Identification of a new isoform of cell-cell adhesion molecule 105 (C-CAM), C-CAM4: a secretory protein with only one Ig domain.
A series of Southern blot hybridization experiments using probes derived from different regions of the rat liver cell-cell adhesion molecule 105 (C-CAM) cDNA revealed the presence of a 9.6 kb EcoRI genomic fragment that seemed to encode a unique C-CAM isoform. An RNase protection study showed that this c-CAM transcript was expressed in placenta, spleen, lung and large intestine. In contrast, the other C-CAM isoforms, C-CAM1 and C-CAM2, are expressed in liver and small intestine. This result also suggests that the new isoform, which we named C-CAM4, was indeed encoded by a new C-CAM gene. A rat placenta cDNA library was then screened and the full-length cDNA coding for C-CAM4 was isolated. The deduced protein contained 142 amino acids and had a calculated molecular mass of 15 kDa. C-CAM4 was composed of a leader sequence and the first V-like Ig domain typical of C-CAM-family proteins. However, C-CAM4 lacked the C-like Ig domains, the transmembrane domain, and the cytoplasmic domain found in other C-CAM isoforms. Thus, C-CAM4 is different from the other known C-CAMs in that it is a secreted protein. We have previously shown that the first Ig domain of C-CAM1 is crucial for its adhesion function. The V-like Ig domain of C-CAM4 had 92% and 89% sequence identity with the corresponding regions of C-CAM1 and C-cam2 respectively. Together these results suggest that C-CAM4 may play a role in regulating the function of other C-CAM family proteins.
Earley
K
K
Department of Molecular Pathology, University of Texas M.D Anderson Cancer Center, Houston 77030, USA.
Luo
W
W
Qiu
Y
Y
Thompson
N L
NL
Chou
J
J
Hixson
D C
DC
Lin
S H
SH
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D001483:Base Sequence; D015815:Cell Adhesion Molecules / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D015698:Genomic Library; D008969:Molecular Sequence Data; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D015347:RNA Probes; D051381:Rats; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid
D015703:Antigens, CD; C069847:CD66 antigens; D015815:Cell Adhesion Molecules; D018076:DNA, Complementary; D015347:RNA Probes; D000251:Adenosine Triphosphatases