Telomerase Activity through c-Myc in Human Ovarian and Breast Epithelial Cells

Aurora-A kinase is frequently overexpressed/activated in human ovarian and breast cancers. A rat mammary tumor model study indicates that alterations of Aurora-A are early events during mammary tumor development (T. M. Goepfert et al., Cancer Res., 62: 4115–4122, 2002), suggesting that Aurora-A plays a pivotal role in transformation. However, the molecular mechanism by which Aurora-A induces ovarian and breast cell transformation remains elusive. Here we show that ectopic expression of Aurora-A induces telomerase activity in human ovarian and breast epithelial cell lines HIOSE118 and MCF-10A. The mRNA and promoter activities of human telomerase reverse transcriptase (hTERT) are stimulated by Aurora-A. Furthermore, we have demonstrated that the c-Myc binding sites of hTERT promoter are required for Aurora-A-induced hTERT promoter activity. Ectopic expression of Aurora-A up-regulates c-Myc. Knockdown of c-Myc by RNA interference attenuates Aurora-A-stimulated hTERT expression and telomerase activity. To our knowledge, these findings demonstrate, for the first time, that Aurora-A induces telomerase activity and hTERT by up-regulation of c-Myc and provides an additional mechanism for the role of Aurora-A in malignant transformation in addition to its cell cycle control.

MicroRNA MiR-214 regulates ovarian cancer cell stemness by targeting p53/Nanog.

Background: Ovarian cancer stem cells (OCSC) play a critical role in chemoresistance and relapse. Results: Expression of miR-214 induces, whereas knockdown of miR-214 decreases, OCSC and Nanog. MiR-214 targets p53, a repressor of Nanog. Conclusion: miR-214 targets p53 to induce OCSC and Nanog. Significance: MiR-214 is a target for OCSC. Previous studies have shown aberrant expression of miR-214 in human malignancy. Elevated miR-214 is associated with chemoresistance and metastasis. In this study, we identified miR-214 regulation of ovarian cancer stem cell (OCSC) properties by targeting p53/Nanog axis. Enforcing expression of miR-214 increases, whereas knockdown of miR-214 decreases, OCSC population and self-renewal as well as the Nanog level preferentially in wild-type p53 cell lines. Furthermore, we found that p53 is directly repressed by miR-214 and that miR-214 regulates Nanog through p53. Expression of p53 abrogated miR-214-induced OCSC properties. These data suggest the critical role of miR-214 in OCSC via regulation of the p53-Nanog axis and miR-214 as a therapeutic target for ovarian cancer.

1,25-Dihydroxyvitamin D3 Suppresses Telomerase Expression and Human Cancer Growth through MicroRNA-498

Background: Telomerase is essential for cancer cell growth. Results: MiR-498 is a novel 1,25(OH)2D3 target gene that decreases telomerase, induces cell death, and suppresses tumor growth. Conclusion: MiR-498 is an important mediator of the anti-tumor activity of 1,25(OH)2D3. Significance: The studies define a new mechanism of telomerase regulation by small non-coding RNAs in response to 1,25(OH)2D3. Telomerase is an essential enzyme that counteracts the telomere attrition accompanying DNA replication during cell division. Regulation of the promoter activity of the gene encoding its catalytic subunit, the telomerase reverse transcriptase, is established as the dominant mechanism conferring the high telomerase activity in proliferating cells, such as embryonic stem and cancer cells. This study reveals a new mechanism of telomerase regulation through non-coding small RNA by showing that microRNA-498 (miR-498) induced by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) decreases the mRNA expression of the human telomerase reverse transcriptase. MiR-498 was first identified in a microarray analysis as the most induced microRNA by 1,25(OH)2D3 in ovarian cancer cells and subsequently validated by quantitative polymerase chain reaction assays in multiple human cancer types. A functional vitamin D response element was defined in the 5-prime regulatory region of the miR-498 genome, which is occupied by the vitamin D receptor and its coactivators. Further studies showed that miR-498 targeted the 3-prime untranslated region of human telomerase reverse transcriptase mRNA and decreased its expression. The levels of miR-498 expression were decreased in malignant human ovarian tumors as well as human ovarian cancer cell lines. The ability of 1,25(OH)2D3 to decrease human telomerase reverse transcriptase mRNA and to suppress ovarian cancer growth was compromised when miR-498 was depleted using the sponges in cell lines and mouse tumor models. Taken together, our studies define a novel mechanism of telomerase regulation by small non-coding RNAs and identify miR-498 as an important mediator for the anti-tumor activity of 1,25(OH)2D3.

