CGM2, a Member of the Carcinoembryonic Antigen Gene Family is Down- Regulated in Colorectal Carcinomas

We have determined the precise chromosomal location, the exon
structure, and the expression pattern of CGM2, a member of the
carcinoembryonic antigen (CEA) gene family. CGM2 cDNA was amplified
by reverse transcription-polymerase chain reaction (RT/PCR) from
the colon adenocarcinoma cell line, LS174T. A defective exon is
missing from this cDNA clone, leading to a novel domain
organization for the human CEA family with two immunoglobulin-like
domains. The derived C-terminal domain predicts that the CGM2
protein is membrane-bound through a glycosyl phosphatidylinositol
anchor. RT/PCR analyses identified CGM2 transcripts in mucinous
ovarian and colonic adenocarcinomas as well as in adjacent colonic
tissue, but not in other tumors including leukocytes from six
chronic myeloid leukemia patients. Thus, unlike several other
family members, CGM2 is not expressed in granulocytes but reveals a
more CEA-like expression pattern. Northern blot analyses identified
a 2.5-kilobase CGM2 mRNA that is strongly down-regulated in colonic
adenocarcinomas compared with adjacent colonic mucosa, suggesting a
possible tumor suppressor function. In addition, a 3.2- kilobase
transcript was observed in a number of colon tumors that is not
detectable in normal colonic tissue. This mRNA species could
represent a tumor-specific CGM2 splice variant.