Follicle-stimulating hormone activates extracellular signal-regulated kinase but not extracellular signal-regulated kinase kinase through a 100-kDa phosphotyrosine phosphatase

In this report we sought to elucidate the mechanism by which the follicle-stimulating hormone (FSH) receptor signals to promote activation of the p42/p44 extracellular signal-regulated protein kinases (ERKs) in granulosa cells. Results show that the ERK kinase MEK and upstream intermediates Raf-1, Ras, Src, and L-type Ca(2+) channels are already partially activated in vehicle-treated cells and that FSH does not further activate them. This tonic stimulatory pathway appears to be restrained at the level of ERK by a 100-kDa phosphotyrosine phosphatase that associates with ERK in vehicle-treated cells and promotes dephosphorylation of its regulatory Tyr residue, resulting in ERK inactivation. FSH promotes the phosphorylation of this phosphotyrosine phosphatase and its dissociation from ERK, relieving ERK from inhibition and resulting in its activation by the tonic stimulatory pathway and consequent translocation to the nucleus. Consistent with this premise, FSH-stimulated ERK activation is inhibited by the cell-permeable protein kinase A-specific inhibitor peptide Myr-PKI as well as by inhibitors of MEK, Src, a Ca(2+) channel blocker, and chelation of extracellular Ca(2+). These results suggest that FSH stimulates ERK activity in immature granulosa cells by relieving an inhibition imposed by a 100-kDa phosphotyrosine phosphatase.     

Conversion of drug-induced differentiation to apoptosis by pharmacologic cyclin-dependent kinase inhibitors

Recently, considerable attention has focused on the clinical development of novel anticancer agents which are intended to induce differentiation (i.e., protein kinase C activators and histone deacetylase inhibitors) or to inhibit cyclin-dependent kinases (CDKs) (i.e., flavopiridol and UCN-01). Because the differentiation process requires cell cycle arrest (e.g., in G(1)), the possibility arises that CDK inhibitors might potentiate the maturation response of neoplastic cells to various differentiation-inducing agents. However, recent findings indicate that contrary to expectations, pharmacologic CDK inhibitors fail to promote differentiation, at least in human leukemia cells; instead, they antagonize the maturation process and induce dysregulation of various cell cycle and apoptotic regulatory proteins that culminate in mitochondrial injury and apoptosis. A brief summary of the events that might contribute to these phenomena in human leukemia cells follows below. A better understanding of interactions between putative differentiation-inducers and cell cycle inhibitors may provide the foundation for the future development of novel chemotherapeutic strategies in hematopoietic and possibly non-hematopoietic malignancies.     

Nucleotide polymorphism at the alcohol dehydrogenase locus of pocket gophers, genus Geomys

Using the strictly neutral model as a null hypothesis, we tested for deviations from expected levels of nucleotide polymorphism at the alcohol dehydrogenase locus (Adh-1) within and among four species of pocket gophers (Geomys bursarius major, G. knoxjonesi, G. texensis llanensis, and G. attwateri). The complete protein-encoding region was examined, and 10 unique alleles, representing both electromorphic and cryptic alleles, were used to test hypotheses (e.g., the neutral model) concerning the maintenance of genetic variation. Nineteen variable sites were identified among the 10 alleles examined, including 9 segregating sites occurring in synonymous positions and 10 that were nonsynonymous. Several statistical methods, including those that test for within-species variation as well as those that examine variation within and among species, failed to reject the null hypothesis that variation (both within and between species of Geomys) at the Adh locus is consistent with the neutral theory. However, there was significant heterogeneity in the ratio of polymorphism to divergence across the gene, with polymorphisms clustered in the first half of the coding region and fixed differences clustered in the second half of the gene. Two alternative hypotheses are discussed as possible explanations for this heterogeneity: an old balanced polymorphism in the first half of the gene or a recent selective sweep in the second half of the gene.      

Evidence that biosynthesis of phosphatidylethanolamine, phosphatidylcholine, and triacylglycerol occurs on the cytoplasmic side of microsomal vesicles

