Corticotropin-releasing hormone (CRH) is the principal regulator of the stress response. CRH stimulates production of ACTH via specific CRH receptors located on pituitary corticotropes. In addition to pituitary and central nervous system effects, peripheral effects of CRH have been observed involving the immune and cardiovascular systems. Specific CRH binding studies in several peripheral organs, as well as functional studies, have implied the existence of peripheral CRH receptors. Although a pituitary/brain CRH receptor has recently been identified, it is expressed at very low levels in peripheral sites where CRH effects have been observed. We report here the identification of a novel murine CRH receptor that is highly expressed in the heart. The newly cloned CRH receptor cDNA (CRH-R2) was isolated from a mouse heart cDNA library and encodes a 430-amino acid protein containing seven putative transmembrane domains characteristic of G protein-coupled receptors. CRH-R2 is 69% identical with the previously identified murine pituitary CRH receptor and is encoded by a distinct gene. In addition to a high level of expression in the heart, weak expression was also observed in the brain and lungs. Functional studies using CRH-R2-transfected cells indicate that CRH and the CRH-related amphibian peptide, sauvagine, bind with high affinity to CRH-R2 and stimulate intracellular accumulation of cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

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Mammalian cells often receive multiple extracellular stimuli under physiological conditions, and the various signaling inputs have to be integrated for the processing of complex biological responses. G protein-coupled receptors (GPCRs) are critical players in converting extracellular stimuli into intracellular signals. In this report, we examined the integration of different GPCR signals by mitogen-activated protein kinases (MAPKs) using the SK-N-MC human brain neuroepithelioma cells as a neuronal model. Stimulation of the G i -coupled neuropeptide Y 1 and G q -coupled muscarinic M 1 acetylcholine receptors, but not the G s -coupled dopamine D 1 receptor, led to the activation of extracellular signal-regulated kinase (ERK). All three receptors were also capable of stimulating c-Jun NH 2 -terminal kinases (JNK) and p38 MAPK. The G i -mediated ERK activation was completely suppressed upon inhibition of Src tyrosine kinases by PP1, while the G q -induced response was suppressed by both PP1 and the In mammals, cross-communication between the signals of different transmembrane receptors enables multiple extracellular signals to be received and then integrated into different neuronal responses such as plasticity and cognition. The G protein-coupled receptors (GPCRs) constitute one of the largest families of cell surface detectors that often play critical roles in neuronal processes. Upon activation by specific ligands, GPCRs regulate a diverse spectrum of effectors according to their overall preferences for G proteins. GPCRs coupled to the G s and G i families of G proteins are linked to stimulation or inhibition of adenylyl cyclase (AC), respectively (Balmforth et al. 1986;Mollereau et al. 1994), while G q -coupled receptors are efficiently coupled to the stimulation of phospholipase C (PLC) activity (Piiper et al. 1997

BackgroundThe FHIT tumor suppressor gene is arguably the most commonly altered gene in cancer since it is inactivated in about 60% of human tumors. The Fhit protein is a member of the ubiquitous histidine triad proteins which hydrolyze dinucleoside polyphosphates such as Ap3A. Despite the fact that Fhit functions as a tumor suppressor, the pathway through which Fhit inhibits growth of cancer cells remains largely unknown. Phosphorylation by Src tyrosine kinases provides a linkage between Fhit and growth factor signaling. Since many G proteins can regulate cell proliferation through multiple signaling components including Src, we explored the relationship between Gα subunits and Fhit.ResultsSeveral members of the Gαq subfamily (Gα16, Gα14, and Gαq) were found to co-immunoprecipitate with Fhit in their GTP-bound active state in HEK293 cells. The binding of activated Gαq members to Fhit appeared to be direct and was detectable in native DLD-1 colon carcinoma cells. The use of Gα16/z chimeras further enabled the mapping of the Fhit-interacting domain to the α2-β4 region of Gα16. However, Gαq/Fhit did not affect either Ap3A binding and hydrolysis by Fhit, or the ability of Gαq/16 to regulate downstream effectors including phospholipase Cβ, Ras, ERK, STAT3, and IKK. Functional mutants of Fhit including the H96D, Y114F, L25W and L25W/I10W showed comparable abilities to associate with Gαq. Despite the lack of functional regulation of Gq signaling by Fhit, stimulation of Gq-coupled receptors in HEK293 and H1299 cells stably overexpressing Fhit led to reduced cell proliferation, as opposed to an enhanced cell proliferation typically seen with parental cells.ConclusionsActivated Gαq members interact with Fhit through their α2-β4 region which may result in enhancement of the growth inhibitory effect of Fhit, thus providing a possible avenue for G protein-coupled receptors to modulate tumor suppression.