I kappa B kinase is critical for TNF-alpha-induced VCAM1 gene expression in renal tubular epithelial cells

The expression of VCAM1 is up-regulated in renal proximal tubular epithelia l cells (TEC) in a variety of inflammatory renal diseases, a prominent exam ple of which is acute renal allograft rejection. VCAM1 may play an importan t role in these diseases because it binds to the integrins very late Ag-4 a nd alpha (4)beta (7) on lymphocytes and monocytes, thereby providing a pote ntial mechanism to recruit these leukocytes to sites of inflammation. The m olecular mechanisms underlying VCAM1 regulation in renal TEC are essentiall y 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-kapp aB binding sites in the VCAM1 promoter are critical for the TNF-alpha -indu ced VCAM1 transcriptional up-regulation, and both sites bind to p65-p50 NF- kappaB complexes. TNF-alpha induces activation of inhibitor of NF-ICB (I ka ppaB) kinase-beta (IKK-beta), a protein kinase that phosphorylates the NF-k appa B inhibitor I kappaB, and thereby targets the latter for degradation v ia the ubiquitin-proteasome pathway. Moreover, dominant negative versions o f IKK inhibit TNF-alpha activation of a VCAM1 promoter reporter. We conclud e that the IKK/NF-kappaB pathway is critical in the TNF-alpha -induced up-r egulation of VCAM1 mRNA in renal TEC.