Biomedical subjects

T Reisine

Publications and source records attributed to T Reisine.

At least 55 records · Page 3Linked to original sources

PubMed1994

Detection of somatostatin receptor subtype 2 (SSTR2) in established tumors and tumor cell lines: evidence for SSTR2 heterogeneity.

The somatostatin receptor subtype 2 (SSTR2) was detected in a wide range of human and rat tumors using in vitro receptor binding ([125I]MK-678), receptor gene expression analysis, and immunoblotting techniques. The highest receptor concentrations were observed in the rat AR42J pancreatic and human small cell lung cancer (SCLC) cell lines, NCI-H69 and NCI-H345, with much lower levels detected in breast, prostate, melanoma, and hepatic tumors. Several human pancreas tumors were devoid of SSTR2. For all tumors showing detectable [125I]MK-678 binding, SSTR2 receptor mRNA was expressed. Furthermore, a mRNA transcript corresponding to a truncated isoform of SSTR2 was detected at low levels in the human SCLC NCI-H69 cell line, and likely represents a human homologue of rodent SSTR2B. Immunoblotting analysis using the SSTR2-specific antibody, 2e3, detected multiple immunoreactive protein species, including a predominant 150-kDa molecule, which could be blocked by the SSTR2-derived 2e3 peptide. Somatostatin (SRIF) peptides with high SSTR2 affinity and antiproliferative properties were potent inhibitors of [125I]MK-678 binding to several tumor types, suggesting that they may exert antitumor effects via the SSTR2 receptor.

Animals↗

PubMed1994

Differential expression of messenger RNAs for somatostatin receptor subtypes SSTR1, SSTR2 and SSTR3 in adult rat brain: analysis by RNA blotting and in situ hybridization histochemistry.

The messenger RNAs encoding three somatostatin receptor subtypes, SSTR1, SSTR2 and SSTR3, were detected in rat by RNA blotting and in situ hybridization histochemistry to identify the sites of synthesis and expression of these somatostatin receptor subtypes. RNA blotting revealed that SSTR1 messenger RNA of 3.8 kilobases was highly expressed in cerebral cortex, hippocampus, midbrain and hypothalamus. In situ hybridization histochemistry revealed that SSTR1 messenger RNA was localized to discrete layers of the cerebral cortex, the piriform cortex and the dentate gyrus of the hippocampus. SSTR1 messenger RNA was expressed at low levels in the cerebellum and pituitary and was not detectable in striatum or other peripheral organs. At least two SSTR2 messenger RNAs were detected by RNA blotting of 2.4 and 2.8 kilobases which correspond to the size of the spliced and unspliced forms of this receptor messenger RNA. SSTR2 messenger RNA detected by in situ hybridization is diffusely expressed in cerebral cortex and amygdala but is discretely localized to dentate gyrus in the hippocampus, medial habenula and ventromedial and dorsomedial nuclei and arcuate nucleus of the hypothalamus. The levels of SSTR2 messenger RNA are very low in the cerebellum and were not observed in the striatum or peripheral tissues other than the pituitary or adrenal gland. A single SSTR3 messenger RNA of 4.0 kilobases was seen in hippocampus, cerebral cortex, midbrain, hypothalamus and pituitary. However, the tissue with the highest levels of SSTR3 messenger RNA is the cerebellum with messenger RNA localized to the granule cell layer. The expression of the three different somatostatin receptor messenger RNAs are distinct but overlapping. Such distinct expression may contribute to the selective biological roles of the receptor subtypes.

Animals↗

PubMed1994

The cloned kappa opioid receptor couples to an N-type calcium current in undifferentiated PC-12 cells.

