Elberg G, Chen L, Elberg D, Chan MD, Logan CJ, Turman MA. MKL1 mediates TGF-␤1-induced ␣-smooth muscle actin expression in human renal epithelial cells. Am J Physiol Renal Physiol 294: F1116-F1128, 2008. First published March 12, 2008 doi:10.1152/ajprenal.00142.2007.-Transforming growth factor-␤1 (TGF-␤1) is known to induce epithelial-mesenchymal transition in the kidney, a process involved in tubulointerstitial fibrosis. We hypothesized that a coactivator of the serum response factor (SRF), megakaryoblastic leukemia factor-1 (MKL1), stimulates ␣-smooth muscle actin (␣-SMA) transcription in primary cultures of renal tubular epithelial cells (RTC), which convert into myofibroblasts on treatment with TGF-␤1. Herein, we study the effect of MKL1 expression on ␣-SMA in these cells. We demonstrate that TGF-␤1 stimulation of ␣-SMA transcription is mediated through CC(A/T) 6-rich GG elements known to bind to SRF. These elements also mediate the MKL1 effect that dramatically activates ␣-SMA transcription in serum-free media. MKL1 fused to green fluorescent protein localizes to the nucleus and induces ␣-SMA expression regardless of treatment with TGF-␤1. Using proteasome inhibitors, we also demonstrate that the proteolytic ubiquitin pathway regulates MKL1 expression. These data indicate that MKL1 overexpression is sufficient to induce ␣-SMA expression. Inhibition of endogenous expression of MKL1 by small interfering RNA abolishes TGF-␤1 stimulation of ␣-SMA expression. Therefore, MKL1 is also absolutely required for TGF-␤1 stimulation of ␣-SMA expression. Western blot and immunofluorescence analysis show that overexpressed and endogenous MKL1 are located in the nucleus in non-stimulated RTC. Chromatin immunoprecipitation assay demonstrates that TGF-␤1 induces binding of endogenous SRF and MKL1 to the ␣-SMA promoter in chromatin. Since MKL1 constitutes a potent factor regulating ␣-SMA expression, modulation of endogenous MKL1 expression or activity may have a profound effect on myofibroblast formation and function in the kidney.epithelial-mesenchymal transition; myocardin; ubiquitin; transcription; myofibroblast RENAL FIBROSIS IS A COMMON feature of various kidney diseases leading to end-stage renal failure (15,44). This process is characterized by the accumulation of myofibroblasts defined by the expression of ␣-smooth muscle actin (␣-SMA). These cells are major contributors to the increased extracellular matrix deposition seen in kidney fibrosis (16,69). A number of studies demonstrate that renal tubular cells (RTC) can convert to myofibroblasts on epithelial-mesenchymal transition (EMT) stimulated by transforming growth factor-␤ (TGF-␤) (9,11,24,45,69).The regulation of ␣-SMA transcription has been extensively studied in smooth muscle cells and in cells from the myocardium and skeletal muscle, which express ␣-SMA in adults and embryos, respectively (66). Studies on the ␣-SMA promoter from chickens, rats, mice, and humans highlight the importance of cell context and species differences for ␣-SMA transcriptional regulat...

Generalized lipodystrophy is characterized by adipose tissue absence, hypoleptinemia, hypertriglyceridemia, insulin resistance, diabetes, hepatomegaly, and nonalcoholic steatohepatitis. In the course of recruiting patients for treatment with recombinant leptin, we were struck by the frequency and severity of proteinuria. We evaluated 25 patients with generalized lipodystrophy. Eighteen were treated with recombinant leptin, and we have followed 15 on leptin for 4-36 months. We followed renal parameters at baseline and during follow-up visits. Renal biopsies were performed as clinically indicated. At baseline, 22 of 25 patients (88%) had elevated urine albumin excretion (>30 mg/24 h), 15 (60%) had macroalbuminuria (>300 mg/24 h), and five (20%) had nephrotic-range proteinuria (>3500 mg/24 h). Twenty-three (92%) had elevated creatinine clearance (>125 ml/min.1.73 m(2)). Eleven of 15 patients (73%) treated with recombinant leptin exhibited reduction in proteinuria, associated with reduction of hyperfiltration. Four patients who did not improve are discussed individually. Renal biopsy findings were remarkable for focal segmental glomerulosclerosis in four patients, membranoproliferative glomerulonephritis in two patients, and diabetic nephropathy in one patient. In conclusion, generalized lipodystrophy is associated with proteinuria and unique renal pathologies, including focal segmental glomerulosclerosis and membranoproliferative glomerulonephritis. The majority treated with recombinant leptin demonstrated reduction in proteinuria and hyperfiltration.

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Somatostatin is known to modulate mesangial and tubular cell function and growth, but the somatostatin receptor (sst) subtypes responsible for these effects have not been defined. There are at least five different sst receptor subtypes (sst(1)-sst(5)). We used RT-PCR to demonstrate that normal human kidney consistently expresses mRNA for sst(1) and sst(2) (9 of 9 donors). Some donors expressed sst(4) or sst(5) mRNA, but none expressed sst(3) mRNA. Expression of sst(1) and sst(2) was further assessed by staining serial sections of normal human kidney with sst(1) and sst(2) antisera, Arachis hypogaea (AH) lectin (to define distal tubule/collecting duct cells), Phaseolus vulgaris lectin (proximal tubules), and Tamm-Horsfall protein (THP) antiserum (thick ascending limb of the loop of Henle). Specificity of antisera was demonstrated by transfection and absorption studies. Sst(2), but not sst(1), was expressed in glomeruli. Intense sst(1) and sst(2) staining localized exclusively to AH+ and THP+ tubules. Thus sst(1) and sst(2) subtype-selective analogs may be useful to beneficially modulate renal cell function in pathological conditions.