Aberrant STYK1 expression in ovarian cancer tissues and cell lines
© Jackson et al; licensee BioMed Central Ltd. 2009
Received: 31 August 2009
Accepted: 21 October 2009
Published: 21 October 2009
Overexpression of STYK1, a putative serine/threonine and tyrosine receptor protein kinase has been shown to confer tumorigenicity and metastatic potential to normal cells injected into nude mice. Mutation of a tyrosine residue in the catalytic STYK1 domain attenuates the tumorigenic potential of tumor cells in vivo, collectively, suggesting an oncogenic role for STYK1.
To investigate the role of STYK1 expression in ovarian cancer, a panel of normal, benign, and ovarian cancer tissues was evaluated for STYK1 immunoreactivity using STYK1 antibodies. In addition, mRNA levels were measured by reverse transcription PCR and real-time PCR of estrogen receptors, GPR30 and STYK1 following treatment of ovarian cell lines with estrogen or G1, a GPR30 agonist, as well as western analysis.
Our data showed higher expression of STYK1 in cancer tissues versus normal or benign. Only normal or benign, and one cancer tissue were STYK1-negative. Moreover, benign and ovarian cancer cell lines expressed STYK1 as determined by RT-PCR. Estradiol treatment of these cells resulted in up- and down-regulation of STYK1 despite estrogen receptor status; whereas G-1, a GPR30-specific agonist, increased STYK1 mRNA levels higher than that of estradiol.
We conclude that STYK1 is expressed in ovarian cancer and is regulated by estrogen through a GPR30 hormone-signaling pathway, to the exclusion of estrogen receptor-alpha.
Ovarian cancer causes more deaths in women than any other gynecological cancer. The number of deaths caused by ovarian cancer is exacerbated by the lack of reliable screening, specific symptoms, and effective treatments. The National Cancer Institute estimates that 21,550 new cases of ovarian cancer will be diagnosed in the US in 2009. Women diagnosed with localized, regional, and distant ovarian cancer have a 93%, 69%, and 30% 5-year survival rate, respectively [1–3]. However, diagnosis of localized ovarian cancer only occurs in about 19% of the cases due to a lack of reliable screening techniques and the absence of specific symptoms.
Ovarian cancer samples overexpress a putative serine-threonine receptor protein kinase, STYK1, as demonstrated by microarray analysis . The human STYK1 kinase domain shares approximately 30-34% identity with FGFR (fibroblast growth factor receptor)/PDGFR (platelet-derived growth factor) family members, which have been shown to function as oncogenes . STYK1 overexpression constitutively activated the RAS/MAPK, STAT1, and STAT3 pathways in NIH3T3 cells . Interestingly, ovarian cancer cells were shown to constitutively express high levels of STAT3 [7, 8]. Furthermore, BaF3 cell lines overexpressing STYK1 proliferated in media without serum or growth factors. Inoculation of these cells into nude mice induced tumor formation within one week and the cells metastasized after 4 weeks. Introducing a tyrosine to phenylalanine point mutation into the catalytic domain of STYK1 blocked cell proliferation as well as STYK1-induced tumorigenesis [6, 9]. STYK1 expression is regulated by estrogen in ERα (estrogen receptor alpha)-negative (MDA-MB-231) and ERα-positive MCF7) breast cancer cells based on microarray analysis and real-time PCR analysis .
Estrogen receptors play a critical role in ovarian tumor cell growth. Ovarian surface epithelial cells produce estradiol and estrone, and the ovary is a key target of estrogen . The postmenopausal ovary produces little or no estrogen; conversely, increased steroid hormone levels have been observed in the plasma of ovarian cancer patients . The occurrence of ovarian cancer increases dramatically in menopausal women. Furthermore, previous studies report a correlation between plasma estradiol, progesterone, and androstenedione with stage of disease [13, 14]. However, the mechanisms by which estrogen receptors contribute to ovarian tumorigenesis are still unclear . GPR30, a novel estrogen receptor, and ERα stimulation by both G-1 (GPR30-specific ligand) and estradiol were shown to synergistically induce proliferation of breast and ovarian cancer lines .
