Five independent loci each control monogenic resistance to gummy stem blight in melon ( Cucumis melo L.).

Inheritance and segregation analysis demonstrated that five independent genes in melon confer monogenic resistance to foliar infection by the fungal pathogen Didymella bryoniae, resulting in the disease known as gummy stem blight (GSB). In this study, two new monogenic sources of GSB resistance were characterized. Resistance in Cucumis melo PI 482398 was monogenic dominant based on segregation analysis of F(1), F(2) and backcross populations, while resistance in C. melo PI 482399 showed monogenic recessive inheritance. Four accessions, PI 482398, PI 157082, PI 511890, and PI 140471, each previously known to carry monogenic dominant resistance to GSB, were intercrossed to determine genetic relationships among these resistance sources. Recovery of susceptible individuals in F(2) populations confirmed that these accessions possess different resistance genes. Resistance loci were designated Gsb-1 (formerly Mc, monogenic dominant resistance from PI 140471), Gsb-2 (monogenic dominant resistance from PI 157082), Gsb-3 (monogenic dominant resistance from PI 511890), Gsb-4 (monogenic dominant resistance from PI 482398) and gsb-5 (monogenic recessive resistance from PI 482399).

BMS-189453, a novel retinoid receptor antagonist, is a potent testicular toxin.

BMS-189453 is a synthetic retinoid that acts as an antagonist at retinoic acid receptors alpha, beta, and gamma. In Sprague Dawley rats at daily oral doses of 15, 60, or 240 mg/kg for 1 month, BMS-189453 produced increases in leukocyte counts, alkaline phosphatase and alanine aminotransferase levels, and marked testicular degeneration and atrophy at all doses. Significant overt signs of toxicity and deaths occurred at 240 mg/kg, whereas body-weight and food-consumption decreases occurred at 60 and 240 mg/kg. When BMS-189453 was administered to male rats at daily doses ranging from 12.5 to 100 mg/kg for 1 week, only minimal testicular changes occurred at all doses, shortly after the dosing period. However, after a 1-month drug-free observation period, marked testicular atrophy was evident at all doses. BMS-189453 was then administered at doses of 2, 10, or 50 mg/kg to male rats for 1, 3, or 7 consecutive days. Dose- and duration-dependent testicular toxicity that occurred after a 1-month observation period did not recover, and, in some cases, was more severe 4 months after the last dose. In rabbits administered BMS-189453 at oral doses of 2, 10, or 50 mg/kg for 1 week, testicular degeneration and atrophy were evident in the high-dose group at 1 month following treatment. These studies indicate that retinoid antagonists can selectively produce progressive and prolonged testicular toxicity after single or repeated oral doses that are otherwise well tolerated.

Shf, a Shb-like adapter protein, is involved in PDGF-alpha-receptor regulation of apoptosis.

Recent work has implicated the importance of adapter proteins in signal transduction. To identify homologues of the previously identified adapter protein Shb, database searches were performed. A Shb-like protein was found which we have named Shf. Shf contains an SH2 domain and four putative tyrosine phosphorylation sites and is mainly expressed in skeletal muscle, brain, liver, prostate, testis, ovary, small intestine, and colon. The SH2 domain of Shf bound to the PDGF-alpha-receptor at tyrosine-720, but not to the PDGF-beta-receptor in PAE cells. Pervanadate induced tyrosine phosphorylation of Shf in NIH3T3 fibroblasts overexpressing this protein, whereas PDGF-AA alone had no detectable effect. NIH3T3 cells overexpressing Shf displayed significantly lower rates of apoptosis than control cells in the presence of PDGF-AA. Our findings suggest a role for the novel adapter Shf in PDGF-receptor signaling and regulation of apoptosis.

The role of SOCS-3 in leptin signaling and leptin resistance.

