MOLECULAR-CLONING AND CHARACTERIZATION OF FICOLIN, A MULTIMERIC PROTEIN WITH FIBRINOGEN-LIKE AND COLLAGEN-LIKE DOMAINS

We have previously identified and purified transforming growth factor- beta1 (TGF-beta1)-binding proteins from porcine uterus membranes (Ichi jo, H., Ronnstrand, L., Miyagawa, K., Ohashi, H., Heldin, C.-H., and M iyazono, K. (1991) J. Biol. Chem. 266, 2245922464). One of these TGF-b eta1-binding proteins, with a molecular weight of 40,000, was purified to homogeneity and subjected to amino acid sequence analysis. The ami no acid sequences obtained were used to isolate two closely related cD NA clones from a porcine uterus cDNA library. The deduced amino acid s equences revealed that both cDNAs encoded proteins that were mainly co mposed of fibrinogen-like and collagen-like domains. Therefore, they w ere denoted ficolin-alpha and ficolin-beta. Expression of ficolin-alph a and -beta cDNA in mammalian cells revealed that ficolin forms dimers , trimers, and several higher order of oligomers, whose molecular weig hts fit well with those of the purified TGF-beta1-binding proteins fro m porcine uterus. Moreover, immunoblotting analysis using a peptide an tiserum against ficolin indicated that the TGF-beta1-binding proteins identified in porcine uterus are ficolin-alpha, -beta, and their oligo mers or closely related molecules. However, recombinant ficolin-alpha and -beta did not bind TGF-beta1, despite the similarities in molecula r weights and immunoreactivity with the material from the natural sour ce. It is possible that a specific posttranslational modification of f icolin or interaction with another component is needed for TGF-beta1 b inding. Analysis by Northern blotting revealed that the expression of ficolin-alpha mRNA is relatively restricted and most abundant in place nta and lung. On the other hand, ficolin-beta was mainly expressed in skeletal muscle. The in vivo functions of ficolin will be discussed.