We have recently reported the cloning of a mouse kappa opioid receptor cDNA. Following transfection of the kappa receptor cDNA into COS-1 cells, a receptor is expressed with the pharmacological specificity of a kappa opioid receptor. To further analyse its functional properties, we have stably expressed the kappa opioid receptor in undifferentiated PC-12 cells, a pheochromocytoma clonal cell line, which do not endogenously express this receptor. We have previously shown that kappa opioid agonists selectively bind to these PC-12 membranes with high affinity. Here we show that kappa selective agonists are able to inhibit accumulation of cyclic adenosine monophosphate in a stereoselective manner. Further, the kappa agonist U-50,488 is able to inhibit an N-type calcium current in a pertussis toxin sensitive manner; this inhibition is blocked by the kappa-selective antagonist norbinaltorphimine. Inhibition of the calcium current via the kappa receptor is stereoselective as the agonist levorphanol is able to mediate inhibition whereas in the same cells dextrorphan is ineffective. This is the first demonstration that the cloned kappa opioid receptor functionally couples to a calcium current, as has been reported for kappa receptors expressed endogenously in the nervous system. Kappa opioid receptors are thought to be important in pain pathways, learning and memory deficits, and seizure activity. A major physiological action of the dynorphins, the endogenous ligands of the kappa receptor, is thought to be inhibition of neurotransmitter release at presynaptic terminals. N-type calcium channels may be important in neurotransmitter release.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1994

Opioid and cannabinoid receptors.

Opioids and cannabinoids are two major classes of drugs with important clinical uses as well as significant side effects. Recently, the three major subtypes of opioid receptors, delta, kappa and mu, have been cloned. Both the endogenous cannabinoids and their receptors have also recently been cloned. These advances are facilitating attempts to understand the structural features of these receptors that are involved in their functioning, which should lead to the development of new and improved clinically useful opioids and cannabinoid-like drugs.

Amino Acid Sequence↗

PubMed1994

Immunological detection of isoforms of the somatostatin receptor subtype, SSTR2.

Somatostatin (SRIF) induces its diverse physiological actions through interactions with different receptor subtypes. Multiple SRIF receptor subtypes have recently been cloned. To analyze the physical properties of receptor subtype SSTR2, two different peptide-directed antibodies were generated against SSTR2. Antibody "2e3," directed against the peptide SSCTINWPGESGAWYT (residues 191-206), corresponding to a region in the predicted third extracellular domain of mouse SSTR2, and antibody "2i4," directed against the peptide SGTEDGERSDS (residues 333-343) from the predicted cytoplasmic tail of mouse SSTR2, were developed. In Chinese hamster ovary (CHO) cells stably expressing the mouse SSTR2 gene (CHOB), the antibody 2e3 recognized specifically a protein of 93-kDa protein by immunoblotting. No specific immunoreactivity was detected by 2e3 in nontransfected CHO cells or CHO cells stably expressing vector alone or human SSTR1 or mouse SSTR3 genes. The antibody 2i4 specifically immunoprecipitated SSTR2 solubilized from CHOB cells that could be labeled with the SSTR2-specific ligand 125I-MK-678. Furthermore, both 2e3 and 2i4 specifically immunoprecipitated 93-kDa [35S]methionine-labeled proteins from CHOB cells, indicating that they recognize the same proteins. In contrast to studies in CHOB cells, immunoblotting studies showed that 2e3 detected specifically a single 148-kDa protein from different regions of the rat brain that have previously been shown to express high levels of SSTR2 mRNA and SRIF receptors with high affinity for 125I-MK-678. In contrast, no immunoreactivity was detected in rat kidney, liver, or lung, which do not express SSTR2. No 93-kDa protein was detected specifically in the rat brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Regulation of mu-opioid receptor mRNA in rat globus pallidus: effects of enkephalin increases induced by short- and long-term haloperidol administration.