We earlier demonstrated that leptin induces expression of SOCS-3 mRNA in the hypothalamus. Furthermore, transfection data suggest that SOCS-3 is an inhibitor of leptin signaling. However, little is known about the regulation of SOCS-3 expression by leptin and the mechanism by which SOCS-3 inhibits leptin action. We here show that in CHO cells stably expressing the long form of the leptin receptor (CHO-OBRl), leptin induces transient expression of endogenous SOCS-3 mRNA but not of CIS, SOCS-1, or SOCS-2 mRNA. SOCS-3 protein levels were maximal after 2-3 h of leptin treatment and remained elevated at 20 h. Furthermore, in leptin-pretreated CHO-OBRl cells, proximal leptin signaling was blocked for more than 20 h after pretreatment, thus correlating with increased SOCS-3 expression. Leptin pretreatment did not affect cell surface expression of leptin receptors as measured by (125)I-leptin binding assays. In transfected COS cells, forced expression of SOCS-3 results in inhibition of leptin-induced tyrosine phosphorylation of JAK2. Finally, JAK2 co-immunoprecipitates with SOCS-3 in lysates from leptin-treated COS cells. These results suggest that SOCS-3 is a leptin-regulated inhibitor of proximal leptin signaling in vivo. Excessive SOCS-3 activity in leptin-responsive cells is therefore a potential mechanism for leptin resistance, a characteristic feature in human obesity.

Identification of SOCS-3 as a potential mediator of central leptin resistance.

Leptin affects food intake and body weight by actions on the hypothalamus. Although leptin resistance is common in obesity, mechanisms have not been identified. We examined the effect of leptin on expression of the suppressors-of-cytokine-signaling (SOCS) family of proteins. Peripheral leptin administration to ob/ob, but not db/db mice, rapidly induced SOCS-3 mRNA in hypothalamus, but had no effect on CIS, SOCS-1, or SOCS-2. A leptin-dependent increase of SOCS-3 mRNA was seen in areas of hypothalamus expressing high levels of the leptin receptor long form. In mammalian cell lines, SOCS-3, but not CIS or SOCS-2, blocked leptin-induced signal transduction. Expression of SOCS-3 mRNA in the arcuate and dorsomedial hypothalamic nuclei is increased in Ay/a mice, a model of leptin-resistant murine obesity. In conclusion, SOCS-3 is a leptin-inducible inhibitor of leptin signaling, and a potential mediator of leptin resistance in obesity.

Stimulation through the T cell receptor leads to interactions between SHB and several signaling proteins.

Shb is a recently described Src homology 2 (SH2) domain-containing adaptor protein. Here we show that Shb is expressed in lymphoid tissues, and is recruited into signaling complexes upon activation of Jurkat T cells. Grb2 binds proline-rich motifs in Shb via its SH3 domains. As a result, a number of proteins detected in anti-Shb and anti-Grb2 immunoprecipitates are shared, including phosphoproteins of 22, 36/38, 55/57 and 70 kDa. Shb-association with p22, which represents the T cell receptor associated zeta chain, occurs through the Shb SH2 domain. The central region of Shb binds p36/38. Since this interaction was inhibited by phosphotyrosine, this region of Shb is likely to contain a non-SH2 PTB (phosphotyrosine binding) domain. The Shb PTB domain was found to preferentially bind the sequence Asp-Asp-X-pTyr when incubated with a phosphopeptide library. A peptide corresponding to a phosphorylation site in 34 kDa Lnk inhibited association between Shb and p36/38. Overexpression of Shb in Jurkat cells led to increased basal phosphorylation of Shb-associated p36/38 and p70 proteins. Inactivation of the Shb SH2 domain by an R522K mutation resulted in a reduced stimulation of tyrosine phosphorylation of several proteins in response to CD3 crosslinking when expressed in Jurkat cells. Together, our results show three distinct domains of Shb all participate in the formulation of multimeric signaling complexes in activated T cells. These results indicate that the Shb protein functions in T cell receptor signaling.

Human GRB-IRbeta/GRB10. Splice variants of an insulin and growth factor receptor-binding protein with PH and SH2 domains.