Oncogenic pathways implicated in ovarian epithelial cancer

Characterization of intracellular signaling pathways should lead to a better understanding of ovarian epithelial carcinogenesis and provide an opportunity to interfere with signal transduction targets involved in ovarian tumor cell growth, survival, and progression. Challenges toward such an effort are significant because many of these signals are part of cascades within an intricate and likely redundant intracellular signaling network (Fig.1). For instance, a given signal may activate a dual intracellular pathway (ie, MEK1-MAPK and PI3K/Akt required for fibronectin-dependent activation of matrix metalloproteinase 9). A single pathway also may transduce more than one biologic or oncogenic signal (ie, PI3K signaling in epithelial and endothelial cell growth and sprouting of neovessels). Despite these challenges, evidence for therapeutic targeting of signal transduction pathways is accumulating in human cancer. For instance, the EGF-specific tyrosine kinase inhibitor ZD 1839 (Iressa) may have a beneficial therapeutic effect on ovarian epithelial cancer. Therapy of this cancer may include inhibitors of PI kinase (quercetin), ezrin and PIP kinase (genistein). The G protein-coupled family of receptors, including LPA, also is an attractive target to drugs, although their frequent pleiotropic functions may be at times toxic and lack specificity. Because of the lack of notable toxicity, PI3K/Akt pathway inhibitors such as FTIs are a promising targeted therapy of ovarian epithelial cancer. Increasing insight into the oncogenic pathways involved in ovarian epithelial cancer also is helping clinicians to understand better the phenomenon of chemoresistance in this malignancy. Oncogenic activation of gamma-synuclein promotes cell survival and provides resistance to paclitaxel, but such a resistance is partially overcome by an MEK inhibitor that suppresses ERK activity. Ovarian epithelial cancer is a complex group of neoplasms with an overall poor prognosis. Comprehension of this cancer pathobiology suffers because of an incomplete understanding of precursor lesions and the absence of an orthotopic animal model until very recently. It can be predicted with confidence, however, that the discovery of potent inhibitors of signal transduction and the development of discovery tools, such as proteomics and metabolomics, may change the way by which clinicians may now address basic biomedical questions in this insidious and lethal disease.

Deregulation of IKBKE Is Associated with Tumor Progression, Poor Prognosis, and Cisplatin Resistance in Ovarian Cancer

I-kappa-B kinase e (IKBKE; IKKepsilon) has been recently identified as a breast cancer oncogene, and its alteration appears to be an early event in breast cancer development. In this study, we demonstrated that IKKepsilon is frequently overexpressed and activated in human ovarian cancer cell lines and primary tumors. Of 96 ovarian cancer specimens examined, 63 exhibited elevated levels of IKKepsilon. Furthermore, alterations of IKKepsilon were associated with late-stage and high-grade tumors, suggesting a role of IKKepsilon in ovarian tumor progression rather than in tumor initiation. Overall survival in patients with elevated levels of IKKepsilon was significantly lower than patients whose tumors expressed normal levels of IKKepsilon. Moreover, both early and late-stage tumors that overexpressed IKKepsilon conferred a poor prognosis, as compared with those that did not possess elevated IKKepsilon levels. Notably, overexpression of IKKepsilon rendered cells resistant to cisplatin, whereas knockdown of IKKepsilon overcame cisplatin resistance in both A2780CP and C13 cells, which express high levels of endogenous IKKepsilon. Therefore, these data demonstrate for the first time that deregulation of IKKepsilon is a highly recurrent event in human ovarian cancer and could play a pivotal role in tumor progression and cisplatin resistance. IKKepsilon could also serve as a prognostic marker and potential therapeutic target for this malignancy.

