Function analysis of estrogenically regulated protein tyrosine phosphatase γ (PTPγ) in human breast cancer cell line MCF-7

Abstract

Protein tyrosine phosphatase γ (PTPγ) is a member of the receptor-like family of tyrosine phosphatases and has been implicated as a tumor suppressor gene in kidney and lung cancers. Based on our previous findings, we hypothesize that PTPγ is a potential estrogen-regulated tumor suppressor gene in human breast cancer. To examine the effects of PTPγ on growth of MCF-7 human breast cancer cells and compare the estrogenic responses of human breast cells with different PTPγ expression levels, we established several stably transfected MCF-7 cell lines expressing different levels of PTPγ, which were confirmed by RT-PCR and immunostaining. In our work, we used the antisense construct to breakdown endogenous PTPγ level in MCF-7 cells. The results from doubling time assay suggested that PTPγ is capable of inhibiting MCF-7 breast cancer cell growth. We further demonstrated that PTPγ is able to inhibit anchorage-independent growth of breast cancer cells in soft agar and reduce the estrogenic responses of MCF-7 cell proliferation to estradiol-17β (E 2) and zeranol (Z, a nonsteroidal growth promoter with estrogenic activity). Our data suggest that PTPγ may function as an important modulator in regulating the process of tumorigenesis in human breast.