Epidermal growth factor induces protein tyrosine phosphorylation and association of p190 with ras-GTP-ase activating protein in Caco-2 cells

Ghrelin promotes intestinal epithelial cell proliferation through PI3K/Akt pathway and EGFR trans-activation both converging to ERK 1/2 phosphorylation

Little is known about ghrelin's effects on intestinal epithelial cells even though it is known to be a mitogen for a variety of other cell types. Because ghrelin is released in close proximity to the proliferative compartment of the intestinal tract, we hypothesized that ghrelin may have potent pro-proliferative effect on intestinal epithelial cells as well. To test this hypothesis, we characterized the effects of ghrelin on FHs74Int and Caco-2 intestinal epithelial cell lines in vitro. We found that ghrelin has potent dose dependent proliferative effects in both cell lines through a yet to be characterized G protein coupled growth hormone secretagogue receptor (GHS-R) subtype. Consistent with above findings, cell cycle flowcytometric analyses demonstrated that ghrelin shifts cells from the G1 to S phase and thereby promotes cell cycle progression. Further characterization of subcellular events, suggested that ghrelin mediates its pro-proliferative effect through Adenylate cyclase (AC)-independent epidermal growth factor receptor (EGFR) trans-activation and PI3K-Akt phosphorylation. Both these pathways converge to stimulate MAPK, ERK 1/2 downstream. The role of ghrelin in states where intestinal mucosal injury and rapid mucosal repair occur warrants further investigation.

Estrogen receptor α (ERα) mediates 17β-estradiol (E2)-activated expression of HBO1

BACKGROUND

HBO1 (histone acetyltransferase binding to ORC1) is a histone acetyltransferase (HAT) which could exert oncogenic function in breast cancer. However, the biological role and underlying mechanism of HBO1 in breast cancer remains largely unknown. In the current study, we aimed to investigate the role of HBO1 in breast cancer and uncover the underlying molecular mechanism.

METHODS

Immunohistochemistry was applied to detect HBO1 protein expression in breast cancer specimens (n=112). The expression of protein level was scored by integral optical density (IOD) for further statistical analyses using SPSS. Real-time PCR was used to simultaneously measure mRNA levels of HBO1. The HBO1 protein expression in breast cancer cells was confirmed by western blot.

RESULTS

HBO1 was highly expressed in breast cancer tissues and significantly correlated with estrogen receptor α (ERα) (p<0.001) and progestational hormone (PR) (p=0.002). HBO1 protein level also correlated positively with histology grade in ERα positive tumors (p=0.016) rather than ERα negative tumors. 17β-estradiol (E2) could upregulate HBO1 gene expression which was significantly inhibited by ICI 182,780 or ERα RNAi. E2-increased HBO1 protein expression was significantly suppressed by treatment with inhibitor of MEK1/2 (U0126) in T47 D and MCF-7 cells.

CONCLUSIONS

HBO1 was an important downstream molecule of ERα, and ERK1/2 signaling pathway may involved in the expression of HBO1 increased by E2.

Constitutive and regulated expression of processed insulin following in vivo hepatic gene transfer

To test whether hepatocytes engineered in vivo can serve as surrogate beta cells by similarly secreting mature insulin in a glucose-sensitive manner, we prepared adenoviral vectors encoding wild-type proinsulin (hIns-wt), a modified proinsulin cleavable by the ubiquitously expressed protease furin (hIns-M3), or each of the two beta cell specific pro-insulin convertases PC2 and PC3. Following a detailed in vitro characterization of the proteins produced by our vectors, we infected the liver and, for comparison, the muscle of a chemically induced murine model of type I diabetes. Insulin expression from the transduced tissues was extensively characterized and showed to be constitutive rather than regulated. To obtain regulated expression, we placed expression of hIns-M3 under the control of the dimerizer-inducible transcription system. Hormone secretion from mouse liver was negligible in the absence of the dimerizer drug rapamycin, was inducible in a dose-dependent manner upon its administration, and reversible following drug withdrawal. These data confirm liver as a promising target for in vivo expression of processed insulin. While suggesting that hepatocytes cannot provide authentic glucose-responsive regulation, these results demonstrate that pharmacological regulation is a promising alternative route to the controlled delivery of insulin following hepatic gene transfer.

Role of p190RhoGAP in beta 2 integrin regulation of RhoA in human neutrophils

We found that engagement of beta(2) integrins on human neutrophils induced activation of RhoA, as indicated by the increased ratio of GTP:GTP + GDP recovered on RhoA and translocation of RhoA to a membrane fraction. The clustering of beta(2) integrins also induced a time-dependent increase in GDP bound to RhoA, which correlated with beta(2) integrin-induced activation of p190RHOGAP: The activation of p190RhoGAP was completely blocked by [4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] (PP1), a selective inhibitor of Src family tyrosine kinases. However, clustering of beta(2) integrins did not increase the basal tyrosine phosphorylation of p190RhoGAP, nor did it affect the amount of p120RasGAP bound to p190RHOGAP: Instead, the beta(2) integrin-induced activation of p190RhoGAP was accompanied by increased tyrosine phosphorylation of a p190RhoGAP-associated protein, p120RasGAP, and accumulation of both p120RasGAP and p190RhoGAP in a membrane fraction. PP1 blocked the beta(2) integrin-induced phosphorylation of p120RasGAP, as well as the translocation of p190RhoGAP and p120RasGAP, but it did not affect the accumulation of RhoA in the membrane fraction. In agreement with the mentioned findings, PP1 also increased the GTP:GTP + GDP ratio recovered on RhoA immunoprecipitated from beta(2) integrin-stimulated cells. Thus, in neutrophils, beta(2) integrin-induced activation of p190RhoGAP requires a signal from a Src family tyrosine kinase, but it does not occur via the signaling pathway responsible for activation of RHOA:

In vivo detection of gene expression in liver by 31P nuclear magnetic resonance spectroscopy employing creatine kinase as a marker gene

In vivo assessment of gene expression is desirable to obtain information on the extent and duration of transduction of tissue after gene delivery. We have developed an in vivo, potentially noninvasive, method for detecting virally mediated gene transfer to the liver. The method employs an adenoviral vector carrying the gene for the brain isozyme of murine creatine kinase (CK-B), an ATP-buffering enzyme expressed mainly in muscle and brain but absent from liver, kidney, and pancreas. Gene expression was monitored by (31)P magnetic resonance spectroscopy (MRS) using the product of the CK enzymatic reaction, phosphocreatine, as an indicator of transfection. The vector was administered into nude mice by tail vein injection, and exogenous creatine was administered in the drinking water and by i.p. injection of 2% creatine solution before (31)P MRS examination, which was performed on surgically exposed livers. A phosphocreatine resonance was detected in livers of mice injected with the vector and was absent from livers of control animals. CK expression was confirmed in the injected animals by Western blot analysis, enzymatic assays, and immunofluorescence measurements. We conclude that the syngeneic enzyme CK can be used as a marker gene for in vivo monitoring of gene expression after virally mediated gene transfer to the liver.

Amphiregulin acts as an autocrine growth factor in two human polarizing colon cancer lines that exhibit domain selective EGF receptor mitogenesis

Colonic enterocytes, like many epithelial cells in vivo, are polarized with functionally distinct apical and basolateral membrane domains. The aims of this study were to characterize the endogenous epidermal growth factor (EGF)-like ligands expressed in two polarizing colon cancer cell lines, HCA-7 Colony 29 (HCA-7) and Caco-2, and to examine the effects of cell polarity on EGF receptor-mediated mitogenesis. HCA-7 and Caco-2 cells were grown on plastic, or as a polarized monolayer on Transwell filters. Cell proliferation was measured by 3H-thymidine incorporation and EGF receptor (EGFR) binding was assessed by Scatchard analysis. EGFR ligand expression was determined by Northern blot analysis, reverse transcription polymerase chain reaction, metabolic labelling and confocal microscopy. We found that amphiregulin (AR) was the most abundant EGFR ligand expressed in HCA-7 and Caco-2 cells. AR was localized to the basolateral surface and detected in basolateral-conditioned medium. Basolateral administration of neutralizing AR antibodies significantly reduced basal DNA replication. A single class of high-affinity EGFRs was detected in the basolateral compartment, whereas the apical compartment of polarized cells, and cells cultured on plastic, displayed two classes of receptor affinity. Basolateral administration of transforming growth factor alpha (TGF-alpha) or an EGFR neutralizing antibody also resulted in a dose-dependent stimulation or attenuation, respectively, of DNA replication. However, no mitogenic response was observed when these agents were added to the apical compartment or to confluent cells cultured on plastic. We conclude that amphiregulin acts as an autocrine growth factor in HCA-7 and Caco-2 cells, and EGFR ligand-induced proliferation is influenced by cellular polarity.

Effect of growth factor on GTPase-activating protein (Ras GAP) in Chinese hamster ovary cells

GTPase-activating proteins (GAPs) stimulate the hydrolysis of GTP bound to small G-proteins and regulate the signal transduction pathway. Changes in the expression of p21-Ras p120-GAP induced by growth factor treatment were examined in cultured Chinese hamster ovary (CHO) and human choriocarcinoma (BeWo) cells. Expression of p120-GAP and GAP activity were measured. Fetal bovine serum induced a significant increased level of GAP in CHO cells, but did not increase GAP in BeWo cells. The results suggest that growth factors affect Ras GAP expression in CHO cells, while they do not in other cells such as BeWo cells.

A 67 kDa non-hormone binding estradiol receptor is present in human mammary cancers

The presence of large amounts of a 67 kDa estradiol receptor that does not bind hormone was observed in 8 to 37 human mammary tumors (34 malignant and 3 benign). This form of receptor was detected by its conversion to hormone binding receptor by an endogenous tyrosine kinase in vitro. All 8 tumors were malignant. In these, the incubation of cytosol with ATP was seen to cause a 1- to 5-fold increase in estradiol-specific binding sites. These sites bound estradiol with physiological affinity, and their appearance was associated with tyrosine phosphorylation of estradiol receptor. The enzyme converting the non-hormone binding receptor into the hormone binding receptor is largely present in cytosol and scarce in membranes. It has been extensively purified. It is a 67 kDa protein under denaturating conditions, binds calmodulin-Sepharose in a Ca2+-dependent manner, is stimulated by Ca2+ and calmodulin, phosphorylates exogenous actin, is activated by the estradiol-receptor complex. The enzyme interacts with antibodies directed against the carboxy-terminal and catalytic domains of c-src. Therefore, it is a putative new member of the large c-src-related kinase family. Human mammary cancers with significant amounts of 67 kDa non-hormone binding receptor show relatively low levels of hormone binding estradiol receptor. The presence of non-hormone binding receptor that can be activated by in vitro tyrosine phosphorylation suggests that functional interaction of estradiol receptor with tyrosine kinases is altered in malignant tumors and has bearing on loss of hormone dependence and progression of the mammary cancer malignancy.