cDNA clones encoding human (h) Grb7 and a previously unknown protein with high homology to hGrb-IR and mGrb10 (where m indicates mouse) were found by screening expressed sequence tag data bases. hGrb7 mRNA expression is greatest in pancreas and restricted to a few other tissues. The second protein termed hGrb-IRbeta/Grb10 contains an intact PH domain and lacks the 80-residue mGrb10 insertion. Expression is greatest in pancreas and muscle but occurs in nearly all tissues. hGrb-IRbeta/Grb10 and hGrb-IR likely arise as alternative mRNA splicing products of a common gene. Reverse transcriptase-coupled polymerase chain reaction shows both mRNAs in muscle. In cells, Grb-IRbeta/Grb10 protein translocates from cytosol to membrane upon insulin stimulation, most likely due to direct interactions with the insulin receptor. These interactions are mediated by the SH2 domain and additional regions of the protein. Studies with mutated receptors and synthetic phosphopeptides show that the hGrb-IRbeta/Grb10 SH2 domain binds at least two sites in the insulin receptor: the kinase activation loop > the juxtamembrane site. hGrb-IRbeta/Grb10 also binds a 135-kDa phosphoprotein in unstimulated 3T3-L1 adipocytes; binding is reduced upon insulin stimulation. In addition, the c-Abl SH3 domain binds Grb-IR/Grb10, whereas Fyn, phosphatidylinositol 3-kinase p85, and Grb2 SH3 domains do not. The site of c-Abl SH3 domain interaction is highly conserved within the Grb-IR/Grb10/Grb7/Grb14 family. hGrb-IRbeta/Grb10 also binds platelet-derived growth factor and epidermal growth factor receptors, suggesting a broader role in the signaling pathways of numerous receptors. We conclude that hGrb-IRbeta/Grb10 is a widely expressed, PH and SH2 domain-containing, SH3 domain-binding protein that functions downstream from activated insulin and growth factor receptors.

The role of a lymphoid-restricted, Grb2-like SH3-SH2-SH3 protein in T cell receptor signaling.

We have characterized an SH3-SH2-SH3 linker protein that is prominently expressed in lymphoid tissues. This protein has 58% sequence identity to Grb2. An identical protein called Grap has been found in hematopoietic cells. In Jurkat cells, T cell receptor activation leads to the association of Grap with phosphoproteins p36/38 and, to a lesser degree, Shc. This interaction is mediated by the Grap SH2 domain, which has similar binding specificity to the Grb2 SH2 domain. Grap also associates via its SH3 domains with Sos, the Ras guanine nucleotide exchange factor; with dynamin, a GTPase involved in membrane protein trafficking; and with Sam68, a nuclear RNA-binding protein that serves as a substrate of Src kinases during mitosis. T cell activation effects an increase in Grap association with p36/38, Shc, Sos, and dynamin. Sam68 binding is constitutive. Phospholipase C-gamma1 and Fyn are also found in activated Grap signaling complexes, although these interactions may not be direct. We conclude that Grap is a prominent component of lymphocyte receptor signaling. Based on the known functions of bound effector molecules, Grap-mediated responses to antigen challenge may include endocytosis of the T cell receptor, cellular proliferation, and regulated entry into the cell cycle.

Didanosine (ddl) and stavudine (d4T): absence of peripheral neurotoxicity in rabbits.

Some 20 male New Zealand White rabbits (five/group) were given either didanosine (ddl) or stavudine (d4T) at 750 and 1500 mg/kg body weight/day by oral intubation for 24 wk. An additional group was given 300 mg/kg body weight/day zidovudine (AZT) as a negative control. After 13 weeks the high dose of ddl was lowered from 1500 to 1000 mg/kg body weight/day following the death of one rabbit and continued inappetence in the dose group. The rabbits were observed daily, plasma drug levels were monitored, and electrophysiological measurements of peripheral nerve conduction were performed during the study. Additionally, body weight and food intake were recorded, and clinicopathological parameters were evaluated. Sections of selected peripheral nerves, and dorsal and ventral spinal nerve roots were examined by light and transmission electron microscopy. Although peripheral neuropathy has been reported in rabbits with the nucleoside analogue zalcitabine (ddC), based on clinical observations, electrophysiological measurements, and light and electron microscopy, no evidence of peripheral neurotoxicity was observed in rabbits given either ddl of d4T.

A novel yeast gene product, G4p1, with a specific affinity for quadruplex nucleic acids.

