title: Rab34 and its effector munc13-2 constitute a new pathway modulating protein secretion in the cellular response to hyperglycemia.
abstract: Diabetic nephropathy (DN) is the leading cause of end-stage renal disease requiring dialysis in the Western world. Clinical studies reveal that stringent control of blood glucose levels reduces the risk of most diabetic complications, underscoring the importance of understanding the cellular response to hyperglycemia. Our work identifies a new pathway of potential significance in this response, linking hyperglycemia to the stimulation of constitutive protein secretion via a pathway involving munc13 and rab34. These two proteins have previously been shown to interact at the Golgi via the munc13 homology domain 2 (MHD2). In the present study, using cultured rat mesangial cells (RMC), we show that high glucose-induced upregulation of endogenous munc13-2 increases secretion of the model protein, vesicular stomatitis virus glycoprotein-green fluorescent protein (VSVG-GFP), while small interfering (si)RNA-mediated knockdown of either munc13-2 or rab34 abolishes this effect. Similarly, increased secretion of VSVG-GFP is observed following transfection of HeLa cells with wild-type munc13-2, but not when HeLa cells are transfected with a mutant protein in which the MHD2 domain is deleted. Finally, we show that high glucose-stimulated secretion of fibronectin in RMC is abolished by siRNA knockdown of munc13-2. Collectively, our results demonstrate that the mechanistic basis for our observed high glucose-induced protein secretion is through interaction of munc13 and rab34, indicating a potentially critical role for this newly described pathway in the pathogenesis of DN.
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Neil M
authors.initials: NM
authors.lastname: Goldenberg
authors.forename: Mel
authors.initials: M
authors.lastname: Silverman
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005089:Exocytosis; D005353:Fibronectins / Q000378:metabolism; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D050527:Mesangial Cells / Q000378:metabolism; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D005353:Fibronectins; C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; C485548:UNC13B protein, human; D014759:Viral Envelope Proteins; D049452:Green Fluorescent Proteins; C474116:RAB39A protein, human; D020691:rab GTP-Binding Proteins; D005947:Glucose