An N-end rule destabilization mutant reveals pre-Golgi requirements for Sec7p in yeast membrane traffic.

Sec7 protein (Sec7p) is required for membrane traffic in the yeast secretory pathway. Because Sec7p regulates more than one stage in the pathway, it has been difficult to assign the most proximal requirement for Sec7p action. We have engineered a novel mutant whose Sec7p levels are regulated by growth conditions and by selective protein destabilization according to the N-end rule. Sec7p depletion causes cell growth arrest and accumulation of transport proteins with post-translational modifications indicative of Sec7p dependence for ER-to-Golgi traffic, in addition to the already characterized Golgi requirements. Immuno-EM of sec7 revealed exaggeration of ER and Golgi membranes with protein accumulation in these exaggerated structures, suggesting that these regions may represent staging areas for cargo sorting and vesicle assembly.

Induction of cytosolic phospholipase A2 by oncogenic Ras in human non-small cell lung cancer.

Mutations in Ras family members that confer oncogenic potential are frequently observed in specific human cancers. We report that human non-small cell lung cancer (NSCLC) lines that harbor oncogenic mutations in Ki-Ras (H460, A549, H2122) synthesized high levels of prostaglandin E2 (PGE2) compared with NSCLC lacking Ras mutations or non-transformed lung epithelial cells (BEAS-2B). This increased PGE2 production was mediated by constitutively high expression of 85-kDa cytosolic phospholipase A2 (cPLA2) and cyclooxygenase 2 (COX-2). The increased expression of cPLA2 protein was mediated through elevated mRNA levels and activation of the cPLA2 promoter. Induction of cPLA2 promoter activity was blocked by expression of dominant-negative forms of Ras. Inhibition of Ras by the farnesyltransferase inhibitor BZA-5B inhibited prostaglandin synthesis in H2122 cells by decreasing expression of both cPLA2 and COX-2. Finally, inhibitors of eicosanoid synthesis blocked anchorage-independent growth of NSCLC lines exhibiting Ki-Ras mutations. These results identify cPLA2 as a novel Ras-inducible regulator of eicosanoid synthesis that participates in cellular transformation.

Suppression of smooth-muscle alpha-actin expression by platelet-derived growth factor in vascular smooth-muscle cells involves Ras and cytosolic phospholipase A2.

Platelet-derived growth factor (PDGF), which is a potent mitogen for vascular smooth-muscle cells (VSMC), also inhibits the expression of specific smooth-muscle proteins, including smooth-muscle alpha-actin (SM-alpha-actin), in these cells. The goal of this study was to identify signalling pathways mediating these distinct effects. In rat aortic VSMC, PDGF caused a rapid activation of Ras and Raf, leading to the activation of mitogen-activated protein kinases (ERKs). Cells stably transfected with constitutively active Ras (H-Ras) expressed low levels of SM-alpha-actin protein. Arginine vasopressin, which stimulated SM-alpha-actin promoter activity in wild-type cells or controls (Neo; transfected with a plasmid lacking an insert), failed to do so in cells transiently expressing H-Ras. The effects of Ras on suppression of SM-alpha-actin expression were not mediated by the Raf/ERK pathway, since cells stably expressing constitutively active Raf (BxB-Raf) had normal levels of SM-alpha-actin protein, and stimulation of SM-alpha-actin promoter activity by vasopressin was unaffected in cells transiently expressing BxB-Raf. Furthermore a specific inhibitor of ERK activation had no effect on SM-alpha-actin expression. Exposure of wild-type VSMC to PDGF, or stable expression of Ras but not Raf, also resulted in constitutive increases in prostaglandin E2 production and cytosolic phospholipase A2 (cPLA2) activity, which was mediated by an increased expression of cPLA2 protein. Transient expression of cPLA2 in wild-type VSMC inhibited the stimulation of SM-alpha-actin promoter activity by vasopressin. These results suggest that PDGF-induced inhibition of SM-alpha-actin expression is mediated through a Ras-dependent/Raf independent pathway involving the induction of cPLA2 and eicosanoid production.

Abnormal function of protein kinase C in cells having phosphatidylethanolamine-deficient and phosphatidylcholine-excess membranes.

When rat mammary carcinoma 64-24 cells are grown in the absence of ethanolamine, their membrane phospholipid composition changes significantly, becoming phosphatidylethanolamine-deficient and phosphatidylcholine-excess due to a reduced de novo rate of phosphatidylethanolamine synthesis, and growth stops. We have assumed that this membrane phospholipid environment is not suitable for membrane-associated functions. We have previously demonstrated that functions normally stimulated by tumor-promoting phorbol ester, phorbol 12,13-dibutyrate, are not stimulated in ethanolamine-deprived cells, suggesting that function of protein kinase C may be abnormal under the altered membrane environment. In the present study, the behavior of protein kinase C in 64-24 cells grown in the presence and absence of ethanolamine (having normal and phosphatidylethanolamine-deficient/phosphatidylcholine-excess phospholipid) was compared by enzyme assay as well as Western blotting. The results show that the nature of association of protein kinase C to the membrane, which is induced by phorbol ester, is abnormal when cells have the altered membrane phospholipid, and thus argue that membrane phospholipid environment is important in the function of protein kinase C.

Forging a vital link in group operations.

Medical secretaries play a vital role in group practice; and for maximum productivity, it is essential that they be adequately trained. At the Scott and White Clinic in Temple, Texas, a thorough examination was conducted of the medical secretary training program. Based on this, a more formal program was developed which included a series of self-directed, competency-based learning modules with built-in program effectiveness monitors. The result of strengthening this one link in the chain of group operations has been not only better qualified and happier secretaries, but also, increased overall productivity. This article contains the key to developing, introducing, implementing, and evaluating a successful medical secretary training program in your group practice.