In this study we examined STYK1 immunoreactivity in normal, benign, and malignant ovarian tissues. To investigate the role of estrogen and GPR30 in STYK1 regulation, we treated a benign and several malignant ovarian cancer cell lines with estradiol and G-1. We describe differences in STYK1 RNA and protein expression levels in treated versus untreated ovarian tumor cells. We also compare estradiol- and G-1-induced STYK1 expression. In the present report, we show that STYK1 expression is associated with ovarian tumorigenesis. Furthermore, we provide evidence for estrogen-mediated STYK1 regulation through an unknown GPR30 signaling pathway.
Materials and methods
17β-estradiol and BSA-conjugated estradiol were purchased from Sigma-Aldrich (Sigma, St. Louis, MO). 1-(4-(6-Bromobenzo[1, 3]dioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G-1) was purchased from Calbiochem (San Diego, CA).
STYK1 and GPR30 antibodies were purchased from AbCam (Cambridge, MA). α-Tubulin antibody was purchased from Millipore (Billerica, MA).
HS832, OvCar3, and CaOv3 were obtained from American Type Culture Collection (Manassas, VA). SkOv3, OvCar5, OvCar8, and IGROV1 were kindly provided by the lab of Dr. Neil Sidell (Emory University School of Medicine, Department of Gynecology and Obstetrics). All cell lines were maintained in DMEM with 10% FBS. Prior to treatment the cells were incubated in phenol-red free DMEM supplemented with 20% charcoal stripped FBS overnight (12-16 h) followed by incubation with 5 × 10-8 M estradiol, 1 × 10-8 M BSA-conjugated estradiol, and 1 × 10-8 M G-1 for 4-18 h. Ethanol, phosphate-buffered saline (PBS), and dimethyl sulfoxide were used as the respective vehicle controls.
Reverse transcriptase (RT) and real time RT-PCR
Treated and untreated cells were rinsed with PBS and pelleted for RNA isolation. RNA was extracted using the RNeasy Midi kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. RNA purity and concentration were determined by spectrophotometry. cDNA was generated at a concentration equivalent to 25 ng/μL of RNA in a 20 μL volume with random hexamers and Superscript II reverse transcriptase (Invitrogen Corporation). The PCR products were visualized on ethidium bromide-stained 2% agarose gels under UV light. Real-time PCR was carried out using the ABI Prism 7000 System. Tubulin was used as an internal control for normalization of each data point. Relative induction was calculated using the 2-ΔΔCT formula . RNA was analyzed from three independent experiments.
Lysates were collected from treated and untreated cells in modified radioimmuno precipitation assay (RIPA) buffer containing EDTA and a protease inhibitor cocktail (Pierce Biotechnology, Rockford, IL) by standard methods. 40 μg of protein was resolved by SDS-PAGE and transferred onto PVDF membranes. The membranes were subjected to immunodetection by incubation with primary antibody for STYK1 (1:500) and GPR30 (1:250). Equal protein loading was controlled by immunoblot of α-tubulin (1:3000). The lysates from three independent experiments were analyzed.
Tissue panel and immunohistochemistry
Formalin-fixed arrays of normal, benign, and malignant ovarian tissues were obtained from Pantomics Inc. (San Franscico, CA). The tissues were stained with a mouse monoclonal antibody for STYK1 and counterstained with hematoxylin by the Winship Cancer Institute Pathology Core Facility at Emory University. Each tissue section was assigned a score of 0 for none, 1 for weak, 2 for moderate, or 3 for strong STYK1 immunoreactivity. Scoring of the tissue sections was done by one of the authors without prior knowledge of the clinical parameters.
Statistical analyses were performed using the one-way ANOVA test in GraphPad Prism (San Diego, CA). The data are presented as mean ± standard error.