Experiments were performed to localize the hepatic microsomal enzymes of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol biosynthesis to the cytoplasmic or lumenal surface of microsomal vesicles. Greater than 90 percent of the activities of fatty acid-CoA ligase (EC 6.2.1.3), sn-glycerol 3-phosphate acyltransferase (EC 2.3.1.15), lysophosphatidic acid acyltransferase, diacylglycerol acyltransferase (EC 2.3.1.20), diacylglycerol cholinephosphotransferase (EC 2.7.8.2), and diacylglycerol ethanolaminephosphotransferase (EC 2.7.8.1) was inactivated by proteolysis of intact microsomal vesicles. The phosphatidic acid phosphatase (EC 3.1.3.4) was not inactivated by any of the protease tested. Under conditions employed, <5 percent of the luminal mannose-6-phosphatase (EC 3.1.3.9) activity was lost. After microsomal integrity was disrupted with detergents, protease treatment resulted in a loss of >74 percent of the mannose-6-phosphatase activity. The latency of the mannose-6-phosphatase activity was not affected by protease treatment. Mannose-6-phosphatase latency was not decreased by the presence of the assay components of several of the lipid biosynthetic activities, indicating that those components did not disrupt the microsomal vesicles. None of the lipid biosynthetic activities appeared latent. The presence of a protease-sensitive component of these biosynthetic activities on the cytoplasmic surface of microsomal vesicles, and the absence of latency for any of these biosynthetic activities suggest that the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol occurs asymmetrically on the cytoplasmic surface of the endoplasmic reticulum. The location of biosynthetic activities within the transverse plane of the endoplasmic reticulum is of particular interest for enzymes whose products may be either secreted or retained within the cell. Phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol account for the vast majority of hepatic glycerolipid biosynthesis. The phospholipids are utilized for hepatic membrane biogenesis and for the formation of lipoproteins, and the triacylglycerols are incorporated into lipoproteins or accumulate within the hepatocyte in certain disease states (14). The enzymes responsible for the biosynthesis of these glycerolipids (Scheme I) from fatty acids and glycerol-3P have all been localized to the microsomal subcellular fraction (12, 16, 29, 30). Microsomes are derived from the endoplasmic reticulum and are sealed vesicles which maintain proper sidedness. (11, 22). The external surface of these vesicles corresponds to the cytoplasmic surface of the endoplasmic reticulum. Macromolecules destined for secretion must pass into the lumen of the endoplasmic reticulum (5, 23). Uncharged molecules of up to approximately 600 daltons are able to enter the lumen of rat liver microsomes, but macromolecules and charged molecules of low molecular weight do not cross the vesicle membrane (10, 11). Because proteases neither cross the microsomal membrane nor destroy the permeability barrier of the microsomal vesicles, only the enzymes and proteins located on the cytoplasmic surface of microsomal vesicles are susceptible to proteolysis unless membrane integrity is disrupted (10, 11). By use of this approach, several enzymes and proteins have been localized in the transverse plane of microsomal membranes (11). With the possible exception of cytochrome P 450, all of the enzymes and proteins investigated were localized asymmetrically by the proteolysis technique (11). By studies of this type, as well as by product localization, glucose-6-phosphate (EC 3.1.3.9) has been localized to the luminal surface of microsomal vesicles (11) and of the endoplasmic reticulum (18, 19). All microsomal vesicles contain glucose-6-phosphatase (18, 19) which can effectively utilize mannose-6-P as a substrate, provided the permeability barrier of the vesicles has been disrupted to allow the substrate access to the active site located on the lumenal surface (4). An exact correspondence between mannose- 6-phosphate activity and membrane permeability to EDTA has been established (4). The latency of mannose-6-phosphatase activity provides a quantitative index of microsomal integrity (4.) Few of the microsomal enzymes in the synthesis of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol have been solubilized and/or purified, and little is known about the topography of these enzymes in the transverse or lateral planes of the endoplasmic reticulum. An asymmetric location of these biosynthetic enzymes on the cytoplasmic or lumenal surface of microsomal vesicles may provide a mechanism for regulation of the glycerolipids to be retained or secreted by the cell, and for the biogenesis of asymmetric phospholipid bilayers. In this paper, we report investigations on the localization of all seven microsomal enzymes (Scheme I) in the biosynthesis of triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine, using the protease technique with mannose-6-phosphatase serving as luminal control activity. The latency of these lipid biosynthetic enzymes was also investigated, using the latency of mannose-6-phosphatase as an index of microsomal integrity.     

Effect of glutaraldehyde treatment of human melanoma cells on the expression of melanoma-associated antigens

Summary Human melanoma cells were treated with different concentrations of glutaraldehyde, and retention of serological reactivity with antisera against melanoma-associated antigens, HLA antigen, and 2-microglobulin was assessed by quantitative absorption analysis in mixed hemadsorption microassays. Glutaraldehyde concentrations of 0.025% or greater significantly impaired binding to melanoma cells of antibody against melanoma-associated antigens. At a concentration of 0.0025% antibody binding was not decreased although plating efficiency was reduced to less than 1%. Glutaraldehyde concentrations of 0.25% or greater significantly reduced binding to the same melanoma cells of antisera against HLA antigen and 2-microglobulin. Glutaraldehyde treatment (up to 2.5%) of HT-29 colon carcinoma cells failed to reduce reactivity of antisera against CEA and blood group A isoantigen, which are present on these cells. These studies indicate that the effect of glutaraldehyde treatment of cells on retention of surface antigens is critically dependent on the concentration of glutaraldehyde used and the type of antigens involved. Abbreviations used in this paper: MAA, melanoma-associated antigens; GA, glutaraldehyde; FCS, fetal calf serum; RPMI, Roswell Park Memorial Institute; 2M, 2-microglobulin; CEA, carcinoembryonic antigen; PBS, phosphate-buffered saline; NGP, normal glycoprotein cross-reacting with CEA; SRBC, sheep red blood cells     

