Oligomerization and Regulated Proteolytic Processing of Angiopoietin-like Protein 4

Abstract

Angiopoietin-like protein 4 (Angptl4) is a recently identified circulating protein expressed primarily in adipose tissue and liver. Also known as peroxisome proliferator-activated receptor (PPAR)-γ angiopoietin-related, fasting induced adipose factor, and hepatic fibrinogen/angiopoietin-related protein, recombinant Angptl4 causes increase of plasma very low density lipoprotein levels by inhibition of lipoprotein lipase activity. Similar to angiopoietins and other angiopoietin-like proteins, Angptl4 contains an amino-terminal coiled-coil domain and a carboxyl-terminal fibrinogen-like domain. We report here that Angptl4 is evolutionarily conserved among several mammalian species and that full-length Angptl4 protein is an oligomer containing intermolecular disulfide bonds. Oligomerized Angptl4 undergoes proteolytic processing to release its carboxyl fibrinogen-like domain, which circulates as a monomer. Angptl4's N-terminal coiled-coil domain mediates its oligomerization, which by itself is sufficient to form higher order oligomeric structure. Adenovirus-mediated overexpression of Angptl4 in 293 cells shows that conversion of full-length, oligomerized Angptl4 is mediated by a cell-associated protease activity induced by serum. These findings demonstrate a novel property of angiopoietin-like proteins and suggest that oligomerization and proteolytic processing of Angptl4 may regulate its biological activities in vivo. Angiopoietin-like protein 4 (Angptl4) is a recently identified circulating protein expressed primarily in adipose tissue and liver. Also known as peroxisome proliferator-activated receptor (PPAR)-γ angiopoietin-related, fasting induced adipose factor, and hepatic fibrinogen/angiopoietin-related protein, recombinant Angptl4 causes increase of plasma very low density lipoprotein levels by inhibition of lipoprotein lipase activity. Similar to angiopoietins and other angiopoietin-like proteins, Angptl4 contains an amino-terminal coiled-coil domain and a carboxyl-terminal fibrinogen-like domain. We report here that Angptl4 is evolutionarily conserved among several mammalian species and that full-length Angptl4 protein is an oligomer containing intermolecular disulfide bonds. Oligomerized Angptl4 undergoes proteolytic processing to release its carboxyl fibrinogen-like domain, which circulates as a monomer. Angptl4's N-terminal coiled-coil domain mediates its oligomerization, which by itself is sufficient to form higher order oligomeric structure. Adenovirus-mediated overexpression of Angptl4 in 293 cells shows that conversion of full-length, oligomerized Angptl4 is mediated by a cell-associated protease activity induced by serum. These findings demonstrate a novel property of angiopoietin-like proteins and suggest that oligomerization and proteolytic processing of Angptl4 may regulate its biological activities in vivo. Until recently, adipose tissue has been thought of as largely a passive energy storage depot for periods of nutritional excess. It releases stored energy in the form of free fatty acids and glycerol upon hydrolysis of esterified lipids by lipases that are under hormonal control (1.Holm C. Osterlund T. Laurell H. Contreras J.A. Annu. Rev. Nutr. 2000; 20: 365-393Crossref PubMed Scopus (349) Google Scholar). The cloning of leptin from adipose tissue and the subsequent discoveries that adipose tissue also releases several other protein factors have changed our view on the function of this tissue. It is now recognized that adipose tissue is also an active endocrine organ, and the expression patterns of these secreted factors are under both nutritional and hormonal controls (2.Ahima R.S. Flier J.S. Trends Endocrinol. Metab. 2000; 11: 327-332Abstract Full Text Full Text PDF PubMed Scopus (1223) Google Scholar, 3.Fruhbeck G. Gomez-Ambrosi J. Muruzabal F.J. Burrell M.A. Am. J. Physiol. 