['To explore the role of protein kinase D3 (PKD3) in the regulation of matrix metalloproteinases 7 (MMP-7) expression in prostate cancer cells.', 'PC-3 cells were either stimulated with 100 nmol/L PMA to activate PKD3 kinase activity, or transiently transfected with PKD3 siRNA, and the relative expression level of MMP-7 mRNA were analyzed by real-time PCR using 2(-delta delta Ct) method. MMP-7 mRNA levels were also analyzed and quantified in HEK293 cells with over-expression of wild-type PKD3, PKD3 knockdown (using PKD3 siRNA), or over-expression of wild-type PKD3 followed by PKD3 knockdown.', 'MMP-7 mRNA expression in PC3 cells was significantly decreased after PMA-induced PKD3 kinase activation. In contrast, PKD3 knockdown by siRNA transfection markedly increased MMP-7 mRNA level (P<0.01). MMP-7 mRNA level in HEK293 cells was significantly decreased by PKD3 over-expression, whereas obviously increased by PKD3 knockdown. Down-regulation of MMP-7 mRNA level in HEK293 induced by PKD3 over-expression was rescued by PKD3 knockdown.'] Is [ Protein kinase D3 involved in negative regulation of MMP-7 in prostate cancer cells ]?