BRCA1 16 years later: risk‐associated BRCA1 mutations and their functional implications

Mutations in the tumor suppressor breast cancer susceptibility gene 1 (BRCA1), an important player in the DNA damage response, apoptosis, cell cycle regulation and transcription, confer a significantly elevated lifetime risk for breast and ovarian cancer. Although the loss of wild‐type BRCA1 function is an important mechanism by which mutations confer increased cancer risk, multiple studies suggest mutant BRCA1 proteins may confer functions independent of the loss of wild‐type BRCA1 through dominant negative inhibition of remaining wild‐type BRCA1, or through novel interactions and pathways. These functions impact various cellular processes and have the potential to significantly influence cancer initiation and progression. In this review, we discuss the functional classifications of risk‐associated BRCA1 mutations and their molecular, cellular and clinical impact for mutation carriers.

Urinary levels of Bcl-2 are elevated in ovarian cancer patients

OBJECTIVE(S) The poor prognosis associated with ovarian cancer is due to the lack of overt early symptoms and the absence of reliable diagnostic screening methods. Since many tumors overexpress anti-apoptotic proteins, the purpose of this study was to determine whether elevated levels of the anti-apoptotic protein Bcl-2 were present in urine from patients with ovarian cancer. METHODS Bcl-2 was assayed by ELISA in urine samples from two cohorts consisting of a total of 77 healthy women, 161 women with benign gynecologic disease and 150 women with ovarian cancer, 13 with early and 137 with late stage disease, respectively. Wherever possible, parallel serum samples were measured for CA125 levels by ELISA. RESULTS Urinary levels of Bcl-2 from healthy individuals or women with benign disease averaged 0.59 ng/ml+/-0.61 and 1.12 ng/ml+/-0.79, respectively. In contrast, urinary levels of Bcl-2 averaged 2.60 ng/ml+/-2.23 and 3.58 ng/ml+/-1.55 from women with early (N=13) and late (N=137) stage ovarian cancer. Further, urinary levels of Bcl-2 were elevated in ovarian cancer patients regardless of tumor grade, stage, size, histologic subtype, creatinine levels or patient age, but appeared to complement CA125 measurements. CONCLUSION(S) Levels of Bcl-2 are elevated in the urine of patients with ovarian cancer and may be of diagnostic and/or prognostic clinical importance. Further studies of urinary Bcl-2 as a biomarker for ovarian cancer alone or in combination with other markers are warranted.

Pyk2/ERK 1/2 mediate Sp1- and c-Myc-dependent induction of telomerase activity by epidermal growth factor.

Epidermal growth factor (EGF) promotes growth of normal ovarian surface as well as malignant ovarian epithelial cells. Further, EGF receptors are present on both normal and malignant ovarian surface epithelial cells and they are often constitutively activated in many cancers. Since telomerase confers cellular immortalization and survival through increased cellular proliferation, we sought to investigate the potential role of EGF to regulate telomerase activity in normal and ovarian cancer cells. While exogenous EGF failed to activate telomerase in normal ovarian surface epithelial cells, in cancer cells we herein report that: exogenous EGF activates telomerase activity and human telomerase reverse transcriptase gene (hTERT) transcription; EGF-induced telomerase activity is ERK 1/2-dependent; EGF targets Sp1 and c-Myc binding sites within the core region of the hTERT promoter; and proline-rich tyrosine kinase 2 (Pyk2) is a key mediator of EGF-mediated telomerase activity. Together, these data show that dysregulation of EGF signaling may promote cancer cell survival through up-regulation of telomerase activity.