The mRNA encoding mu-opioid receptors is expressed in neurons of the globus pallidus, a region of the basal ganglia that receives a dense enkephalinergic innervation from the striatum. The regulation of the mRNAs encoding the opioid peptide enkephalin in the striatum and the mu-opioid receptor in the globus pallidus was examined with in situ hybridization histochemistry following short- or long-term haloperidol treatments, which alter striatal enkephalin mRNA levels. Animals were administered haloperidol daily for 3 or 7 days (1 mg/kg, s.c.) or continuously for 8 months (1 mg/kg, depot followed by oral). Enkephalin and mu-opioid receptor mRNA levels were unchanged after 3 days of haloperidol treatment. In contrast, the enkephalin mRNA level was increased in the striatum, and mu-opioid receptor mRNA levels were markedly decreased in the globus pallidus after 7 days of haloperidol administration. Similar effects were observed in rats treated with haloperidol for 8 months. The results provide the first evidence of regulation of mu-opioid receptor mRNA in vivo.

Animals↗

PubMed1994

Molecular mechanisms of agonist-induced desensitization of the cloned mouse kappa opioid receptor.

Prolonged exposure of opioid receptors to agonists can cause desensitization, a cellular event linked to tolerance. Although evidence exists for mu and delta opioid receptor desensitization, much less information is available concerning the in vitro regulation of kappa opioid receptors because no cell lines exist that specifically express this class of opioid receptor. Recently we have cloned the mouse kappa opioid receptor. After expression in COS-7 cells, this protein exhibits the pharmacological specificity of a kappa 1 receptor and mediates agonist inhibition of cAMP formation. Continuous exposure of COS-7 cells expressing the kappa receptor to the agonist trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide methanesulfonate salt (U50,488) reduces the specific binding of the kappa-selective agonist [3H]U69,593. Furthermore, the potency of U50,488 to inhibit the binding of the opiate antagonist [3H]naloxone to the kappa receptor is reduced. However, total specific binding of [3H]naloxone is not altered, indicating that short-term (2-4 hr) agonist treatment of the kappa receptor reduces the affinity of the receptor for agonists but does not reduce the density of kappa receptors. The reduction in affinity of the kappa receptor for agonists is dependent on the time of agonist exposure and is reversible. The reduced affinity of the receptor for agonists is associated with kappa receptor desensitization, because kappa receptor-mediated inhibition of cAMP formation is lost in cells pretreated with U50,488. The desensitization of the kappa receptor is dependent on the time and concentration of agonist treatment, is blocked by the kappa-selective antagonist nor-binaltorphimine and is reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1994

Characterization of cloned human somatostatin receptor SSTR5.

The recent molecular cloning of the genes encoding six distinct somatostatin (SRIF) receptor subtypes from various species has allowed for the individual expression and characterization of these receptors in mammalian cells. In the present study, we have cloned the human homologue of the SRIF receptor subtype SSTR5 (formerly termed SSTR4) and characterized its pharmacological and functional properties, as well as its distribution. Although there is 80.5% sequence homology between the cloned rat and human SSTR5 receptors, their pharmacological profiles differ. We have labeled both rat and human SSTR5, expressed in Chinese hamster ovary (CHO-K1) cells, with 125I-Tyr11-SRIF and performed inhibition studies using SRIF analogues of differing structures, including cyclic penta-, hexa-, and octapeptide SRIF analogues. Whereas rat SSTR5 bound compounds in all structural classes with high to moderate affinities, human SSTR5 bound most SRIF analogues with much lower affinity, with the exceptions of SRIF, SRIF-28, and L-362,855. Like rat SSTR5, human SSTR5 mediated the inhibition by SRIF of forskolin-stimulated cAMP accumulation. However, the clinically used SRIF analogue SMS 201-995, which potently inhibited cAMP formation via interaction with rat SSTR5, did not inhibit cAMP accumulation in cells expressing human SSTR5. The distribution of expression of human SSTR5 mRNA, as analyzed by reverse transcription-polymerase chain reaction, shows selective expression in small intestine, heart, adrenal, cerebellum, pituitary, placenta, and skeletal muscle but not in kidney, liver, pancreas, uterus, thymus, testis, spleen, lung, thyroid, ovary, or mammary gland. The structural differences between cloned rat and human SSTR5 receptors suggest useful strategies for identifying regions of this receptor subtype that may be involved in ligand binding specificities. Identification of subtype-selective SRIF analogues may lead to more specific pharmacological therapeutic interventions.

