Recruitment of p300/CBP in p53-dependent signal pathways

The products of the p53 and CBP/p300 genes have been individually implicated in control of cell growth and regulation of transcription. p53 is known to act as a positive and negative regulator of gene expression. Here we show that p53, in both wild-type and mutant conformation, forms a specific protein complex with p300. However, in its wild-type but not mutant conformation, p53 inhibits a promoter containing the DNA-binding sequences for the transcription factor AP1, in a p300-dependent manner. p300 stimulates the transcriptional activity of p53 on p53-regulated promoters, and it enhances the responsiveness to a physiological upstream modulator of p53 function, ionizing radiation. A dominant negative form of p300 prevents transcriptional activation by p53, and it counteracts p53-mediated G1 arrest and apoptosis. The data implicate p300 as an important component of p53-signaling, thus providing new insight into the mechanisms of cellular proliferation.

Neuropeptide Y: a potent inducer of consummatory behavior in rats

Neuropeptide Y (NPY) is a 36 amino acid peptide with potent cardiovascular effects. In the present study, intraventricular injection of NPY was shown to markedly stimulate feeding and drinking during the illuminated period of the light/dark cycle, a time when rats ingest small amounts of food. It also enhanced nocturnal food and water intake following a 24 hour period of food deprivation and during nocturnal feeding. The NPY induction of food intake was suppressed by the opiate antagonist, naloxone, and by the dopamine antagonist, haloperidol. Phentolamine, an alpha adrenergic antagonist, failed to suppress NPY-induced feeding. Based on the maximum quantity of food which was ingested following central administration of NPY, this peptide appears to represent one of the most potent stimulators of feeding yet to be described.

Opioid modulation of appetite

The discovery of opiate receptors and endogenous opioid peptides within the central nervous system has resulted in a number of speculations concerning the physiological significance of these peptides. In the present article, we review the evidence suggesting a primary role for some of the opioid peptides as regulators of ingestive behavior. In particular, we elaborate a hypothesis in which we suggest that in some species opioid peptides may play a role as a tonic inducer of ingestive behaviors, held in check by a variety of neuropeptides and monoamines. This review explores in detail the role of the opioid peptides as major mediators of the reward system and as a link between reward and feeding behaviors. Finally, a teleological role for opioid peptides in species preservation, which may explain the discrepancies in the role of the opioid peptides in feeding behavior in different species is proposed. It is suggested that the feeding profile of the animal provides important clues as to whether or not the animal has an opiate-sensitive feeding system. We stress that interactions with ingested nutrients and the milieu interieur provide an important means by which animals modulate the opiate-entrained feeding drives.

The DDB1-CUL4ADDB2 ubiquitin ligase is deficient in xeroderma pigmentosum group E and targets histone H2A at UV-damaged DNA sites

Xeroderma pigmentosum (XP) is a heritable human disorder characterized by defects in nucleotide excision repair (NER) and the development of skin cancer. Cells from XP group E (XP-E) patients have a defect in the UV-damaged DNA-binding protein complex (UV-DDB), involved in the damage recognition step of NER. UV-DDB comprises two subunits, products of the DDB1 and DDB2 genes, respectively. Mutations in the DDB2 gene account for the underlying defect in XP-E. The UV-DDB complex is a component of the newly identified cullin 4A-based ubiquitin E3 ligase, DDB1-CUL4A(DDB2). The E3 ubiquitin ligases recognize specific substrates and mediate their ubiquitination to regulate protein activity or target proteins for degradation by the proteasomal pathway. In this study, we have addressed the role of the UV-DDB-based E3 in NER and sought a physiological substrate. We demonstrate that monoubiquitinated histone H2A in native chromatin coimmunoprecipitates with the endogenous DDB1-CUL4A(DDB2) complex in response to UV irradiation. Further, mutations in DDB2 alter the formation and binding activity of the DDB1-CUL4A(DDB2) ligase, accompanied by impaired monoubiquitination of H2A after UV treatment of XP-E cells, compared with repair-proficient cells. This finding indicates that DDB2, as the substrate receptor of the DDB1-CUL4A-based ligase, specifically targets histone H2A for monoubiquitination in a photolesion-binding-dependent manner. Given that the loss of monoubiquitinated histone H2A at the sites of UV-damaged DNA is associated with decreased global genome repair in XP-E cells, this study suggests that histone modification, mediated by the XPE factor, facilitates the initiation of NER.

