HUMAN INTER-ALPHA-TRYPSIN INHIBITOR HEAVY-CHAIN H3 GENE - GENOMIC ORGANIZATION, PROMOTER ANALYSIS, AND GENE LINKAGE

To understand more about the human inter-alpha-trypsin inhibitor heavy chain H3 (ITIH3) expression and the relationship between this gene an d the family of other ITI heavy chain genes, an analysis of the struct ure of the ITIH3 gene and its promoter region was performed. This gene is a single copy gene, 14 kilobase pair in length and consists of 22 exons, ITIH3 shares highly conserved exon size and intron-exon borders with other ITI heavy chain genes. We determined that the human ITIH1, ITIH3, and ITIH4 genes are closely linked within a 45-kilobase pair. They are arranged in the order of H1-H3-H4, with the ITIH4 gene transc ribed in the opposite direction. A model for the evolution of the ITI heavy chain gene family is presented that involves multiple rounds of gene duplication plus inversion events. The minimum promoter region (- 135 to +75) is identified in HepG2 cells. The transient transfection s tudy in various cell lines indicates that the activity of the ITIH3 pr omoter is not liver-specific. DNase I footprinting, mobility shift ass ays, and cotransfection experiments reveal a functional CCAAT/enhancer -binding protein site (C/EBP, -1344 to -1305) which interacts with C/E BP alpha and C/EBP beta factors. The latter factors control the transc ription of the ITIH3 gene positively.