miR-200b targets Ets-1 and is down-regulated by hypoxia to induce angiogenic response of endothelial cells.

The miR-200 family plays a crucial role in epithelial to mesenchymal transition via controlling cell migration and polarity. We hypothesized that miR-200b, one miR-200 family member, could regulate angiogenic responses via modulating endothelial cell migration. Delivery of the miR-200b mimic in human microvascular endothelial cells (HMECs) suppressed the angiogenic response, whereas miR-200b-depleted HMECs exhibited elevated angiogenesis in vitro, as evidenced by Matrigel® tube formation and cell migration. Using in silico studies, miR target reporter assay, and Western blot analysis revealed that v-ets erythroblastosis virus E26 oncogene homolog 1 (Ets-1), a crucial angiogenesis-related transcription factor, serves as a novel direct target of miR-200b. Knocking down endogenous Ets-1 simulated an anti-angiogenic response of the miR-200b mimic-transfected cells. Certain Ets-1-associated genes, namely matrix metalloproteinase 1 and vascular endothelial growth factor receptor 2, were negatively regulated by miR-200b. Overexpression of Ets-1 rescued miR-200b-dependent impairment in angiogenic response and suppression of Ets-1-associated gene expression. Both hypoxia as well as HIF-1α stabilization inhibited miR-200b expression and elevated Ets-1 expression. Experiments to identify how miR-200b modulates angiogenesis under a low oxygen environment illustrated that hypoxia-induced miR-200b down-regulation de-repressed Ets-1 expression to promote angiogenesis. This study provides the first evidence that hypoxia-sensitive miR-200b is involved in induction of angiogenesis via directly targeting Ets-1 in HMECs.

Arsenic trioxide induces down-regulation of gp46 via protein oxidation: proteomics analysis of oxidative modified proteins in As2O3-treated HTLV-1-infected cells.

Adult T-cell leukemia (ATL) is a severe chemotherapy-resistant malignancy associated with prolonged infection by the human T cell-lymphotropic virus 1 (HTLV-1) retrovirus. Epidemiology studies strongly indicate that an increase in HTLV-1 virus load is an important factor during the onset of ATL. Therefore, inhibition of the growth/transmission of HTLV-1 infected cells is a promising strategy in preventing the disease. In our previous study, we revealed that arsenic trioxide (As2O3), a drug used to treat acute promyelocytic leukemia (APL), exerts an inhibitory effect on syncytium formation between HTLV-1 infected cells and HeLa cells via suppression of HTLV-1 envelope protein gp46 expression at low concentrations. In this study, we analyze the mechanism of action of As2O3 using a proteomics approach. Our results suggest that down-regulation of gp46 might be related to As2O3-induced oxidation of the 71-kDa heat shock cognate protein (HSC70) and the 78-kDa glucose-regulated protein (BiP/GRP78). We postulate that AS2O3 exerts an inhibitory effect on HTLV-1 virus transmission via down-regulation of gp46-production, which might be caused by oxidative modification of various proteins such as chaperones.

Frequent expression of gp46 in adult T-cell leukemia/lymphoma: an immunohistochemical study of 40 cases.

Adult T-cell leukemia/lymphoma (ATLL) is a lymphoproliferative disease caused by human T-cell lymphotropic virus type 1 (HTLV-1) infection. HTLV-1 is spread by cell-to-cell transmission via the gp46-197 region, from Asp197 to Leu216, in the envelope protein gp46. A correlation exists between the prevalence and titer of the antibody recognizing the gp46-197 region (anti-gp46-197 antibody) and the severity of ATLL. In the present study, immunohistochemical staining was performed on samples of paraffin embedded lymph nodes of three different histological types of ATLL (anaplastic large cell type, n = 10; pleomorphic type, n = 10; and Hodgkin's-like type, n = 10) from 30 cases and 10 cases of HTLV-associated lymphadenitis. Of the three ATLL subtypes, gp46 expression was highest in the anaplastic large cell type, followed by the pleomorphic type and Hodgkin's-like type (mean: 53.4%, 34.9% and 16.0%, respectively; P= 0.0003). In HTLV-1 associated lymphadenitis cases, gp46 positive cells were rarely seen (4.0%). These results suggest that gp46-197 immunohistochemical staining can be a useful histological indicator for prediction of the aggressiveness of ATLL and prognosis for ATLL patients.

