Abstract
Basal cell adhesion molecule (BCAM), known to be a splicing variant of Lutheran glycoprotein (LU), is an immunoglobulin superfamily membrane protein that acts as a laminin α5 receptor. The high affinity of BCAM/LU for laminin α5 is thought to contribute to the pathogenesis of sickle red blood cells and to various developmental processes. However, the function of BCAM in carcinogenesis is poorly understood. Based on microarray expression analysis, we found that BCAM was one of the target genes of the oncogenic 14-3-3β-FBI1/Akirin2 complex, which acts as a transcriptional repressor and suppresses MAPK phosphatase-1 gene expression. To elucidate the detailed function of BCAM in malignant tumors, we established BCAM-expressing hepatoma K2 cells. These cells lost the malignant characteristics of parental cells, such as anchorage-independent growth, migration, invasion, and tumorigenicity. Moreover, luciferase reporter assays and chromatin immunoprecipitation analysis revealed that the 14-3-3β-FBI1/Akirin2 complex bound to the BCAM promoter and repressed transcription. Thus, these data indicate that BCAM is a suppressive oncoprotein, and that FBI1/Akirin2 is involved in tumorigenicity and metastasis of hepatoma through the downregulation of suppressive oncogenes.
Highlights
Basal cell adhesion molecule (BCAM), known to be a splicing variant of Lutheran glycoprotein (LU), is an immunoglobulin superfamily membrane protein that acts as a laminin a5 receptor
We chose BCAM as one that is possibly suppressed by the 14-3-3b-fourteen-three-three beta interactant 1 (FBI1)/Akirin2 complex for further functional analysis in malignant progression of K2 cells
In order to analyze the function of BCAM protein in tumor cell growth, we introduced a BCAM cDNA expression vector into K2 cells
Summary
Basal cell adhesion molecule (BCAM), known to be a splicing variant of Lutheran glycoprotein (LU), is an immunoglobulin superfamily membrane protein that acts as a laminin a5 receptor. Based on microarray expression analysis, we found that BCAM was one of the target genes of the oncogenic 14-3-3b-FBI1/Akirin complex, which acts as a transcriptional repressor and suppresses MAPK phosphatase-1 gene expression. Luciferase reporter assays and chromatin immunoprecipitation analysis revealed that the 14-3-3b-FBI1/Akirin complex bound to the BCAM promoter and repressed transcription. These data indicate that BCAM is a suppressive oncoprotein, and that FBI1/Akirin is involved in tumorigenicity and metastasis of hepatoma through the downregulation of suppressive oncogenes. Our results suggest that BCAM functions as a tumor suppressor in rat hepatocellular carcinoma K2 cells
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