[Abstract unavailable

Type I programmed cell death (PCD) or apoptosis is critical for cellular self-destruction for a variety of processes such as development or the prevention of oncogenic transformation. Alternative forms, including type II (autophagy) and type III (necrotic) represent the other major types of PCD that also serve to trigger cell death. PCD must be tightly controlled since disregulated cell death is involved in the development of a large number of different pathologies. To counter the multitude of processes that are capable of triggering death, cells have devised a large number of cellular processes that serve to prevent inappropriate or premature PCD. These cell survival strategies involve a myriad of coordinated and systematic physiological and genetic changes that serve to ward off death. Here we will discuss the different strategies that are used to prevent cell death and focus on illustrating that although anti-apoptosis and cellular survival serve to counteract PCD, they are nevertheless mechanistically distinct from the processes that regulate cell death.

To characterize cell specific expression of sstr subtypes in the pituitary we have analyzed mRNA for sstr1-5 in rat pituitary somatotrophs by reverse transcriptase polymerase chain reaction and determined the pattern and level of expression of mRNA for sstr subtypes 2 and 5 in individual pituitary cell subpopulations by double label in situ hybridization. Purified somatotrophs expressed mRNA for all 5 sstrs. In situ hybridization analysis revealed sstr5 mRNA in 70% of somatotrophs, 57% of thyrotrophs, 38% of corticotrophs, 33% of lactotrophs, and 21% of gonadotrophs. mRNA for sstr2 occurred in 40% of somatotrophs, 36% of thyrotrophs, 26% of lactotrophs, 3% of corticotrophs, and 8% of gonadotrophs. Not only were more cells positive for sstr5 mRNA but the average number of autoradiographic grains/cell was also higher for sstr5 than sstr2. These results show expression of multiple sstr genes in individual pituitary cells. mRNA for sstr2 and 5 occur in each of the 5 major pituitary cell subsets, sstr5 mRNA being more widely and more abundantly expressed than sstr2.

SUMMARYThe ligand binding domain of G protein-coupled receptors for peptide ligands consists of a pocket formed by extracellular and transmembrane domain (TM) residues. In the case of somatostatin (SRIF), however, previous studies have suggested that the binding cavity of the octapeptide analog SMS201-995 (SMS) is lined by residues in TMs III-VII. The additional involvement of the extracellular domains for binding SMS or the natural SRIF ligands (SRIF-14, SRIF-28) has not been clarified. Using a cassette construct cDNA for the human somatostatin 5 receptor (sst 5 R), we systematically examined the role of exofacial structures in ligand binding by creating a series of mutants in which the extracellular portions have been altered by conservative segment exchange (CSE) mutagenesis for the extracellular loops (ECLs) and by deletion (for the NH 2 -terminal segment) or truncation analysis (ECL3). CHO-K1 cells were stably transfected with wild type or mutant human sst 5 R constructs, and agonist binding was assessed using membrane binding assays with 125 I-LTT SRIF-28 ligand. Deletion of the NH 2 terminus or CSE mutagenesis of ECL1 and ECL3 produced minor 2-8-fold decreases in affinity for SRIF-14, SRIF-28, and SMS ligands. Truncation of ECL3 to mimic the size of this loop in sst 1 R and sst 4 R (the two subtypes that do not bind SMS) did not interfere with the binding of SMS, SRIF-14, or SRIF-28. In contrast, both ECL2 mutants failed to bind 125