Association of Asef and Cdc42 expression to tubular injury in diseased human kidney.

Cdc42 is a small guanosine-5'-triphosphatase of the Rho family and plays essential roles in the establishment of cellular polarity and tight junctions in epithelial cells. Adenomatous polyposis coli-associated exchange factor (Asef) is a canonical guanine nucleotide exchange factor of Cdc42 and renders Cdc42 to be guanosine-5'-triphosphate bound and activated. The expression patterns and their significance in human renal diseases are unknown. We examined the expression of Cdc42 and Asef in kidney biopsy specimens of 15 patients and in normal kidney tissue using immunofluorescence and correlated the expression patterns with the clinical characteristics. We also analyzed the coexpression pattern of Ki-67, a marker indicating cell division, and Asef in selected patients. Expression of Asef and Cdc42 together was associated with tubular injury with 100% specificity. Expression of Asef, regardless of Cdc42, also showed a significant diagnostic odds ratio for the presence of the injury. Expression of Asef was associated with lower estimated glomerular filtration rate at the time of biopsy and larger area of interstitial fibrosis. All Ki-67-expressing tubular cells expressed Asef. Induction of Asef and Cdc42 in the renal tubules is a cellular response to injury. Asef induction seems a necessary step for injured tubular cells to enter cell cycle.