DNA-BINDING OF ACTIVATOR PROTEIN-1 IS INCREASED IN HUMAN MESANGIAL CELLS CULTURED IN HIGH GLUCOSE-CONCENTRATIONS

Human mesangial cells (HMC) grown in high glucose environments synthes ize excessive amounts of extracellular matrix proteins (ECM). The prom oter regions of certain ECM genes contain TPA (phorbol ester)-responsi ve element (TRE) motifs that bind the transcription factor. activator protein-1 (AP-1), a complex of Jun and other phosphoproteins. AP-1 bin ding to the TRE promoter is regulated by the quantity, composition and post-translational modifications of proteins in the AP-1 complex. We report an increased binding of AP-1 to TRE oligonucleotides in HMC cul tured chronically (5 days) in high glucose environments (30 mM d-gluco se). This increased binding is not due to differences in the nuclear q uantity of AP-1 proteins or in the composition of the: AP-1 complex wh en compared to AP-1 proteins from tells grown in normal glucose (5 mM d-glucosc). A 30 mM 1-glucose environment also increased AP-1 binding, but to a degree less than d-glucose. The increased AP-1 binding was p artly reversed by treatment of HMC with Calphostin C or Bisindolylmale imide I suggesting a partial role of the protein kinase C (PKC) pathwa y in mediating AP-1 binding. AP-1 binding was unaffected by treatment of cells with the MEK inhibitor PD 98059. In addition, increased AP-1 binding persisted for at least 48 hours after media glucose concentrat ions were normalized. The level of Jun-NH2-terminal kinase (JNK) activ ity and the phosphorylation of the JNK kinase, SEK1, were unchanged by chronic high glucose concentrations. These studies suggest that in HM C cultured in chronic high glucose. post-translational modifications i ncrease the binding of AP-1 to the TRE motif.