Feeding response to central orexins

Orexin A and orexin B were microinjected into the perifornical hypothalamus (PFH), lateral hypothalamus (LH), hypothalamic paraventricular nucleus (PVN), and ventral tegmental area (VTA) of male Sprague-Dawley rats. Orexin B (15 nmol) was also injected into the lateral cerebral ventricle (i.c.v.). Orexin A (>/=500 pmol) stimulated feeding in the PFH and LH, but not in the VTA or PVN. Orexin B stimulated feeding only when injected i.c.v.

Stress-induced eating is mediated through endogenous opiates

The interaction of endogenous opiates and stress-induced eating in rats was evaluated by pharmacological manipulation. Eating induced by the tail-pinch method was inhibited by the opitate antagonist naloxone; after being repeatedly stressed over a 10-day period and then given nalozone, the rats behaved in a manner indistinguishable from the "wet-dog" shakes of opiate withdrawal. Thus endogenous opiates may have a role in the control of stress-related eating, a finding that may have therapeutic implications for humans.

The Saccharomyces cerevisiae RAD30 gene, a homologue of Escherichia coli dinB and umuC, is DNA damage inducible and functions in a novel error-free postreplication repair mechanism

Damage-inducible mutagenesis in prokaryotes is largely dependent upon the activity of the UmuD'C-like proteins. Since many DNA repair processes are structurally and/or functionally conserved between prokaryotes and eukaryotes, we investigated the role of RAD30, a previously uncharacterized Saccharomyces cerevisiae DNA repair gene related to the Escherichia coli dinB, umuC and S. cerevisiae REV1 genes, in UV resistance and UV-induced mutagenesis. Similar to its prokaryotic homologues, RAD30 was found to be damage inducible. Like many S. cerevisiae genes involved in error-prone DNA repair, epistasis analysis clearly places RAD30 in the RAD6 group and rad30 mutants display moderate UV sensitivity reminiscent of rev mutants. However, unlike rev mutants, no defect in UV-induced reversion was seen in rad30 strains. While rad6 and rad18 are both epistatic to rad30, no epistasis was observed with rev1, rev3, rev7 or rad5, all of which are members of the RAD6 epistasis group. These findings suggest that RD30 participates in a novel error-free repair pathway dependent on RAD6 and RAD18, but independent of REV1, REV3, REV7 and RAD5.

CRF antagonist partially reverses CRF- and stress-induced effects on feeding

Exogenous corticotropin releasing factor (CRF) causes centrally mediated behavioral changes including decreased feeding and increased grooming. These behavioral changes are also seen in response to some stressors. However, the role of endogenous CRF in the behavioral response to stressors has not been investigated fully. We report below our findings on the behavioral effects of alpha-helical CRF (9-41), a recently discovered competitive antagonist of CRF-induced ACTH release. Alpha-helical CRF (9-41) partially reversed the decrement in feeding induced by CRF. Furthermore, the reduction in food intake due to restraint stress was partially reversed by alpha-helical CRF (9-41). These results indicate that changes in endogenous CRF release induced by the restraint stressor may play a role in stress-induced anorexia.

Abnormal zinc metabolism in type II diabetes mellitus

Zinc metabolism in 20 patients with stable type II diabetes mellitus was investigated. Twenty-five percent of these patients had depressed serum zinc concentrations, and all demonstrated hyperzincuria. Urinary zinc loss was greater when proteinuria was present and correlated with the mean serum glucose concentration. Studies of gastrointestinal zinc absorption suggested zinc malabsorption in patients with type II diabetes mellitus. Glucose infusion in normal dogs produced hyperzincuria without a diminution in serum zinc. It is concluded that hyperzincuria, resulting from a glucose-mediated process that is not osmotic, interacts with impaired zinc absorption to produce zinc deficiency in patients with type II diabetes mellitus.

