ISOFORMS OF APOLIPOPROTEIN-A-I IN THE SERUM OF BROWN BULLHEADS (AMEIURUS-NEBULOSUS) WITH LIVER-CANCER

Brown bullheads (Ameiurus nebulosus) express two different isoforms of apolipoprotein A-I in the serum, a predominant form characterized by a pI of 6.9 and a more acidic isoform with a pI of 6.65. The two proteins were identified by N-terminal amino acid sequencing, with 50 residues for the pI 6.9 isoform and 20 residues for the pI 6.65 isoform. Sequences for the two proteins were identical for the first 20 amino acids; however, differences in their primary sequences were deduced by analysis of peptide maps obtained through proteolytic digestion. The ratio of the isoforms changes from 75% pI 6.9/25% pI 6.65 (no tumors) to equal amounts of both isoforms in bullheads with hepato- or cholangio-cellular carcinomas. This is the first report of these serum isoforms in feral fish showing that the expression of these proteins is directly related to both cholangio- and hepato-cellular carcinomas. The potential use of these proteins as tumor biomarkers is discussed.