Cloning and characterization of cDNA for inter-alpha-trypsin inhibitor family heavy chain-related protein (IHRP), a novel human plasma glycoprotein.

The cDNA encoding inter-alpha-trypsin inhibitor family heavy chain-related protein (IHRP) was cloned from human liver cDNA libraries. Oligonucleotide primers of human liver cDNA for PCR were constructed from internal amino acid sequences obtained with proteolytic fragments of IHRP. The amplified cDNA served as a hybridization probe for the screening of human liver cDNA libraries. The cDNA of 2,977 bp contained an entire reading frame coding 930 amino acids. The N-terminal 28 residues corresponded to a signal peptide for secretion. The N-terminal 600 residues of the mature form exhibited considerable homology to those of ITI heavy chains, while the C-terminal 300 residues showed no homology with the heavy chains and low homology with ATP-dependent proteases. IHRP was readily cleaved into 85- and 35-kDa fragments when plasma was incubated at 37 degrees C. The cleaved site, Arg-Arg-Leu, was within a proline-rich region. Northern blot analysis of poly(A) RNAs from various human tissues only showed hybridization to liver RNA.