Arsenic trioxide inhibits human t cell-lymphotropic virus-1-induced syncytiums by down-regulating gp46.

Adult T-cell leukemia (ATL) is a severe chemotherapy-resistant malignancy associated with prolonged infection by the human T cell-lymphotropic virus 1 (HTLV-1). One approach to prevent the onset of ATL is to inhibit the growth/transmission of HTLV-1 infected cells using arsenic trioxide (As(2)O(3)). However, there are no reports on the transmission inhibitory effect of As(2)O(3). In this study, we reveal that As(2)O(3) exerts an inhibitory effect on syncytium formation between HTLV-1 infected MT-2 and HeLa cells. In addition, Western blot analysis revealed that the HTLV-1 derived envelope protein gp46 was down regulated by As(2)O(3) treatment, suggesting that As(2)O(3) may inhibit HTLV-1 virus transmission via down-regulation of gp46. These results suggest that As(2)O(3) may be a promising drug to treat refractory HTLV-1-related diseases.

Regulation of the Dbl proto-oncogene by heat shock cognate protein 70 (Hsc70).

The dbl oncogene product is the defining member of a family of onco-proteins known as Dbl guanine nucleotide exchange factors (GEFs) that facilitate the activation of the small GTP-binding proteins Cdc42, Rac, and Rho. Oncogenic activation of proto-Dbl occurs through loss of the amino-terminal 497 residues, rendering the protein constitutively active. Because both onco- and proto-Dbl contain the structural elements required for GEF activity (i.e. the Dbl homology (DH) and pleckstrin homology (PH) domains), it is thought that the amino terminus of proto-Dbl somehow inhibits the biochemical activity of the protein. To better understand the molecular basis of this regulation, we set forth to identify cellular proteins that preferentially bind the proto-oncogenic form of Dbl. We identified the molecular chaperone heat shock cognate protein (Hsc70) as a binding partner that preferentially interacts with the proto-oncogenic form of Dbl. Dbl is complexed with Hsc70 in transfected cells, as well as in native mouse brain extracts. The interaction between Hsc70 and proto-Dbl is mediated by at least two regions in Dbl, the aminoterminal spectrin homology domain (residues 224-417) and the pleckstrin homology domain (residues 711-808). Overexpression of a dominant negative Hsc70 mutant leads to activation of proto-Dbl GEF activity, indicating that the chaperone negatively regulates proto-Dbl function in vivo. We propose that Hsc70 attenuates Dbl activity by maintaining an inactive conformation in which the amino terminus is "folded over" the catalytic DH-PH domain.

Expression of recombinant small hydrophobic protein for serospecific detection of avian pneumovirus subgroup C.

The small hydrophobic (SH) gene of the avian pneumovirus (APV) Colorado isolate (CO), which belongs to subgroup C (APV/C), was expressed with a baculovirus vector. The recombinant SH protein was evaluated as a potential subgroup-specific diagnostic reagent in order to differentiate infections resulting from APV/C from those induced by APV/A, APV/B, and human metapneumovirus (hMPV). When the recombinant baculovirus was used to infect insect cells, a 31- to 38-kDa glycosylated form of the SH protein was produced and subsequently tested for reactivity with antibodies specific for APV/A, APV/B, APV/C, and hMPV. Western blot analysis showed that the expressed recombinant SH protein could only be recognized by APV/C-specific antibodies. This result was consistent with sequence analysis of the APV/C SH protein, which had very low (24%) amino acid identity with the corresponding protein of hMPV and no discernible identity with the SH protein of APV/A or APV/B. A recombinant SH protein-based enzyme-linked immunosorbent assay (ELISA) was developed, and it further confirmed the lack of reactivity of this protein with antisera raised to APV/A, APV/B, and hMPV and supported its designation as a subgroup-specific antigen. This finding indicated that the recombinant SH protein was a suitable antigen for ELISA-based detection of subgroup-specific antibodies in turkeys and could be used for serologically based differential diagnosis of APV and hMPV infections.

