Expression of multiple somatostatin receptor genes in AtT-20 cells. Evidence for a novel somatostatin-28 selective receptor subtype.
The pattern of expression of somatostatin receptor (SSTR) genes and gene products in AtT-20 cells was characterized in an attempt to explain the SST-28 binding selectivity that typifies these cells. AtT-20 cells expressed multiple SSTR mRNAs. Paradoxically, this included mRNA for three of the four SST-14 selective receptors: SSTR2 ( +), SSTR1 (+), SSTR4 (+). The SST-28 selective SSTR5 was expressed as a 3.8-kilobase (kb) transcript of relatively low abundance (+) in contrast to normal mouse pituitary which displayed high levels ( ) of a 2.4-kb SSTR5 mRNA. Immunoblot analysis of solubilized membranes with an antipeptide SSTR2 antibody revealed a single SSTR2 protein of 72 +/- 2 kDa. Preincubation of AtT-20 cell membranes with SSTR2 antibody reduced 125I-[Leu8,D-Trp22,Tyr25]SST-28 binding sites by 38%. Residual binding sites exhibited a 4.9-fold increase in affinity for SST-28, a 2.6-fold decrease in affinity for SST-14, and an SST-28:SST-14 potency ratio of 40:1 compared with a potency ratio of 3.5:1 in control membranes. These results demonstrate the expression of four SSTR genes in AtT-20 cells of which SSTR2 predominates. Blockade of SSTR2 with antibody exposes high affinity SST-28 selective sites with comparable binding characteristics to those reported for cloned SSTR5. These SST-28 binding sites may arise from a SSTR5 variant encoded by a high molecular weight 3.8-kb transcript or more likely from another as yet undiscovered member of the SST-28 selective SSTR subfamily.
Patel
Y C
YC
Fraser Laboratories, McGill University, Department of Medicine, Royal Victoria Hospital, Montreal, Quebec, Canada.
Panetta
R
R
Escher
E
E
Greenwood
M
M
Srikant
C B
CB
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D015870:Gene Expression; D051379:Mice; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D010902:Pituitary Gland / Q000737:chemistry; D012333:RNA, Messenger / Q000235:genetics; D017481:Receptors, Somatostatin / Q000235:genetics*; D013004:Somatostatin / Q000378:metabolism*; D053561:Somatostatin-28
D010455:Peptides; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; D013004:Somatostatin; D053561:Somatostatin-28