REGULATION OF CORTICOTROPIN-RELEASING FACTOR-RECEPTOR FUNCTION IN HUMAN Y-79 RETINOBLASTOMA CELLS - RAPID AND REVERSIBLE HOMOLOGOUS DESENSITIZATION BUT PROLONGED RECOVERY

Homologous receptor desensitization is an important regulatory respons e to continuous activation by agonist that involves the uncoupling of a receptor from its G protein. When human retinoblastoma Y-79 cells ex pressing corticotropin-releasing factor (CRF) receptors were preincuba ted with CRF for 10 min-4 h, a time-dependent reduction in both the pe ak and sensitivity of CRF-stimulated intracellular cyclic AMP (cAMP) a ccumulation developed with a t(1/2) of 38 min and an EC50 of 6-7 nM CR F. CRF receptor desensitization was slowly reversible after a 4-h CRF preincubation with a t(1/2) of 13 h and a full restoration of cAMP res ponsiveness to CRF at 24 h following the removal of 10 nM CRF. Because the ability of vasoactive intestinal peptide, forskolin, or (-)-isopr oterenol to stimulate cAMP accumulation was not diminished in Y-79 cel ls desensitized with 10 nM CRF, the observed desensitization was consi dered to be a specific homologous action of CRF. CRF receptor desensit ization was markedly attenuated by CRF receptor antagonists, which alo ne did not produce any appreciable reduction in CRF-stimulated cAMP ac cumulation. Although recent reports have demonstrated a rapid decline in steady-state levels of CRF receptor type 1 (CRF-R1) mRNA in anterio r pituitary cells during several hours of exposure to CRF, there was n o observed reduction in CRF-R1 mRNA levels when Y-79 cells were preinc ubated with 10 nM CRF for 10 min-24 h despite a rapid time- and concen tration-dependent loss of CRF receptors from the retinoblastoma cell s urface.