Simian virus-40 large-T antigen binds p53 in human mesotheliomas

We found that simian virus 40 (SV40) induces mesotheliomas in hamsters and that 60% of human mesotheliomas contain and express SV40 sequences, results now confirmed by others [ref. 3-5, and presentations by D. Griffiths & R. Weiss, F. Galateau-SallE, and H.I.P. at "Simian virus 40: A possible human polyoma virus," NIH workshop, 27-28 January 1997, Bethesda, MD (transcript available through SAG Corp., Washington, DC 20008)]. Mesothelioma, an aggressive malignancy resistant to therapy, originates from the serosal lining of the pleural, pericardial and peritoneal cavities. The incidence of mesothelioma continues to increase worldwide because of exposure to crocidolite asbestos. However, at least 20% of mesotheliomas in the United States are not associated with asbestos exposure, and only a minority of people exposed to high concentrations of asbestos develop mesothelioma. Thus, other carcinogens may induce mesothelioma in individuals not exposed to asbestos, and/or may render particular individuals more susceptible to the carcinogenic effect of asbestos. We investigated whether the expression of the SV40 large T-antigen (Tag) interferes with the normal expression of the tumor suppressor gene p53 in human mesotheliomas. We found that SV40 Tag retains its ability to bind and to inactivate p53, a cellular protein that when normally expressed plays an important role in suppressing tumor growth and in inducing sensitivity to therapy. Our findings do not establish a cause-and-effect relation, but indicate that the possibility that SV40 contributes to the development of human mesotheliomas should be carefully investigated.

Behavioral effects of corticotropin-releasing factor: localization and characterization of central effects

Corticotropin-releasing factor (CRF) has potent behavioral effects when administered intracerebroventricularly to rats. CRF and its receptors are found in an uneven distribution in the brain. In an effort to localize the site of the anorectic effect of CRF, exogenous CRF or saline was injected into cannulas directed toward the paraventricular hypothalamic nucleus (PVN), lateral hypothalamus, ventromedial hypothalamus, globus pallidus, or striatum of rats. CRF decreased food intake only when injected into the PVN. In subsequent experiments PVN injections of CRF were shown to (1) increase grooming and movement; (2) not induce a conditioned taste aversion to saccharin in a single bottle test; and (3) inhibit the increase in feeding induced by injections of norepinephrine into the PVN. These results suggest that CRF induces not only anorexia, but also increased movement and grooming by action in the PVN.

Orphanin FQ, agonist of orphan opioid receptor ORL1, stimulates feeding in rats

It has long been known that opioids, whether administered exogenously or released endogenously, play a role in feeding behavior, and that blockade of opioid receptors with various antagonists can inhibit feeding. Recently, the orphan opioid receptor, ORL1, and its presumed ligand, orphanin FQ, have been identified in human and rodent brain, and show structural similarity to classical opioid receptors and peptides, respectively. While it has been shown that central administration of orphanin FQ induces hyperalgesia, the effects of this peptide on food intake have not been studied. In the present study, we report that central injection of orphanin FQ induces feeding in satiated rats and that this effect can be blocked by peripheral administration of the opioid antagonist naloxone.

Stable binding of human XPC complex to irradiated DNA confers strong discrimination for damaged sites

Nucleotide excision repair (NER) of DNA damage requires an efficient means of discrimination between damaged and non-damaged DNA. Cells from humans with xeroderma pigmentosum group C do not perform NER in the bulk of the genome and are corrected by XPC protein, which forms a complex with hHR23B protein. This complex preferentially binds to some types of damaged DNA, but the extent of discrimination in comparison to other NER proteins has not been clear. Recombinant XPC, hHR23B, and XPC-hHR23B complex were purified. In a reconstituted repair system, hHR23B stimulated XPC activity tenfold. Electrophoretic mobility-shift competition measurements revealed a 400-fold preference for binding of XPC-hHR23B to UV damaged over non-damaged DNA. This damage preference is much greater than displayed by the XPA protein. The discrimination power is similar to that determined here in parallel for the XP-E factor UV-DDB, despite the considerably greater molar affinity of UV-DDB for DNA. Binding of XPC-hHR23B to UV damaged DNA was very fast. Damaged DNA-XPC-hHR23B complexes were stable, with half of the complexes remaining four hours after challenge with excess UV-damaged DNA at 30 degrees C. XPC-hHR23B had a higher level of affinity for (6-4) photoproducts than cyclobutane pyrimidine dimers, and some affinity for DNA treated with cisplatin and alkylating agents. XPC-hHR23B could bind to single-stranded M13 DNA, but only poorly to single-stranded homopolymers. The strong preference of XPC complex for structures in damaged duplex DNA indicates its importance as a primary damage recognition factor in non-transcribed DNA during human NER.

