C-CAM1, a candidate tumor suppressor gene, is abnormally expressed in primary lung cancers.
Previous studies have shown that the expression of the cell-cell adhesion molecule (C-CAM1), located at chromosome 19, is down-regulated in several types of human cancers, including prostate and breast cancers. Two major isoforms of C-CAM1, the long or L-form C-CAM1 and the short or S-form C-CAM1, are derived from the C-CAM1 gene through alternative splicing. Tumor cells transfected with L-form C-CAM1, which contains a cytoplasmic domain, display significantly lower growth rates and less tumorigenicity in both in vitro and in vivo models compared with untransfected tumor cells, suggesting that L-form C-CAM1 may be a tumor suppressor. The transfection of the cytoplasmic domain of L-form C-CAM1 could also cause suppression of tumor growth, further supporting the role of L-form C-CAM1 in tumorigenesis. In contrast to reports of most of the tumor types tested, Ohwada et al. (Am. J. Respir. Cell Mol. Biol., 11: 214-220, 1994) reported that C-CAM1 was not down-regulated or even up-regulated in lung cancer. Because the cytoplasmic domain of L-form C-CAM1 is critical for the tumor suppressor function of C-CAM1, we hypothesized that switching of the isoform rather than down- regulation of C-CAM1 gene expression occurs during lung tumorigenesis. To test this hypothesis, we analyzed pairs of tumor tissue and corresponding normal-appearing lung tissue from 51 patients with non-small cell lung cancer (NSCLC) and 43 cell lines to determine expression profiles of L-form C-CAM1 and S-form C-CAM1 using reverse transcription-PCR. We found that L-form C-CAM1 was the predominant form (75%; 38 of 51) in normal-appearing lung tissue, whereas most (84%; 43 of 51) of the primary NSCLC tissue samples expressed predominantly S-form C-CAM1 (P < 0.0001). Similarly, 19 (79%) of the 24 NSCLC cell lines and 17 (85%) of the 20 small cell lung cancer cell lines expressed predominantly S-form C-CAM1. The frequent alteration of the C-CAM1 expression pattern suggests that C-CAM1 has an important role in lung tumorigenesis.
Wang
L
L
Department of Thoracic/Head and Neck Medical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Lin
S H
SH
Wu
W G
WG
Kemp
B L
BL
Walsh
G L
GL
Hong
W K
WK
Mao
L
L
D000251:Adenosine Triphosphatases / Q000096:biosynthesis / Q000235:genetics*; D000368:Aged; D000595:Amino Acid Sequence; D015703:Antigens, CD; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018288:Carcinoma, Small Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D006801:Humans; D008168:Lung / Q000378:metabolism / Q000502:physiology; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D015703:Antigens, CD; C069847:CD66 antigens; D015815:Cell Adhesion Molecules; D020033:Protein Isoforms; D000251:Adenosine Triphosphatases