Exogenous p27KIP1 expression induces anti-tumour effects and inhibits the EGFR/PI3K/Akt signalling pathway in PC3 cells

p27 is a cyclin-dependent kinase inhibitor that regulates the progression of cells from G(1) to S phase of the cell cycle. Loss of p27 has been associated with disease progression and with an unfavourable outcome in prostate cancer. In this study, we investigated whether exogenous p27 expression in the human androgen-independent prostate cancer PC3 cell line had any effect on cell growth, and we studied the molecular mechanisms involved. p27 expression was restored in PC3 cells by plasmid delivery. Cell proliferation and apoptosis were assessed in PC3 cells transfected with p27. We also investigated the effects of p27 on the epidermal growth factor receptor (EGFR)/phosphatidylinositol 3-kinase (PI3K)/Akt signalling pathway in PC3 cells. By restoring p27 expression in PC3 cells, we observed that p27 reduced proliferation and induced arrest in G(0)/G(1) phase. Moreover, p27-transfected PC3 cells underwent apoptosis, as shown by flow cytometric analysis and western blotting analysis of Bcl-2, Bax, Bad, caspase-3 and poly(ADP-ribose) polymerase expression. Furthermore, the p27-induced anti-tumour action correlated with inhibition of the EGFR/PI3K/Akt signalling pathway, as confirmed by western blotting analysis and densitometry of EGFR, PI3K (p85), Akt and p-Akt(S473) expression. Our results suggest that exogenous expression of p27 inhibits the proliferation of PC3 cells through induction of G(1) arrest and apoptosis, and this process correlates with inhibition of the EGFR/PI3K/Akt signalling pathway.