Cyclic AMP inhibits stretch-induced overexpression of fibronectin in glomerular mesangial cells

p38 MAP kinase mediates mechanically induced COX-2 and PG EP4receptor expression in podocytes: implications for the actin cytoskeleton

A dynamic cytoskeleton allows podocytes to withstand significant mechanical stress on elevation of intraglomerular capillary pressure (Pgc). However, vasoactive hormones, such as prostaglandin E2(PGE2), may challenge the integrity of the actin cytoskeleton, alter podocyte morphology, and compromise glomerular permeability. PGE2synthesis correlates with the onset of proteinuria and increased Pgcfollowing reduced nephron mass. We investigated the interplay among mechanical stress, cyclooxygenase (COX), E-prostanoid (EP) receptor expression, and the actin cytoskeleton, using an in vitro model of cell stretch. Immortalized mouse podocytes grown on flexible silicone membranes were cyclically stretched (5% elongation, 0.5 Hz) for 2 h. EP4and COX-2 mRNA increased three- and sevenfold above nonstretched controls, whereas EP1and COX-1 levels were unchanged. Six hours of stretch resulted in a threefold increase in PGE2-stimulated cAMP accumulation, a measure of EP4receptor function, and an increase in COX-2 protein. The stretch-induced effects on COX-2/EP4expression and EP4-induced cAMP production were attributable to p38 MAP kinase, as blockade of this pathway, but not of ERK or JNK, abrogated the response. These stretch-induced changes in expression were transcriptionally dependent as they were actinomycin D sensitive. Finally, we investigated the influence of enhanced EP4signaling on the actin cytoskeleton. Addition of PGE2resulted in actin filament depolymerization observable only in stretched cells. Our results indicate that key components of the eicosanoid pathway are upregulated by mechanically stimulated p38 MAP kinase in podocytes. Enhanced EP4receptor signaling may undermine podocyte cytoskeletal dynamics and thereby compromise filtration barrier function under conditions of increased Pgc.

Progesterone receptor (hPR) upregulates the fibronectin promoter activity in human decidual fibroblasts

Previous studies have shown that progestin induces the production of fibronectin (FN) and its mRNA content in human endometrial stromal cells. The mechanism of the upregulation was unclear. In the present study, we provide evidence that hPR regulates the FN promoter activity mainly through the CRE/AP1 site located in the proximal region of the promoter in human decidual fibroblasts. Various lengths of the proximal region of the FN promoter were linked to the reporter vector to construct promoter-reporter plasmids and were then transfected into human decidual fibroblasts. Deletion and mutation analysis showed that CRE/AP1 and Sp1 sites in the proximal region mediated the basal promoter activity. To evaluate progestin-mediated transcriptional activation, decidual fibroblasts were transfected with p300 (FN promoter-reporter construct) and hPR expression vector. Cells treated with medroxyprogesterone acetate (MPA) increased the promoter activity ranging from 2.5- to 9-fold determined in 10 decidual specimens. hPRA enhanced activation was stronger than that of hPRB. Structural analysis of hPR showed that DNA and ligand binding domains are essential for the activation, and missing the TAF1 domain weakens the activation. The proximal promoter region of the FN gene lacks a canonical PRE site. Mutation at the CRE/AP1 site eliminated the upregulation by progestin. To evaluate the interaction of hPR with the CRE/AP1 site, the CRE/AP1 site was mutated to the consensus AP1 cis-element (TGACGTCA, -172 to -165 bp, mutated to TGAC_TCA) which eliminated the CREB binding. FN promoter activity derived from p300AP1 mutant was found to be higher than that of p300. These results showed that hPR interacts with the AP1 binding proteins, but not with CREB. Progestin treatment or overexpression hPR did not alter appreciably the content of c-jun or c-fos in decidual fibroblasts nuclear extracts. Antibody to hPR (hPRa3), which precipitated hPR also coprecipitated c-jun and c-fos, whereas CREB was not precipitated by hPRa3. The observation implies that hPRs are brought to the FN promoter region by AP1 proteins to enhance the transcription. In summary, this study provides molecular evidence that the CRE/AP1 site and c-jun/c-fos in decidual fibroblasts mediate the hPR-enhanced activation of FN transcription.