Involvement of p38 MAPK signaling pathway in IFN-gamma and HTLV-I expression in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis.

We analyzed the relationship between the expression of interferon (IFN)-gamma and HTLV-I p19 antigen and activation of p38 mitogen-activated protein kinase (p38 MAPK) in two HTLV-I-infected T cell lines derived from two patients (HCT-1 and HCT-4) with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and three HTLV-I-infected T cell lines derived from three patients with adult T cell leukemia (ATL). Expression of phosphorylated (activated)-p38 MAPK was markedly increased concomitant with high levels of both IFN-gamma and HTLV-I p19 antigen expression in both HCT-1 and HCT-4 compared with cell lines derived from ATL patients. Treatment with SB203580, a specific inhibitor of p38 MAPK, suppressed IFN-gamma and HTLV-I p19 antigen expression levels in HCT-1, HCT-4 and peripheral blood CD4(+) T cells of HAM/TSP patients. These findings strongly suggest that activation of p38 MAPK signaling pathway is involved in the up-regulation of IFN-gamma expression with high HTLV-I proviral load in HAM/TSP patients.

Requirements for pYXXM motifs in Cbl for binding to the p85 subunit of phosphatidylinositol 3-kinase and Crk, and activation of atypical protein kinase C and glucose transport during insulin action in 3T3/L1 adipocytes.

Cbl is phosphorylated by the insulin receptor and reportedly functions within the flotillin/CAP/Cbl/Crk/C3G/TC10 complex during insulin-stimulated glucose transport in 3T3/L1 adipocytes. Cbl, via pYXXM motifs at tyrosine-371 and tyrosine-731, also activates phosphatidylinositol (PI) 3-kinase, which is required to activate atypical protein kinase C (aPKC) and glucose transport during thiazolidinedione action in 3T3/L1 and human adipocytes [Miura et al. (2003) Biochemistry 42, 14335-14341]. Presently, we have examined the importance of Cbl in activating PI 3-kinase and aPKC during insulin action in 3T3/L1 adipocytes by expressing Y371F and Y731F Cbl mutants, which nullify pYXXM binding of Cbl to SH2 domains of downstream effectors. Interestingly, these mutants inhibited insulin-induced increases in (a) binding of Cbl to both Crk and the p85 subunit of PI 3-kinase, (b) activation of Cbl-dependent PI 3-kinase, (c) activation and translocation of aPKC to the plasma membrane, (d) translocation of Glut4 to the plasma membrane, (e) and glucose transport. Importantly, coexpression of wild-type Cbl reversed the inhibitory effects of Cbl mutants. In contrast to Cbl-dependent PI 3-kinase, Cbl mutants did not significantly inhibit the activation of PI 3-kinase by IRS-1, which is also required during insulin action. Our findings suggest that (a) Cbl uses pYXXM motifs to simultaneously activate PI 3-kinase and Crk/C3G/TC10 pathways and (b) Cbl, along with IRS-1, functions upstream of PI 3-kinase and aPKCs during insulin-stimulated glucose transport in 3T3/L1 adipocytes.

Expression of Cbl linking with the epidermal growth factor receptor system is associated with tumor progression and poor prognosis of human gastric carcinoma.

