Calcitriol inhibits lipopolysaccharide-induced proliferation,migration and invasion of prostate cancer cells through suppressing STAT3 signal activation

Increasing evidence suggests that infection promotes the initiation and progression of prostate cancer. This study investigated the effects of lipopolysaccharide (LPS), a major component of Gram-negative bacilli, on proliferation, migration and invasion of prostate cancer cells and the protective effects of 1α,25(OH)₂D₃ (calcitriol). PC-3 and DU145 cells were stimulated with LPS (2.0 μg/mL) in the presence or absence of 1α,25(OH)₂D₃ (100 nM). Our results shown that 1α,25(OH)₂D₃ reduced the proportion of S phase cells in LPS-stimulated PC-3 and DU145 cells, and down-regulated the nuclear protein levels of Cyclin D1 and PCNA in LPS-stimulated PC-3 cells. In addition, 1α,25(OH)₂D₃ inhibited migration and invasion, as determined by wound healing and transwell assay, in LPS-stimulated PC-3 and DU145 cells. Of interest, we observed that 1α,25(OH)₂D₃ inhibits NF-κB activation and subsequent synthesis and secretion of IL-6 and IL-8 by promoting VDR and NF-κB p65 interaction. Surprisingly, 1α,25(OH)₂D₃ blocks nuclear translocation of pSTAT3 by promoting physical interaction between VDR and pSTAT3 (Tyr705) in LPS-stimulated PC-3 and DU145 cells. These results suggest that 1α,25(OH)₂D₃ inhibits LPS-induced proliferation, migration and invasion in prostate cancer cells by directly and indirectly blocking STAT3 signal transduction.