Transduction of interphase cells by avian sarcoma virus

It has been generally believed that oncoretroviruses are dependent on mitosis for efficient nuclear entry of viral DNA. We previously identified a nuclear localization signal in the integrase protein of an oncoretrovirus, avian sarcoma virus (ASV), suggesting an active import mechanism for the integrase-DNA complex (G. Kukolj, R. A. Katz, and A. M. Skalka, Gene 223:157-163, 1998). Here, we have evaluated the requirement for mitosis in nuclear import and integration of ASV DNA. Using a modified ASV encoding a murine leukemia virus amphotropic env gene and a green fluorescent protein (GFP) reporter gene, DNA nuclear import was measured in cell cycle-arrested avian (DF-1) as well as human (HeLa) and mouse cells. The results showed efficient accumulation of nuclear forms of ASV DNA in gamma-irradiation-arrested cells. Efficient transduction of a GFP reporter gene was also observed after infection of cells that were arrested with gamma-irradiation, mitomycin C, nocodazole, or aphidicolin, confirming that nuclear import and integration of ASV DNA can occur in the absence of mitosis. By monitoring GFP expression in individual cells, we also obtained evidence for nuclear import of viral DNA during interphase in cycling cells. Lastly, we observed that ASV can transduce postmitotic mouse neurons. These results support an active nuclear import mechanism for the oncoretrovirus ASV and suggest that this mechanism can operate in both nondividing and dividing cells.

GPR56, a novel secretin-like human G-protein-coupled receptor gene

A novel gene product, GPR56, with homology to the seven transmembrane-domain receptor superfamily, has been cloned by PCR amplification using degenerate oligonucleotide primers and subsequent screening of a human heart cDNA library. The isolated 2.8-kb cDNA clone encodes a protein of 693 amino acids that shows highest identity (32%) to HE6, a member of a subclass of the class B secretin-like G-protein-coupled receptors. Northern analysis of various human tissues revealed a wide distribution of the transcript with highest levels found in thyroid gland, brain, and heart. In situ hybridization analysis of human thyroid gland as well as rat heart and brain tissue confirms these results and identifies the hippocampus and hypothalamic nuclei as brain areas with particularly high expression of GPR56 mRNA. The high level of mRNA expression, its wide distribution, and the mucin-like extracellular domain of the receptor protein suggest a possible role for this receptor in cell-cell interaction processes. The human gene for GPR56 has been isolated and its exon-intron structure determined. The total length of the human GPR56 gene is approximately 15 kb, and it consists of 13 exons. Fluorescence in situ hybridization, PCR analysis of somatic cell hybrids, and interspecific mouse backcross mapping have localized the genes to human chromosome 16q13 and mouse chromosome 8.

Assignment of the Y4 receptor gene (PPYR1) to human chromosome 10q11.2 and mouse chromosome 14

The human and mouse genes for the neuropeptide Y4 receptor have been isolated, sequenced, and shown to contain no introns within the coding region of the gene. Nonisotopic in situ hybridization and interspecific mouse backcross mapping have localized the genes to human chromosome 10q11.2 and mouse chromosome 14. Five nucleotide variants, which do not alter the protein sequence, have been identified within the coding region of the human receptor gene. The human Y4 subtype is most closely related to the Y1-receptor subtype (42%), suggesting that it evolved from an ancestral Y1-like receptor via an RNA-mediated transpositional event.

Overlapping gene structure of the human neuropeptide Y receptor subtypes Y1 and Y5 suggests coordinate transcriptional regulation

The human y1 and y5 receptor genes are transcribed in opposite directions from a common promoter region on chromosome 4q31-q32. One of the alternately spliced 5' exons of the y1 receptor gene (1C) is also an integral part of the coding region of a novel neuropeptide Y receptor, Y5. Exon 1C of the y1 receptor gene, if translated from the opposite strand, encodes sequences corresponding to the large third intracellular loop of the Y5 receptor. The close proximity of the two neuropeptide Y receptor genes suggests that they have evolved from a gene duplication event with the small intron interrupting the coding sequence of the y1 gene being converted into a functional sequence within the y5 gene, while the reverse complementary sequence was utilized as an alternatively spliced 5' exon for the y1 gene. The transcription of both genes from opposite strands of the same DNA sequence suggests that transcriptional activation of one will have an effect on the regulation of gene expression of the other. As both Y1 and Y5 receptors are thought to play an important role in the regulation of food intake, coordinate expression of their specific genes may be important in the modulation of NPY activity.

Intron 17 of the human retinoblastoma susceptibility gene encodes an actively transcribed G protein-coupled receptor gene

The human retinoblastoma susceptibility gene, a member of the tumor suppressor gene family, is located on chromosome 13q14.12-13q14.2 and consists of 27 exons that are distributed over 180 kb. This study shows that intron 17, the largest in size, consisting of nearly 72,000 bp, contains an open reading frame encoding a novel G protein-coupled receptor in the reverse orientation relative to the transcription of the retino-blastoma susceptibility gene. Correction of a frameshift mutation revealed that this novel G protein-coupled receptor is the human homolog of a chicken T-cell-specific receptor cDNA. This is an additional description of an actively transcribed protein-encoding gene positioned within an intron of another gene, suggesting that introns can have important structural functions.

Synergistic interaction of Y1-neuropeptide Y and alpha 1b-adrenergic receptors in the regulation of phospholipase C, protein kinase C, and arachidonic acid production

Neuropeptide Y (NPY) and norepinephrine, found colocalized in sympathetic neurons innervating blood vessels, exert synergistic responses on vasoconstriction. To examine the signaling mechanisms involved, free of complications associated with mixed receptor populations, we have established a stable Chinese hamster ovary cell line expressing both Y1-NPY and alpha 1b-adrenergic receptors. Occupation of either receptor species, with 100 nM peptide YY (PYY) or 10 microM phenylephrine (PE), respectively, resulted in a rapid increase in the cytoplasmic free calcium concentration ([Ca2+]i) as assessed with Fura-2/AM. The rise due to PYY, but not that due to PE, was abolished by pretreatment with pertussis toxin. Both responses were largely maintained in the absence of extracellular Ca2+, but abolished by prior depletion of intracellular Ca2+ pools with either thapsigargin or 2,5-di-(t-butyl)-1,4-benzohydroquinone. Using cells prelabeled with myo-[3H]inositol, PE promoted a rapid (5 s) rise in inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) as analyzed by anion-exchange high pressure liquid chromatography, whereas the response to PYY (first significant at > 15 s post-stimulation) was too slow to play a causative role in Ca2+ mobilization. Combination of PE and PYY resulted in increases in [Ca2+]i which were at best additive, whereas they promoted a clearly synergistic rise in Ins(1,4,5)P3 at both 15 and 60 s. Co-stimulation also resulted in a synergistic activation of both protein kinase C (PKC) and [3H]arachidonic acid release. In either instance PYY alone was without effect. The potentiation of arachidonic acid release was abolished by depletion of cellular PKC following chronic treatment with phorbol esters. It is suggested that the ability of PYY to mobilize Ca2+ in an Ins(1,4,5)P3-independent fashion minimizes the functional importance of the capacity to potentiate PE-stimulated Ins(1,4,5)P3 generation. Instead the major consequences of the synergistic activation of phospholipase C are mediated via PKC, the other route of the signaling pathway.