MAMMALIAN PROTEIN HOMOLOGOUS TO VAT-1 OF TORPEDO-CALIFORNICA - ISOLATION FROM EHRLICH ASCITES TUMOR-CELLS, BIOCHEMICAL-CHARACTERIZATION, AND ORGANIZATION OF ITS GENE

Recently, interest has focused on the human gene encoding the putative protein homologous to VAT-1, the major protein of the synaptic vesicl es of the electric organ of the Pacific electric ray Torpedo californi ca, after it has been localized on chromosome locus 17q21 in a region encompassing the breast cancer gene BRCA1. Chromosomal instability in this region is implicated in inherited predisposition for breast and o varian cancer. Here we describe isolation and biochemical characteriza tion of a mammalian 48 kDa protein homologous to the VAT-1 protein of Torpedo californica. This VAT-1 homolog was isolated from a murine bre ast cancer cell line (Ehrlich ascites tumor) and identified by sequenc ing of cleavage peptides. The isolated VAT-1 homolog protein displays an ATPase activity and exists in two isoforms with isoelectric points of 5.7 and 5.8. cDNA was prepared from Ehrlich ascites tumor cells, an d the murine VAT-1 homolog sequence was amplified by polymerase chain reaction and partially sequenced. The known part of the murine and the human translated sequences share 97% identity. By Northern blots, the size of the VAT-1 homolog mRNA in both murine and human (T47D) breast cancer cells was determined to be 2.8 kb. Based on the presented data , a modified gene structure of the human VAT-1 homolog with an extende d exon 1 is proposed. VAT-1 and the mammalian VAT-1 homolog form a sub group within the protein superfamily of medium-chain dehydrogenases/re ductases. (C) 1998 Wiley-Liss, Inc.