Overexpression of insulin-like growth factor binding protein-5 helps accelerate progression to androgen-independence in the human prostate LNCaP tumor model through activation of phosphatidylinositol 3'-kinase pathway.
Although insulin-like growth factor (IGF) binding protein-5 (IGFBP-5) is highly up-regulated in normal and malignant prostate tissues after androgen withdrawal, its functional role in castration-induced apoptosis and androgen-independent progression remains undefined. To analyze the functional significance of IGFBP-5 overexpression in IGF-I-mediated mitogenesis and progression to androgen-independence, IGFBP-5-overexpressing human androgen-dependent LNCaP prostate cancer cells were generated by stable transfection. The growth rates of IGFBP-5-transfected LNCaP cells were significantly faster, compared with either the parental or vector-only transfected LNCaP cells in both the presence and absence ofdihydrotestosterone. IGFBP-5-induced increases in LNCaP cell proliferation occurs through both IGF-I-dependent and -independent pathways, with corresponding increases in the cyclin D1 messenger RNA expression and the fraction of cells in S + G2/M phases of the cell cycle. Changes in Akt/protein kinase B, a downstream component of phosphatidylinositol 3'-kinase (PI3K) pathway, in the LNCaP sublines also paralleled changes in their growth rates. Although treatment with a PI3K inhibitor induced apoptosis in both control and IGFBP-5-overexpressing LNCaP cells, this PI3K inhibitor-induced apoptosis was prevented by exogenous IGF-I treatment only in IGFBP-5 transfectants, suggesting that IGFBP-5 overexpression can potentiate the antiapoptotic effects of IGF-I. Furthermore, tumor growth and serum prostate-specific antigen levels increased several fold faster in mice bearing IGFBP-5-transfected LNCaP tumors after castration, despite having similar tumor incidence and tumor growth rates with controls when grown in intact mice before castration. Collectively, these data suggest that IGFBP-5 overexpression in prostate cancer cells after castration is an adaptive cell survival mechanism that helps potentiate the antiapoptotic and mitogenic effects of IGF-I, thereby accelerating progression to androgen independence through activation of the PI3K-Akt/ protein kinase B signaling pathway.
Miyake
H
H
The Prostate Centre, Vancouver General Hospital, British Columbia, Canada.
Nelson
C
C
Rennie
P S
PS
Gleave
M E
ME
D000728:Androgens / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D019938:Cyclin D1 / Q000235:genetics; D013196:Dihydrotestosterone / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D006801:Humans; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
D000728:Androgens; D019938:Cyclin D1; D013196:Dihydrotestosterone; D004791:Enzyme Inhibitors; D018975:Insulin-Like Growth Factor Binding Protein 5; D007334:Insulin-Like Growth Factor I; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017430:Prostate-Specific Antigen; D012333:RNA, Messenger