Silibinin impairs constitutively active TGFalpha-EGFR autocrine loop in advanced human prostate carcinoma cells.
OBJECTIVE
Epidermal growth factor (EGF) and transformation growth factor-alpha (TGFalpha) 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.


METHODS
LNCaP and DU145 human PCA cells were treated with silibinin (100-200 microM) for different time points, and the levels of TGFalpha, 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 TGFalpha were analyzed by RT-PCR.


RESULTS
Treatment of cells (LNCaP and DU145) with silibinin resulted in a decrease in TGFalpha 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 TGFalpha-EGFR-Erk1/2 signaling in both androgen-dependent (LNCaP) and -independent (DU145) advanced human prostate carcinoma cells.


CONCLUSIONS
This study, for the first time, identifies the inhibitory effect of silibinin on constitutively active TGFalpha-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.
Tyagi
Alpna
A
Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Denver, Denver, Colorado 80262, USA.
Sharma
Yogesh
Y
Agarwal
Chapla
C
Agarwal
Rajesh
R
D000728:Androgens / Q000378:metabolism; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D019898:Autocrine Communication / Q000187:drug effects*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D048056:Mitogen-Activated Protein Kinase 9 / Q000378:metabolism; D009376:Neoplasms, Hormone-Dependent / Q000201:enzymology / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000517:prevention & control; D012333:RNA, Messenger / Q000378:metabolism; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology; D013997:Time Factors; D016211:Transforming Growth Factor alpha / Q000235:genetics / Q000378:metabolism*
D000728:Androgens; D016588:Anticarcinogenic Agents; D000972:Antineoplastic Agents, Phytogenic; D012333:RNA, Messenger; D012838:Silymarin; D016211:Transforming Growth Factor alpha; D000077385:Silybin; D048056:Mitogen-Activated Protein Kinase 9; C512478:EGFR protein, human; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048055:Mitogen-Activated Protein Kinase 8