CLONING AND CHARACTERIZATION OF HCKROX, A TRANSCRIPTIONAL REGULATOR OF EXTRACELLULAR-MATRIX GENE-EXPRESSION

cKrox is a novel zinc finger-containing transcription factor that bind s to the alpha 1(I) and alpha 2(I) collagen gene promoters. The gene c oding for cKrox is a new member of a family of early growth response g enes, that play important roles in development. In the mouse, cKrox is expressed, beginning at 9.5 days of gestation and at 10.5 days in reg ions destined to become skin. In adult animals, expression is predomin antly in skin, one of the two major organs where type I collagen is ex pressed. We have isolated cDNA clones for human cKrox. Theoretical tra nslation of the nucleic acid sequence reveals 90% conservation of amin o acids between the mouse and human proteins; however, the human gene product contains a 117-amino-acid N-terminal extension. The amino acid sequences of the zinc-finger DNA binding domains of mouse and human c Krox are identical. RT-PCR analysis of human fibroblasts indicates con stitutive low-level expression of cKrox which can be transiently eleva ted by treatment with retinoic acid. Transient transfection assays ind icate that hcKrox represses transcription of the alpha 1(I) procollage n promoter, and electrophoretic mobility shift assays demonstrate that hcKrox binds to both the human and murine promoter DNA. Deletion deri vatives of hcKrox demonstrate transcription-activating potential that is promoter-dependent. NIH3T3 cells permanently expressing hcKrox demo nstrate a threefold and 10-fold decrease in alpha 1(I) procollagen and fibronectin mRNA levels, respectively, compared to control cells. Con sistent with this finding, a fibronectin promoter reporter construct i s repressed more than 80% by hcKrox. These data suggest that hcKrox re presses collagen transcription directly, and it may function as a repr essor of fibronectin and possibly other matrix genes. (C) 1997 Elsevie r Science B.V.