SUMOylation And SENP3 Regulate STAT3 Activation In Head And Neck Cancer

Signal transducer and activator of transcription 3?STAT3?is one of the critical mediators of cytokine and growth factors signaling.STAT3 are typically activated by interleukin 6?IL-6?family of cytokines or growth factors that can be constitutively and excessively secreted by epithelial tumor cells,stromal or immune cells to form inflammatory microenvironment.STAT3 activation is mainly to promote proliferation and resistance to apoptosis.Sustained activation of STAT3 promotes cell malignant transformation and maintenance of the malignant phenotype.Aberrant hyperphosphorylation and sustained activation of STAT3 have been found in head and neck cancer?HNC?.HNC arises in the upper aerodigestive tract.The development and progression of HNC occur through a stepwise and progressive accumulation of genetic and epigenetic alterations mainly due to direct and repeated exposures to carcinogens including tobacco,alcohol,and viral infections.Strong basic carcinogenic and epidemiologic data have established tobacco as the carcinogenic factor in the overwhelming majority of HNC.Tobacco and IL-6 induce STAT3 activation in head and neck cancer.Inhibition of STAT3 leads to growth inhibition,increases apoptosis and radiation/chemotherapy sensitivity.Therefore,STAT3 represents the candidate oncogene to head and neck cancer.STAT3 mediates the communication between cancers and their microenvironment,which plays an important role in the development of head and neck cancer.However,how tobacco extracts promote sustained activation of STAT3 and in turn mediates the effect of downstream are not clear.Moreover,whether therer is a common regulatory factor exists in the microenvironment induced by tobacco and IL-6 to modulate STAT3 activition and the corresponding biological effects by changing STAT3 protein modification and signal transduction events is worthy exploration.We demonstrated that exposure of HNC cell lines?hep-2,KB and HN30?to tobacco-specific nitrosamines?NNK,the main component of tobacco carcinogens?induced a rapid Y705 phosphorylation of STAT3?STAT3 activation,STAT3-pY705?,a rapid generation of reactive oxygen species and an increase of SUMO protease SENP3 as well.The rapid increase of STAT3-pY705 could be blocked by antioxidant and SENP3knockdown.These results indicate that NNK can activate STAT3 in HNC cells in a ROS and SENP3 dependent manner.We demonstrated that exposure of HNC cell lines to IL-6induced a rapid increase of STAT3-pY705 in SENP3 dependent manner.Our previous studies showed that the rapid increase of SENP3 protein level was resulted from a mild oxidative stress.To understand how SENP3 regulates the activation of STAT3,we investigated the mechanisms and biological effects of the relationship between SENP3 and STAT3.We utilized immune coprecipitation revealed that SUMOylation at lysine 451 site benefited the binding of STAT3 with its phosphotase TC45.SENP3 could thus enhance STAT3 phosphorylation through de-conjugating SUMO2/3 modification of STAT3.The capabilities of colonigenesis,growth,migration and transcriptional activity of STAT3were stronger in Lys⁴⁵¹SUMO mutant STAT3 compare to wild-type STAT3.We also demonstrated a significant correlation between SENP3 protein level and STAT3 Y705phosphorylation level in human laryngeal carcinoma specimens in aspects of positive smoking history,more lymph node metastasis,later tumor stages?T?and poorer clinical?TNM?stages.These findings identified SUMOylation as a previously undescribed and an important post-translational modification of STAT3,which benefits the binding of STAT3 with its phosphotase TC45.SENP3 enhances STAT3 phosphorylation through de-conjugating SUMO2/3 modification of STAT3,and it is the critical modulator to mediate the development of head and neck cancer under the microenvironment that is characterized by field tobacco carcinogens and inflammatory cytokines.