Expression of STYK1 in normal, benign, and malignant ovarian tissues
Expression of estrogen receptors and STYK1 in ovarian cancer cell lines
Estradiol and GPR30-specific G-1 induce STYK1 RNA but not protein expression in ovarian cancer cell lines
Discussion and Conclusion
STYK1 mRNA levels have been reported in human benign and/or malignant tissues, but the immunoreactivity of STYK1 has not been reported. Several reports demonstrate STYK1 mRNA expression in various normal tissues and STYK1 overexpression in breast and lung cancer tissues and cell lines, as well as in patients with acute leukemia [17–19]. Moreover, Moriai et. al reported high levels of STYK1 expression even in early stages of breast cancer. In this study, we demonstrated the presence of STYK1 immunoreactivity, in benign and malignant ovarian tissues and cell lines but not in normal ovarian tissue. Moreover, benign ovarian tissues displaying immunoreactivity for STYK1 displayed weak staining. Moderate and strong STYK1 staining was seen only in the high grade ovarian cancer tissues. This data suggests that STYK1 is associated with tumorigenic and malignant phenotypes in ovarian tissue. However, it should be noted that duplicates of only two normal tissue sections were analyzed in this study. With more samples this data should support the need for future studies to validate STYK1 as a potential prognostic tool for detecting multiple stages of ovarian carcinogenesis.
Our lab previously demonstrated that estradiol increases STYK1 mRNA levels in ERα negative, ERβ positive MDA-MB 231 breast cancer cells . In the current study estradiol downregulated STYK1 in OvCar5 cells expressing ERβ but not ERα but did not have a notable affect on STYK1 mRNA levels in OvCar8 cells, which have the same estrogen receptor expression profile (Fig. 3A). This might be due to the presence of higher levels of GPR30 downstream signaling proteins or EGFR/HER protein levels, which are involved in signaling through GPR30. This would be supported in the increase of STYK1 due to G1 treatment, OvCar5 versus OvCar8. It is notable that the level of GPR30 mRNA is not reflective of the relative levels of GPR30 protein. Further investigation into the mechanism of GPR30 expression and regulation is underway. However, the higher ERβ levels in the OvCar8 cells could account for the difference in STYK1 regulation. Interestingly, the highest STYK1 induction was seen in the HS832 cells (8 h, p < 0.01; 18 h, p < 0.001), which are ERα and ERβ negative while the ERα and ERβ positive SkOv3 cells had a marked reduction in STYK1 expression in response to estradiol treatment. This data suggests that there is an inverse relationship between estradiol-mediated STYK1 regulation and ERα/ERβ expression. A similar observation was observed in MCF7, ERα positive, ERβ negative versus MDA-MB-231 which is ERα negative, ERβ positive . ERα was previously shown to downregulate the FN1 gene in ovarian cancer cells and ERβ expression is inversely correlated with tumorigenesis in ovarian cells [11, 20]. Regulation of STYK1 expression in cells negative for ERα and ERβ points to estradiol-mediated regulation through a nontraditional hormone receptor pathway, possibility GPR30.
GPR30, a novel estrogen receptor was recently reported to mediate changes in gene expression and growth in ovarian cancer cells treated with estradiol . We showed that G-1, a GPR30-specific ligand, induced STYK1 at a higher level in the ovarian tumor cells than estradiol. A significant increase (p < 0.001) in G-1-induced STYK1 expression was seen in OvCar5 cells, which do not express ERα, the primary estradiol receptor, but expresses ERβ at very weak levels. In contrast, G-1 downregulated STYK1 in OvCar8 cells, which expressed no ERα and the highest ERβ levels of the analyzed cell lines. We speculate that STYK1 is a downstream target of estrogen-mediated GPR30 activation in ovarian cancer cells and that the affect of GPR30 on STYK1 expression is more pronounced in the absence of ERα and ERβ. This difference in STYK1 regulation could be due to the loss preferential or competitive binding of estradiol to ERα and/or ERβ. It is important to note that one study reported that estradiol does not activate GPR30 . It would also imply that the affect ERα and/or ERβ on GPR30-mediated regulation of STYK1 expression occurs through a mechanism other than competitive ligand binding.
The cellular localization of GPR30 is controversial. It has been reported to localize to the cell membrane and the endoplasmic reticulum membrane [21, 22]. We addressed this issue; G-1-induced STYK1 expression was compared to that in cells treated with BSA-conjugated estradiol (E2B), which is too large to enter the cell. Therefore, any estradiol-induced STYK1 expression would occur through binding of estradiol to a cell membrane receptor. E2B induced STYK1 expression at a level similar to the estradiol induction in each cell line except OvCar5, where STYK1 expression doubled. However, E2B-induction was consistently lower than that seen in G-1-treated cells. This data supports localization of GPR30 to the cell membrane but does not controvert reports of its intracellular localization and provides further evidence of estradiol binding to GPR30.
