Downregulation of integrin-linked kinase mRNA expression by nitric oxide in rat glomerular mesangial cells

Inflammatory glomerular diseases are accompanied by changes in the expression patterns of growth factors, mediators and matrix-associated proteins in mesangial cells and by the production of nitric oxide via the cytokine-inducible form of the nitric oxide synthase. Nitric oxide has been shown to act potently on gene transcription. To identify genes that are differentially expressed by endogenously produced nitric oxide, we forced rat mesangial cells to produce high amounts of nitric oxide by exposure to inflammatory cytokines and compared the mRNA expression patterns of cytokine-stimulated mesangial cells with cells that were additionally treated with the nitric oxide synthase inhibitor L-NMMA to block endogenous NO synthesis. We used a modification of a low stringency RT-PCR approach designated as RNA arbitrarily-primed polymerase chain reaction (RAP-PCR). In this way, we identified among others the integrin-linked kinase (ILK) as an NO-regulated gene. The NO-mediated changes in the mRNA and protein expression patterns of ILK were compared to that of "secreted protein acidic and rich in cystein" (SPARC), a gene that was identified as NO-regulated in the same set of experiments (Walpen et al., J. Am. Soc. Nephrol., 11, 468-476). ILK and SPARC mRNA levels by were downregulated by cytokines via endogenously produced nitric oxide in a comparable manner as verified by Northern blot analysis. In contrast, cytokine- induced NO production or administration of exogenous NO-donors strongly reduced SPARC protein levels without altering ILK protein content in mesangial cells over a period up to 72 hours. Blocking de novo protein synthesis showed a short halflife of SPARC (< 2 hours) whereas ILK-protein was stable over a period of 7 hours, indicating that NO-mediated reduction of ILK mRNA levels does not influence protein content of ILK in mesangial cells under the time limitations given under cell culture conditions. However, a role for cytokines/NO in ILK-long-term regulation in chronic inflammatory diseases that may influence phenotypic responses such as apoptosis or cell proliferation remains to be elucidated.