Cbl proteins play important roles in downregulation of growth factor receptors by acting as ubiquitin ligases and multi-adapter proteins. Ligand-induced desensitization of the epidermal growth factor receptor (EGFR) has been shown to be controlled by Cbl. In the present study, we examined the expression of Cbl in gastric carcinomas and studied the correlation of Cbl expression with clinicopathological characteristics as well as EGFR expression. Cbl protein was expressed in 67% (82/122) of gastric carcinomas, and diffuse expression of Cbl was detected in 29% (35/122) of the cases. The incidence of cases with diffuse expression of Cbl was significantly higher in advanced cases (28/70, 40%) than in early cases (7/52, 14%) (P=0.0010). Diffuse expression of Cbl was significantly associated with metastasis of tumor cells in lymph nodes (P=0.0318). Diffuse expression of EGFR was significantly associated with depth of invasion (P=0.0057), lymph-node metastasis (P=0.0371) and tumor stages (P=0.0278). As the grades of Cbl expression became stronger, the cases with diffuse EGFR expression increased, the positive correlation being significant (P=0.049). All the cases with diffuse expression of Cbl and EGFR were found to show nodal metastasis and to be at an advanced stage. Moreover, the prognosis of the patients with synchronous diffuse expression of Cbl and EGFR was significantly poorer than that of the patients negative for Cbl and focal or negative for EGFR (P=0.0086). The expression of Cbl protein was clearly induced in gastric carcinoma cell lines by transforming growth factor-alpha treatment. These results suggest that Cbl in connection with the EGFR system may be associated with stomach carcinogenesis, invasion and metastasis. Cbl may serve as a novel molecular marker for aggressive gastric carcinoma.

HTLV-1 Rex is required for viral spread and persistence in vivo but is dispensable for cellular immortalization in vitro.

Human T-cell leukemia virus type 1 (HTLV-1) is associated with leukemia/lymphoma and neurologic disorders. Although the viral transcriptional activator Tax is the critical viral oncoprotein, Rex, which regulates the expression of the viral structural and enzymatic genes, is essential for efficient viral replication. Herein, we investigate the contribution of Rex in HTLV-1 immortalization of primary T cells in vitro and viral survival in an infectious rabbit animal model. A Rex-deficient HTLV-1 (HTLVRex-) was constructed and characterized for viral gene expression, protein production, and immortalization capacity. Cells transiently transfected with the HTLVRex- proviral clone produced low detectable levels of p19 Gag. 729HTLVRex- stable transfectants produced functional Tax, but undetectable levels of Rex or p19 Gag. Coculture of irradiated 729HTLVRex- cells with peripheral blood mononuclear cells (PBMCs) resulted in sustained interleukin-2 (IL-2)-dependent growth of primary T lymphocytes. These cells carried the HTLVRex- genome and expressed tax/rex mRNA but produced no detectable Rex or p19 Gag. Rabbits inoculated with irradiated 729HTLVRex- cells or 729HTLVRex- cells transiently transfected with a Rex cDNA expression plasmid failed to become persistently infected or mount a detectable antibody response to the viral gene products. Together, our results provide the first direct evidence that Rex and its function to modulate viral gene expression and virion production is not required for in vitro immortalization by HTLV-1. However, Rex is critical for efficient infection of cells and persistence in vivo.

The cytotoxic T-lymphocyte response against a poorly immunogenic mammary adenocarcinoma is focused on a single immunodominant class I epitope derived from the gp70 Env product of an endogenous retrovirus.

The TS/A mouse mammary adenocarcinoma is a poorly immunogenic tumor widely used in preclinical models of cancer immunotherapy. CTLs have often been indicated as important in TS/A tumor destruction, but their generation in this model has been rarely studied, nor have their precise target(s) been identified. We hypothesized that the gp70 Env product of an endogenous murine leukemia virus could be a target antigen for TS/A-specific CTLs and investigated this possibility in four different TS/A cell lines engineered with the genes that encode IFN-alpha, IFN-gamma, interleukin-4, and B7.1, respectively. All tumor cell lines expressed gp70, albeit at different levels, as demonstrated by reverse transcription-PCR analysis. Transfected tumor cells exhibited a delayed growth in vivo, and partial tumor regression. Spleen cells from mice that displayed tumor regression had high percentages of CD8(+) T cells that were specifically stained with L(d) tetramers loaded with gp70(423-431), the antigenic epitope of gp70 protein. Mixed leukocyte-peptide and mixed leukocyte-tumor cultures, set up by stimulating splenocytes with the immunogenic peptide and with transfected TS/A tumor cells, respectively, resulted in similar large increases in tetramer-reactive CD8(+) T cells and showed high lytic activity specific for gp70(423-431). Finally, in a Cold Target Inhibition assay, lytic activity of a mixed leukocyte-tumor culture was inhibited in an overlapping fashion by both the TS/A line used for restimulation and 293L(d) cells loaded with gp70(423-431) peptide, but not by 293L(d) cells pulsed with an irrelevant H-2 L(d) epitope, thus demonstrating that all or most of the cytotoxic activity was directed exclusively against this antigenic epitope.

