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 carcinoma was examined. SS at 1 microM had no effect on ACTH secretion from the cells on either short-term or long-term incubation. Studies by the reverse transcription-polymerase chain reaction (RT-PCR) showed that mRNA transcripts of the somatostatin receptor (SSTR) 2, SSTR3 and SSTR4 genes were present in COR-L103 cells. Extra bands were obtained by PCR-single strand conformation polymorphism (SSCP) analysis of the SSTR2 gene Sequence analysis of the SSTR2 gene demonstrated one point mutation in codon 188 of TGG for tryptophan to TGA for a stop codon causing loss of 182 C-terminal amino acid residues of SSTR2. The nucleotide sequences of the SSTR3 and SSTR4 genes in COR-L103 cells were normal. Binding studies using 125I-Tyr11-SS-14 showed specific affinity binding sites on COR-L103 cells and mouse pituitary tumor AtT-20 cells. Octreotide acetate suppressed the binding of 125I-Tyr11-SS-14 to these two cell lines, but the Kd of COR-L103 cells (160 nM) was 60-fold higher than that of AtT-20 cells (2.6 nM). Affinity cross-linking studies using 125I-Tyr11-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 that this may have no influence on the effect of SS on ACTH secretion.
Zhang
C Y
CY
First Department of Internal Medicine, School of Medicine, University of Tokushima, Japan.
Yokogoshi
Y
Y
Yoshimoto
K
K
Fujinaka
Y
Y
Matsumoto
K
K
Saito
S
S
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D018288:Carcinoma, Small Cell / Q000235:genetics*; D002460:Cell Line; D003062:Codon; D017931:DNA Primers; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms / Q000235:genetics*; D008969:Molecular Sequence Data; D017354:Point Mutation; D016133:Polymerase Chain Reaction / Q000379:methods; D017481:Receptors, Somatostatin / Q000235:genetics* / Q000378:metabolism; D013004:Somatostatin / Q000378:metabolism / Q000494:pharmacology
D003062:Codon; D017931:DNA Primers; D017481:Receptors, Somatostatin; D013004:Somatostatin; D000324:Adrenocorticotropic Hormone; C093733:somatostatin receptor 2