J. Biol. Chem., Vol. 265, Issue 14, 7872-7879, May, 1990
cDNA and gene analyses imply a novel structure for a rat carcinoembryonic antigen-related protein
S Rebstock, K Lucas, JA Thompson and W Zimmermann
Institut fur Immunbiologie, Universitat Freiburg, Federal Republic of Germany.
The gene encoding the human tumor marker carcinoembryonic antigen (CEA)
belongs to a gene family which can be subdivided into the CEA and the
pregnancy-specific glycoprotein subgroups. The corresponding proteins are
members of the immunoglobulin superfamily, characterized through the
presence of one IgV-like domain and a varying number of IgC-like domains.
Since the function of the CEA family is not well understood, we decided to
establish an animal model in the rat to study its tissue- specific and
developmental stage-dependent expression. To this end, we have screened an
18-day rat placenta cDNA library with a recently isolated fragment of a rat
CEA-related gene. Two overlapping clones containing the complete coding
region for a putative 709 amino acid protein (rnCGM1; Mr = 78,310) have
been characterized. In contrast to all members of the human CEA family,
this rat CEA-related protein consists of five IgV-like domains and only one
IgC-like domain. This novel structure, which has been confirmed at the
genomic level might have important functional implications. Due to the
rapid evolutionary divergence of the rat and human CEA gene families it is
not possible to assign rnCGM1 to its human counterpart. However, the
predominant expression of the rnCGM1 gene in the placenta suggests that it
could be analogous to one of the human pregnancy-specific glycoprotein
genes.