Forced expression of Akt isoforms inhibited cell proliferation in MDA231 breast cancer cells?by?isoform specific mechanisms.

Abstract

The Akt isoforms are activated by growth factors to regulate pleiotropic cellular activities. However, there are limited information about the specificities of three Akt isoforms. To gain insight into isoform-specific roles?of Akt, constitutively active(myristoylated) Akt isoforms were introduced into MDA231 cells via retroviral infection. We have investigated cell proliferation and cell motility, a key phenotype of invasive carcinomas. Proliferation assays indicated that Akt2 inhibited the growth of MDA231 cells while Akt1 led to a relatively modest decrease in cell growth. Wound healing assays revealed that Akt1 and Akt2 overexpressing MDA231 cells showed decrease in motility as compared to control. Western blot analyses indicated that Akt1 overexpression could lead to down-regulation of p-ERK by phosphorylating c-Raf, an upstream kinase of Erk?to inhibit its?downstream signaling while Akt2 overexpression induced upregulation of p27. Cycloheximide decay assays?showed that Akt2 could increase stability of p27 protein. These results?suggest that inhibition of cell prolliferation by Akt isoforms might be mediated by isoform-specific different mechanisms.