Rat mesangial cell hypertrophy in response to transforming growth factor-β1

Rat mesangial cell hypertrophy in response to transforming growth factor-β1. Central features of progressive glomerular sclerosis are initial glomerular hypertrophy and subsequent accumulation of extracellular matrix proteins. Since TGF-β1 may play a key role in this glomerular response to injury, the present study sought to explore further TGF-β1 actions and regulated expression of its receptor in rat mesangial cells. The rat TGF-β type II receptor (TGF-βRII) homolog was cloned by screening a rat kidney cDNA library with a human TGF-βRII cDNA probe, and sequenced. Expression of this receptor subtype in rat mesangial cells was then demonstrated by RNase protection assay, and by Northern blot analysis of poly (A)+ RNA, TGF-βRII expression was down-regulated in cells treated with exogenous TGF-β1. Affinity cross linking studies demonstrated presence of this receptor on cell surface. Rat mesangial cells also expressed TGF-β1 and autoinduction by TGF-β1 was observed in the same cells, suggesting that this polypeptide may act in an autocrine fashion on mesangial cells, and that it may stimulate a positive autoamplification loop. TGF-β1 inhibited mesangial cell proliferation and stimulated significant overall protein and collagen production. Furthermore, mesangial cell size increased in response to chronic TGF-β1 treatment. These findings demonstrate that rat mesangial cells express key components of the TGF-β system and raise the intriguing possibility that in the glomerular mesangium, TGF-β1 may not only induce extracellular matrix synthesis, but may also participate in the process of glomerular hypertrophy in response to injury

Mammalian Ste20-Like Kinase and SAV1 Promote 3T3-L1 Adipocyte Differentiation by Activation of PPARγ

The mammalian ste20 kinase (MST) signaling pathway plays an important role in the regulation of apoptosis and cell cycle control. We sought to understand the role of MST2 kinase and Salvador homolog 1 (SAV1), a scaffolding protein that functions in the MST pathway, in adipocyte differentiation. MST2 and MST1 stimulated the binding of SAV1 to peroxisome proliferator-activated receptor γ (PPARγ), a transcription factor that plays a key role in adipogenesis. The interaction of endogenous SAV1 and PPARγ was detected in differentiating 3T3-L1 adipocytes. This binding required the kinase activity of MST2 and was mediated by the WW domains of SAV1 and the PPYY motif of PPARγ. Overexpression of MST2 and SAV1 increased PPARγ levels by stabilizing the protein, and the knockdown of SAV1 resulted in a decrease of endogenous PPARγ protein in 3T3-L1 adipocytes. During the differentiation of 3T3-L1 cells into adipocytes, MST2 and SAV1 expression began to increase at 2 days when PPARγ expression also begins to increase. MST2 and SAV1 significantly increased PPARγ transactivation, and SAV1 was shown to be required for the activation of PPARγ by rosiglitazone. Finally, differentiation of 3T3-L1 cells was augmented by MST2 and SAV1 expression and inhibited by knockdown of MST1/2 or SAV1. These results suggest that PPARγ activation by the MST signaling pathway may be a novel regulatory mechanism of adipogenesis

Expression of rat fibroblast growth factor receptor 1 as three splicing variants during kidney development

Fibroblast growth factors (FGF) are known to participate in the processes of embryogenesis and angiogenesis. This study was undertaken to examine the transcriptional and posttranscriptional regulation of the FGF receptor 1 (FGFR-1) subclass in the embryonic rat kidney. Two full-length FGF receptor cDNAs were cloned using low-stringency screening of a neonatal rat kidney library with a chicken FGFR-1 cDNA probe. Sequencing revealed these cloned cDNAs to be rat homologues of the FGFR-1 subtype, with the two clones representing splicing variants ?? and ?? of the FGFR-1. Evidence for renal expression of a third splicing variant (??) was obtained by use of the polymerase chain reaction. Splicing variants ?? and ?? of FGFR-1 are predicted to produce cell-surface FGF receptors with three and two immunoglobulin-like domains, respectively, whereas the ??-isoform may represent an intracellular form of the receptor. Although all three splicing variants were expressed in the developing kidney at days 14, 17, and 20 of gestation, at neonatal days 1 and 7 and in mature rats the ??-isoform was present in vastly larger abundance than ??- and ??-isoforms at all stages studied. Northern blot analysis revealed enhanced expression of FGFR-1 in the neonatal compared with the mature kidney. It is concluded that FGFR-1 is expressed in the kidney predominantly as the ??-isoform splicing variant and that expression of this receptor is enhanced during kidney development.open171