Abstract
Genistein is a candidate cancer chemopreventive drug being tested in clinical trials. We have shown that genistein blocks prostate cancer (PCa) cell invasion, that p38 mitogen-activated protein (MAP) kinase regulates activation of matrix metalloproteinase type 2 (MMP-2) and cell invasion, and that genistein prevents transforming growth factor β (TGFβ) from activating p38 MAP kinase. More recently, we identified MAP kinase-activated protein kinase 2 (MAPKAPK2) and the 27-kDa heat shock protein (HSP27) as downstream regulators of p38 MAP kinase. However, MAPKAPK2 and HSP27 can be regulated by factors other than p38 MAP kinase, and HSP27 is up-regulated during PCa progression. The current study was undertaken to examine the role of MAPKAPK2 and HSP27 in modulating genistein-mediated regulation of PCa cell invasion. Genistein inhibited TGFβ-mediated phosphorylation of MAPKAPK2 and HSP27. Inhibitory effects by genistein upon cell signaling, inhibition of MMP-2, and inhibition of invasion were retained when both PC3 and PC3-M cells were transfected with either wild-type MAPKAPK2 or HSP27. However, transfection with dominant-negative MAPKAPK2 or nonphosphorylatable mutant HSP27 led to decreases in cell invasion and to abrogation of responsiveness to either TGFβ-mediated increases or genistein-mediated decreases in MMP-2 and cell invasion. It is noteworthy that, after transfection with constitutive active MAPKAPK2 or with pseudophosphorylated HSP27, levels of MMP-2 activation and cell invasion were high and overcame any inhibitory effect of genistein. These findings demonstrate that genistein-mediated inhibition of cell invasion rests upon blocking activation of the MAPKAPK2-HSP27 pathway, and that its activation during cancer progression has the potential to mitigate therapeutic efficacy.
Footnotes
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This work was funded by the following grants to R.C.B.: a merit review award from the Veterans Administration and a Specialized Program of Research Excellence grant CA90386, from the National Cancer Institute, National Institutes of Health, Department of Health and Human Services.
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ABBREVIATIONS: PCa, prostate cancer; genistein, 4′,5,7-trihydroxyflavone; TGFβ, transforming growth factor β; MAP, mitogen-activated protein; MMP-2, matrix metalloproteinase type 2; MAPKAPK2, mitogen-activated protein kinase-activated protein kinase 2; HSP27, 27-kDa heat shock protein; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; WT, wild-type; MK2 WT, wild-type pcDNA3mycMK2; MK2 DN, dominant-negative kinase inactive mutant of pcDNA3mycMK2; MK2 EE, constitutive active mutant of pcDNA3mycMK2; HSP27 3D, pseudophosphorylated mutant of pcDNA3.1-HSP27; HSP27 3G, nonphosphorylatable mutant of pcDNA3.1-HSP27; TBST, Tris-buffered saline/Tween 20; BSA, bovine serum albumin; HRP, horseradish peroxidase; PBS, phosphate-buffered saline; VC, vector control.
- Received March 2, 2006.
- Accepted June 13, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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