2001; 280: E827-E847Crossref PubMed Google Scholar, 4.Kim S. Moustaid-Moussa N. J. Nutr. 2000; 130: 3110-3115Crossref PubMed Google Scholar). One of the recently identified secreted factors from adipose tissue is angiopoietin-like protein 4 (Angptl4) 1The abbreviations used are: Angptl, angiopoietin-like protein; PPAR, peroxisome proliferator-activated receptor; FBS, fetal bovine serum; HRP, horseradish peroxidase; PBS, phosphate-buffered saline; GFP, green fluorescent protein; PNGase, peptide N-glycosidase F., also named PPARγ angiopoietin related, fasting induced adipose factor, or hepatic fibrinogen/angiopoietin-related protein. It is a secreted protein selectively expressed in adipose tissue, liver, and placenta (5.Kim I. Kim H.G. Kim H. Kim H.H. Park S.K. Uhm C.S. Lee Z.H. Koh G.Y. Biochem. J. 2000; 346: 603-610Crossref PubMed Scopus (235) Google Scholar, 6.Kersten S. Mandard S. Tan N.S. Escher P. Metzger D. Chambon P. Gonzalez F.J. Desvergne B. Wahli W. J. Biol. Chem. 2000; 275: 28488-28493Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar, 7.Yoon J.C. Chickering T.W. Rosen E.D. Dussault B. Qin Y. Soukas A. Friedman J.M. Holmes W.E. Spiegelman B.M. Mol. Cell Biol. 2000; 20: 5343-5349Crossref PubMed Scopus (343) Google Scholar). Mouse Angptl4 is composed of 410 amino acids that include an N-terminal signal sequence, a coiled-coil domain, and a fibrinogen-like motif at the carboxyl terminus. Such domain organization is preserved in both angiopoietins and angiopoietin-like proteins. Transcriptional regulation of Angptl4 is rather complex. Several transcription factors have been identified as having a role in Angptl4 transcription, including two members of the peroxisome proliferator-activated receptor family of transcription factors, PPARα and PPARγ (6.Kersten S. Mandard S. Tan N.S. Escher P. Metzger D. Chambon P. Gonzalez F.J. Desvergne B. Wahli W. J. Biol. Chem. 2000; 275: 28488-28493Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar, 7.Yoon J.C. Chickering T.W. Rosen E.D. Dussault B. Qin Y. Soukas A. Friedman J.M. Holmes W.E. Spiegelman B.M. Mol. Cell Biol. 2000; 20: 5343-5349Crossref PubMed Scopus (343) Google Scholar), as well as hypoxia-inducible factor 1α (8.Belanger A.J. Lu H. Date T. Liu L.X. Vincent K.A. Akita G.Y. Cheng S.H. Gregory R.J. Jiang C. J. Mol. Cell Cardiol. 2002; 34: 765-774Abstract Full Text PDF PubMed Scopus (118) Google Scholar). As a transcriptional target of PPARγ, Angptl4 has been hypothesized to play a role in the modulation of adipogenesis, insulin sensitivity, or energy metabolism (7.Yoon J.C. Chickering T.W. Rosen E.D. Dussault B. Qin Y. Soukas A. Friedman J.M. Holmes W.E. Spiegelman B.M. Mol. Cell Biol. 2000; 20: 5343-5349Crossref PubMed Scopus (343) Google Scholar). Mice heterozygous for PPARγ knockout have reduced Angptl4 mRNA expression in adipose tissue, where PPARγ is normally abundantly expressed. Mice with PPARα deficiency also exhibit undetectable Angptl4 mRNA levels in liver, where PPARα is normally abundantly expressed. Conversely, when mice are treated with a potent agonist of PPARα, WY14643, Angptl4 transcription is increased (6.Kersten S. Mandard S. Tan N.S. Escher P. Metzger D. Chambon P. Gonzalez F.J. Desvergne B. Wahli W. J. Biol. Chem. 2000; 275: 28488-28493Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar). In vitro, treatment of NIH 3T3 cells stably expressing PPARγ with its agonist, pioglitazone, caused an increase of at least 10-fold in Angptl4 mRNA levels in the absence of protein synthesis (7.Yoon J.C. Chickering T.W. Rosen E.D. Dussault B. Qin Y. Soukas A. Friedman J.M. Holmes W.E. Spiegelman B.M. Mol. Cell Biol. 2000; 20: 5343-5349Crossref PubMed Scopus (343) Google Scholar). PPARα and hypoxia-inducible factor 1α also cause the synergistic activation of Angptl4 transcription in cardiomyocytes (8.Belanger A.J. Lu H. Date T. Liu L.X. Vincent K.A. Akita G.Y. Cheng S.H. Gregory R.J. Jiang C. J. Mol. Cell Cardiol. 2002; 34: 765-774Abstract Full Text PDF PubMed Scopus (118) Google Scholar). In a recent report, Angptl4 was found to be one of nine genes silenced by methylation in human gastric cancers (9.Kaneda A. Kaminishi M. Yanagihara K. Sugimura T. Ushijima T. Cancer Res. 2002; 62: 6645-6650PubMed Google Scholar). In aggregate, these data suggest that Angptl4 may play a variety of roles in vivo, ranging from adipogenesis and angiogenesis to carcinogenesis (10.Le Jan S. Amy C. Cazes A. Monnot C. Lamande N. Favier J. Philippe J. Sibony M. Gasc J.M. Corvol P. Germain S. Am. J. Pathol. 