Isolation and characterization of genomic and cDNA clones encoding mouse senescence marker protein-30 (SMP30)

We isolated and characterized genomic and cDNA clones encoding mouse senescence marker protein-30 (SMP30), the protein amounts of which are known to decrease with aging in the livers of rats. This decrease in the expression of SMP30 is independent of androgen. SMP30 is a calcium binding protein also called regucalcin. The expression of SMP30 in aged mouse liver and 5' flanking sequence of the genome were also characterized. The cDNA contained an open reading frame encoding 299 amino acids with a calculated molecular weight of 33-404. The amino acid sequence of mouse SMP30 showed 94% similarity to rat SMP30 and 89% to human SMP30. Northern blot analysis specifically detected mouse SMP30 transcript in the liver and also confirmed its significant decrease with aging. Analysis of the murine genomic clone revealed that SMP30 was organized by seven exons and six introns, spanning approx. 17.5 kb. Primer extension analysis revealed that two major transcription initiation sites were localized at 101 bp and 102 bp upstream from ATG translation initiation codon. The nucleotide (nt) sequence of 5' flanking region showed a TATA-like sequence, a CAAT box, and SP-1 sites at nt -29, -72 and -169 in the promoter region, respectively. Interestingly, we found two classes of C/EBP sites which are highly and constantly expressed in the liver, in addition to AP-2, AP-1, GATA-1, AP-1/GRE and GAGA sites. These results provide important clues for understanding the regulatory mechanism of SMP30 gene expression and its relationship to aging.