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

Collagen expression is coupled to cell structure in connective tissue. We p ropose that nuclear matrix architectural transcription factors link cell sh ape with collagen promoter geometry and activity. We previously indicated t hat nuclear matrix proteins (NP/NMP4) interact with the rat type I collagen alpha1(I) polypeptide chain (COL1A1) promoter at two poly(dT) sequences (s ites A and B) and bend the DNA, Here, our objective was to determine whethe r NP/NMP4-COL1A1 binding influences promoter activity and to clone NP/NMP4. Promoter-reporter constructs containing 3.5 kilobases (kb) of COL1A1 5' fl anking 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 lib rary using site B as a probe. These clones expressed proteins with molecula r weights and COL1A1 binding activity similar to NP/NMP4. Antibodies to the se proteins disrupted native NP/NMP4-COL1A1 binding activity, Overexpressio n of specific clones in UMR-106 cells repressed COL1A1 promoter activity. T he isolated cDNAs encode isoforms of Cys(2)His(2) zinc finger proteins that contain an AT-hook, a motif found in architectural transcription factors. Some of these isoforms recently have been identified as Gas-interacting zin c finger proteins (CIZ) that localize to fibroblast focal adhesions and enh ance 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.