p27Kip1 Stabilization and G1 Arrest by 1,25-Dihydroxyvitamin D3 in Ovarian Cancer Cells Mediated through Down-regulation of Cyclin E/Cyclin-dependent Kinase 2 and Skp1-Cullin-F-box Protein/Skp2 Ubiquitin Ligase

Abstract

p27Kip1 (p27) is a tumor suppressor whose stability is controlled by proteasome-mediated degradation, a process directed in part by cyclin-dependent kinase 2 (CDK2)-mediated phosphorylation of p27 at Thr 187 and its subsequent interaction with the Skp1-Cullin-F-box protein/Skp2 (Skp2) ubiquitin ligase. 1 is a lipophilic hormone essential for bone homeostasis and the maintenance of serum calcium (1). The classical target tissues for 1,25(OH) 2 D 3 include bone, intestine, and kidney. In addition to the above well defined role, 1,25(OH) 2 D 3 regulates the proliferation and differentiation of both normal and malignant cells of many tissue types (2). 1,25(OH) 2 D 3 and its synthetic analogs inhibit carcinogenesis in mouse skin (3, 4), decrease the size of transplanted sarcomas, reduce lung metastasis in mice (5), suppress the growth of human colonic cancer cell-derived xenografts in immune-suppressed mice (6), and increase the differentiation and decrease the proliferation of leukemia (7), breast cancer (8), prostate cancer (9), colon cancer (10), and squamous carcinoma (11) cells. Growth analyses have demonstrated that 1,25(OH) 2 D 3 causes cancer cells to accumulate in G 1 (9) or G 2 (12, 13) or undergo apoptosis (14, 15), suggesting that 1,25(OH) 2 D 3 or its synthetic analogs are potential agents for cancer treatment or chemo-prevention.Together with breast and prostate cancers, ovarian epithelial cancer (OCa) mortality and incident rates are lower in countries within 20 degrees of the equator (16) where the amount of sunlight exposure is high. For women between the ages of 45-54, the OCa mortality rate is five times greater for those living in the northern United States than in the southern United States (17). In the epidermis, sunlight controls the first step of 1,25(OH) 2 D 3 synthesis, namely, the photoconversion of 7-dehydrocholesterol to pre-vitamin D 3 . Exposure to sunlight, rather than food consumption, has been shown to be the primary source of 1,25(OH) 2 D 3 (18). Therefore, the inverse correlation between sunlight exposure and OCa mortality suggests that decreased synthesis of 1,25(OH) 2 D 3 may contribute to OCa initiation and/or progression. Immunohistochemical analyses and ligand binding assays have found vitamin D receptor in rat (19) and hen (20) ovaries, indicating that the ovary is a target organ for 1,25(OH) 2 D 3 . Studies have also described vitamin D receptor expression in gynecologic neoplasms including OCa (21, 22), raising the possibility that 1,25(OH) 2 D 3 or its synthetic analogs may be effective against OCa.Previous studies have indeed shown that the growth of OVCAR3 cells is suppressed by 1,25(OH) 2 D 3 (22) and that 1,25(OH) 2 D 3 arrests OVCAR3 cells in G 2 /M by a mechanism involving GADD45 (13). The current study shows that 1,25(OH) 2 D 3 arrests OCa cells in G 1 by increasing the abundance of p27, an inhibitor of cyclin-dependent kinase (CDK) activity. 1,25(OH) 2 D 3 stabilized the p27 protein by decreasing the activity of cyclin E-associated CDK2 and the abundance of Skp2. 1...

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

“…Published studies have shown that 1,25(OH) 2 D 3 and its synthetic analogs suppress OCa cell growth (24,25) and induce apoptosis (26,33), raising the potential of using synthetic vitamin D analogs as an alternative or complementary method for OCa intervention (43). Published studies have identified EGF receptor (44) and GADD45 (24) as primary target genes for 1,25(OH) 2 D 3 to induce cell cycle arrests in OCa cells.…”

“…After ligand binding, the VDR forms a heterodimer with retinoid X receptor (RXR) and binds to vitamin D-responsive elements (VDREs) in the regulatory region of target genes to activate or repress their transcription (23). Previous studies have shown that the growth of multiple human ovarian cancers was suppressed by 1,25(OH) 2 D 3 (24,25) and that 1,25(OH) 2 D 3 -induced apoptosis involved down-regulation of telomerase activity (26). This study identifies miR-498 as a primary target gene for 1,25(OH) 2 D 3 , which binds to the 3Ј-UTR of hTERT and decreases its mRNA expression to induce cell death.…”

Induction of Ovarian Cancer Cell Apoptosis by 1,25-Dihydroxyvitamin D3 through the Down-regulation of Telomerase

“…Our recent studies have shown that the growth of multiple OCa cell lines is suppressed by 1,25(OH) 2 VD 3 (6), suggesting that active vitamin D compounds are potential therapeutic agents for OCa treatment and prevention. Molecular analyses have identified GADD45 as a primary target gene that mediates the effect of 1,25(OH) 2 VD 3 on G 2 /M arrest (7) and the p27 CDK inhibitor as the mediator for the arrest at G 1 /S checkpoint (6).…”

Prolactin Receptor Isoforms in Human Breast Cancer

“…Strong epidemiological associations were made between vitamin D deficiency and breast and prostate cancers. The VDR system may arrest the tumor cell cycle at G1/G0 through several mechanisms such as by induction of p21 gene transcription [24] or by inducing the synthesis and/or stabilization of p27 [25]. Recent work in tumor-derived endothelial cells has implicated VDR as an antiproliferative factor inducing cell cycle arrest in G1/G0 and tumor angiogenesis [26].…”