1,25(OH)2D3 and Initial Regulation of Smad2/3 Activity in PC-3 Prostate Cancer Cells
The vitamin D metabolite 1,25(OH)2D3 has long been known to inhibit growth of prostate cancer cells and this mainly through a VDR-mediated pathway controlling target gene expression, resulting in cell cycle arrest, apoptosis and differentiation. Another major way in which 1,25(OH)2D3 inhibits cell growth in prostate cancer is via membrane-initiated steroid signalling, which triggers activation of signal cascades upon steroid binding to a receptor complex, leading to induction of genes regulating cell growth, proliferation and apoptosis. The main prostate cancer inhibiting membrane-initiated route is the TGFβ signalling pathway, elicited by the protein TGFβ. Two other important proteins downstream in this cascade are Smad2 and Smad3. In this study the early effects of 1,25(OH)2D3 on activated Smad2/3 levelsin PC-3 prostate cancer cells were examined. PC-3 cells were incubated for 3, 5, 10, 30 and 60 minutes as well as 38 hours both together with 1,25(OH)2D3 of the concentrations 10-10 and 10-7 M and without. Western Blots were then performed on supernatants from the cells treated followed by treatment of the membranes with primary antibodies against phosphorylated Smad2/3 C-terminal linker regions, alkaline phosphatase conjugated secondary antibodies and finally visualization with BCIP/ NBT tablets. As the downstream cascade protein JNK is a proposed activator of Smad2/3, this procedure was also repeated with a JNK inhibitor. This is a follow-up to an earlier study which examined the influence of 1,25(OH)2D3 on TGFβ levels using the same doses and time points and which found that 1,25(OH)2D3 initially lowered the level of active TGFβ, then increased it. The results of this study indicated a 1,25(OH)2D3 mediated induction of the same pattern in the levels of active Smad2 and 3, both with and without JNK inhibitor. The results did not indicate that 1,25(OH)2D3 activates the Smad2/3 C-terminal linker region via the JNK pathway.
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