Induction of autocrine epidermal growth factor receptor ligands in human keratinocytes by insulin/insulin-like growth factor-1

Autocrine activation of the epidermal growth factor (EGF) receptor on keratinocytes has been recognized as an important growth regulatory mechanism involved in epithelial homeostasis, and, possibly, hyperproliferative diseases. Insulin-like growth factor (IGF)-1 and insulin have been shown to be paracrine keratinocyte mitogens that bind to the type I IGF receptor which is expressed on actively proliferating keratinocytes in situ. In this report, we demonstrate that IGF-1/insulin induced production of keratinocyte-derived autocrine growth factors that bind to the EGF receptor. Increased steady-state mRNA levels for transforming growth factor alpha (TGF-α) and for amphiregulin (AR) were observed upon incubation of keratinocytes with mitogenic concentrations of IGF-1. IGF-1 also induced production and secretion of TGF-α and AR proteins as detected by immunoassays. An EGF receptor antagonistic monoclonal antibody abolished the mitogenic effect of IGF-1 on cultured keratinocytes. These results suggest that stimulation of keratinocyte growth by IGF-1 requires activation of an EGF receptor-mediated autocrine loop. © 1995 Wiley-Liss, Inc.     

Phospholipase C-gamma, a substrate for PDGF receptor kinase, is not phosphorylated on tyrosine during the mitogenic response to CSF-1.

Quiescent mouse NIH3T3 cells expressing a transduced human c-fms gene encoding the receptor for colony stimulating factor-1 (CSF-1) were stimulated with mitogenic concentrations of platelet-derived growth factor (PDGF) or CSF-1. Immunoprecipitated phospholipase C-gamma (PLC-gamma) was phosphorylated on tyrosine and calcium was mobilized following treatment of intact cells with PDGF. In contrast, only trace amounts of phosphotyrosine were incorporated into PLC-gamma and no intracellular calcium signal was detected after CSF-1 stimulation. Similarly, CSF-1 treatment did not stimulate phosphorylation of PLC-gamma on tyrosine in a CSF-1-dependent. SV40-immortalized mouse macrophage cell line that expresses high levels of the CSF-1 receptor. In fibroblasts, antiserum to PLC-gamma co-precipitated a fraction of the tyrosine phosphorylated form of the PDGF receptor (PDGF-R) after ligand stimulation, implying that phosphorylated PDGF-R and PLC-gamma were associated in a stable complex. Pre-treatment of cells with orthovanadate also led to tyrosine phosphorylation of PLC-gamma which was significantly enhanced by PDGF, but not by CSF-1. Thus, although the PDGF and CSF-1 receptors are structurally related and appear to be derived from a single ancestor gene, only PDGF-induced mitogenesis in fibroblasts correlated with tyrosine phosphorylation of PLC-gamma.     

Characterization and cDNA cloning of phospholipase C-gamma, a major substrate for heparin-binding growth factor 1 (acidic fibroblast growth factor)-activated tyrosine kinase.

Heparin-binding growth factors (HBGFs) bind to high-affinity cell surface receptors which possess intrinsic tyrosine kinase activity. A Mr 150,000 protein phosphorylated on tyrosine in response to class 1 HBGF (HBGF-1) was purified and partially sequenced. On the basis of this sequence, cDNA clones were isolated from a human endothelial cell library and identified as encoding phospholipase C-gamma. Phosphorylation of phospholipase C-gamma in intact cells treated with HBGF-1 was directly demonstrated by using antiphospholipase C-gamma antibodies. Thus, HBGF-1 joins epidermal growth factor and platelet-derived growth factor, whose receptor activation leads to tyrosine phosphorylation and probable activation of phospholipase C-gamma.     

Induction of neurite outgrowth by v-src mimics critical aspects of nerve growth factor-induced differentiation.

PC12 cells treated with nerve growth factor (NGF) or infected with Rous sarcoma virus differentiate into sympathetic, neuronlike cells. To compare the differentiation programs induced by NGF and v-src, we have established a PC12 cell line expressing a temperature-sensitive v-src protein. The v-src-expressing PC12 cell line was shown to elaborate neuritic processes in a temperature-inducible manner, indicating that the differentiation process was dependent on the activity of the v-src protein. Further characterization of this cell line, in comparison with NGF-treated PC12 cells, indicated that the events associated with neurite outgrowth induced by these two agents shared features but could be distinguished by others. Both NGF- and v-src-induced neurite outgrowths were reversible. In addition, NGF and v-src could prime PC12 cells for NGF-induced neurite outgrowth, and representative early and late NGF-responsive genes were also induced by v-src. However, unlike NGF-induced neurite growth, v-src-induced neurite outgrowth was not blocked at high cell density. A comparison of phosphotyrosine containing-protein profiles showed that v-src and NGF each increase tyrosine phosphorylation of multiple cellular proteins. There was overlap in substrates; however, both NGF-specific and v-src-specific tyrosine phosphorylations were observed. One protein which was found to be phosphorylated in both the NGF- and v-src-induced PC12 cells was phospholipase C-gamma 1. Taken together, these results suggest that v-src's ability to function as an inducing agent may be a consequence of its ability to mimic critical aspects of the NGF differentiation program and raise the possibility that Src-like tyrosine kinases are involved in mediating some of the events triggered by NGF.     

