Stress activated p38 MAPK regulates cell cycle via AP-1 factors in areca extract exposed human lung epithelial cells.

Areca nut chewing habits are associated with several oral manifestations like leukoplakia, submucous fibrosis and oral squamous cell carcinoma. Although numerous evidence on areca toxicity is known but the mechanistic pathway of disease causation is to be studied. Aqueous areca nut extract treated A549 cells showed reduced cell viability by 48 h with IC₅₀ value of 0.50%. The toxic nature of areca nut induced the production of reactive oxygen species with decreased anti-oxidant glutathione S transferase levels lead to altered redox homeostasis. PCR studies showed decreased mRNA levels of Jun and Fos AP-1 subunits on extract treatment by 48 h. The protein levels of PCNA, CDK4, RB, p53, c-Jun and c-Fos were found to be downregulated with upregulated CDK inhibitor p21 on extract treatment as compared to control. Results of FACS analysis further confirm G₁/S phase cell cycle arrest on areca nut extract exposure. The regulation of downstream AP-1 subunits by MAPKs was studied by using specific inhibitors of ERK, JNK and p38 along with areca nut extract. Results showed the redox activation of MAP kinases down regulated the mRNA levels of AP-1 subunits in aqueous areca nut extract treated cells. Hence the present study aids in elucidating the role of MAP kinases in regulating the AP-1 subunits and their implications on target genes that are involved regulation of various cellular processes. Further, it would help in understanding the mechanistic aspects of the diseased state which may facilitate in designing of new therapeutic modalities that could help in cancer management.