Timothy W. Lovenberg

Corticotrophin-releasing factor receptors: from molecular biology to drug design

Corticotrophin-releasing factor (CRF) acts within both the brain and the periphery to coordinate the overall response of the body to stress. The involvement of the CRF systems in a variety of both CNS and peripheral disease states has stimulated great interest in this peptide as a potential site of therapeutic intervention. The recent cloning of multiple CRF receptor subtypes has precipitated a new era in CRF research that has allowed precise molecular, pharmacological and anatomical examination of mammalian CRF receptors. In this article, Derek Chalmers and colleagues highlight the major differences between the two classes of CRF receptors, CRF1 and CRF2, and a functionally related CRF-binding protein, and discuss the relevance of these sites to the ongoing development of CRF-based therapeutics.

Corticotropin-releasing factor CRF1, but not CRF2, receptors mediate anxiogenic-like behavior

The recent identification and differential localization in brain of three binding sites for corticotropin-releasing factor (CRF)-like peptides (CRF1 and CRF2 receptors as well as CRF-binding protein) suggest the existence of functionally distinct neurobiological systems which mediate CRF activation. For instance, evidence from receptor knockdown and pharmacological studies suggest involvement of the CRF1 receptor in anxiogenic-like behavior and the CRF-binding protein in learning and memory processes. The present studies examined the potential functional significance of the CRF2 receptor in relation to the CRF1 receptor using two animal models of anxiety and endocrine reactivity to a stressor. CRF1 and CRF2 receptor knockdown was achieved and confirmed autoradiographically within brain regions relevant to behavioral reactivity to stressors by chronic, central administration of antisense oligonucleotides. CRF1 but not CRF2, know down produced a significant anxiolytic-like effect in the Defensive Withdrawal relative to vehicle-treated and two missense oligonucleotide negative control groups. In contrast, neither antisense treatment altered endocrine or behavioral reactivity to a swim stressor. Thus, the present data support the reported role of CRF1 receptors in the mediation of anxiogenic-like behavior and suggest a functionally distinct for role for CRF2 receptors in brain.

Characterization of Corticotropin‐releasing Factor Receptor Subtypesa

Stress, or disruptions of homeostasis, can result from physical, psychological, as well as immunological challenges. As first described by Selye,’ stress elicits a wide spectrum of changes within the nervous, endocrine, and immune systems. A key neurohormone that plays a significant role in integrating the response to stress throughout the neuro-endocrine-immune axis is corticotropin-releasing factor (CRF). CRF has been widely reported to play a major role in coordinating the endocrine, autonomic, and behavioral response to stress through actions both in the brain and in the periphery. CRF is produced and secreted primarily from parvocellular neurons of the paraventricular hypothalamic nuclei. The secreted CRF activates corticotrophs in the anterior pituitary, which, in turn, secrete adrenocorticotropin (ACTH), which subsequently stimulates adrenal glucocorticoid release. This CRF-ACTH-glucocorticoid axis is central to the endocrine response to stress and has been extensively reviewed.2-s In addition to its endocrine effects, immunohistochemical localization of CRF has demonstrated that the hormone has a broad extrahypothalamic distribution in the central nervous system (CNS).@ CRF produces a wide spectrum of autonomic, electrophysiological. and behavioral effects consistent with a neurotransmitter or neuromodulator role in the brain.2” Intracerebroventricular administration of CRF provokes stress-like responses, including activation of the sympathetic nervous system3*4*1k12 and inhibition of the parasympathetic nervous ~ystem>*~.”*’~ The behavioral profile following central administration of CRF is also characteristic of a compound that increases arousal and emotional reactivity to the environment. These effects of CRF include general arousal, as exhibited by increased locomotion, sniffing, grooming, and rearing in familiar surroundings and increased agitation in unfamiliar surr o u n d i n g ~ . ~ * ~ * ~ ~ * ~ ~ By contrast, sexual re~eptivity~’.~~ and feeding19 are decreased. In addition to the neuromodulatory and neuroendocrine actions of CRF, recent evidence suggests that CRF may also play a significant role in a variety of peripheral functions,

CLONING OF A CDNA ENCODING A NOVEL INTERLEUKIN-1 RECEPTOR RELATED PROTEIN (IL1R-RP2)

We have identified and isolated both the rat and human cDNAs for a novel putative receptor related to the interleukin-1 type 1 receptor. We have named this protein interleukin 1 receptor related protein two (IL 1R-rp2). The rat cDNA for IL1R-rp2 was first identified using oligonucleotides of degenerate sequence in a polymerase chain reaction (PCR) paradigm with rat brain mRNA as the template. The protein encoded by both of these cDNAs are 561 amino acids long and exhibit 42% and 26% overall identity with the interleukin-1 type 1 and type 2 receptors, respectively. RNase protection assays from rat tissues revealed a predominant expression for IL 1R-rp2 in the lung and epididymis with lower levels detected in the testis and cerebral cortex. By in situ hybridization we were able to determine that the expression in rat brain appeared to be non-neuronal and associated with the cerebral vasculature. When expressed transiently in COS-7 cells the receptor was incapable of high affinity binding to either [125I]-recombinant human IL 1 alpha or [125I]-recombinant human IL 1 beta. Together, these data demonstrate the existence of a novel protein that is related to the interleukin-1 receptor but does not bind IL-1 by itself.

Chapter 3. Heterogeneity of Corticotropin Releasing Factor Receptors: Multiple Targets for the Treatment of CNS and Inflammatory Disorders

Publisher Summary This chapter describes some of the recent studies on a variety of corticotropin-releasing factor (CRF) related targets, including three functionally distinct receptor subtypes and the CRF-binding protein (CRF-BP). The characteristics of the CRF receptors, including their sequence homologies, pharmacological profiles, and second messenger activities, are described in the chapter. In addition, the differential localization of messenger RNA (mRNA) for CRF receptors and CRF-BP is discussed in the chapter. As clinical data suggest that CRF may be implicated in psychiatric, neurologic, and immunological disorders, the chapter includes a brief description of the role of CRF, its receptors, and its binding protein in the etiology and pathophysiology of these diseases. Finally, the chapter provides an update on small molecule, nonpeptide CRF receptor antagonists. CRF, a 41-residue peptide, plays a crucial role in integrating the bodys overall response to stress. The actions of CRF in the brain and in the periphery are mediated through multiple binding sites. There is heterogeneity of CRF binding sites with respect to sequence, pharmacology, and tissue distribution. There are three receptors; CRF1, CRF2α, and CRF2β, which encode 411, 415, and 431 amino acid proteins, respectively, comprising seven putative membrane-spanning domains characteristic of the G s -coupled receptors. All three receptors transduce a signal that involved stimulation of cyclic adenosine monophosphate (cAMP) production. CRF receptor antagonists may represent novel agents for the treatment of disorders associated with the elevated levels of CRF. The recent identification of high-affinity nonpeptide CRF receptor antagonists is expected to allow for rapid progress in drug development of the CRF receptor antagonists. In addition to the receptors, the actions of CRF in brain and in the periphery can also be modulated by a binding protein of 322 amino acids. While the precise function of the CRF-BP remains to be determined, it appears to play a role in binding and functionally inactivating CRF, and CRF-BP ligand inhibitors may represent a potential mechanism for increasing the endogenous CRF levels.