ErbB-2 signaling is involved in regulating PSA secretion in androgen-independent human prostate cancer LNCaP C-81 cells.
The expression and secretion of prostate-specific antigen (PSA) are regulated by androgens in normal prostate secretory epithelial cells. In prostate cancer patients, the serum PSA level is usually elevated and cancer cells are initially responsive to androgens. However, those cancer cells become androgen-independent after androgen ablation therapy. In hormone-refractory cancer patients, even in an androgen-deprived environment, the circulation level of PSA rebounds and is constitutively elevated through a yet unknown mechanism. Tyrosine phosphorylation of ErbB-2 is involved in regulating the androgen-responsive phenotype of prostate cancer cells, and it is at least partly regulated by the cellular form of prostatic acid phosphatase (PAcP), a prostate-unique protein tyrosine phosphatase. We investigated the ErbB-2 signal pathway in androgen-independent PSA secretion. LNCaP C-81 cells, which are androgen-independent LNCaP cells lacking endogenous PAcP expression with a hypertyrosine phosphorylated ErbB-2, secreted a higher level of PSA in conditioned media than did androgen-sensitive LNCaP C-33 parental cells. A restored expression of cellular PAcP in C-81 cells was concurrent with a decrease in tyrophosphorylation of ErbB-2 and reduction of PSA secretion. Moreover, transient transfection of C-33 cells with the wild-type ErbB-2 or a constitutively active mutant of MEK1 cDNA resulted in an increased level of secreted PSA. The elevation of secreted PSA level by the forced expression of ErbB-2 was inhibited by an MEK inhibitor, PD98059. In C-81 cells, the expression of a dominant negative mutant of ErbB-2 reduced the secreted level of PSA. The inhibition of ErbB-2 or mitogen-activated protein (MAP) kinases by specific inhibitors AG879, AG825, or PD98059 led to a decrease in PSA secretion. Taken together, our data clearly indicate that the ErbB-2 signal pathway via MAP kinases (ERK1/2) is involved in regulating the secretion of PSA by androgen-independent human prostate cancer LNCaP C-81 cells in an androgen-depleted environment.
Lee
Ming-Shyue
MS
Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha 68198, USA.
Igawa
Tsukasa
T
Yuan
Ta-Chun
TC
Zhang
Xiu-Qing
XQ
Lin
Fen-Fen
FF
Lin
Ming-Fong
MF
D000135:Acid Phosphatase; D000728:Androgens / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D017077:Culture Media, Conditioned / Q000378:metabolism; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011471:Prostatic Neoplasms; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D017027:Protein Tyrosine Phosphatases / Q000502:physiology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000502:physiology
D000135:Acid Phosphatase; D000728:Androgens; D017077:Culture Media, Conditioned; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases; D017430:Prostate-Specific Antigen; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases; D018719:Erb-b2 Receptor Tyrosine Kinases; C482576:MAP3K1 protein, human; C428439:prostatic acid phosphatase