Molecular and immunohistochemical analysis of signaling adaptor protein Crk in human cancers.

Crk is a signaling adaptor protein which is mostly composed of SH2 and SH3 domains, and has been shown to play a pivotal role in cell proliferation, differentiation, and migration. Because Crk was originally isolated as an avian sarcoma virus CT10 encoding oncoprotein v-Crk, we examined a potential role for c-Crk in the carcinogenesis of human cancers. First, to analyze gene mutations of c-Crk, we isolated a human bacterial artificial chromosome clone containing Crk genome and exon/intron structures. However, polymerase chain reaction-single strand conformation polymorphism methods failed to show any genomic mutations in the Crk exon which could be related to carcinogenesis. Second, immunohistochemical analysis of c-Crk-II demonstrated that the levels of c-Crk-II were significantly elevated in most of the tumors, particularly in the colon and lung cancers. Furthermore, immunoblot analysis using human lung cancer cell lines revealed that the expression levels of c-Crk-II were correlated to growth rates of cells. The elevated expression levels of c-Crk-II might be related to the development of human cancers.

Induction of the immediate early genes egr-1 and c-fos by methamphetamine in mouse brain.

Methamphetamine (METH) is one of the most commonly abused psychostimulant, and is known to induce dopaminergic neurotoxicity by generating oxidative stress and free radicals. In the present study we investigated the effects of METH on egr-1 and c-fos immediate early gene induction in different regions of mouse brain, at different doses and different time courses. We also measured the tissue levels of monoamines in order to correlate their changes with gene expression. A single injection of METH (40 mg/kg) significantly increased egr-1 and c-fos mRNA expression within 30 min in frontal cortex, nucleus accumbens, caudate putamen, septum and CA1 region of hippocampus. Time course studies showed that in most cases, both genes were expressed within 30 min and decreased after 60 min. METH produced a significant decrease in striatal dopamine level, reaching a very low level after 24 h. Striatal serotonin level significantly increased and returned to control levels after 2 h. These data show that METH induced egr-1 and c-fos mRNA expression in selective brain areas, which correlated with an alteration in monoamines.

Cell-free entry of human T-cell leukemia virus type 1 to mouse cells.

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent for adult T-cell leukemia and HTLV-1-associated myelopathy / tropical spastic paraparesis. Recently we infected newborn mice by inoculating HTLV-1-producing human cells, and found that T-cells, B-cells and granulocytes were infected in vivo. To understand the mechanism of viral-cell interaction and the pathogenesis of HTLV-1 using the mouse model, it is important to clarify the cellular tropism using a cell-free HTLV-1 transmission system. We employed a highly transmissible cell-free HTLV-1 produced by a feline kidney cell line, c77, and studied the susceptibility of 9 kinds of mouse cell lines, EL4, RLm1, CTLL-2, J774.1, DA-1, Ba / F3, WEHI-3, NIH3T3 and B1, and two kinds of human cell lines, Molt-4 and Hut78. HTLV-1 proviral sequence was found by PCR in all 9 mouse cell lines as well as in 2 human cell lines and viral entry was blocked with sera from an HTLV-1 carrier and an adult T-cell leukemia patient. Unexpectedly, mouse cell lines EL4 and RLm1 and human cell lines Molt-4 and Hut78 showed similar efficiency for viral entry. These results suggest a wide distribution of HTLV-1 receptor in mouse cells.