Liu et. al reported tumorigenesis and metastasis of normal cells (NIH3T3 and BaF3) overexpressing STYK1 in nude mice . Their group suggested that abnormal expression of STYK1 results in a constitutively active state caused by disruption of an inactive vs. active state equilibrium. However, we did not see an appreciable difference in total STYK1 protein levels in cells treated with estradiol and G-1 compared to untreated controls. It is possible that changes in STYK1 protein levels occur early in tumorigenesis and that estradiol does not further induce STYK1 overexpression. Nonetheless, studies show that STYK1 activity is regulated by phosphorylation and dephosphorylation of several tyrosine residues within exon 11 [6, 9]. Therefore, both STYK1 and GPR30 might be model therapeutic targets for the development of more effective ovarian cancer treatments. These molecular targets may also be especially important in treating triple negative (ERα negative, HER2 negative, progesterone receptor negative) breast cancers, which are often nonresponsive to standard chemotherapeutic medications that target traditional hormone receptors .
Thanks to Neil Sidell for his comments and review of the manuscript. This work was supported in part by the Fellowships in Research and Science Teaching (FIRST) postdoctoral program at Emory University School of Medicine NIH K12-GM000680 and NIH 5P60 MD000525-02.
- Lingeman CH: Etiology of cancer of the human ovary: a review. J Natl Cancer Inst 1974, 53: 1603–1618.PubMedGoogle Scholar
- Scott M, McCluggage WG, Hillan KJ, Hall PA, Russell SE: Altered patterns of transcription of the septin gene, SEPT9, in ovarian tumorigenesis. Int J Cancer 2006, 118: 1325–1329. 10.1002/ijc.21486PubMedView ArticleGoogle Scholar
- Smith T, Stein KD, Mehta CC, Kaw C, Kepner JL, Buskirk T, Stafford J, Baker F: The rationale, design, and implementation of the American Cancer Society's studies of cancer survivors. Cancer 2007, 109: 1–12. 10.1002/cncr.22387PubMedView ArticleGoogle Scholar
- Wu F, Safe S: Differential activation of wild-type estrogen receptor alpha and C-terminal deletion mutants by estrogens, antiestrogens and xenoestrogens in breast cancer cells. J Steroid Biochem Mol Biol 2007, 103: 1–9. 10.1016/j.jsbmb.2006.07.007PubMedView ArticleGoogle Scholar
- Liu L, Yu XZ, Li TS, Song LX, Chen PL, Suo TL, Li YH, Wang SD, Chen Y, Ren YM, et al.: A novel protein tyrosine kinase NOK that shares homology with platelet- derived growth factor/fibroblast growth factor receptors induces tumorigenesis and metastasis in nude mice. Cancer Res 2004, 64: 3491–3499. 10.1158/0008-5472.CAN-03-2106PubMedView ArticleGoogle Scholar
- Li YH, Zhong S, Rong ZL, Ren YM, Li ZY, Zhang SP, Chang Z, Liu L: The carboxyl terminal tyrosine 417 residue of NOK has an autoinhibitory effect on NOK-mediated signaling transductions. Biochem Biophys Res Commun 2007, 356: 444–449. 10.1016/j.bbrc.2007.02.154PubMedView ArticleGoogle Scholar
- Ho SM: Estrogen, progesterone and epithelial ovarian cancer. Reprod Biol Endocrinol 2003, 1: 73. 10.1186/1477-7827-1-73PubMed CentralPubMedView ArticleGoogle Scholar
- Syed V, Ulinski G, Mok SC, Ho SM: Reproductive hormone-induced, STAT3-mediated interleukin 6 action in normal and malignant human ovarian surface epithelial cells. J Natl Cancer Inst 2002, 94: 617–629.PubMedView ArticleGoogle Scholar