G4 nucleic acids are four-stranded helical structures that are formed in vitro by nucleic acids that contain guanine tracts. These structures anneal readily under physiological conditions and are unusually stable once formed. G4 nucleic acids are thought to participate in telomere function, retroviral genome dimerization, chromosome alignment during homologue pairing, and mitotic recombination, although the in vivo demonstration of these structures in any of these situations has not yet been achieved. Here we purify and characterize an activity from yeast, G4p1, which has a high and specific affinity for G4 nucleic acids. G4p1 prefers substrates containing multiple G4 domains, has an equal affinity for parallel and antiparallel G4 structures, and binds equivalently to RNA and DNA in G4 form. The Keq for G4p1 binding to a G4 DNA oligomer is 5.0 x 10(8) M-1, under near physiological conditions. G4p1 was purified and shown to derive from a 42-kDa protein (p42). We have cloned and sequenced the gene encoding p42 and show it to encode a novel protein with a region significantly homologous to bacterial methionyl-tRNA synthetase dimerization domains. We have reconstituted the G4p1 binding activity with recombinant p42 and present evidence that G4p1 is a homodimer of p42.

A yeast gene product, G4p2, with a specific affinity for quadruplex nucleic acids.

G4 nucleic acids are quadruplex structures involving guanine-rich sequences that form in vitro under moderate conditions. Experimental evidence exists supporting biological functions for these elements; however, direct demonstration of G4 nucleic acids in vivo has not yet been achieved. Here we purify and characterize a yeast protein, G4p2, which has a specific affinity for G4 nucleic acids. G4p2 binds equivalently to RNA and DNA in G4 form. The Keq for G4p2 binding to a G4 DNA oligomer is 2.2 x 10(8) M-1 under near physiological conditions. We have cloned and sequenced the gene encoding G4p2 and have shown it to be identical to MPT4 and STO1. MPT4 was isolated in a screen for multicopy suppressors of staurosporine sensitivity in POP2 cells. Pop2 is a complex regulatory factor that participates, in part, in the repression of certain genes in the absence of glucose (Sakai, A., Chibazakura, T., Shimizu, Y., and Hishinuma, F. (1992) Nucleic Acids Res. 20, 6227-6233). STO1 was isolated as a multicopy suppressor of TOM1, an uncharacterized mutation that leads to temperature-sensitive cell cycle arrest at the G2/M boundary. Suppression of these mutations by G4p2 indicate this G4 nucleic acid binding protein may function in signal transduction pathways regulated by protein kinases, which control carbon source utilization, and in cell cycle progression.

BR96-doxorubicin conjugate (BMS-182248) versus doxorubicin: a comparative toxicity assessment in rats.

The toxicity of BMS-182248, an immunoglobulin (cBR96)-cytotoxic drug (doxorubicin) conjugate, was investigated in Sprague-Dawley rats at single intravenous doses of 508, 1,200, and 2,550 mg/m2 (conjugated doxorubicin doses of 14.7, 34.8, and 74 mg/m2, respectively) and compared to that obtained from administration of free doxorubicin at single doses of 33.6 and 72 mg/m2 (approximately equivalent to that contained in the 1,200- and 2,550-mg/m2 doses of BMS-182248, respectively). Necropsies were conducted on day 8, upon death/moribund sacrifice, or after an approximate 3-mo observation period following completion of treatment. Death/moribundity of all rats that received 72 mg/m2 and of 9 of 20 rats given 33.6 mg/m2 free doxorubicin were attributed primarily to delayed cardiotoxicity and glomerulonephropathy. With BMS-182248, death from glomerulonephropathy and cardiotoxicity occurred in only 4 of 20 rats given 2,550 mg/m2 (74 mg/m2 doxorubicin equivalent). No deaths or cardiotoxicity occurred in rats given 508 or 1,200 mg/m2 BMS-182248. Additional effects noted with either drug included testicular atrophy, axonal degeneration of sciatic nerve and nerve tracts of brain and spinal cord, teeth (incisor) abnormalities, thymic atrophy, bone marrow hypocellularity, splenic lymphoid and red-pulp depletion, and increased extramedullary hematopoiesis in the spleen and liver. Also noted were altered chief cells in the stomach, vacuolation of adrenal gland and corpora lutea in the ovary, uterine and seminal vesicle atrophy, ulceration and myocyte regeneration/degeneration in the tongue, increased osteoclasts and osteoblasts in bone, and lymphoid hyperplasia of mandibular lymph node. In general, these effects were more severe in doxorubicin-treated rats. All changes observed with BMS-182248 were considered primarily due to the effects of doxorubicin and were substantially less severe (most notably cardiotoxicity) compared to those produced by an equivalent amount of doxorubicin.

Identification and characterization of a nuclease activity specific for G4 tetrastranded DNA.

