Desensitization of the δ-Opioid Receptor Correlates with Its Phosphorylation in SK-N-BE Cells: Involvement of a G Protein-Coupled Receptor Kinase

Abstract: Phosphorylation of G protein-coupled receptors is considered an important step during their desensitization. In SK-N-BE cells, recently presented as a pertinent model for the studies of the human δ-opioid receptor, pretreatment with the opioid agonist etorphine increased time-dependently the rate of phosphorylation of a 51-kDa membrane protein. Immunological characterization of this protein with an antibody, raised against the amino-terminal region of the cloned human δ-opioid receptor, revealed that it corresponded to the δ-opioid receptor. During prolonged treatment with etorphine, phosphorylation increased as early as 15 min to reach a maximum within 1 h. Phosphorylation and desensitization of adenylyl cyclase inhibition paralleled closely and okadaic acid inhibited the resensitization, a result strongly suggesting that phosphorylation of the δ-opioid receptor plays a prominent role in its rapid desensitization. The increase in phosphorylation of the δ-opioid receptor, as well as its desensitization, was not affected by H7, an inhibitor of protein kinase A and protein kinase C, but was drastically reduced by heparin or Zn²⁺, known to act as G protein-coupled receptor kinase (GRK) inhibitors. These results are the first to show, on endogenously expressed human δ-opioid receptor, that a close link exists between receptor phosphorylation and agonist-promoted desensitization and that desensitization involves a GRK.     

Evidence for species differences in the pattern of androgen receptor distribution in relation to species differences in an androgen‐dependent behavior

Chickens (Gallus gallus domesticus) and Japanese quail (Coturnix japonica), two closely related gallinaceous bird species, exhibit a form of vocalization—crowing—which differs between the species in two components: its temporal acoustic pattern and its accompanying postural motor pattern. Previous work utilizing the quail‐chick chimera technique demonstrated that the species‐specific characteristics of the two crow components are determined by distinct brain structures: the midbrain confers the acoustic pattern, and the caudal hindbrain confers the postural pattern. Crowing is induced by androgens, acting directly on androgen receptors. As a strategy for identifying candidate neurons in the midbrain and caudal hindbrain that could be involved in crow production, we performed immunocytochemistry for androgen receptors in these brain regions in both species. We also investigated midbrain‐to‐hindbrain vocal‐motor projections. In the midbrain, both species showed prominent androgen receptor immunoreactivity in the nucleus intercollicularis, as had been reported in previous studies. In the caudal hindbrain, we discovered characteristic species differences in the pattern of androgen receptor distribution. Chickens, but not quail, showed strong immunoreactivity in the tracheosyringeal division of the hypoglossal nucleus, whereas quail, but not chickens, possessed strong immunoreactivity in a region of the ventrolateral medulla. Some of these differences in hindbrain androgen receptor distribution may be related to the species differences in the postural component of crowing behavior. The results of the present study imply that the spatial distribution of receptor proteins can vary even between closely related species. Such variation in receptor distribution could underlie the evolution of species differences in behavior. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 203–220, 2002     

Cancer chemotherapy and somatic cell mutation

The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm.     

Structural studies on rhodopsin

Bovine rhodopsin is the prototypical G protein coupled receptor (GPCR). It was the first GPCR to be obtained in quantity and studied in detail. It is also the first GPCR for which detailed three dimensional structural information has been obtained. Reviewed here are the experiments leading up to the high resolution structure determination of rhodopsin and the most recent structural information on the activation and stability of this integral membrane protein.     

Pheromone receptors in Bombyx mori and Antheraea pernyi

Summary The cellular organization of freeze-substituted antennal sensilla trichodea, which contain the sex pheromone receptors, was studied in male silkmoths of two species (Bombyx mori, Bombycidae; Antheraea pernyi, Saturniidae). The cellular architecture of these sensilla is complex, but very similar in both species. A three-dimensional reconstruction of a sensillum trichodeum of B. mori is presented. Two receptor cells (in A. pernyi 1–3) and three auxiliary cells are present. Of the latter, only the thecogen cell forms a true sheath around the receptor cells. A unique thecogen-receptor cell junction extends over the entire area of contact. Septate junctions occur between all sensillar cells apically, and in the region of the axonal origin basally. Gap junctions are also found between all cells except the receptor cells. The trichogen and tormogen cells show many structural indications of secretory activity and are thought to secrete the receptor lymph. Their apical membrane bordering the receptor-lymph space is enlarged by microvilli and microlamellae, but only those of the trichogen cell show regularly arranged membrane particles (portasomes), indicating secretory specialization among the auxiliary cells. Epidermal cells are found as slender pillars between sensilla, but extend apically along the non-sensillar cuticle and basally along the basal lamina.     

Regional and Cortical Laminar Distributions of Serotonin S2, Benzodiazepine, Muscarinic, and Dopamine D2 Receptors in Human Brain

Serotonin S2, benzodiazepine, and muscarinic receptors showed different regional distributions in the human brain but were present in all cortical areas. The laminar distributions of [3H]ketanserin, [3H]diazepam, and [3H]quinuclidinylbenzilate were investigated in the temporal cortex and revealed a high density in the IIIrd and IVth layers. Dopamine D2 receptors were not detected in the cortex.     

Serum concentrations of 1,25-dihydroxyvitamin D3 in Platyrrhini and Catarrhini: A phylogenetic appraisal

We measured the serum concentration of 25-hydroxyvitamin D₃ (25-OH-D₃) and 1,25-dihydroxyvitamin D₃ (1,25-[OH]₂-D₃) in 23 different Platyrrhines from four different genera and in 21 Catarrhines from six different genera in residence at the Los Angeles Zoo. The mean (±S.E.) serum concentration of 1,25-(OH)₂-D₃ was significantly greater in Platyrrhines (810 ± 119 pg/ml) than in Catarrhines (61 ± 5 pg/ml), suggesting that high circulating concentrations of the active vitamin D hormone were a characteristic of New World primates in both the Cebidae and Callitrichidae family. This increase in the serum concentration of 1,25-(OH)₂-D₃ is probably an adaptational response on the part of Platyrrhini to offset a relative decrease in the concentration of specific receptor for 1,25-(OH)₂-D₃ in target tissues for the hormone.     

Collagen receptors mediate early events in the attachment of epithelial (MDCK) cells

Summary Madin-Darby canine kidney (MDCK) cells kept in suspension culture for 12–15 hr displayed high-affinity binding sites for¹²⁵I-lathyritic (soluble) collagen (120,000/cell,K _D =30nm) and preferred collagens types I and IV over laminin or fibronectin as substrates during the first hour of attachment. On the other hand, after 4 hr, attachment to all four substrates was equally efficient. Upon challenge with a collagen substrate, the high-affinity sites were rapidly recruited on it (T1/2=6 min). Their occupancy by soluble collagen triggered the exocytosis of a second large population of low-affinity collagen binding sites that included laminin and seems to be involved in a second cell-attachment mechanism. These results are compatible with a twostep model of MDCK cell attachment to the substrate: first, via high-affinity collagen binding sites, and second, via laminin of cellular origin.