Lack of TCF2/vHNF1 in mice leads to pancreas agenesis.

Heterozygous mutations in the human POU-homeobox TCF2 (vHNF1, HNF1beta) gene are associated with maturity-onset diabetes of the young, type 5, and abnormal urogenital tract development. Recently, pancreas atrophies have been reported in several maturity-onset diabetes of the young type 5 patients, suggesting that TCF2 is required not only for adult pancreas function but also for its normal development. Tcf2-deficient mice die before gastrulation because of defective visceral endoderm formation. To investigate the role of this factor in pancreas development, we rescued this early lethality by tetraploid aggregation. We show that TCF2 has an essential function in the first steps of pancreas development, correlated with its expression domain that demarcates the entire pancreatic buds from the earliest stages. Lack of TCF2 results in pancreas agenesis by embryonic day 13.5. At earlier stages, only a dorsal bud rudiment forms transiently and expresses the transcription factors Ipf1 and Hlxb9 but lacks the key transcription factor involved in the acquisition of a pancreatic fate, Ptf1a, as well as all endocrine precursor cells. Regional specification of the gut also is perturbed in Tcf2-/- embryos as manifested by ectopic expression of Shh and lack of Ihh and Ipf1 in the posterior stomach and duodenum. Our results highlight the requirement of Tcf2 for ensuring both accurate expression of key regulator molecules in the stomach-duodenal epithelium and proper acquisition of the pancreatic fate. This study provides further insights into early molecular events controlling pancreas development and may contribute to the development of cell-replacement strategies for diabetes.

The biological and biochemical effects of CP-654577, a selective erbB2 kinase inhibitor, on human breast cancer cells.

Aberrant expression or activity of epidermal growth factor receptor (EGFr) or the closely related p185(erbB2) can promote cell proliferation and survival and thereby contribute to tumorigenesis. Specific antibodies and low molecular-weight tyrosine kinase inhibitors of both proteins are in clinical trials for cancer treatment. CP-654577 is a potent inhibitor selective for p185(erbB2), relative to EGFr tyrosine kinase, and selectively reduces erbB2 autophosphorylation in intact cells. Treatment of SKBr3 human breast cancer cells with CP-654577 reduces the levels of the activated form of mitogen-activated protein kinase, increases the levels of cyclin-dependent kinase inhibitor p27(kip1) and reduces expression of cyclins D and E. These biochemical changes result in a reduced level of phosphorylated retinoblastoma protein and an inhibition of cell-cycle progression at G(1). Apoptosis is triggered in both SKBr3 and another high erbB2-expressing cell line, BT474, by exposure to 1 micro M CP-654577, but this effect is not observed in MCF7 cells that express low erbB2. Levels of activated Akt, an important positive regulator of cell survival, are reduced within 2 h of exposure to 250 nM CP-654577, and this may contribute to the increased apoptosis. These biochemical effects are distinct from those produced by Tarceva, a selective EGFr inhibitor. The antitumor activity of CP-654577 was investigated in athymic mice bearing s.c. tumors from Fischer rat embryo fibroblasts transfected with erbB2. CP-654577 produced a dose-dependent reduction of p185(erbB2) autophosphorylation and inhibited the growth of these tumors. CP-654577 warrants further evaluation in tumors with high expression of p185(erbB2) and may differ from selective EGFr inhibitors or nonselective dual EGFr/erbB2 inhibitors in efficacy and therapeutic index.

Inhibition of epidermal growth factor receptor-associated tyrosine phosphorylation in human carcinomas with CP-358,774: dynamics of receptor inhibition in situ and antitumor effects in athymic mice.