We have identified a nuclease activity that is specific for G4 tetrastranded DNA. This activity, found in a partially purified fraction for a yeast telomere-binding protein, binds to DNA molecules with G4 tetrastranded structure, regardless of their nucleotide sequences, and cleaves the DNA in a neighboring single-stranded region 5' to the G4 structure. Competition with various G4-DNA molecules inhibits the cleavage reaction, suggesting that this nuclease activity is specific for G4 tetrastranded DNA. The existence of this enzymatic activity that reacts with G4 DNAs but not with single-stranded or Watson-Crick duplex DNAs suggests that tetrastranded DNA may have a distinct biological function in vivo.

The histopathological and biochemical response of the stomach of male F344/N rats following two weeks of oral dosing with ethyl acrylate.

Male F344/N rats were dosed with ethyl acrylate (EA) either by daily gavage or in the drinking water for 2 weeks. The gavage dose levels were 0, 2, 10, 20, 50, 100, and 200 mg/kg; the drinking water dose concentrations were 0, 200, 1,000, 2,000, and 4,000 ppm (corresponding to 0, 23, 99, 197, and 369 mg/kg/day, respectively). In those animals dosed by gavage, irritation of the forestomach increased in incidence and severity over the 20-200 mg/kg dose range. In those animals dosed with EA in the drinking water, a much lower incidence of forestomach irritation and less severe lesions were observed at corresponding dose levels. No lesions were observed in the glandular stomach from either of the 2 modes of oral administration. Following 2 weeks of gavage dosing with EA, the total non-protein sulfhydryl (NPSH) content of the forestomach and glandular stomach, and the NPSH concentration of the liver were determined 2-24 hr after the last gavage dose. Animals dosed at 200 mg/kg reached approximately 11% of the initial NPSH content in the forestomach at 6 hr after dosing. NPSH depletion of this magnitude has been associated with cytotoxicity of other tissues in other studies. By contrast, either the glandular stomach nor liver were depleted of NPSH to levels generally associated with toxicity. These observations are consistent with the conclusion that bolus dosing of EA induces severe depletion of critical cellular thiols in the forestomach with toxic consequences, but not in the glandular stomach or liver. Changing the mode of oral administration for EA to continued small doses in the drinking water allowed efficient detoxification and did not induce sulfhydryl depletion or comparable forestomach toxicity at the same daily body burden.

Antiulcer agents. 3. Structure-activity-toxicity relationships of substituted imidazo[1,2-a]pyridines and a related imidazo[1,2-a]pyrazine.

Investigation of the interrelationship between structure, antiulcer activity, and toxicology screening data derived from a series of compounds selected from structure-activity studies directed toward identifying a successor to 3-(cyanomethyl)-2-methyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine, Sch 28080 (1), has identified 3-(cyanomethyl)-2,7-dimethyl-8-(phenylmethoxy)imidazo[1,2 -a]pyridine (5), 3-amino-2-methyl-8-(2-phenylethyl)imidazo[1,2-a]pyridine (6), and 3-amino-2-methyl-8-(phenylmethoxy)imidazo[1,2-a]pyrazine (7). These analogues exhibit a combination of antisecretory and cytoprotective activity in animal models, while eliminating the adverse effects of the prototype 1. One of these, 3-amino-2-methyl-8-(phenylmethoxy)imidazo[1,2-a]pyrazine, Sch 32651 (7), has a profile meeting all criteria.

Expression of human class II major histocompatibility complex antigens using retrovirus vectors.

Retrovirus vectors [direct orientation (DO) vectors] that permit the simultaneous expression of an inserted protein-coding sequence and a dominant-acting selectable marker have been constructed. In these vectors, an internal simian virus 40 or human metallothionein promoter sequence serves to drive the expression of the bacterial neomycin phosphotransferase or guanine-xanthine phosphoribosyltransferase genes, whereas the viral long terminal repeat sequences are utilized to promote expression of inserted sequences. In some of the vectors, the viral 5' splice site, normally used in the biogenesis of the subgenomic env-encoding mRNA, has been eliminated. These vectors yield high transient and stable titers of virus after transfection of viral packaging cell lines, show little or no depression of virus titer with a variety of inserts, and faithfully transmit recombinant proviral sequences to recipient cells. To characterize the expression potential of these vectors, a variety of inserts encoding the alpha and beta subunits of the human major histocompatibility complex class II antigen HLA-DR have been introduced into these vectors. NIH 3T3 cells infected by viruses containing HLA-DR alpha or beta cDNAs express these proteins as shown by immunoprecipitation of metabolically labeled extracts. In addition, through the sequential infection of cells with retrovirus constructions expressing two different selectable markers, both subunits of the class II antigen have been introduced into NIH 3T3 cells. Such infected cells express HLA-DR molecules at the cell surface.

