The fact that the genetic alterations of PTEN are frequently found in hormone-dependent cancers, such as endometrial, breast, and prostate cancers, might suggest the involvement of PTEN in the hormone-dependent cell growth of such tumors. Estrogen promotes the cell growth of the tumors by inducing peptide growth factors in part. We analyzed the possible involvement of PTEN in peptide-growth factor-dependent cell growth in endometrial carcinoma cells. PTEN-null Ishikawa cells were efficiently infected with recombinant adenovirus at 20 MOI (multiplicity of infection) to express PTEN protein. In PTEN-IK cells, phospho-Akt/PKB was down-regulated regardless of the consistent expression of Akt/PKB. The cell growth of parental IK cells was significantly stimulated by EGF and IGF-I, and PTEN-IK cells were further sensitized to the EGF-or IGF-I-growth stimulation. EGFR antibody could completely compromise the stimulatory effects of EGF in both cell lines. Wortmannin, a PI3K inhibitor, or UO126, a MAPK inhibitor, partly suppressed EGF-mediated cell growth stimulation in both cell lines. EGF augmented the level of phospho-Akt/PKB of PTEN-IK cells more effectively than that of parental IK cells. These results imply that the dysfunction of PTEN leads cells into a less-sensitive phenotype to peptide growth factors by constitutive activation of the PI3K/Akt/PKB signaling pathway in endometrial carcinoma.

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