Up-regulation of Cks1 and Skp2 with TNFα/NF-κB signaling in chronic progressive nephropathy

The cyclin-dependent kinase (CDK) inhibitor p27 level is associated with progression of renal damage. We previously reported that mRNA of Skp2, a component of Skp/Cullin/F-box (SCF)-ubiquitin ligase which targets to p27, was increased in unilateral ureteral obstructive kidneys in mice and that the nephritis was attenuated in Skp2-deficient mice. However, the details have not been fully clarified. Here, we found that not only Skp2 but also cdc kinase subunit 1 (Cks1), an essential cofactor for the SCF-Skp2 ubiquitin ligase in targeting p27, was increased in another chronic progressive model, anti-thymocyte serum (ATS) rat nephropathy. After induction of ATS nephropathy, Skp2(+)/Cks1(+)/Ki67(+) tubular epithelial cell numbers increased, and p27(+) tubular epithelial cells decreased transiently. Moreover, we found that TNF alpha was involved in expression of both Skp2 and Cks1 in NRK cell line as well as the in ATS nephropathy. Nuclear accumulations of NF-kappa B subunits RelB and p52 were increased in the tubular epithelial cells of the nephritic kidney. Both Skp2 and Cks1 were colocalized with RelB in these cells. These data suggest that both Skp2 and Cks1 are up-regulated by the TNF alpha-RelB/p52 pathway in the early stages of renal damage and are collaboratively involved in down-regulation of p27 in proliferative tubular dilation and the progression of chronic nephropathy.