Purification of senescence marker protein-30 (SMP30) and its androgen-independent decrease with age in the rat liver.

Age-associated changes in the soluble proteins from rat liver were examined by a newly developed two-dimensional cellulose acetate membrane electrophoresis (2D-CAME). We detected and isolated a novel rat liver protein, the amounts of which decreased androgen-independently with aging. We designated this protein, whose molecular mass was 30 kDa and pI value was 4.9, as senescence marker protein-30 (SMP30). The expression of SMP30 was not modified by castration or treatment with testosterone propionate after castration. Age-associated decrease of SMP30 level was also recognized in aged female. We noted another protein with a pI value of 7.3 that decreased with aging. Its expression seemed to be androgen-dependent and it was markedly expressed only in young and adult male rat livers. We then purified SMP30 and prepared an anti-serum to SMP30. Immunohistochemical analysis showed that the localization of SMP30 was restricted to liver and kidney among numerous organs tested. Although the amount of SMP30 in the liver was relatively large and the tissue distribution was characteristic, no known protein corresponds to this protein.