Amino Acid Sequence↗

PubMed1994

Pharmacological characterization of the cloned kappa-, delta-, and mu-opioid receptors.

Opioid drugs, such as morphine, and the endogenous opioid peptides, namely the enkephalins, endorphins, and dynorphins, exert a wide spectrum of physiological and behavioral effects, including effects on pain perception, mood, motor control, and autonomic functions. These effects are mediated via membrane-bound receptors, of which the best characterized are the kappa, delta, and mu receptors. The existence of these distinct types of opioid receptors has recently been confirmed by molecular cloning. In the present study, we have examined the pharmacological profiles of the cloned kappa, delta, and mu receptors using a battery of widely employed opioid agents. Our results suggest that the cloned kappa and mu receptors have pharmacological characteristics similar to those of the endogenously expressed kappa 1 and mu receptors, respectively. The cloned delta receptor displays a pharmacological profile consistent with that of a delta 2 receptor. Opioid agents with abuse potential possess high affinities for the mu receptor. The availability of the cloned receptors will facilitate the identification and development of more specific and selective compounds with greater therapeutic potential and fewer undesirable side effects.

Analgesics↗

PubMed1994

Gi alpha 1 selectively couples somatostatin receptor subtype 3 to adenylyl cyclase: identification of the functional domains of this alpha subunit necessary for mediating the inhibition by somatostatin of cAMP formation.

A major cellular action of the neuropeptide somatostatin (SRIF) is the inhibition of adenylyl cyclase activity. SRIF induces this effect after its interaction with membrane-bound receptors. Five SRIF receptors (SSTRs), which differ in their functional coupling to adenylyl cyclase, have recently been cloned. The third SSTR cloned, SSTR3, effectively mediates the inhibition of adenylyl cyclase by SRIF. The molecular mechanism by which SRIF modulates intracellular cAMP synthesis via SSTR3 was investigated by initially identifying which G alpha subunits are involved in coupling SSTR3 to adenylyl cyclase. SRIF did not inhibit cAMP formation in Chinese hamster ovary cells stably expressing SSTR3 and Gi alpha 2 or Gi alpha 3 but lacking Gi alpha 1. However, SRIF did inhibit forskolin-stimulated cAMP formation in Chinese hamster ovary cells stably expressing SSTR3 and Gi alpha 1, indicating that Gi alpha 1 selectively couples SSTR3 to adenylyl cyclase. To investigate the functional domains of Gi alpha 1 necessary for interaction with SSTR3, a chimeric alpha subunit (Gi alpha 2/Gi alpha 1) was constructed, consisting of the amino-terminal two thirds of Gi alpha 2 ligated to the carboxyl-terminal third of Gi alpha 1. SRIF inhibited cAMP formation in cells expressing SSTR3 and the Gi alpha 2/Gi alpha 1 chimera. These findings indicate that the carboxy-terminal third of Gi alpha 1 interacts with SSTR3 and is important in transmitting the signal of SSTR3 activation to adenylyl cyclase. In contrast, a similar Gi alpha 2/Gi alpha 3 chimera did not couple SSTR3 to adenylyl cyclase, further indicating that Gi alpha 3 does not contribute to SRIF inhibition of adenylyl cyclase activity. These findings demonstrate that Gi alpha 1 selectively couples SSTR3 to adenylyl cyclase, and they indicate that the carboxyl-terminal region of this alpha subunit is involved in mediating SRIF inhibition of adenylyl cyclase activity.

Adenylyl Cyclases↗

PubMed1993

A single residue, aspartic acid 95, in the delta opioid receptor specifies selective high affinity agonist binding.

