Angiotensin II stimulates fibronectin protein synthesis via a Gßγ/arachidonic acid-dependent pathway.

In rabbit proximal tubular cells, ANG II type 2-receptor (AT2)-induced arachidonic acid release is PLA2 coupled and dependent of G protein ßγ (Gßγ) subunits. Moreover, ANG II activates ERK1/2 and transactivates EGFR via a c-Src-dependent mechanism. Arachidonic acid has been shown to mimic this effect, at least in part, by an undetermined mechanism. In this study, we determined the effects of ANG II on fibronectin expression in cultured rabbit proximal tubule cells and elucidated the signaling pathways associated with such expression. We found that ANG II and transfection of Gßγ subunits directly increased fibronectin protein expression, and this increase was inhibited by overexpression of ß-adrenergic receptor kinase (ßARK)-ct or DN-Src. Moreover, ANG II-induced fibronectin protein expression was significantly abrogated by the AT2 receptor antagonist PD123319. In addition, inhibition of cystolic PLA2 diminished ANG II-induced fibronectin expression. Endogenous arachidonic acid mimicked ANG II-induced fibronectin expression. We also found that overexpression of Gßγ subunits induced c-Src, ERK1/2, and EGFR tyrosine phosphorylation, which can be inhibited by overexpression of ßARK-ct or DN-Src. Gßγ also induced c-Src SH2 domain association with the EGFR. Supporting these findings, in rabbit proximal tubular epithelium, immunoblot analysis indicated that ßγ expression was significant. Interestingly, arachidonic acid- and eicosatetraenoic acid-induced responses were preserved in the presence of ßARK-ct. This is the first report demonstrating the regulation of EGFR, ERK1/2, c-Src, and fibronectin by Gßγ subunits in renal epithelial cells. Moreover, this work demonstrates a role for Gßγ heterotrimeric proteins in ANG II, but not arachidonic acid, signaling in renal epithelial cells.

Increase in mastectomies performed in patients in the community setting undergoing MRI.

This study is designed to determine whether the use of magnetic resonance imaging (MRI) leads to an increased number of unnecessary mastectomies in breast cancer patients in the community setting. This is a retrospective study of the records of 178 patients from the local offices of three community physicians. The medical records of patients over the age of 18 with breast cancer who underwent both MRI and mammogram imaging were reviewed. MRI detected more lesions than mammogram; however, these lesions were not cancerous. The lesions detected by mammogram correlated more with pathologic lesions. Of the 59 patients who underwent mastectomies, 78% had MRI and 22% did not have the imaging. Of the 100 patients who had both MRI and mammogram, 48% underwent lumpectomy and 46% had mastectomy. More patients who had both imaging modalities underwent mastectomies compared to those who had mammogram alone. The addition of MRI evaluation in patients with breast cancer is related to increased unnecessary mastectomies.

Intraperitoneal chemotherapy: standard of care for patients with minimal residual stage III ovarian cancer?

Epithelial ovarian cancer is the leading cause of death from gynecological cancer in most of the Western world, and long-term survival remains poor despite good initial response to systemic therapy after debulking surgery. Even after complete pathological response, the risk of recurrence in the first few years is substantial. The peritoneum is the predominant site of failure and the disease remains confined to the peritoneal cavity for much of its course. Efforts to improve clinical outcomes in this group of patients included investigation of intraperitoneal administration of active agents to expose the low-volume postoperative residual disease in the peritoneum to high concentrations of these drugs. In spite of three National Cancer Institute-sponsored randomized trials demonstrating clinical benefit with intraperitoneal therapy in patients with advanced ovarian cancer, the fact remains that it is not uniformly accepted by the gynecologic oncology community in the USA and is rarely used by clinicians in Europe. Intraperitoneal regimens are perceived to be too toxic for administration, although most of the toxicity is reversible. In this article we discuss the available evidence for intraperitoneal chemotherapy, challenges facing the gynecologic oncology community to make this modality more widely acceptable, the selection of patients most likely to tolerate intraperitoneal therapy and ongoing research in this field.

Cyclic stretch-induced cPLA2 mediates ERK 1/2 signaling in rabbit proximal tubule cells.

BACKGROUND: Recent evidence from this laboratory have demonstrated a critical role of phospholipase A2 (PLA2) and arachidonic acid in angiotensin II type 2 (AT2) receptor-mediated kinase activation in renal epithelium independent of phosphoinositide- specific phospholipase C (PLC) and without the necessity of eicosanoid biosynthesis. In the present study, we investigated whether cyclic stress phosphorylates and activates the mitogen-activated protein kinase (MAPK) pathway and whether PLA2 activation mediates mechanotransduction in renal epithelial cells. The rational for studying kidney epithelial cells relates to their similarity to podocytes, which undergo mechanical stretch related to changes in intraglomerular pressure. METHODS: To produce strain or stretch, primary cultures of rabbit proximal tubular cell cells are grown in tissue culture wells having a collagen-coated Silastic deformable membrane bottoms and applying vacuum to the well to generate alternating cycles of stretch and relaxation (30 cycles/min). RESULTS: We found that cyclic stretching of rabbit proximal tubular cells caused a time- and intensity-dependent activation of extracellular signal-regulated kinases 1 and 2 (ERK 1/2) in proximal tubular cells as detected by its phosphorylation. In addition, mechanical stretch induced PLA2 activation and a subsequent rapid release of arachidonic acid. Inhibition of PLA2 by mepacrine and methyl arachidonyl fluorophosphonate ketone (AACOCF3) attenuated both arachidonic acid release and ERK 1/2 activation by cyclic stretch, supporting the importance of PLA2 as a mediator of mechanotransduction in renal proximal tubular cells. A requirement for extracellular Ca2+ and stretch-activated Ca2+ channels was also documented. Complete inhibition of ERK 1/2 by PD98059, a MAPK kinase (MEK) inhibitor, did not suppress stretch- induced PLA2 activation and arachidonic acid release, suggesting the later events were upstream of ERK 1/2. Cyclic stretch also caused rapid phosphorylation of the EGF receptor kinase and c-Src. Furthermore, arachidonic acid itself induced time- and dose-dependent phosphorylation of c-Src. In addition, the c-Src inhibitor PP2 and selective EGF receptor kinase inhibitor AG1478 attenuated both ERK 1/2 and EGF receptor phosphorylation by cyclic stretch. CONCLUSION: PLA2 dependence for ERK 1/2 activation in response to cyclic stretch in proximal tubular epithelial cells was established in this report. In addition, these findings indicate cyclic stretch increased the tyrosine phosphorylation of the EGF receptor and c-Src and that c-Src acts upstream of the EGF receptor to mediate its phosphorylation, whereby both are critical for stretch- induced ERK 1/2 activation in rabbit proximal tubular cells. These observations documents for the first time a mechanism of mechanical stretch-induced kinase activation mediated by stretch activated Ca2+ channels and PLA2-dependent release of arachidonic acid.