TGF-β1 stimulates migration of type II endometrial cancer cells by down-regulating PTEN via activation of SMAD and ERK1/2 signaling pathways

PTEN acts as a tumor suppressor primarily by antagonizing the PI3K/AKT signaling pathway. PTEN is frequently mutated in human cancers; however, in type II endometrial cancers its mutation rate is very low. Overexpression of TGF-beta 1 and its receptors has been reported to correlate with metastasis of human cancers and reduced survival rates. Although TGF-beta 1 has been shown to regulate PTEN expression through various mechanisms, it is not yet known if the same is true in type II endometrial cancer. In the present study, we show that treatment with TGF-beta 1 stimulates the migration of two type II endometrial cancer cell lines, KLE and HEC-50. In addition, TGF-beta 1 treatment down-regulates both mRNA and protein levels of PTEN. Overexpression of PTEN or inhibition of PI3K abolishes TGF-beta 1-stimulated cell migration. TGF-beta 1 induces SMAD2/3 phosphorylation and knockdown of common SMAD4 inhibits the suppressive effects of TGF-beta 1 on PTEN mRNA and protein. Interestingly, TGF-beta 1 induces ERK1/2 phosphorylation and pre-treatment with a MEK inhibitor attenuates the suppression of PTEN protein, but not mRNA, by TGF-beta 1. This study provides important insights into the molecular mechanisms mediating TGF-beta 1induced down-regulation of PTEN and demonstrates an important role of PTEN in the regulation of type II endometrial cancer cell migration.