- Chen Y, Li YH, Chen XP, Gong LM, Zhang SP, Chang ZJ, Zhang XF, Fu XY, Liu L: Point mutation at single tyrosine residue of novel oncogene NOK abrogates tumorigenesis in nude mice. Cancer Res 2005, 65: 10838–10846. 10.1158/0008-5472.CAN-05-1091PubMedView ArticleGoogle Scholar
- Kimbro KS, Duschene K, Willard M, Moore JA, Freeman S: A novel gene STYK1/NOK is upregulated in estrogen receptor-alpha negative estrogen receptor-beta positive breast cancer cells following estrogen treatment. Mol Biol Rep 2008, 35: 23–27. 10.1007/s11033-006-9047-1PubMedView ArticleGoogle Scholar
- Cunat S, Hoffmann P, Pujol P: Estrogens and epithelial ovarian cancer. Gynecol Oncol 2004, 94: 25–32. 10.1016/j.ygyno.2004.03.026PubMedView ArticleGoogle Scholar
- Roa BR, Slotman BJ: Action and counter-action of hormones in human ovarian cancer. Anticancer Res 1989, 9: 1005–1007.PubMedGoogle Scholar
- Backstrom T, Sanders D, Leask R, Davidson D, Warner P, Bancroft J: Mood, sexuality, hormones, and the menstrual cycle. II. Hormone levels and their relationship to the premenstrual syndrome. Psychosom Med 1983, 45: 503–507.PubMedView ArticleGoogle Scholar
- Mahlck CG, Backstrom T, Kjellgren O: Androstenedione production by malignant epithelial ovarian tumors. Gynecol Oncol 1986, 25: 217–222. 10.1016/0090-8258(86)90102-2PubMedView ArticleGoogle Scholar
- Albanito L, Madeo A, Lappano R, Vivacqua A, Rago V, Carpino A, Oprea TI, Prossnitz ER, Musti AM, Ando S, Maggiolini M: G protein-coupled receptor 30 (GPR30) mediates gene expression changes and growth response to 17beta-estradiol and selective GPR30 ligand G-1 in ovarian cancer cells. Cancer Res 2007, 67: 1859–1866. 10.1158/0008-5472.CAN-06-2909PubMedView ArticleGoogle Scholar
- Yalcin A: Quantification of thioredoxin mRNA expression in the rat hippocampus by real-time PCR following oxidative stress. Acta Biochim Pol 2004, 51: 1059–1065.PubMedGoogle Scholar
- Moriai R, Kobayashi D, Amachika T, Tsuji N, Watanabe N: Diagnostic relevance of overexpressed NOK mRNA in breast cancer. Anticancer Res 2006, 26: 4969–4973.PubMedGoogle Scholar
- Amachika T, Kobayashi D, Moriai R, Tsuji N, Watanabe N: Diagnostic relevance of overexpressed mRNA of novel oncogene with kinase-domain (NOK) in lung cancers. Lung Cancer 2007, 56: 337–340. 10.1016/j.lungcan.2007.01.002PubMedView ArticleGoogle Scholar
- Kondoh T, Kobayashi D, Tsuji N, Kuribayashi K, Watanabe N: Overexpression of serine threonine tyrosine kinase 1/novel oncogene with kinase domain mRNA in patients with acute leukemia. Exp Hematol 2009, 37: 824–830. 10.1016/j.exphem.2009.04.010PubMedView ArticleGoogle Scholar
- O'Donnell AJ, Macleod KG, Burns DJ, Smyth JF, Langdon SP: Estrogen receptor-alpha mediates gene expression changes and growth response in ovarian cancer cells exposed to estrogen. Endocr Relat Cancer 2005, 12: 851–866. 10.1677/erc.1.01039PubMedView ArticleGoogle Scholar
- Otto C, Fuchs I, Kauselmann G, Kern H, Zevnik B, Andreasen P, Schwarz G, Altmann H, Klewer M, Schoor M, et al.: GPR30 does not mediate estrogenic responses in reproductive organs in mice. Biol Reprod 2009, 80: 34–41. 10.1095/biolreprod.108.071175PubMedView ArticleGoogle Scholar
- Funakoshi T, Yanai A, Shinoda K, Kawano MM, Mizukami Y: G protein-coupled receptor 30 is an estrogen receptor in the plasma membrane. Biochem Biophys Res Commun 2006, 346: 904–910. 10.1016/j.bbrc.2006.05.191PubMedView ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.