The enkephalins, dynorphins, and endorphins are endogenous opioids which function as neurotransmitters, neuromodulators, and hormones and are involved in the perception of pain, modulation of behavior, and regulation of autonomic and neuroendocrine function. Pharmacological studies have defined three classes of opioid receptors, designated as delta, kappa, and mu. To investigate mechanisms by which agonists and antagonists interact with the delta opioid receptor, we have substituted aspartic acid 95 in the transmembrane segment 2 of the cloned mouse delta opioid receptor with an asparagine (D95N). The D95N mutant receptor had reduced affinity for delta receptor-selective agonists such as enkephalin, [D-Pen2,D-Pen5]enkephalin and [D-Ser2,Leu5]enkephalin-Thr6 such that it did not bind these peptides even at micromolar concentrations. The binding of delta-selective non-peptide agonists was also reduced. In contrast, the delta receptor-selective antagonists, such as naltrindole, the benzofuran analog of naltrindole, and 7-benyllidenenaltrexone, bound equally well to the wild-type and mutant receptor. Similarly, non-selective opioid agonists such as bremazocine and buprenorphine, which interact with delta, kappa, and mu opioid receptors, showed no difference in binding to the wild-type and mutant delta receptor. The D95N mutant remained coupled to G proteins, and the receptor was functionally active since it mediated agonist inhibition of cAMP accumulation. These results indicate that selective agonists and antagonists bind differently to the delta receptor and show that Asp-95 contributes to high affinity delta-selective agonist binding. The identification of a key residue involved in selective agonist binding to the delta opioid receptor will facilitate the development of novel therapeutic reagents that can be used for the treatment of chronic pain and other conditions.

Animals↗

PubMed1993

Development of polyclonal antibodies against angiotensin type 2 receptors.

Murine neuroblastoma N1E-115 cells are a useful system in which to study neuronal angiotensin II (AngII) receptors. N1E-115 cells possess both type 1 (AT1) and type 2 (AT2) AngII receptor subtypes, as does mammalian brain. AT2 receptors in brain or N1E-115 cells can be solubilized in 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. In the present study, heparin-Sepharose chromatography was used to partially purify solubilized N1E-115 membranes to produce an enriched population of AT2 receptors. Subsequently, an eluted peak, containing the majority of AT2 binding activity, was used as an immunogen in the development of protein-directed polyclonal antibodies. The antibodies specifically detected immunoreactive proteins of approximately 110 and 66 kDa in both solubilized N1E-115 cells, as well as the original protein material that eluted from the heparin-Sepharose column, whereas no such immunoreactivity was detected in a kidney epithelial cell line that lacks any specific 125I-labeled AngII (125I-AngII) binding activity. Moreover, the antibodies immunoreacted with affinity-purified AT2 receptors. These antibodies were also able to immunoprecipitate AT2 receptors from solubilized N1E-115 cells, as revealed by the pharmacologic profile of 125I-AngII binding to the precipitated protein. Similarly, the antibodies were able to immunoprecipitate a 66-kDa protein that had been covalently crosslinked with 125I-AngII by use of the homobifunctional crosslinker dithiobis(succinimidyl propionate). Collectively, these results demonstrate the development of a specific AT2 receptor antibody that may be used to further characterize this receptor subtype at both the cellular and molecular levels.

Angiotensin II↗

PubMed1993

Cloning and functional comparison of kappa and delta opioid receptors from mouse brain.