2003; 162: 1521-1528Abstract Full Text Full Text PDF PubMed Scopus (274) Google Scholar). Because both ischemic tissue and solid tumor tissue are in a hypoxic state, Angptl4 could be playing a shared role of modulating angiogenesis under both conditions. The expression of angpt4 is also under nutritional and hormonal control. Under fasting conditions, transcription of Angptl4 in both liver and adipose tissue is induced independently of the presence of PPARα (6.Kersten S. Mandard S. Tan N.S. Escher P. Metzger D. Chambon P. Gonzalez F.J. Desvergne B. Wahli W. J. Biol. Chem. 2000; 275: 28488-28493Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar). Circulating levels of Angptl4 are also increased in genetically obese mice (ob/ob or db/db) that lack leptin signaling (7.Yoon J.C. Chickering T.W. Rosen E.D. Dussault B. Qin Y. Soukas A. Friedman J.M. Holmes W.E. Spiegelman B.M. Mol. Cell Biol. 2000; 20: 5343-5349Crossref PubMed Scopus (343) Google Scholar). However, in rodents fed a high-fat diet, circulating levels of Angptl4 are reduced, providing further evidence that Angptl4 may play a role in response to the availability of nutrients (6.Kersten S. Mandard S. Tan N.S. Escher P. Metzger D. Chambon P. Gonzalez F.J. Desvergne B. Wahli W. J. Biol. Chem. 2000; 275: 28488-28493Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar). The function of Angptl4 is not completely understood. Recently, it was reported that Angptl4 is a potent hyperlipidemia-inducing factor and an inhibitor of lipoprotein lipase (11.Yoshida K. Shimizugawa T. Ono M. Furukawa H. J. Lipid Res. 2002; 43: 1770-1772Abstract Full Text Full Text PDF PubMed Scopus (313) Google Scholar). To obtain better insight on the structural basis of Angptl4 function, we have now determined that full-length Angptl4 is an oligomer, similar to angiopoietin 1 (12.Davis S. Papadopoulos N. Aldrich T.H. Maisonpierre P.C. Huang T. Kovac L. Xu A. Leidich R. Radziejewska E. Rafique A. Goldberg J. Jain V. Bailey K. Karow M. Fandl J. Samuelsson S.J. Ioffe E. Rudge J.S. Daly T.J. Radziejewski C. Yancopoulos G.D. Nat. Struct. Biol. 2003; 10: 38-44Crossref PubMed Scopus (179) Google Scholar). In contrast to angiopoietin 1, however, Angptl4 undergoes regulated proteolysis to release its carboxyl-terminal fibrinogen-like domain both in vitro and in vivo, the first example of proteolysis-mediated processing of a member of this family of proteins. Reagents—All PCR primers were synthesized by Sigma-Genosys or IDT Technologies. All restriction endonucleases as well as PNGase F were from New England Biolabs, Inc. (Beverly, MA). Taq DNA polymerase and protease inhibitor mixture tablets were from Roche (Indianapolis, IN). ECL-Western blotting reagents and Superdex 200 column (10/30) were from Amersham Biosciences. TALON Metal Affinity resin was from BD Biosciences Clontech. Polyclonal antibodies against Angptl4 were generated in rabbits by Covance Research Products, Inc. (Denver, PA). Fetal bovine serum (FBS) was from Gemini Bio-Products (Woodland, CA). SuperScript II RNase H– reverse transcriptase was from Invitrogen. Cloning of Rat Angptl4 and Construction of Adenoviral Expression Vectors—To amplify cDNA encoding full-length Angptl4 from rat adipose tissue, first-strand cDNA was generated by reverse transcription of total RNA SuperScript II RNase H– reverse full-length Angptl4 and the amino-terminal coiled-coil domain of Angptl4 were the It contains an for the mammalian expression and has the the of the full-length and the amino-terminal coiled-coil domain of Angptl4 were by primers and containing a for the The are: containing from and were by and To encoding the N-terminal coiled-coil domain or full-length rat the was with a S. J. B. S. A. PubMed Scopus Google Scholar). to of Angptl4 proteins, in the were with the carboxyl-terminal as a and to the of The was with the and with cells to recombinant were by an of DNA of from was to the presence of this DNA was cells and used for low 293 cells as L. C. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). of Angptl4 with or serum from 293 cells were and a and were to and by with of 200 and of TALON Metal Affinity resin was with of and of was to the and resin were at 4 was with of and proteins were with of containing containing Angptl4 protein were and further by on a Superdex 200 column at of were by by blotting to the presence of Angptl4 protein. of Polyclonal against Angptl4 Angptl4 was from mammalian cells or and for of antibodies expression 1 was from carboxyl of Angptl4 from containing of 293 cells as Angptl4 protein was on and the Angptl4 was with was and New rabbits for was generated a expression cDNA encoding the carboxyl fibrinogen-like domain of Angptl4 was and the of protein was expressed