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.