Phosphorylation of tyrosine residues on the epidermal growth factor (EGF) receptor (EGFr) is an important early event in signal transduction, leading to cell replication for major human carcinomas. CP-358,774 is a potent and selective inhibitor of the EGFr tyrosine kinase and produces selective inhibition of EGF-mediated tumor cell mitogenesis. To assess the pharmacodynamic aspects of EGFr inhibition, we devised an ex vivo enzyme-linked immunosorbent assay for quantification of EGFr-specific tyrosine phosphorylation in human tumor tissue specimens obtained from xenografts growing s.c. in athymic mice. When coupled with pharmacokinetic analyses, this measurement can be used to describe the extent and duration of kinase inhibition in vivo. CP-358,774 is an effective, orally active inhibitor of EGFr-specific tyrosine phosphorylation (ED(50) = 10 mg/kg, single dose). It has a significant duration of action, producing, on average, a 70% reduction in EGFr-associated phosphotyrosine over a 24-h period after a single 100 mg/kg dose. Inhibition of EGFr phosphotyrosine in an ex vivo assay format effectively estimates the potency and degree of inhibition of EGFr-dependent human LICR-LON-HN5 head and neck carcinoma tumor growth. Substantial growth inhibition of human tumor xenografts was achieved with p.o. doses of the compound (ED(50) = 10 mg/kg q.d. for 20 days). Combination chemotherapy with cisplatin produced a significant response above that of cisplatin alone with no detectable effects on body weight or lethal toxicity. Taken together, these observations suggest that CP-358,774 may be useful for the treatment of EGFr-driven human carcinomas.

Variant hepatocyte nuclear factor 1 is required for visceral endoderm specification.

Genetic and molecular evidence indicates that visceral endoderm, an extraembryonic cell lineage, is required for gastrulation, early anterior neural patterning, cell death and specification of posterior mesodermal cell fates. We show that variant Hepatocyte Nuclear Factor 1 (vHNF1), a homeodomain-containing transcription factor first expressed in the primitive endoderm, is required for the specification of visceral endoderm. vHnf1-deficient mouse embryos develop normally to the blastocyst stage, start implantation, but die soon afterwards, with abnormal or absent extraembryonic region, poorly organised ectoderm and no discernible visceral or parietal endoderm. However, immunostaining analysis of E5.5 nullizygous mutant embryos revealed the presence of parietal endoderm-like cells lying on an abnormal basal membrane. Homozygous mutant blastocyst outgrowths or differentiated embryonic stem cells do not express early or late visceral endoderm markers. In addition, in vHnf1 null embryoid bodies there is no activation of the transcription factors HNF-4alpha1, HNF1alpha and HNF-3gamma. Aggregation of vHnf1-deficient embryonic stem cells with wild-type tetraploid embryos, which contribute exclusively to extraembryonic tissues, rescues periimplantation lethality and allows development to progress to early organogenesis. Our results place vHNF1 in a preeminent position in the regulatory network that specifies the visceral endoderm and highlight the importance of this cell lineage for proper growth and differentiation of primitive ectoderm in pregastrulating embryos.

Pathogenic poxviruses reveal viral strategies to exploit the ErbB signaling network.

Virulence of poxviruses, the causative agents of smallpox, depends on virus-encoded growth factors related to the mammalian epidermal growth factor (EGF). Here we report that the growth factors of Shope fibroma virus, Myxoma virus and vaccinia virus (SFGF, MGF and VGF) display unique patterns of specificity to ErbB receptor tyrosine kinases; whereas SFGF is a broad-specificity ligand, VGF binds primarily to ErbB-1 homodimers, and the exclusive receptor for MGF is a heterodimer comprised of ErbB-2 and ErbB-3. In spite of 10- to 1000-fold lower binding affinity to their respective receptors, the viral ligands are mitogenically equivalent or even more potent than their mammalian counterparts. This remarkable enhancement of cell growth is due to attenuation of receptor degradation and ubiquitination, which leads to sustained signal transduction. Our results imply that signal potentiation and precise targeting to specific receptor combinations contribute to cell transformation at sites of poxvirus infection, and they underscore the importance of the often ignored low-affinity ligand-receptor interactions.

Induction of apoptosis and cell cycle arrest by CP-358,774, an inhibitor of epidermal growth factor receptor tyrosine kinase.

The epidermal growth factor receptor (EGFR) is overexpressed in a significant percentage of carcinomas and contributes to the malignant phenotype. CP-358,774 is a directly acting inhibitor of human EGFR tyrosine kinase with an IC50 of 2 nM and reduces EGFR autophosphorylation in intact tumor cells with an IC50 of 20 nM. This inhibition is selective for EGFR tyrosine kinase relative to other tyrosine kinases we have examined, both in assays of isolated kinases and whole cells. At doses of 100 mg/kg, CP-358,774 completely prevents EGF-induced autophosphorylation of EGFR in human HN5 tumors growing as xenografts in athymic mice and of the hepatic EGFR of the treated mice. CP-358,774 inhibits the proliferation of DiFi human colon tumor cells at submicromolar concentrations in cell culture and blocks cell cycle progression at the G1 phase. This inhibitor produces a marked accumulation of retinoblastoma protein in its underphosphorylated form and accumulation of p27KIP1 in DiFi cells, which may contribute to the cell cycle block. Inhibition of the EGFR also triggers apoptosis in these cells as determined by formation of DNA fragments and other criteria. These results indicate that CP-358,774 has potential for the treatment of tumors that are dependent on the EGFR pathway for proliferation or survival.

