The Roles Of Central CRF Receptors In Cocaine Withdrawal And Peripheral CRF Receptors In Prostate Cancer Cell Apoptosis

Corticotropin-releasing factor (CRF) related peptides and their receptors aredistributed in central nervous system (CNS) and periphery, which display quitedifferent pharmacological profiles. In CNS, CRF related peptides and their receptorsare critical in regulating behavioral response, mood activity, food intake, drugaddiction and so on. In periphery, CRF related peptides and their receptors playimportant roles in cardiovascular system, inflammatory response, metabolism,cancer and so on.The distinct roles of CRF related peptides depend on the quantity and types ofthe ligands, which are also related to diverse subtypes and distributions of receptors.Both CRF related peptides and their receptors have been detected in the striatum ofthe CNS and prostate cancer tissues, however, the detailed effects of CRF receptorson cocaine addiction in corticostriatal circuit and the apoptosis of prostate cancercells are far from clear. Based on the present observation in CNS, CRF familypeptides enhanced corticostriatal LTP under cocaine withdrawal condition, whichmay contribute to stress-induced relapse of cocaine abuse. Importantly, CRFreceptors mediated subtype-specific functional changes. CRFR1 appeared toenhance corticostriatal LTP under both physiological and cocaine withdrawalcondition, whereas CRFR2 was involved in modulating neuroadaptive changes onlyduring cocaine withdrawal. In periphery, CRF induced apoptosis via CRFR1 inRM-1 murine prostate cancer cells, which was associated with the upregulation of Bax and downregulation of Bcl-2. On the contrary, UCN2 repressed apoptosis viaCRFR2 in RM-1 cells, which was accompanied with phosphorylation of Akt andCREB, downregulation of Bax and upregulation of Bcl-2 .In summary, we investigated the roles and relevant mechanisms of CRF relatedpeptides and their receptors in rats corticostriatal synaptic plasticity under cocainewithdrawal condition and in apoptosis of RM-1 murine prostate cancer cells, aimedto elaborate the different roles of CRF receptors in CNS and periphery.Part 1 Roles of CRF receptors in long-term potentiation in ratcorticostriatal synapses under cocaine withdrawalSimilar to other abused drugs, main characteristics of cocaine addiction arecompulsive drug use and high rates of relapse during periods of abstinence. In the last15 years, a large number of studies were conducted to study the effects ofhypothalamic and extrahypothalamic CRF systems on cocaine abuse. Cocaineaddiction mechanisms may be similar to those that underlie learning and memoryprocesses which require the participation of corticostriatal circuit. Corticostriatalcircuit has been widely accepted as a brain center to form habits and storage. Thus far,the underlying roles of CRF related peptides and receptors in corticostriatal synapticplasticity during cocaine withdrawal are not well illustrated, yet. Long termpotentiation (LTP) has been regarded as an important cellular model of synapticplasticity. In the first part, the roles of two subtypes of CRFRs in rat corticostriatalsynaptic plasticity during cocaine withdrawal were investigated. Based on theobservations, cocaine withdrawal did not affect the basic electrophysiological properties of striatal neurons or the LTP in rats corticostriatal slices. Importantly, itwas found for the first time that CRF dose-dependently enhanced rats corticostriatalLTP in both the cocaine-withdrawal group and the saline group, which maycontribute to stress-induced relapse of cocaine abuse. In addition, the enhanced LTPwas reduced by pretreatment with either the CRFR1 selective antagonist (NBI 27914)or the CRFR2 selective antagonist (astression2B) in the cocaine withdrawal group.However, in the saline group, enhanced LTP was significantly attenuated only by theCRFR1 selective antagonist (NBI 27914). Futhermore, UCN2, the CRFR2 selectiveagonist, only potentiated corticostriatal LTP in the cocaine withdrawal group,meanwhile, that effect of UCN2 could be completely blocked by pretreatment withastression2B. Taken together, CRFR1 enhanced rats corticostriatal LTP under bothphysiological and cocaine withdrawal condition, but CRFR2 mediated that fuctiononly under cocaine withdrawal condition.In conclusion, CRF family peptides enhanced rats corticostriatal LTP undercocaine withdrawal condition. Importantly, CRF receptors mediated subtype-specificfunction. CRFR1 appeared to enhance corticostriatal LTP under both physiologicaland cocaine withdrawal condition, whereas CRFR2 was involved in modulatingneuroadaptive changes only under cocaine withdrawal condition. Therefore, thestate-dependent changes of CRFR2 function might be an important mechanism thatcontributes to cocaine relapse, which might be an attractive novel target for thetreatment of relapse during cocaine withdrawal.Part 2 Different roles of CRF receptors in apoptosis of RM-1murine prostate cancer cells Roles of CRF related peptides and their receptors in periphery, especially incancer cells have become confusing recently. It is reported that UCN has beendetected in human prostate tumor specimens. But till now, there was no studyexploring CRFRs'expression in prostate tumor cells and the correspondingphysiological and pathological effects. In the second part, the expressions andpotential mechanisms of CRFRs'effects on apoptosis in RM-1 cells wereinvestigated for the first time. Here, the expressions of CRFR1 and CRFR2 at bothmRNA and protein levels in RM-1 were detected using semi-quantitative RT-PCR,immunofluorescence and Western blotting analysis. CRF treatment was accompaniedwith Bcl-2 (anti-apoptotic gene) downregulation, Bax (pro-apoptotic gene)upregulation, hyperpolarization of the mitochondrial membrane potential andactivation of caspase-9. On the contrary, the inhibited apoptosis by UCN2 wasassociated with upregulating Bcl-2 and downregulating Bax expressions. All effectsof CRF/UCN2 were abolished by antarlamin/antisauvagine-30, selective CRFR1 andCRFR2 antagonist, respectively. Meanwhile, UCN2 repressed apoptosis via CRFR2,which was accompanied with time-dependent phosphorylation of Akt andsubsequently phosphorylation of CREB in a short time. LY29004, a PI3K inhibitor,significantly inhibited both CREB phosphorylation and subsequent Bcl-2 expressiontriggered by UCN2, which suggested that Akt&CREB may be involved inanti-apoptosis in RM-1 murine prostate cancer cells mediated by CRFR2.In summary, the present study first demonstrated the expression of two subtypesof CRFRs, which had opposite apoptotic effects in RM-1 murine prostate cancer cells.These findings accumulated theoretical evidences for illuminating the roles of CRFsystem in prostate tumor cells, especially provided a potential target for the treatmentof prostate tumor.