Shp1 positively regulates EGFR signaling by controlling EGFR protein expression in mammary epithelial cells

SH2-domain containing protein tyrosine phosphatase 1 (Shp1/PTPN6) is mainly expressed in hematopoietic cells and acts a negative signaling regulator. Although Shp1 is also expressed in epithelial cells, the function of shp1 in normal epithelial is still less well understood, especially in regulating the growth of epithelial cells. In this study, different shRNAs and siRNAs against Shp1 were used to knockdown Shp1 expression in MCF10A, an immortalized mammary epithelial cell line. Shp1 knockdown resulted in inhibited cell growth in part due to lower percentage of MCF10A cells entering into S phase and reduced cyclin D1 expression. Accordingly, EGF-induced tyrosyl phosphorylation of EGFR and Stat5 was significantly inhibited in cells with Shp1 knockdown compared with control whereas EGF-induced Akt and Erk phosphorylation was not affected by Shp1 knockdown. Further analysis revealed that Shp1 knockdown lead to decreased EGFR protein expression without affecting EGFR mRNA expression or increasing EGFR protein degradation. Our data indicate that Shp1 functions as a positive regulator and acts in a novel mechanism through promoting EGFR protein expression in mammary epithelial cells.