While trying to identify new members of the somatostatin receptor family of G protein-coupled receptors, we isolated cDNAs from a mouse brain library encoding two related receptor-like proteins, designated msl-1 and msl-2, of 380 and 372 amino acids, respectively. There was 61% identity and 71% similarity between the sequences of msl-1 and msl-2. Among members of the G protein-coupled receptor superfamily, the sequences of both msl-1 and msl-1 were most closely related to those of the somatostatin receptors (SSTRs), having approximately 35% identity with the sequence of SSTR1. Transient expression in COS-1 cells showed that msl-1 and msl-2 did not bind somatostatin. Rather they bound opioids selectively and with high affinity and had the pharmacological properties of kappa and delta opioid receptors, respectively. Indeed, the sequence of msl-2 was identical to that of a delta opioid receptor recently cloned by other workers. Functional characterization of kappa/msl-1 and delta/msl-2 opioid receptors showed that they were coupled to G proteins and mediated opioid receptor class-specific agonist inhibition of forskolin-stimulated cAMP formation. RNA blotting studies and in situ hybridization histochemistry showed that kappa opioid receptor mRNA was expressed at high levels in brain in the neocortex, hippocampus, amygdala, medial habenula, hypothalamus (arcuate and paraventricular nuclei), locus ceruleus, and parabrachial nucleus, suggesting that this receptor may play a role in arousal and regulation of autonomic and neuroendocrine functions.

Amino Acid Sequence↗

PubMed1993

Gi alpha 3 and G(o) alpha selectively associate with the cloned somatostatin receptor subtype SSTR2.

The interaction of the SRIF receptor subtype SSTR2 with pertussis toxin-sensitive G proteins was investigated using an immunoprecipitation approach employing peptide-directed antisera against Gi alpha and G(o) alpha. Antisera directed against either the COOH terminus of Gi alpha or Go alpha uncoupled SSTR2-G protein complexes from CHO cells stably expressing the cloned receptor indicating that both G proteins form complexes with SSTR2. Chinese hamster ovary cells primarily express Gi alpha 3 and G(o) alpha 2 immunoreactivity, with much lower levels of the other pertussis toxin-sensitive G proteins. Antiserum against Gi alpha 3 uncoupled SSTR2/G protein complexes to a similar extent as Gi alpha common antiserum while antisera against Gi alpha 1 and Gi alpha 2 did not. These findings indicate that SSTR2 expressed in Chinese hamster ovary cells predominantly associates with Gi alpha 3 and G(o) alpha 2. In HEK 293 cells which endogenously express low densities of SSTR2 and similar levels of Gi alpha 1 and Gi alpha 3 immunoreactivity but no G(o) alpha, only antiserum directed against Gi alpha 3 immunoprecipitated SSTR2-G protein complexes, indicating that in these cells SSTR2 primarily associates with Gi alpha 3. SRIF can not inhibit forskolin-stimulated cAMP formation in wild-type HEK 293 cells nor in HEK 293 cells transfected with SSTR2. In contrast, SRIF can inhibit cAMP formation in HEK 293 cells expressing the cloned SRIF receptor SSTR3, which requires the presence of Gi alpha 1 to functionally couple to adenylyl cyclase. The lack of efficient association of SSTR2 with Gi alpha 1 may be the cause of its inability to mediate inhibition of cAMP formation. Differences in the G protein-coupling domains of the cloned SRIF receptors may be responsible for their differences in G protein association and ability to effect various signaling pathways.

Adenylate Cyclase Toxin↗

PubMed1993

Molecular biology of somatostatin receptors.

The neuropeptide somatostatin (SRIF) has diverse physiological actions in the brain and endocrine organs. A family of SRIF receptors has recently been cloned that may mediate the distinct biological effects of SRIF. These receptors have a high degree of amino acid sequence similarity among themselves, but their sequences are different from any other receptors, indicating that they represent a distinct neurotransmitter receptor subfamily. The availability of the cloned receptors will now allow for detailed structure-function analysis of SRIF receptors and will facilitate development of subtype-selective agonists and antagonists that could be useful in the treatment of central nervous system and endocrine disorders.

Amino Acid Sequence↗

PubMed1993

Molecular biology of opioid receptors.