A MEK inhibitor, PD98059 enhances IL-1-induced NF-kappaB activation by the enhanced and sustained degradation of IkappaBalpha.

Interleukin-1 (IL-1) mediates numerous host responses through rapid activation of nuclear factor-kappaB (NF-kappaB), but signal pathways leading to the NF-kappaB activation appear to be complicated and multiplex. We propose a novel regulatory system for NF-kappaB activation by the extracellular signal-related kinase (ERK) pathway. In a human glioblastoma cell line, T98G, IL-1-induced NF-kappaB activation was significantly augmented by the pretreatment of a specific MEK inhibitor, PD98059. In contrast, ectopic expression of a constitutive activated form of Raf (v-Raf) reduced IL-1-induced NF-kappaB activation, and this inhibition was completely reversed by PD98059. Interestingly, PD98059 sustained IL-1-induced NF-kappaB DNA binding activity by an electrophoretic mobility shift assay and also IkappaBalpha degradation, presumably by augmenting and sustaining the proteasome activation. Concomitantly, two NF-kappaB dependent genes, A20 and IkappaBalpha expression were prolonged with PD98059. These data suggested that MEK-ERK pathway exerts a regulatory effect on NF-kappaB activation, providing a novel insight on the role of MEK-ERK pathway.

IFN-gamma can promote tumor evasion of the immune system in vivo by down-regulating cellular levels of an endogenous tumor antigen.

Although IFN-gamma has been generally thought to enhance antitumor immune responses, we found that IFN-gamma can promote tumor escape in the CT26 colon carcinoma by down-regulating the protein expression of an endogenous tumor Ag. gp70, the env product of the endogenous ecotropic murine leukemia virus, has been reported to be the immunodominant Ag of CT26. We show that IFN-gamma down-regulates intracellular and surface levels of gp70 protein resulting in a reduced lysis by CTL, which is restored by pulsing IFN-gamma-treated CT26 with the L(d)-restricted immunodominant AH1 epitope derived from gp70. To investigate the role of CT26 sensitivity to IFN-gamma in vivo, we constructed two variants of CT26, CT26.mugR and CT26.IFN, that are unresponsive to IFN-gamma or express IFN-gamma, respectively. We demonstrate using these variants that tumor responsiveness to IFN-gamma promotes a reduction in tumor immunogenicity in vivo that is correlated with an increased tumor incidence in immune mice. Analysis of the tumors from mice challenged with CT26 or CT26.mugR revealed infiltration of CD8 T cells secreting IFN-gamma. We conclude that IFN-gamma secreted by tumor-infiltrating T cells promotes tumor escape through the down-regulation of the endogenous tumor Ag gp70. These findings have impact on the design of effective antitumor vaccine strategies.

Geranylgeranylated RhoB is sufficient to mediate tissue-specific suppression of Akt kinase activity by farnesyltransferase inhibitors.

Farnesyltransferase inhibitors (FTIs) induce apoptosis by elevating the levels of geranylgeranylated RhoB (RhoB-GG) in cells. However, the mechanism by which RhoB-GG acts is unclear. Here we report that RhoB-GG is sufficient to mediate the suppressive effects of FTIs on the activity of the survival kinase Akt-1 in epithelial cells. This mechanism is tissue-specific insofar as it does not operate in fibroblasts. We discuss how the cell survival functions of RhoB and Akt may be linked biochemically in certain cell types.

Distinct involvement of cdc42 and RhoA GTPases in actin organization and cell shape in untransformed and Dbl oncogene transformed NIH3T3 cells.

