Role of PI3K/AKT/mTOR signaling in the cell cycle progression of human prostate cancer

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Abstract

Prostate cancer is one of the most common cancers among men. Recent studies demonstrated that PI3K signaling is an important intracellular mediator which is involved in multiple cellular functions including proliferation, differentiation, anti-apoptosis, tumorigenesis, and angiogenesis. In the present study, we demonstrate that the inhibition of PI3K activity by LY294002, inhibited prostate cancer cell proliferation and induced the G1 cell cycle arrest. This effect was accompanied by the decreased expression of G1-associated proteins including cyclin D1, CDK4, and Rb phosphorylation at Ser780, Ser795, and Ser807/811, whereas expression of CDK6 and β-actin was not affected by LY294002. The expression of cyclin kinase inhibitor, p21CIP1/WAF1, was induced by LY294002, while levels of p16INK4 were decreased in the same experiment. The inhibition of PI3K activity also inhibited the phosphorylation and p70S6K, but not MAPK. PI3K regulates cell cycle through AKT, mTOR to p70S6K. The mTOR inhibitor rapamycin has similar inhibitory effects on G1 cell cycle progression and expression of cyclin D1, CDK4, and Rb phosphorylation. These results suggest that PI3K mediates G1 cell cycle progression and cyclin expression through the activation of AKT/mTOR/p70S6K signaling pathway in the prostate cancer cells.

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Materials and methods

Reagents and cell culture. PI3K inhibitor, LY294002, and mTOR/FRAP inhibitor, rapamycin, were purchased from Calbiochem (San Diego, CA). Propidium iodide (PI) was from Molecular Probes (Eugene, OR). The antibodies against p16INK4, p21CIP1/WAF1, CDC25A, CDK4, CDK6, cyclin D1, and β-actin were from Santa Cruz Biotechnology (Santa Cruz, CA); and the antibodies against Rb, Phospho-Rb (Ser780), Phospho-Rb (Ser795), Phospho-Rb (Ser807/811), Phospho-AKT (Ser473), Phospho-p44/42 MAPK, p70S6K,

PI3K regulates G1 cell cycle progression in prostate cancer cells

To elucidate the role of PI3K in regulating the proliferation, DU145 and PC-3 cells were seeded and cultured for 24 h, followed by incubation in the presence or absence of the PI3K inhibitor, LY294002. Total cell numbers were counted 24, 48, and 72 h after the incubation. As shown in Fig. 1A, the number of both OVCAR-3 and A2780-CP70 cells was greatly increased over the period of 72 h culture in the absence of LY294002. The proliferation of DU145 cells was significantly inhibited by LY294002 in a

Discussion

PI3K plays an important role in many cellular functions in response to growth factor. It has been reported that PI3K is required for cellular transformation induced by several viral oncoproteins such as Src and Ab1 [40], [41], [42]. An oncogenic form of PI3K, v-p3k, was discovered recently in avian sarcoma virus 16 and v-p3k is the viral homolog of a gene encoding for PI3K catalytic subunit [7]. Although PI3K signaling has been hypothesized to play an important role in human prostate cancer

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    This work was supported in part by National Institutes of Health NCI Grant RR16440 and American Heart Association Grant 0160166B (to B.H.J.).

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