Complete cDNA cloning, genomic organization, chromosomal assignment, functional characterization of the promoter, and expression of the murine bamacan gene

Abstract

Bamacan is a chondroitin sulfate proteoglycan that abounds in basement membranes. To gain insights into the bamacan gene regulation and transcriptional control, we examined the genomic organization and identified the promoter region of the mouse bamacan gene. Secondary structure analysis of the protein reveals a sequential organization of three globular regions interconnected by two α-helix coiled-coils. The N- and the C-terminal ends carry a P-loop and a DA box motif that can act cooperatively to bind ATP. These features as well as the high sequence homology with members of the SMC (structural maintenance of chromosome) protein family led us to conclude that bamacan is a member of this protein family. The gene comprises 31 exons and is driven by a promoter that is highly enriched in GC sequences and lacks TATA and CAAT boxes. The promoter is highly functional in transient cell transfection assays, and step-wise 5' deletions identify a strong enhancer element between -659 and -481 base pairs that includes Jun/Fos proto- oncogene-binding elements. Using backcrossing experiments we mapped the Bam gene to distal chromosome 19, a locus syntenic to human chromosome 10q25. Bamacan is differentially expressed in mouse tissues with the highest levels in testes and brain. Notably, bamacan mRNA levels are low in normal cells and markedly reduced during quiescence but are highly increased when cells resume growth upon serum stimulation. In contrast, in all transformed cells tested, bamacan is constitutively overexpressed, and its levels do not change with cell cycle progression. These results suggest that bamacan is involved in the control of cell growth and transformation.