omega-Conotoxin-sensitive Ca2+ voltage-gated channels modulate protein secretion in cultured rat Sertoli cells.

Recent results have demonstrated that substantial calcium influx in rat Sertoli cells is mediated by cation channels of both L- and N-type. In this report we have investigated the possible role of such channels in the protein secretion of immature rat Sertoli cell monolayers. The blocking of N-type voltage-gated channels by omega-conotoxin (omega-CTX) GVIA results in a 50-60% inhibition of the protein secretion in the culture medium while total protein and RNA synthesis are not affected. The same extent of protein secretion inhibition is obtained in FSH-stimulated Sertoli cells. L-type voltage-gated channels apparently are not involved in such a modulation. These data, showing that a major fraction of secreted proteins from cultured rat Sertoli cells is Ca2+ dependent, represent the first evidence of a physiological role of voltage-operated Ca2+ channels in mammalian testis.

Identification and characterization of an ecto-ATPase activity in rat Sertoli cells.

A membrane associated extracellular ATPase (ecto) has been identified on rat Sertoli cells. Sertoli cell ecto-ATPase demonstrated a Km for ATP of 114 muM and a V(max) of 1.79 mumol/min/2 x 10(5) cells and was activated by either Mg2+ or Ca2+. This ecto-ATPase hydrolyzes other nucleoside triphosphates, but is inactive with ADP. The effects of some possible inhibitors of ectonucleotidases on the breakdown of extracellular ATP by Sertoli cells were also investigated.

Inhibition of the oncogene product p185erbB-2 in vitro and in vivo by geldanamycin and dihydrogeldanamycin derivatives.

The erbB-2 oncogene encodes a transmembrane protein tyrosine kinase which plays a pivotal role in signal transduction and has been implicated when overexpressed in breast, ovarian, and gastric cancers. Naturally occurring benzoquinoid ansamycin antibiotics herbimycin A, geldanamycin (GDM), and dihydrogeldanamycin were found to potently deplete p185, the erbB-2 oncoprotein, in human breast cancer SKBR-3 cells in culture. Chemistry efforts to modify selectively the quinoid moiety of GDM afforded derivatives with greater potency in vitro and in vivo. Analogs demonstrated inhibition of p185 phosphotyrosine in cell culture and in vivo after systemic drug administration to nu/nu nude mice bearing Fisher rat embryo cells transfected with human erbB-2 (FRE/erbB-2). Specifically, dosed intraperitoneally at 100 mg/kg, 17-(allylamino)-17-demethoxygeldanamycin and other 17-amino analogs were effective at reducing p185 phosphotyrosine in subcutaneous flank FRE/erbB-2 tumors. Modifications to the 17-19-positions of the quinone ring revealed a broad structure-activity relationship in vitro.

erbB-2 oncogene inhibition by geldanamycin derivatives: synthesis, mechanism of action, and structure-activity relationships.

Overexpression of the erbB-2 oncogene has been linked to poor prognosis in breast, ovarian, and gastric cancers. Naturally occurring benzoquinoid ansamycin antibiotics herbimycin A, geldanamycin (GDM), and dihydrogeldanamycin were found to potently deplete p185, the erbB-2 oncoprotein, in human breast cancer SKBR-3 cells in culture. Chemistry efforts to modify selectively the ansa ring of GDM afforded derivatives with greater potency in vitro and in vivo. Analogs demonstrated inhibition of p185 phosphotyrosine in cell culture and in vivo after systemic drug administration to nu/nu nude mice bearing Fisher rat embryo cells transfected with human erbB-2. Functional group modification in the ansa ring was performed stereoselectively and regiospecifically without the need for protection strategies. Essential functional groups that were required for anti-erbB-2 activity were the 7-carbamate and the 2,3-double bond. Modification of the functional groups at the other positions was permitted. Structure-activity relationships are described for 1-5-, 7-9-, 11-, 15-, and 22-substituted geldanamycins.