Two different zinc sites in bovine 5-aminolevulinate dehydratase distinguished by extended X-ray absorption fine structure

The zinc coordination in 5-aminolevulinate dehydratase was investigated by extended X-ray absorption fine structure (EXAFS) associated with the zinc K-edge. The enzyme binds 8 mol of zinc/mol of octameric protein, but only four zinc ions seem sufficient for full activity. We have undertaken a study on four forms of the enzyme: (a) the eight-zinc native enzyme; (b) the enzyme with only the four zinc sites necessary for full activation occupied; (c) the enzyme with the vacant sites of (b) occupied by four lead ions; (d) the product complex between (b) and porphobilinogen. We have shown that two structurally distinct types of zinc sites are available in the enzyme. The site necessary for activity has an average zinc environment best described by two/three histidines and one/zero oxygen from a group such as tyrosine or a solvent molecule at 2.06 +/- 0.02 A, one tyrosine or aspartate at 1.91 +/- 0.03 A, and one cysteine sulfur at 2.32 +/- 0.03 A with a total coordination of five ligands. The unoccupied site in (b), obtained by taking the difference spectrum between the spectra from samples (a) and (b), is dominated by a single contribution of four cysteinyl sulfur atoms at 2.28 +/- 0.02 A. Spectra from samples (c) and (d) show only small changes from that of (b), reflecting a slight rearrangement of the ligands around the zinc atom.     

Identification of oral Neisseria species of animals

Ninety-seven strains of presumptive Neisseria spp. obtained from the dental plaque of a wide variety of animals and 21 strains from culture collections were compared by physiological tests, enzyme electrophoresis and isoelectric focusing of proteins. Three physiological groups based on the fermentation of maltose and production of extracellular polysaccharide were established. The ability of strains within these groups to reduce nitrate and nitrite differed. The electrophoretic mobility of dehydrogenases and isoelectric focusing patterns of proteins were not, however, characteristic of species or physiological groups. It is difficult, therefore, to identify new isolates of Neisseria because the criteria for describing species overlap. A rapid spot test was devised to distinguish Branhamella catarrhalis from other Neisseria by the absence of glucose-6-phosphate dehydrogenase.     

Inhibition of the MAPK pathway abrogates BCL2-mediated survival of leukemia cells after exposure to low-dose ionizing radiation.

The ability of low-dose ionizing radiation (1 Gy) to modulate the activities of the mitogen-activated protein kinase (MAPK) and Jun NH2-terminal kinase (JNK1) cascades in human myeloid leukemia (HL60/pCEP4) cells and in cells overexpressing the anti-apoptosis protein BCL2 (HL60/Bcl-2) was investigated. Radiation exposure caused prolonged (3-4 h) activation of MAPK in HL60 cells. The ability of radiation to activate the MAPK pathway was attenuated by 30% in cells overexpressing BCL2. In contrast, low-dose irradiation of HL60/pCEP4 and HL60/Bcl-2 cells failed to modulate JNK1 activity. Inhibition of the MAPK pathway by use of the specific MEK1/2 inhibitor (10 microM PD98059) in both HL60/pCEP4 and HL60/Bcl-2 cells prior to irradiation permitted a similar prolonged radiation-induced activation of JNK1. Furthermore, combined treatment with PD98059 and radiation in both cell types caused a large decrease in growth of cells in suspension culture, a large increase in apoptosis, and a 90% decline in clonogenicity when compared to either treatment alone. Reduced proliferation after combined irradiation and PD98059 treatment in both cell types correlated with reduced Cdc2 activity and arrest in G2/M phase of the cell cycle. These data demonstrate that inhibition of MEK1/2 leading to blockade of the MAPK activation increases the radiation sensitivity of HL60 cells and decreases the ability of these cells to recover from the radiation-induced arrest at the G2/M-phase cell cycle checkpoint. In addition, our data demonstrate that elevated expression of BCL2 does not abrogate the ability of inhibition of MAPK to potentiate radiation-induced cell death in HL60 cells.