NP/NMP4 transcription factors have distinct osteoblast nuclear matrix subdomains

The mechanisms underlying the coupling of type I collagen and matrix metall oproteinase (MMP) expression to cell structure and adhesion are poorly unde rstood. We propose that nuclear matrix architectural transcription factors link cell structure and transcription via their association with nuclear ma trix subdomains and by their capacity for altering promoter geometry. NP/NM P4 are nuclear matrix proteins that contain from five to eight Cys(2)His(2) zinc fingers. Some NP/NMP4 isoforms bind to the rat type I collagen alpha1 (I) polypeptide chain promoter in the manner of architectural transcription factors and alter basal transcription in osteoblast-like cells (Thunyakitp isal ct al. in review). Certain isoforms of NP/NMP4 are identical to CIZ, G as-interacting zinc finger protein, a nucleocytoplasmic shuttling protein t hat associates with focal adhesions and regulates MMP expression [Nakamoto ct al. (2000): Mol Cell Biol 20:1649-1658]. To better understand the role o f subnuclear architecture in collagen and MMP expression, we mapped the ost eoblast nuclear distribution of NP/NMP4 proteins and identified the functio nal motifs necessary for nuclear localization and nuclear matrix targeting. Immunofluorescence microscopy was used to determine the cellular and subnu clear distribution of native NP/NMP4 proteins and green fluorescent protein (GFP)-NP/NMP4 fusion proteins in osteoblast-like cells. All GFP-NP/NMP4 fu sion proteins localized to the nucleus, but accumulated in distinct nuclear matrix subdomains. The zinc finger domain was necessary and sufficient For nuclear import and matrix targeting. We conclude that the arrangement of t he NP/NMP4 zinc fingers largely determines the subnuclear location of these isoforms. (C) 2000 Wiley-Liss, Inc.