Insights into the heparan sulphate-dependent externalisation of transglutaminase-2 (TG2) in glucose-stimulated proximal-like tubular epithelial cells

Anal Biochem. 2020 Aug 15:603:113628. doi: 10.1016/j.ab.2020.113628. Epub 2020 Feb 16.


The extracellular matrix crosslinking enzyme transglutaminase 2 (TG2) is highly implicated in tissue fibrosis that precedes end-stage kidney failure. TG2 is unconventionally secreted through extracellular vesicles in a way that depends on the heparan sulphate (HS) proteoglycan syndecan-4 (Sdc4), the deletion of which reduces experimental kidney fibrosis as a result of lower extracellular TG2 in the tubule-interstitium. Here we establish a model of TG2 externalisation in NRK-52E tubular epithelial cells subjected to glucose stress. HS-binding TG2 mutants had reduced extracellular TG2 in transfected NRK-52E, suggesting that TG2-externalisation depends on an intact TG2 heparin binding site. Inhibition of N-ethylmaleimide sensitive factor (NSF) vesicle-fusing ATPase, which was identified in the recently elucidated TG2 kidney membrane-interactome, led to significantly lower TG2-externalisation, thus validating the involvement of membrane fusion in TG2 secretion. As cyclin-G-associated kinase (GAK) had emerged as a further TG2-partner in the fibrotic kidney, we investigated whether glucose-induced TG2-externalisation was accompanied by TG2 phosphorylation in consensus sequences of cyclin-dependent kinase (CDK). Glucose stress led to intense TG2 phosphorylation in serine/threonine CDK-target. TG2 phosphorylation by tyrosine kinases was also increased by glucose. Although the precise role of glucose-induced TG2 phosphorylation is unknown, these novel data suggest that phosphorylation may be involved in TG2 membrane-trafficking.

Keywords: Chronic kidney disease (CKD); Extracellular vesicles; Glucose stress; Heparan sulphate (HS) proteoglycan; Phosphorylation; Syndecan-4 (Sdc4); Transglutaminase 2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Cell Line
  • Cyclins / metabolism
  • Epithelial Cells / enzymology
  • Epithelial Cells / metabolism*
  • Extracellular Matrix / enzymology
  • Extracellular Matrix / metabolism
  • Fibrosis
  • GTP-Binding Proteins / metabolism*
  • Glucose / metabolism
  • Glucose / toxicity
  • Heparitin Sulfate / metabolism
  • Kidney / pathology
  • Kidney Tubules / enzymology*
  • Kidney Tubules / metabolism
  • Kidney Tubules / physiology
  • Membrane Fusion
  • Protein Glutamine gamma Glutamyltransferase 2
  • Protein Serine-Threonine Kinases / metabolism
  • Protein Transport / physiology
  • Rats
  • Syndecan-4 / metabolism
  • Transglutaminases / metabolism*


  • Cyclins
  • Gak protein, rat
  • Sdc4 protein, rat
  • Syndecan-4
  • Tgm2 protein, rat
  • Heparitin Sulfate
  • Protein Glutamine gamma Glutamyltransferase 2
  • Transglutaminases
  • Protein Serine-Threonine Kinases
  • GTP-Binding Proteins
  • Glucose