Multilevel Regulation of Protein Kinase CδI Alternative Splicing by Lithium Chloride

Lithium chloride (LiCl) is commonly used in treatment of mood disorders; however, its usage leads to weight gain, which promotes metabolic disorders. Protein kinase C delta (PKCδ), a serine/threonine kinase, is alternatively spliced to PKCδI and PKCδII in 3T3-L1 cells. We previously demonstrated that PKCδI is the predominantly expressed isoform in 3T3-L1 preadipocytes. Here, we demonstrate that LiCl treatment decreases PKCδI levels, increases formation of lipid droplets, and increases oxidative stress. Hence, we investigated the molecular mechanisms underlying the regulation of PKCδI alternative splicing by LiCl. We previously demonstrated that the splice factor SFRS10 is essential for PKCδI splicing. Our results demonstrate that glycogen synthase kinase 3 beta (GSK3β) phosphorylates SFRS10, and SFRS10 is in a complex with long noncoding RNA NEAT1 to promote PKCδI splicing. Using PKCδ splicing minigene and RNA immunoprecipitation assays, our results demonstrate that upon LiCl treatment, NEAT1 levels are reduced, GSK3β activity is inhibited, and SFRS10 phosphorylation is decreased, which leads to decreased expression of PKCδI. Integration of the GSK3β signaling pathway with the ribonucleoprotein complex of long noncoding RNA (lncRNA) NEAT1 and SFRS10 enables fine-tuning of PKCδI expression during adipogenesis. Knowledge of the molecular pathways impacted by LiCl provides an understanding of the ascent of obesity as a comorbidity in disease management.