Epidermal growth factor (EGF) stimulates association and kinase activity of Raf-1 with the EGF receptor.

Raf-1 serine- and threonine-specific protein kinase is transiently activated in cells expressing the epidermal growth factor (EGF) receptor upon treatment with EGF. The stimulated EGF receptor coimmunoprecipitates with Raf-1 kinase and mediates protein kinase C-independent phosphorylation of Raf-1 on serine residues. Hyperphosphorylated Raf-1 has lower mobility on sodium dodecyl sulfate gels and has sixfold-increased activity in immunocomplex kinase assay with histone H1 or Raf-1 sequence-derived peptide as a substrate. Raf-1 activation requires kinase-active EGF receptor; a point mutant lacking tyrosine kinase activity in inactive in Raf-1 coupling and association. It is noteworthy that tyrosine phosphorylation of c-Raf-1 induced by EGF was not detected in these cells. These observations suggest that Raf-1 kinase may act as an important downstream effector of EGF signal transduction.     

Expression of insulin-like growth factor-I and its receptor by SV40-transformed rat granulosa cells

Cellular proliferation is a dominant aspect of ovarian follicular development in the rat, and insulin-like growth factor I (IGF-I) has been proposed as a mediator of cellular growth and differentiation in the ovary. An SV40-transformed rat granulosa cell line (RGA-41S) has been established as a model for studies on dividing cells of granulosa origin. Granulosa cells from the ovaries of immature diethylstilbestrol-treated rats were infected with the tsA255 mutant of SV40, followed by cloning in serum-free medium to select transformed cell lines which were serum independent. At the permissive temperature (33 C), RGA-41S cells exhibited a transformed phenotype and rapidly formed high density multilayers of compact cells that readily overgrew nontransformed cells. At the nonpermissive temperature (40 C) cell replication declined and division ceased after 4 days. Furthermore, at 40 C the cells grew as a monolayer and assumed a tetrahedral shape with a high cytoplasm-to-nucleus ratio, and displayed reduced ability to overgrow nontransformed cells. The transformed ovarian cells did not express detectable gonadotropin receptors and steroidogenic activity but retained their epithelial phenotype as demonstrated by cytokeratin staining of the cytoskeleton, the presence of microvilli, and the formation of tight junctions between cells. In support of the proposed autocrine-paracrine actions of IGF-I in the ovary, assay of conditioned serum-free culture medium revealed secretion of IGF-I-immunoreactive material by RGA-41S cells. HPLC-purified IGF-I immunoreactivity from these cells eluted with the same retention time as recombinant human IGF-I. When hybridized with a 32P-labeled rat IGF-I cDNA probe, poly(A)+ mRNA prepared from RGA-41S cells grown at both temperatures showed the typical three size classes of IGF-I mRNA on Northern blots (7.5, 1.7, and 0.8-1.2 kilobase kb), although the levels were somewhat higher at 33 C. The presence of IGF-I receptors in transformed cells was demonstrated by specific 125I-IGF-I binding to intact cells. Scatchard analysis indicated a single class of high affinity receptors at a density of 10(5) binding sites per cell and a dissociation constant (Kd) = 0.52 x 10(-9) M. Furthermore, hybridization of a 32P-labeled IGF-I receptor probe to Northern blots of poly(A+) RNA prepared from cells grown at 33 C and 40 C revealed an 11-kilobase rat IGF-I receptor mRNA. Physiological concentrations of IGF-I increased [3H]aminoisobutyric acid uptake by RGA-41S cells grown at either temperature, attesting to the retention of responsiveness to IGF-I in these transformed granulosa cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Synergistic activity of a Bacillus thuringiensis delta-endotoxin and a bacterial endochitinase against Spodoptera littoralis larvae.

In an attempt to increase the insecticidal effect of the delta-endotoxin crystal protein CryIC on the relatively Cry-insensitive larvae of Spodoptera littoralis, a combination of CryIC and endochitinase was used. CryIC comprising the first 756 amino acids from Bacillus thuringiensis K26-21 and endochitinase ChiAII encoded by Serratia marcescens were separately produced in Escherichia coli carrying the genes in overexpression vectors. The endochitinase on its own, even at very low concentrations (0.1 microgram/ml), perforated the larval midgut peritrophic membrane. When applied together with low concentrations of CryIC, a synergistic toxic effect was obtained. In the absence of chitinase, about 20 micrograms of CryIC per ml was required to obtain maximal reduction in larval weight, while only 3.0 micrograms of CryIC per ml caused a similar toxic effect in the presence of endochitinase. Thus, a combination of the Cry protein and an endochitinase could result in effective insect control in transgenic systems in which the Cry protein is not expressed in a crystalline form.     

Biosynthesis of Leishmania lipophosphoglycan: solubilization and partial characterization of the initiating mannosyiphosphoryltransferase

Lipophosphoglycan (LPG) is the predominant surface glycoconjugateof Leishmania promastigotes and consists of a capped polymerof Gal(ß1,4)Man(