Characterization of EHD4, an EH domain-containing protein expressed in the extracellular matrix.

To identify proteins that promote assembly of type VI collagen tetramers or stabilize type VI collagen filaments, a two-hybrid screen of a human placenta library was used and a new extracellular protein discovered. The cDNA sequence of the new protein encodes 541 amino acid residues. This cDNA sequence is identical to EHD4, a recently described member of the EH domain family of proteins. Two mRNAs of 4.4 and 3.0 kilobases were present in human skin fibroblasts and most tissues tested but were most prevalent in the heart. The chromosomal localization of the gene for this new protein was determined to be at 15q14-q15. Three polyclonal peptide antibodies were made against synthetic EHD4 peptides. The affinity-purified antibodies were used in immunofluorescent staining of developing limbs and matrices produced by human skin fibroblasts and mouse NIH3T3 fibroblasts in culture. Embryonic rat limb cartilage was strongly stained throughout development, and cultured fibroblasts deposited an extracellular filamentous network containing EHD4. In non-denaturing extracts of fetal bovine cartilage and in human skin fibroblast culture media, two components of approximately 220 and 158 kDa were observed, which, after reduction, migrated as a 56-kDa component on SDS-polyacrylamide gel electrophoresis. EHD4 is the first extracellular matrix protein described that contains an EH domain.