Inflammatory mediators increase surface expression of integrin ligands, adhesion to lymphocytes, and secretion of interleukin 6 in mouse Sertoli cells.

The expression of the cell adhesion molecules ICAM-1, ICAM-2, and VCAM-1 and the secretion of the cytokine interleukin 6 have been measured in mouse Sertoli cells cultured in vitro. Cytometric analysis revealed that, in basal conditions, low levels of ICAM-1 and VCAM-1 were present on the surface of the cells, whereas treatment with interleukin 1, tumor necrosis factor alpha, lipopolysaccharide, or interferon gamma induced, with different kinetics, increases in their expression. ICAM-2 was not detectable in basal conditions, nor was it inducible. Electron microscopic analysis and binding experiments using 51Cr-labeled lymphocytes demonstrated that increased expression of ICAM-1 and VCAM-1 on the surface of Sertoli cells, induced by inflammatory mediators, determines an augmented adhesion between the two cell types. The same stimuli, with the exception of interferon gamma, produced a rapid and remarkable increment of interleukin 6 production by Sertoli cells. These results suggest the presence of both direct and paracrine mechanisms of interaction between Sertoli and immune-competent cells, possibly involved in the control of immune reactions in the testis. Such mechanisms are of interest for the understanding of autoimmune pathologies of the testis and, if confirmed in humans, they could be involved in the sexual transmission of human immunodeficiency virus infection.

The structural basis for the specificity of epidermal growth factor and heregulin binding.

Heregulin is a ligand for the erbB3 and erbB4 receptors, with a region of high homology to epidermal growth factor (EGF). Despite this homology, these ligands bind to their corresponding receptors with great specificity. We report here the synthesis of heregulin beta 177-241 and show that a region consisting of amino acids 177-226 is sufficient both for binding and stimulation of receptor phosphorylation. Studies of chimeric EGF/heregulin peptides revealed that amino acids 177-181 of heregulin provide the specificity for binding to the heregulin receptor. The substitution of amino acids 177-181 of heregulin for the N terminus of EGF produced a unique bifunctional agonist that binds with high affinity to both the EGF receptor and the heregulin receptor.

TNF-alpha induces surface modifications in mouse Sertoli cells: physiopathological implications.

The expression of the adhesion molecules ICAM-1 and VCAM-1 has been measured in mouse Sertoli cells cultured in vitro. Cytometric analysis revealed that, in basal conditions, low levels of ICAM-1 and VCAM-1 were present on the surface of the cells, whereas treatment with TNF-alpha induced an increase in their expression. Binding experiments using both 51Cr-labelled lymphocytes, for quantitative analysis, and scanning electron microscopy demonstrated that increased expression of ICAM-1 and VCAM-1 on the surface of Sertoli cells, induced by TNF-alpha, determines an augmented adhesion between the two cell types. These results suggest the presence of a specific mechanism of interaction between Sertoli and immune-competent cells, possibly involved in the control of the immune response in the testis following an inflammatory reaction in situ. Such mechanism is of interest for the understanding of auto-immune pathologies of the testis and, if confirmed in humans, it could be involved in the sexual transmission of HIV infection.

Binding of benzoquinoid ansamycins to p100 correlates with their ability to deplete the erbB2 gene product p185.

Several benzoquinoid ansamycins, e.g., herbimycin A and geldanamycin, have been widely used as inhibitors of tyrosine kinases. We recently reported that exposure to herbimycin A and several analogs depletes the erbB2 gene product p185 in human breast cancer cells. In order to explore the mechanism of this specific degradation of p185, a biologically active ansamycin incorporating a photoaffinity label was synthesized. This compound, CP202509, specifically bound to a 100 kD protein (p100) in intact SKBr3 cells and in fibroblasts transfected with the c-erbB2 or v-src oncogenes. Binding of other ansamycin analogs to p100, as measured indirectly by their ability to inhibit CP202509 binding, correlated with their ability to lower p185 protein and phosphotyrosine in SKBr3 cells. These results suggest that the ansamycins may deplete tyrosine kinases through binding to this protein.