Role of areca nut induced JNK/ATF2/Jun axis in the activation of TGF-beta pathway in precancerous Oral Submucous Fibrosis

Oral submucous fibrosis (OSF) is potentially premalignant with progressive and irreversible extracellular matrix deposition accompanied by epithelial atrophy and like other fibrotic disorders, is primarily a TGF-beta driven disease. OSF is caused by prolonged chewing of areca nut. Our previous studies reported a pivotal role for TGF-beta activation and its effects contributing to OSF. However, the mechanism for activation of TGF-beta signaling in OSF is still unknown. In this study we demonstrate activation of TGF-beta signaling with sub-cytotoxic dose of areca nut in epithelial cells and discovered a key role for pJNK in this process. In good correlation; pJNK was detected in OSF tissues but not in normal tissues. Moreover, activation of JNK was found to be dependent on muscarinic acid receptor induced Ca2+/CAMKII as well as ROS. JNK dependent phosphorylation of ATF2/c-Jun transcription factors resulted in TGF-beta transcription and its signaling. pATF2/p-c-Jun were enriched on TGF-beta promoter and co-localized in nuclei of epithelial cells upon areca nut treatment. In corroboration, OSF tissue sections also had nuclear pATF2 and p-c-Jun. Our results provide comprehensive mechanistic details of TGF-beta signaling induced by etiological agent areca nut in the manifestation of fibrosis which can lead to new therapeutic modalities for OSF