RNA-binding protein IGF2BP2/IMP2 is required for laminin-β2 mRNA translation and is modulated by glucose concentration.

Laminin-β2 (LAMB2) is a critical component of the glomerular basement membrane as content of LAMB2 in part determines glomerular barrier permeability. Previously, we reported that high concentrations of glucose reduce expression of this laminin subunit at the translational level. The present studies were undertaken to further define systems that control Lamb2 translation and the effect of high glucose on those systems. Complementary studies were performed using in vitro differentiation of cultured podocytes and mesangial cells exposed to normal and elevated concentrations of glucose, and tissues from control and diabetic rats. Together, these studies provide evidence for regulation of Lamb2 translation by IMP2, an RNA binding protein that targets Lamb2 mRNA to the actin cytoskeleton. Expression of Imp2 itself is regulated by the transcription factor HMGA2, which in turn is regulated by the microRNA let-7b. Elevated concentrations of glucose increase let-7b, which reduces HMGA2 expression, in turn reducing IMP2 and LAMB2. Correlative changes in kidney tissues from control and streptozotocin-induced diabetic rats suggest these control mechanisms are operative in vivo and may contribute to proteinuria in diabetic nephropathy. To our knowledge, this is the first time that translation of Lamb2 mRNA has been linked to the actin cytoskeleton, as well as to specific RNA-binding proteins. These translational control points may provide new targets for therapy in proteinuric disorders such as diabetic nephropathy where LAMB2 levels are reduced.