IκB kinase is critical for TNF-α-induced VCAM1 gene expression in renal tubular epithelial cells

The expression of VCAM1 is up-regulated in renal proximal tubular epithelial cells (TEC) in a variety of inflammatory renal diseases, a prominent example of which is acute renal allograft rejection. VCAM1 may play an important role in these diseases because it binds to the integrins very late Ag-4 and alpha (4)beta (7) on lymphocytes and monocytes, thereby providing a potential mechanism to recruit these leukocytes to sites of inflammation. The molecular mechanisms underlying VCAM1 regulation in renal TEC are essentially unknown. We now report that VCAM1 mRNA is dramatically up-regulated in C1, a cell line derived from renal TEC, on exposure to TNF-alpha. Two NF-kappaB binding sites in the VCAM1 promoter are critical for the TNF-alpha -induced VCAM1 transcriptional up-regulation, and both sites bind to p65-p50 NF-kappaB complexes. TNF-alpha induces activation of inhibitor of NF-ICB (I kappaB) kinase-beta (IKK-beta), a protein kinase that phosphorylates the NF-kappa B inhibitor I kappaB, and thereby targets the latter for degradation via the ubiquitin-proteasome pathway. Moreover, dominant negative versions of IKK inhibit TNF-alpha activation of a VCAM1 promoter reporter. We conclude that the IKK/NF-kappaB pathway is critical in the TNF-alpha -induced up-regulation of VCAM1 mRNA in renal TEC.