The Dbl oncogene is a putative exchange factor for the small GTPases RhoA and Cdc42, which are involved in actin polymerization into stress fibers and filopodia, respectively. We report here that, upon adhesion to fibronectin, Dbl-transformed NIH3T3 cells display a contracted, polygonal shape with a high number of short stress fibers. In contrast, untransformed NIH3T3 cells acquire the characteristic fibroblast morphology and organize a regular mesh of long stress fibers. We show that in Dbl-transformed and in untransformed NIH3T3 cells the different shape and actin cytoskeleton organization observed in the early steps of adhesion involves activation of distinct GTPases. Upon adhesion to fibronectin, cell morphology of Dbl-transformed NIH3T3 cells depends on activation of RhoA and not of Cdc42. In contrast Cdc42 activation is necessary to untransfected NIH3T3 cells to acquire their fibroblast shape. In both Dbl-transformed and in untransformed NIH3T3 cells a basal Rac activation is necessary to support stress fiber organization, while constitutive Rac activation promotes ruffles and lamellipodia formation. As a consequence of RhoA activation, Dbl-transformed cells show high activity of ROCK-alpha and CRIK kinases, two known RhoA effectors. In addition Dbl-transformed and NIH3T3 cells expressing the constitutive active form of RhoA are less motile on fibronectin than cells expressing constitutive active Cdc42. We conclude that in NIH3T3 cells in response to fibronectin the expression of the Dbl oncogene leads to a predominant activation of RhoA which both supports the peculiar cell shape and actin cytoskeleton organization in stress fibers and regulates cell motility.

A hydrophobic patch in ecotropic murine leukemia virus envelope protein is the putative binding site for a critical tyrosine residue on the cellular receptor.

In the receptor for ecotropic murine leukemia viruses, tyrosine 235 contributes a critical hydrophobic side chain to the virus-receptor interaction (14). Here we report that tryptophan 142 in ecotropic Moloney murine leukemia virus envelope protein is essential to virus binding and infection. Replacement of tryptophan 142 by alanine or serine resulted in misfolding. However, replacement by methionine (W142M) allowed correct folding of the majority of glycoprotein molecules. W142M virus showed a marked reduction in virus binding and was almost noninfectious, suggesting that tryptophan 142 is involved in receptor binding. In contrast, W142Y virus containing a replacement of tryptophan 142 with an aromatic residue (tyrosine) was as efficient as wild-type virus in infection and binding of cells expressing the wild-type receptor. However, W142Y virus was 100-fold less efficient than wild-type virus in infection of cells expressing a mutant receptor containing tryptophan instead of the critical tyrosine. These results strongly support tryptophan 142 being an essential residue on the virus envelope protein that interacts directly with the critical hydrophobic residue at position 235 of the ecotropic receptor. Tryptophan 142 forms one side of a shallow hydrophobic pocket on the surface of the envelope protein, suggesting that it might comprise the complete putative binding site for tyrosine 235. We discuss the implications of our findings with respect to two models of the envelope protein trimer. Interestingly, both models place tryptophan 142 at the interface between adjacent subunits of the trimer.

Targeted expression of an oncogenic adaptor protein v-Crk potentiates axonal growth in dorsal root ganglia and motor neurons in vivo.

The ability of neurons to survive and to target axonal growth requires a coordinated series of cell extrinsic and intrinsic events. Previously, in a cellular model for neuronal differentiation, we showed that pheochromocytoma (PC12) cells expressing v-Crk, an oncogenic form of the SH2/SH3-containing c-Crk adaptor protein, potentiates axonal growth and prolongs nerve growth factor (NGF)-independent survival. In the present study, we have generated transgenic mice that express v-Crk in sensory, motor, and enteric neurons by placing v-crk under the control of the neuron-specific peripherin promoter. In contrast to wild-type (wt) mice, dorsal root ganglia (DRG) neurons explanted from post-natal day 1 transgenic mice demonstrated a reduced dependence on trophic factors for both survival and axonogenesis. v-Crk also caused an increase in the number of surviving spinal motor neurons (SMN), and interestingly, upon staining of sternomastoid muscle fibers with rhodamine conjugated alpha-bungarotoxin, many muscle fibers displayed an apparent increase in volume of motor end plates, and an increase in complexity of neuromuscular junctions (NMJ). Our data suggest that v-Crk may be involved in transducing extracellular signals to regulate cytoskeletal organization, and may act on an intrinsic determinant for axonal growth in a variety of neural types including sensory and motor neurons during development.