SOCS1 induced by NDRG2 expression negatively regulates STAT3 activation in breast cancer cells

Although NDRG2 inactivation has recently been found to have an important role in some tumorigenesis, its role in intracellular signal transduction pathways remains poorly defined. In the present study, we demonstrate that NDRG2 overexpression in malignant breast cancer cells specifically inhibits Akt phosphorylation and induces phosphorylation of p38 MAP kinase and SAPK/JNK. In addition, we investigated whether NDRG2 expression affects JAK/STAT- or mitogen-activated protein kinase-mediated signal activation. JAK2 or STAT3 activation in both resting and IGF-stimulating cells was remarkably inhibited by NDRG2 expression. Furthermore, NDRG2 has been found to highly up-regulate the expression level of SOCS1 mRNA and protein. We have found that NDRG2 was able to regulate cytokine signaling in breast cancer cells through the regulation of SOCS1 expression. Finally, inhibition of p38 MAPK activity blocked the induction of SOCS1 expression by NDRG2, resulting in the recovery of STAT3 phosphorylation level. Together, these data demonstrate that NDRG2 expression in breast cancer cells is able to inhibit STAT3 activation via SOCS1 induction in a p38 MAPK dependent manner, implicating NDRG2 as a growth inhibitory gene in signal transduction pathways of breast tumor cells.