S-Nitrosylation of mitogen activated protein kinase phosphatase-1 suppresses radiation-induced apoptosis.

Radiotherapy is a key modality for head and neck cancer (HNC) treatment. Mitogen activated protein kinase phosphatase-1 (MKP-1) protein levels are elevated in various tumors and are negatively correlated with efficacy of chemo- or radio-therapy. However, the mechanisms underlying the moderate radiosensitivity of HNC and the increased MKP-1 protein levels are still dismal. Here we show that S-nitrosylation of MKP-1 on Cysteine 258 enhances MKP-1 protein stability, phosphatase activity, and MKP-1-mediated anti-apoptotic effect on HNC radiotherapy. Co-culturing MKP-1 transfected HNC cell lines with activated macrophages for mimicking the microenvironment of the irradiated cancer cells further confirms that S-nitrosylation-mediated increase of MKP-1 activity correlates with decrease of HNC radiosensitivity. Therefore, S-nitrosylation of MKP-1 presents a novel mechanism underlying the enhanced MKP-1 expression levels and MKP-1-mediated radio-resistance in head and neck cancer.