Site-specific expression of IQGAP1 in human nephrons.

IQGAP1 is a multifunctional, 190-kDa scaffolding protein that plays an important role in the regulation of cell adhesion, migration, proliferation, differentiation, polarization and cytoskeletal remodeling. IQGAP1 is ubiquitously expressed in human organs and is highly expressed in the kidney. Currently, the site-specific expression of IQGAP1 in the human nephrons is unclear. We performed Western blotting analysis, immunohistochemistry and double-immunolabeling confocal microscopic analysis of IQGAP1 with specific biomarkers of each nephron segment to study the expression and distribution of IQGAP1 in human nephrons. We found that IQGAP1 was strongly expressed in human podocytes and glomerular endothelial cells, but weakly expressed in glomerular mesangial cells. In human renal tubules, IQGAP1 was strongly expressed in the collecting duct, moderately expressed in the proximal tubule, medullary loop, distal convoluted tubule and connecting tubule. IQGAP1 staining was much stronger in the apical membrane in the proximal tubule, thick descending limb and thick ascending limb of medullary loop and collecting duct. However, the expression of IQGAP1 was mainly in the basolateral membrane of the connecting tubule, and diffusely in the thin limb of medullary loop and distal convoluted tubule. The interaction between IQGAP1 and F-actin suggested that cytoskeleton regulation may be the underlying mechanism mediating the effect of IQGAP1 in human nephrons. To the best of our knowledge, this is the first report of specific expression and differential subcellular location of IQGAP1 in human nephrons. The site-specific expression pattern of IQGAP1 suggests that IQGAP1 may play diverse roles in various human nephron segments.