in and to the The protein was also used for was generated a protein of Angptl4 as Angptl4 cDNA the signal was to the carboxyl of and expressed in protein was on and with was and New rabbits for In of the antibodies was determined by of by with the signal recognized by the and by with serum. All are recombinant Angptl4 expressed or Expression and of Angptl4 in 293 cells were in was with with or encoding Angptl4 were at a of of of was determined on the by of and of of of from to was and to obtain 200 of and was to the and was with for protease were used of Angptl4 protein from the of 293 was in in for and where are were with with or and to were to was with in and Angptl4 protein was with a or antibodies as the ECL-Western blotting from Amersham Biosciences. was to for domain of Angptl4 is sufficient to form oligomeric similar to full-length encoding full-length or N-terminal coiled-coil domain of Angptl4 are at the carboxyl with a and to of recombinant protein. signal under the the of signal and the amino of blotting of the of full-length or coiled-coil domain of Angptl4 in a The of and are on the of Angptl4 are composed of of and as of full-length Angptl4 or its coiled-coil domain under or in are of 293 cells with full-length Angptl4 its coiled-coil domain or a control encoding GFP, by a Angptl4 protein was by the are on the were for with similar of Angptl4 Superdex 200 column (10/30) was with containing at 4 at a of The column was first by the of protein 200 of of Angptl4 was to the Because of the expression containing recombinant was first column of were and was by blotting or for To recombinant Angptl4 by containing from was first treated with containing for to in The was with for and were as for Mice to Angptl4 in encoding Angptl4 or green fluorescent protein were the at a of 1 as L. C. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, H. Huang L. T. C. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). were from the to the levels of Angptl4 protein by blotting Mice were and for tissue and was by the and at the of at of Angptl4 cells were in were with and was with of serum; encoding full-length Angptl4 were to cells at a of of was to cells to a of was to which was used as control. was at from to of and used for blotting to recombinant protease were to at of Angptl4 To proteolytic activity is and causes release of proteolytic was from 293 cells in with or by the control of Angptl4 protein was with at for and used for blotting with with were also in in the absence or presence of protease inhibitor mixture to processing of recombinant Angptl4 be protein 1 was in and at for One of PNGase F was and at for in with treatment of the with PNGase Angptl4 protein was by and Angptl4 and and human Angptl4 and amino (7.Yoon J.C. Chickering T.W. Rosen E.D. Dussault B. Qin Y. Soukas A. Friedman J.M. Holmes W.E. Spiegelman B.M. Mol. Cell Biol. 2000; 20: 5343-5349Crossref PubMed Scopus (343) Google Scholar). However, Angptl4 contains 410 amino that of contains amino To rat Angptl4 with and human we reverse transcription PCR on the first-strand cDNA from total RNA of rat adipose tissue. The full-length of rat Angptl4 was similar to human rat Angptl4 also a protein of amino However, it with the human protein. the other rat Angptl4 has a with amino with the conserved domain and fibrinogen-like domain and rat proteins. In in this rat Angptl4 cDNA was The of rat Angptl4 has been to under The of the amino of and human Angptl4 is in Angptl4 a 1, the member of angiopoietin and angiopoietin-like protein family of secreted proteins, of for receptor and (12.Davis S. Papadopoulos N. Aldrich T.H. Maisonpierre P.C. Huang T. Kovac L. Xu A. Leidich R. Radziejewska E. Rafique A. Goldberg J. Jain V. Bailey K. Karow M. Fandl J. Samuelsson S.J. Ioffe E. Rudge J.S. Daly T.J. Radziejewski C. Yancopoulos G.D. Nat. Struct. Biol. 2003; 10: 38-44Crossref PubMed Scopus (179) Google Scholar). To Angptl4 also higher order we rat Angptl4 in 293 cells of encoding full-length Angptl4 secreted recombinant Angptl4 was by were recognized by the The of an of and a of that the full-length Angptl4 protein, the is the proteolytic of to its carboxyl fibrinogen-like domain. The amino of the are not known the of both are when to One for the of the is the of proteolysis the is by the carboxyl-terminal antibodies fibrinogen-like domain or of The containing recombinant Angptl4 was a Superdex 