Type II cGMP-dependent protein kinase inhibits EGF-induced MAPK/JNK signal transduction in breast cancer cells

Our previous research data showed that type II cGMP- dependent protein kinase (PKGII) inhibited EGF-induced MAPK/ERK-mediated signal transduction through blocking the phosphorylation of EGFR caused by EGF. Since EGFR also mediates other MAPK-mediated signal transduction path- ways, this study was designed to investigate whether PKGII inhibits EGF-induced MAPK/c-Jun N-terminal kinase (JNK) signal transduction. MCF-7 human breast cancer cells were infected with adenoviral constructs encoding the cDNA of PKGII (pAd-PKGII) to increase the expression of PKGII and treated with 8-pCPT-cGMP to activate the enzyme. Western blotting was applied to detect the phosphorylation/activation of EGFR, JNK, MKK7 and c-Jun. The Pull-down method was used to detect the activation of Ras protein. Co-IP was used to analyze the binding between Grb2 and Sos1. TUNEL staining was used to detect the apoptosis of MCF-7 cells. The results showed that EGF treatment increased the phosphorylation of EGFR, the binding between Grb2 and Sos1, the activation of Ras, and the phosphorylation/activation of MKK7, JNK and c-Jun, but decreased the apoptosis of the cells. Increase of PKGII activity through infection with pAd-PKGII and stimulation with 8-pCPT-cGMP efficiently reversed the above changes caused by EGF. The results suggest that PKGII also inhibits EGF-induced MAPK/JNK-mediated signal transduc- tion and further confirmed that PKGII can block the activation of EGFR.