POINT MUTATION OF THE SOMATOSTATIN RECEPTOR-2 GENE IN THE HUMAN SMALL-CELL LUNG-CANCER CELL-LINE COR-L103

The effect of somatostatin (SS) on adrenocorticotrophic hormone (ACTH) secretion from COR-L103 cells derived from a human small cell lung ca rcinoma was examined. SS at 1 mu M had no effect on ACTH secretion fro m the cells on either short-term or long-term incubation. Studies by t he reverse transcription-polymerase chain reaction (RT-PCR) showed tha t mRNA transcripts of the somatostatin receptor (SSTR) 2, SSTR3 and SS TR4 genes were present in COR-L103 cells. Extra bands were obtained by PCR-single strand conformation polymorphism (SSCP) analysis of the SS TR2 gene. Sequence analysis of the SSTR2 gene demonstrated one point m utation in codon 188 of TGG for tryptophan to TGA for a stop codon cau sing loss of 182 C-terminal amino acid residues of SSTR2. The nucleoti de sequences of the SSTR3 and SSTR4 genes in COR-L103 cells were norma l. Binding studies using I-125-Tyr(11)-SS-14 showed specific affinity binding sites on COR-L103 cells and mouse pituitary tumor AtT-20 cells . Octreotide acetate suppressed the binding of I-125-Tyr(11)-SS-14 to these two cell lines, but the Kd of COR-L103 cells (160 nM) was 60-fol d higher than that of AtT-20 cells (2.6 nM). Affinity cross-linking st udies using I-125-Tyr(11)-SS-14 gave three bands of 72 KDa, 55 KDa and 32 KDa from AtT-20 cells, but only two bands of 55kDa and 32kDa from COR-L103 cells. These findings suggest that SSTR2 is not expressed in the plasma membranes of COR-L103 cells due to a point mutation, but th at this may have no influence on the effect of SS on ACTH secretion. ( C) 1995 Academic Press, Inc.