Abstract:
Nasopharyngeal carcinoma (NPC) is the most common head and neck cancer in Southeast Asia. Despite radiotherapy being the primary treatment modality, new drugs for NPC has been slow in development. NPC has always been associated with Epstein Barr virus oncoproteins. However, very little has been done to target these molecules. Using high-throughput short-hairpin RNA (shRNA) library screen, several key target candidates were found to play an important role in the survival and proliferation of NPC cells. Gene ontology analysis revealed several enrichment of genes involved in mitogen-activated protein kinase (MAPK) signaling to be strongly associated with NPC cell survival. Here, c-jun N-terminal kinase (JNK) was selected due to its role in regulating the survival of NPC cells. This is evident from the significantly reduced cell viability (p<0.01) and dramatic changes in cell morphology following the depletion of JNK mRNA in HK1 and CNE1 cell lines with moderate effect on TWO1 cell line. No effect was observed in SUNE1 and normal cell lines (NP69 and NP460). Using shotgun proteomic analysis, JNK ablation in HK1 cell line resulted in differentially regulated proteins associated with the Rho-GTPase pathway, such as cell division cycle 42 protein (CDC42) and Ras homolog family member A (RhoA). Finally, JNK inhibition resulted in an increased expression of CDC42 by >14 fold, followed by subsequent activation of the protein. It is well established that CDC42 is a distinct up-stream molecule of JNK and its activation leads to JNK-dependent apoptosis. However, the study found a novel pathway in which CDC42 may be a possible downstream target of JNK. In summary, JNK may have a putative role in the suppression of CDC42 in HK1 cell leading to its continued survival.
