Heterogeneous nuclear ribonucleoprotein K enhances insulin-induced expression of mitochondrial UCP2 protein.

The uncoupling protein 2, UCP2, is a member of a family of inner mitochondrial membrane ion carriers involved in a host of metabolic processes. UCP2 protein is encoded by nuclear genome, but the protein is found exclusively in the mitochondria. The heterogeneous nuclear ribonucleoprotein K (hnRNPK) is an RNA-binding protein involved in many processes that compose gene expression, including mRNA processing and translation. The yeast three-hybrid screen revealed K protein bound to ucp2 mRNA through sites located in the 3'-untranslated region of the transcript. ucp2 mRNA-K protein complexes were associated with polysome-coated mitochondria. Expression of exogenous K protein augmented the insulin-induced mitochondrial level of UCP2 protein that was not accompanied by a corresponding increase in ucp2 mRNA. These results suggest the insulin stimulates translation of ucp2 mRNA in a process that involves K protein.