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Vitamin D is a steroid hormone that regulates calcium homeostasis and bone metabolism. The active form of vitamin D [1α,25-dihydroxyvitamin D3 (1,25D3)] acts through both genomic and nongenomic pathways. 1,25D3 has antitumor effects in a variety of cancers, including colorectal, prostate, breast, ovarian, and skin cancers. 1,25D3 exerts growth-inhibitory effects in cancer cells through the induction of apoptosis, cell cycle arrest, and differentiation. The mechanisms regulating 1,25D3-induced apoptosis remain unclear. We investigated the role of nongenomic signaling in 1,25D3-mediated apoptosis in squamous cell carcinoma (SCC) cells. 1,25D3 induced rapid and sustained activation of phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) 1/2 pathways in SCC cells. These effects were nongenomic: they occurred rapidly and were not inhibited by cycloheximide or actinomycin D. To examine whether the nongenomic activation of Akt and ERK1/2 plays a role in 1,25D3-mediated apoptosis, the expression of Akt or ERK1/2 was reduced by small interfering RNA (siRNA). siRNA-Akt significantly enhanced 1,25D3-induced apoptosis as indicated by increased levels of Annexin V–positive cells and increased sub-G1 population and DNA fragmentation. In contrast, siRNA-ERK1/2 had no effects on 1,25D3-induced apoptosis. In addition, siRNA-Akt transfection followed by 1,25D3 treatment induced apoptosis much sooner than 1,25D3 alone. siRNA-Akt and 1,25D3 induced caspase-10 activation, suppressed the expression of c-IAP1 and XIAP, and promoted 1,25D3-induced caspase-3 activation. These results support a link between 1,25D3-induced nongenomic signaling and apoptosis. 1,25D3 induces the activation of phosphatidylinositol 3-kinase/Akt, which suppresses 1,25D3-mediated apoptosis and prolongs the survival of SCC cells. (Cancer Res 2006; 66(16): 8131-8)

1,25D3, the most active vitamin D metabolite, has broad spectrum anti-tumor activity. We demonstrated that 1,25D3 affects squamous cell carcinoma (SCC) cell adhesion to extracellular matrix and inhibits cell motility, markers of metastasis. In this study, we extended these observations. In situ zymography assay revealed that 1,25D3 strongly suppressed the ability of SCC cells to degrade gelatin. 1,25D3 reduced the adhesion of SCC cells to laminin, and by flow cytometry, the expression of the laminin receptors integrin α6 and β4. 1,25D3 promoted the activation of focal adhesion kinase (FAK) and the formation of focal adhesion as shown by immunofluorescence. To study the effects of 1,25D3 on cell-cell adhesion, the expression level of cadherins were examined by flow cytometry. 1,25D3 enhanced the expression of E-cadherin and R-cadherin, but did not alter that of N-cadherin. Of note, a 1,25D3-resistant variant of SCC (SCC-DR) was developed and these findings were not observed in SCC-DR cells. To investigate the in vivo effect of 1,25D3, C3H/HeJ mice were injected i.v. into tail vein with 104 SCC cells, and then half of the mice received 0.625 μg of 1,25D3 i.p. daily for 3 days while the other half received saline. Treatment with 1,25D3 dramatically inhibited the development of pulmonary tumor formation, as assessed by MRI analysis and colony counts. Our study suggests that 1,25D3 suppresses SCC metastasis, possibly through the promotion of E-cadherin-mediated cell-cell adhesion and the inhibition of cell motility and invasion. This study was supported by NIH/NCI grants CA067267, CA095045 and CA085142. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5123.