Mechanism of pain in diabetic peripheral neuropathy. Effect of glucose on pain perception in humans

Animal studies have suggested an altered response to opiate agonists and antagonists as well as an altered pain threshold in diabetic animals. In the studies reported herein, a 50 g glucose infusion in normal subjects resulted in a significant decrease in both the threshold level of pain and the maximal level of pain tolerated, as measured by responses to electrical pain induced by a Grass stimulator. In addition, patients with diabetes mellitus were hyperalgesic when compared with normal subjects. It is concluded that elevated glucose levels and/or rapid fluxes in glucose levels result in a decrease in pain tolerance. These findings have potential clinical implications in the pathophysiology and management of painful diabetic neuropathy and the use of narcotic agents in diabetes mellitus.

Feeding effects of hypothalamic injection of melanocortin 4 receptor ligands

It has been reported that intraventricular administration of the melanocortin 4 receptor (MC4-R) agonist MT II and antagonist SHU9119 alter food intake. We found that MT II and SHU9119 have extremely potent effects on feeding when injected in the paraventricular nucleus (PVN), a site where MC4-R gene expression is very high. Our finding provides direct evidence that MC4-R signaling is important in mediating food intake and that melanocortin neurons in the PVN exert a tonic inhibition of feeding behavior. Chronic disruption of this inhibitory signal is a possible explanation of the agouti-obesity syndrome.

Opioids and consummatory behavior

Since the second decade of this century it has been known that opiates can influence ingestive behaviors. Generally, opioid agents enhance feeding and opioid antagonists decrease feeding. The present paper reviews the responsiveness of different animal species to opiates in relation to ingestive behaviors, the opioid receptors involved in such consummatory behaviors, the site of action of opioid modulation of feeding, the role of glucose in opioid induced feeding, and endocrine effects on opioid feeding systems. We emphasize the finding that more than one opioid receptor is involved in the modulation of feeding. A large body of evidence indicates a major role for the dynorphin/alpha-neo-endorphin kappa opioid receptor as one of the receptors involved in feeding modulation. Opioids appear to exert their effect predominantly within the central nervous system, though peripheral effects on taste and gastrointestinal function may play a role in opioid-induced feeding. Although opioid blockade acutely blocks food intake, chronic administration of opiate antagonists to humans and laboratory animals has not proven to be an effective means of decreasing body weight. Chronic opiate administration decreases body weight and autosensitization of beta-endorphin increases body weight. Thus, although it is clear that opioids can effect food intake, it is not clear what effect chronic administration of opioids has no food intake or body weight.

Opioids and food intake: distributed functional neural pathways?

Agonists of the mu, delta, kappa and ORL(1)opioid receptors increase food intake while opioid receptor blockade decreases food intake. The majority of the collected data related to opioids and feeding has led to the speculation that opioids are involved in meal maintenance and orosensory reward; however, some data suggest that opioids may impact feeding associated with energy needs. Based on the wide distribution of CNS opioid receptors and the presence of other neuropeptides in the vicinity of opioidergic pathways, it seems likely that opioids affect multiple feeding systems. For example, opioids in the hindbrain might be involved in both sensory and metabolic aspects of food intake, those in the amygdala in processing of 'emotional' properties of foods, and those in the hypothalamus in energy needs. In this review we present data which support functional diversity of opioids in feeding behavior.

Minireview. Stress induced eating

The relationship of oral behaviors to stress has long been recognized both in humans and in wild animals. In the last decade numerous advances have been made in our understanding of stress-induced feeding predominately because of the development of the simple tail-pinch model of stress induced feeding in rats. Present evidence strongly implicates monoamines and the endogenous opioid peptides as well as other neuropeptides as playing a role in the central regulation of stress-induced eating.

Involvement of dynorphin and the kappa opioid receptor in feeding

Dynorphin-(1-17) produces a highly specific increase in food ingestion. Similar enhancement of food ingestion is found with dynorphin fragments (1-10), (1-11), (1-13) and (3-13) but not with (1-8) and (1-9). Dynorphin B (rimorphin) also enhances food intake. The highly specific kappa agonist U-50,488 also enhances food intake as do a number of other kappa-opiate receptor agonists. These studies provided further for the role of a highly specific dynorphin-kappa opioid receptor in the modulation of feeding.