Human fibulin-1D: molecular cloning, expression and similarity with S1-5 protein, a new member of the fibulin gene family.
Fibulin-1 is an extracellular matrix (ECM) component of basement membranes and connective tissue elastic fibers, and a blood protein. Multiple forms of fibulin-1 that differ in their C-terminal regions are produced through the process of alternative splicing of their precursor RNA. Two transcripts of 2.4 and 2.7 kb are the predominant fibulin-1 mRNAs expressed in human tissues and cultured cells. While the 2.4 kb transcript had been shown to encode fibulin-1C, the 2.7 kb transcript did not correspond to any of the previously identified human fibulin-1 variants. Herein, we report on the isolation and sequencing of cDNA corresponding to the 2.7 kb fibulin-1 transcript which encodes a novel, alternatively spliced form of human fibulin-1 that we term the D form. The deduced amino acid sequence of the D form is identical in its first 566 residues to the three known fibulin-1 variants (fibulin-1A-C); however, it has a unique 137 amino acid-C-terminal segment encoded by the alternatively spliced portion of its transcript. RNA hybridization analysis showed that the fibulin-1D transcript is coordinately expressed with that of fibulin-1C both in tissues and in cultured cells. Using antibodies specific to the unique C-terminal segment of fibulin-1D and -1C, both proteins were found to be expressed in human placenta. Recombinant fibulin-1D generated in transfected mammalian cells displayed similar ligand-binding properties as placenta-derived fibulin-1 and recombinant fibulin-1C, and it was capable of incorporating into cultured cell ECM in the absence of other fibulin-1 forms. A comparative sequence analysis revealed that the unique C-terminal region of fibulin-1D is similar to the C-terminal regions of fibulin-1C and fibulin-2. Furthermore, the C-terminal regions of fibulin-1C, -1D and -2 are similar to the C-terminal region of a recently described protein termed S1-5. In addition to this C-terminal similarity, S1-5 also contains repeated EGF-like modules and a conserved N-terminal element, thereby leading to the conclusion that S1-5 is a third member of the fibulin gene family.
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Biochemistry Department, American Red Cross, Rockville, Maryland, USA.
Mattei
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Godyna
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Argraves
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002135:Calcium-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D003001:Cloning, Molecular; D005109:Extracellular Matrix / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics* / Q000502:physiology; D005260:Female; D005340:Fibrinogen / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D015870:Gene Expression / Q000235:genetics* / Q000502:physiology; D005796:Genes / Q000235:genetics* / Q000502:physiology; D006801:Humans; D007536:Isomerism; D008969:Molecular Sequence Data; D010920:Placenta / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000235:genetics / Q000502:physiology
D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D005353:Fibronectins; D012333:RNA, Messenger; C060820:fibulin; D005340:Fibrinogen