Cloning and functional analysis of a family of nuclear matrix transcription factors (NP/NMP4) that regulate type I collagen expression in osteoblasts.

Abstract

Collagen expression is coupled to cell structure in connective tissue. We propose that nuclear matrix architectural transcription factors link cell shape with collagen promoter geometry and activity. We previously indicated that nuclear matrix proteins (NP/NMP4) interact with the rat type I collagen alpha1(I) polypeptide chain (COL1A1) promoter at two poly(dT) sequences (sites A and B) and bend the DNA. Here, our objective was to determine whether NP/NMP4-COL1A1 binding influences promoter activity and to clone NP/NMP4. Promoter-reporter constructs containing 3.5 kilobases (kb) of COL1A1 5' flanking sequence were fused to a reporter gene. Mutation of site A or site B increased promoter activity in rat UMR-106 osteoblast-like cells. Several full-length complementary DNAs (cDNAs) were isolated from an expression library using site B as a probe. These clones expressed proteins with molecular weights and COLIA1 binding activity similar to NP/NMP4. Antibodies to these proteins disrupted native NP/NMP4-COL1A1 binding activity. Overexpression of specific clones in UMR-106 cells repressed COL1A1 promoter activity. The isolated cDNAs encode isoforms of Cys2His2 zinc finger proteins that contain an AT-hook, a motif found in architectural transcription factors. Some of these isoforms recently have been identified as Cas-interacting zinc finger proteins (CIZ) that localize to fibroblast focal adhesions and enhance metalloproteinase gene expression. We observed NP/NMP4/CIZ expression in osteocytes, osteoblasts, and chondrocytes in rat bone. We conclude that NP/NMP4/CIZ is a novel family of nuclear matrix transcription factors that may be part of a general mechanical pathway that couples cell structure and function during extracellular matrix remodeling.