Abstract Evidence from cDNA cloning has shown that calcitonin receptors (CTRs) have seven potential trans- membrane domains. In this study, structural analysis of CTRs from ten cultured human tumor cell lines and 117 human blood samples demonstrated allelic variants at the 1377th nucleotide in intracellular domain 4, expressing either proline or leucine as the 463rd amino acid. It was found that the variant with proline at this site was the more prevalent type of CTR among the Japanese popula- tion. Introduction Calcitonin (CT) is a 3.4-kDa polypeptide hormone se- creted by parafollicular cells of the thyroid gland (Busso- lati and Pearse 1967). CT inhibits osteoclastic bone re- sorption and stimulates urinary calcium excretion (Bijvoet et al. 1971). CT receptors (CTRs) have seven potential transmembrane domains and they are known to occur in osteoclasts (Nicholson et al. 1986), renal tubular epithe- lium (Marx et al. 1973; Chabardes et al. 1976), testis (Chausmer et al. 1980), brain (Goltzman 1985), and ovary (Gorn et al. 1992). We have reported two types of CTR cDNA in humans, one (hCTR-1) having an insertion of 16 amino acids in in- tracellular domain 1 and the other (hCTR-2) lacking such an insertion (Frendo et al. 1994; Gorn et al. 1995; Naka- mura et al. 1995; Nussenzveig et al. 1995). The expres- sion of these two isoforms was reported to be regulated by alternative splicing (Nakamura et al. 1995; Nussenzveig et al. 1995). hCTR-1 was first isolated from a cDNA li- brary of the ovarian carcinoma cell line BIN-67 and later from other tissues. hCTR-2 was first isolated from a cDNA library of the mammary carcinoma cell line T47D and later from other cell lines and tissues. The possibility was discussed that structural differences in intracellular domain 1 might produce functional differences in signal pathways (Nussenzveig et al. 1994). In addition, these isoforms involve a single nucleotide difference at position 1377, which is C in BIN-67 and T in T47D. Kuestner et al. (1994) discussed the possibilities that this difference might reflect individual variation in the source of the cloned DNA or that it might represent a cloning artifact. In this study, we analyzed ten cultured tumor cell lines and 117 human blood samples. The results demonstrated a single nucleotide difference at position 1377 of human CTR cDNA, reflecting a difference between allelic vari- ants. Materials and methods Human tumor cell lines Ten human cell lines were used in this study. A549, LU65, and EBC-1 lung carcinomas, NUGC-3 gastric carcinoma, NH-6 adrenal carcinoma, T24 bladder carcinoma, YMB-1 mammary car- cinoma, and VMRC-RCW renal cell carcinoma were obtained from the Health Science Research Resources Bank. J82 bladder carcinoma was obtained from the American Type Culture Collec- tion. TT thyroid carcinoma was a generous gift from K. Shimaoka (Rosewell Park Memorial Institute, Buffalo, USA). Blood samples Blood samples were collected from 117 Japanese volunteers. Misa Nakamura · Zhi-qiang Zhang · Liang Shan · Tomoyuki Hisa · Mitsuyo Sasaki · Ryuichi Tsukino · Toyoharu Yokoi · Akio Kaname · Kennichi Kakudo Allelic variants of human calcitonin receptor in the Japanese population Hum Genet (1997) 99 : 38–41 © Springer-Verlag 1997 Received: 21 June 1996 ORIGINAL INVESTIGATION M. Nakamura () · Z. Zhang · L. Shan · T. Hisa · T. Yokoi · K. Kakudo Second Department of Pathology, Wakayama Medical College, 27-Kyubancho Wakayama City, Wakayama, 640 Japan Tel.: +81 734-26-8315; Fax: +81 734-33-2053 M. Sasaki Department of Pediatrics, Wakayama Medical College Kihoku Hospital, Wakayama, 649-71 Japan R. Tsukino Department of Pediatrics, Arita City Hospital, Wakayama, 649-03 Japan A. Kaname Kaname Clinic, Wakayama, 647 Japan