Opium and its derivatives are potent analgesics that also have many other pharmacological effects in the nervous system. These agents and the endogenous opioid peptides exert their effects by interacting with high-affinity receptors. Complementary DNAs encoding the delta, kappa and mu opioid receptors have been isolated and characterized. These receptors, which are members of the superfamily of seven-transmembrane spanning receptors, share a high degree of amino acid sequence similarity with approximately 50% of the residues being identical. The cloned opioid receptors mediate agonist inhibition of cyclic AMP formation and have pharmacological properties similar to the endogenous proteins. The cloning of these receptors will facilitate the development of new clinically useful compounds as well as studies of the molecular basis of tolerance and drug addiction.

Amino Acid Sequence↗

PubMed1993

Developmental changes in expression of a 60-kDa somatostatin receptor immunoreactivity in the rat brain.

The neuropeptide somatostatin (SRIF) exerts several important physiological actions in the adult CNS through interactions with membrane-bound receptors. SRIF expression is developmentally regulated and this regulation is most apparent in the cerebellum, where SRIF immunoreactivity is expressed at early postnatal ages and then disappears toward adulthood. The transitory nature of SRIF expression at a time of major changes in cerebellum suggests that this peptide may have a role in cerebellar development. To further investigate the role of the SRIF transmitter system during development, we have examined the levels of expression of SRIF receptors in the developing rat brain by immunoblotting using antiserum selective for a 60-kDa brain SRIF receptor. In whole rat brain, SRIF receptor immunoreactivity first appears at embryonic day 13 (E13), is elevated at E16, increases at birth, peaks at early postnatal ages, and then gradually declines with age. No apparent changes in size of the receptor occur with age. No consistent changes in levels of SRIF receptor immunoreactivity are detected from early postnatal ages to adulthood in the hippocampus, cerebral cortex, and striatum, but levels gradually decline in the hypothalamus. In contrast, SRIF receptor immunoreactivity is expressed transiently in cerebellum. SRIF receptor immunoreactivity is detectable in cerebellum at E16, increases in levels at birth, is apparent from postnatal day 3 to postnatal day 8, and then disappears. The transitory nature of SRIF receptor expression in cerebellum is unique and parallels the expression of SRIF immunoreactivity in this brain region. These findings support the hypothesis that SRIF has a role in cerebellar development.

Aging↗

PubMed1993

Splice variant of the somatostatin receptor 2 subtype, somatostatin receptor 2B, couples to adenylyl cyclase.

The diverse biological actions of somatostatin (SRIF) are mediated by a family of receptors, of which five have been cloned and characterized. One of the SRIF receptor subtypes, SSTR2, has been shown to exist in two forms. SSTR2A and SSTR2B are 369 and 346 amino acids in size, respectively, and differ in length and amino acid sequence in their intracellularly located carboxyl termini. SSTR2A and SSTR2B are generated by alternative splicing of SSTR2 mRNA. We previously characterized mouse SSTR2A and showed that it could be distinguished from other cloned SRIF receptor subtypes by its high affinity for MK-678 and its lack of coupling to adenylyl cyclase. To determine whether the properties of mouse SSTR2A and SSTR2B differ, we have expressed both in COS-7 cells and characterized their ligand-binding properties and ability to couple to adenylyl cyclase. The two receptors exhibited similar affinities for a number of SSTR2-selective agonists such as MK-678. Pretreatment with SRIF of COS-7 cells expressing each receptor reduced high affinity agonist binding to both SSTR2A and SSTR2B, indicating that both receptors can be regulated. Furthermore, agonist binding to both receptors was reduced by GTP analogs and Na+, indicating that they both associate with G proteins. As shown previously, SSTR2A could not mediate SRIF inhibition of forskolin-stimulated cAMP formation. In contrast, SSTR2B was coupled to adenylyl cyclase and was able to mediate SRIF inhibition of forskolin-stimulated cAMP formation. Thus, SSTR2A and SSTR2B differ in their ability to couple to adenylyl cyclase. Because SSTR2A and SSTR2B differ only in the length and amino acid sequence of their carboxyl termini, these findings imply that the carboxyl-terminal 15 residues of SSTR2B may be involved in coupling this receptor to adenylyl cyclase.

Adenylyl Cyclases↗