Silibinin Impairs Constitutively Active TGFα-EGFR Autocrine Loop in Advanced Human Prostate Carcinoma Cells
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Epidermal growth factor (EGF) and transformation growth factor-α (TGFα) are potent mitogens that regulate proliferation of prostate cancer cells via autocrine and paracrine loops, and promote tumor metastasis. They exert their action through binding to the cell surface receptor, epidermal growth factor receptor (EGFR), and cause activation of Erk1/2 mediated mitogenic signaling in human prostate cancer (PCA) at both advanced and androgen-independent stages. Thus, we rationalized that inhibiting this mitogenic pathway could be useful in controlling advanced PCA growth.
LNCaP and DU145 human PCA cells were treated with silibinin (100–200 μM) for different time points, and the levels of TGFα, activated signaling molecules (EGFR, Erk1/2 and Jnk1/2) and Erk1/2 kinase activity were analyzed employing ELISA, immunoprecipitation and/or immunoblotting techniques. The mRNA levels of TGFα were analyzed by RT-PCR.
Treatment of cells (LNCaP and DU145) with silibinin resulted in a decrease in TGFα protein at both secreted and cellular levels together with a decrease in its mRNA level. Silibinin also caused an inhibition of EGFR activation followed by that of Erk1/2 without any change in their protein levels. The kinase activity of Erk1/2 to Elk1 was also inhibited by silibinin at least in DU145 cells. In other study, silibinin caused strong inhibition of Jnk1/2 activation in LNCaP cells while in DU145 cells, a strong induction in Jnk1/2 activation was observed. These results suggest that silibinin impairs TGFα-EGFR-Erk1/2 signaling in both androgen-dependent (LNCaP) and -independent (DU145) advanced human prostate carcinoma cells.
This study, for the first time, identifies the inhibitory effect of silibinin on constitutively active TGFα-EGFR autocrine loop in advanced human PCA cells, which plausible contributes to the strong efficacy of silibinin in PCA prevention and intervention, as reported in recent studies.
Key wordsEGFR Erk1/2 prostate cancer silibinin TGFα
epidermal growth factor receptor
extracellular signal-regulated kinase
c-Jun N-terminal protein kinase
transforming growth factor-α
This work was supported by the NCI RO1 grant CA102514.
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