Skin and mucous membrane ulceration in beagle dogs following oral dosing with an experimental aminoglycoside antibiotic.

G-418 is a unique aminoglycoside antibiotic that is structurally related to gentamicin; however, unlike gentamicin, G-418 inhibits growth of both procaryotic and eucaryotic cells. In a preliminary acute oral safety study, adult male and female beagles were given a single oral dose of either 2000, 1000, 500, 200, or 50 mg/kg of G-418. Ulceration of the lip, tongue, and/or gingiva occurred in all G-418-dosed dogs 1 to 9 days after dosing. Ulceration of the glans penis, penis sheath, and scrotum occurred 7 to 14 days after a single oral dose with 1000 and 500 mg/kg G-418, and ulceration of the vaginal mucosa of the 2000-, 1000-, 500-, and 50-mg/kg-dosed female dogs occurred 2 to 8 days after dosing. Ulcers of the lip and vaginal area began at the mucocutaneous border and were more severe at these borders. In some dogs a yellow membrane formed over these lesions. Ulceration of the oral and vaginal mucosa disappeared 10 days after the first occurrence and reoccurred 3-7 days later. All ulcers healed within 30 days after the single oral dose; however, at necropsy hemorhagic areas of the urinary bladder were observed in at least one of two dogs at each dose level. Similar lesions have not been reported in animals treated with any other aminoglycoside antibiotics. The etiology of these lesions is unknown.

Subchronic toxicity studies of N-D-ornithyl amphotericin B methyl ester in dogs and rats.

Two subchronic studies were conducted to assess the potential toxicity of N-D-ornithyl amphotericin B methyl ester (OAME). In both studies the comparative control substance was amphotericin B (AMB). Dogs (5/sex/group) were given OAME (82% pure, based on high-pressure liquid chromatographic (HPLC) analysis) at 0.6, 2.5, and 10 mg/kg or AMB at 0.6 mg/kg intravenously once daily for 3 months. Two dogs per sex per group were retained for a 7-week postdose observation period. Rats (15/sex/group) were given daily doses of OAME at 4, 12, 24, and 36 mg/kg or AMB at 5 and 12 mg/kg intraperitoneally for 3 months. The principal organs of toxicity in both species were the liver, kidneys, and circulating erythrocytes. Hepatic changes in dogs consisted of periportal and centrilobular inflammation in animals of all dosed groups and were equivalent in dogs given 0.6 mg/kg OAME or AMB. In rats, acute hepatic necrosis with periportal, centrilobular, or panlobular distribution in animals of all OAME (except 4 mg/kg) and AMB-dosed groups was observed. These changes were equivalent in the 36-mg/kg OAME- and 12-mg/kg AMB-dosed animals. Renal changes, evidenced by increases in serum urea nitrogen water consumption, urine volume, decreased urine osmolality, and renal tubular changes (ranging from degeneration and regeneration to necrosis), were observed in both species. In dogs, these changes in the OAME-dosed animals were less severe at all doses than those observed in the AMB-dosed dogs. Renal changes in rats, which were mild in comparison to the dogs, were equivalent at doses of 5 and 12 mg/kg AMB and 36 mg/kg OAME. Decreased erythrocyte counts, hematocrit, and hemoglobin values were observed in both species. Unique to the dog study, however, were irreversible behavioral (somnolence, ataxia, tremors, and compulsive searching) and/or morphologic brain changes (gliosis with astrocytic hypertrophy and hyperplasia) at doses of 2.5 and 10 mg/kg OAME. Similar changes were observed in two dogs given 10 mg/kg OAME (100% pure, based on HPLC analysis) in a 6-week pilot study, indicating that the neurological changes were induced by OAME rather than by an impurity. These changes appear related to prolonged exposure to high plasma concentrations of OAME.