Sougata Saha

Arginylation was previously found to promote stabilization of heat shock protein 70.3 (Hsp70.3) mRNA and cell survival in mouse embryonic fibroblasts (MEFs) on exposure to heat stress (HS). In search of a factor responsible for these phenomena, the current study identified human antigen R (HuR) as a direct target of arginylation. HS induced arginylation of HuR affected its stability and RNA binding activity. Arginylated HuR failed to bind Hsp70.3 3′ UTR, allowing the recruitment of cleavage stimulating factor 64 (CstF64) in the proximal poly-A-site (PAS), generating transcripts with short 3′UTR. However, HuR from Ate1 knock out (KO) MEFs bound to proximal PAS region with higher affinity, thus excluded CstF64 recruitment. This inhibited the alternative polyadenylation (APA) of Hsp70.3 mRNA and generated the unstable transcripts with long 3′UTR. The inhibition of RNA binding activity of HuR was traced to arginylation-coupled phosphorylation of HuR, by check point kinase 2 (Chk2). Arginylation of HuR occurred at the residue D15 and the arginylation was needed for the phosphorylation. Accumulation of HuR also decreased cell viability upon HS. In conclusion, arginylation dependent modifications of HuR maintained its cellular homeostasis, and promoted APA of Hsp70.3 pre-mRNA, during early HS response.

Background: Phytoextracts, due to its complex nature of formulations yet little or no side effects, have been pursued as alternative medicine for the treatment of complex metabolic disorders such as obesity. One of the appealing strategies to achieve this is the modulation of adipocyte development and function with the treatment of phytoextracts. The current study explored the activity of Terminalia chebula fruit, a component of Ayurveda formulation “Triphala” on these aspects of adipogenesis. Materials and Methods: The effect of T. chebula aqueous fruit extract (CAFE) on the process of adipocyte development and function was investigated. To test the effect of CAFE on adipocyte development, 3T3-L1 preadipocytes were differentiated in the presence and absence of CAFE followed by estimation of lipid content and expression of adipogenic genes. To test its effect on adipocyte function, mature 3T3-L1 adipocytes were treated with the extract followed by estimation of lipolysis. Results: Treatment of 3T3-L1 preadipocytes with this extract had efficiently inhibited differentiation and lipid accumulation in these cells. Gene expression of key adipogenic regulators, peroxisome proliferative-activated receptor γ and C/CAAT enhancer-binding protein α, was suppressed due to the treatment with CAFE. Preadipocytes exposed to CAFE also showed suppressed expression of important adipogenic effector genes such as perilipin 1 and fatty acid synthase. Treatment of differentiated adipocytes with CAFE did not affect total lipid contents of the cells. However, CAFE treatment reduced lipolysis to a small extent. Conclusion: CAFE is an anti-adipogenic and anti-lipolytic agent which inhibits adipocyte differentiation by downregulating expression of key adipogenic genes.