Published in:
01-08-2003 | Article
Erk 1,2 phosphorylates p27Kip1: Functional evidence for a role in high glucose-induced hypertrophy of mesangial cells
Published in: Diabetologia | Issue 8/2003
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Aims/hypothesis
Mesangial cell hypertrophy is one of the earliest morphological abnormalities of diabetic nephropathy. We have previously shown that high glucose induces p27Kip1 by a post-transcriptional mechanism and that mesangial cell hypertrophy depends on G1-phase arrest mediated by this CDK-inhibitor. However, it remains poorly understood how high glucose stimulates p27Kip1 expression in mesangial cells.
Methods
Mesangial cells were isolated from p27Kip1 +/+ and –/– mice and characterized by light microscopy and immunohistochemistry. It was tested by Western blotting and autoradiography whether high glucose medium activates Erk 1,2 and whether this activation phosphorylates p27Kip1. The three consensus phosphorylation sites of p27Kip1 were mutated and these constructs were expressed in p27Kip1 –/– mesangial cells. Hypertrophy was assessed by different methods.
Results
High glucose stimulates phosphorylation of MAP kinases Erk 1,2 in p27Kip1 +/+ and –/– mesangial cells. Activation of Erk 1,2 leads to phosphorylation of p27Kip1 in vitro and in vivo. Mutations of serine10 or threonine187 still supported high glucose-induced hypertrophy. In contrast, a mutation of serine178 converted the hypertrophic response into a proliferative phenotype. Mutation of serine178 leads to the attenuated expression of p27Kip1 protein in the presence of high glucose.
Conclusions/interpretation
Our study shows that high glucose stimulates Erk 1,2 that phosphorylate p27Kip1 at serine178 increasing its expression. This is an important molecular mechanism of high glucose-induced hypertrophy of mesangial cells.