200 and were and by blotting to the of Angptl4 protein. shows that Angptl4 first in an the of the which proteins of and It to a to a that to a protein of of in a column that similar to (12.Davis S. Papadopoulos N. Aldrich T.H. Maisonpierre P.C. Huang T. Kovac L. Xu A. Leidich R. Radziejewska E. Rafique A. Goldberg J. Jain V. Bailey K. Karow M. Fandl J. Samuelsson S.J. Ioffe E. Rudge J.S. Daly T.J. Radziejewski C. Yancopoulos G.D. Nat. Struct. Biol. 2003; 10: 38-44Crossref PubMed Scopus (179) Google Scholar), also We also density with similar to by not the of recombinant Angptl4 from total a proteolytic of full-length as an from the Superdex 200 is recognized by both a which the to the carboxyl of as well as a generated in the carboxyl fibrinogen-like domain of Angptl4 as not These demonstrate that the carboxyl fibrinogen-like domain is from full-length the carboxyl fibrinogen-like domain of Angptl4 the to form higher order structure. of protein disulfide protein as S. M. G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). We the oligomerization of full-length Angptl4 also disulfide Angptl4 shows that when full-length Angptl4 was treated with containing or the presence of caused Angptl4 protein to at a of a in the absence of that at the of a and higher also Because the of proteins in a are to it is to the of Angptl4 that in disulfide The from this are with the of full-length Angptl4 protein of Angptl4 to of the carboxyl fibrinogen-like domain of Angptl4 in that this domain is to form an To the N-terminal coiled-coil domain, in the absence of fibrinogen-like domain, is sufficient to Angptl4 oligomerization, we generated expressing the N-terminal coiled-coil domain the full-length and the domain of Angptl4 were with and at the carboxyl to of recombinant proteins. of 293 cells with encoding full-length Angptl4 or N-terminal coiled-coil domain of Angptl4 was on a Superdex 200 column and with the both proteins at similar as very These demonstrate that the N-terminal coiled-coil domain is sufficient to form oligomeric is also by the that under conditions, both full-length and N-terminal domain of Angptl4 as species of Angptl4 to processing of full-length, oligomerized Angptl4 is was used to 293 cells and cells were in the presence or absence of serum to the presence of serum is for Angptl4 shows that when 293 cells were with encoding Angptl4 or and in Angptl4 is secreted as a full-length protein of In the presence of Angptl4 protein in the as a full-length protein as that secreted or as a of or of cells with the full-length and the carboxyl fibrinogen-like domain of Angptl4 were by the which the carboxyl of Angptl4 and antibodies against Angptl4 not Angptl4 was in total when cells were in or that of full-length not the of Angptl4 to plasma The amino at the of the are not known that the of both are not We full-length Angptl4 expressed in also similar proteolytic processing as in The which full-length was mice and recombinant Angptl4 was by blotting from both liver and shows that in the of Angptl4 was which is in from that in tissue and the of full-length Angptl4 protein in vivo. from cells or liver full-length Angptl4 protein and these demonstrate that proteolytic processing of Angptl4 is induced in the presence of serum both in vitro and in vivo. To a better of the of full-length we expressed Angptl4 in the presence of protease Angptl4 secreted the under or in the presence of protease inhibitor mixture for to We determined the conversion of full-length, oligomerized Angptl4 to form is mediated by a protease activity in serum or that induced in the presence of serum. of full-length Angptl4 protein with from cells in the presence of with or by control shows that the protease is not was processing a caused by These demonstrate that proteolytic processing of full-length, oligomerized Angptl4 the presence of serum as well as from The of protease is in Angptl4 was first to in for serum was to serum the of the of proteolytic activity. In aggregate, these demonstrate that the proteolytic processing of Angptl4 its release mediated by a cell-associated protease activity that is by serum. the and the of Angptl4 full-length Angptl4 from or secreted under as a protein with an of that from its amino 1 and we to Angptl4 is 293 cells were treated with and in under or to obtain full-length or Angptl4 protein. which the N-terminal coiled-coil domain of was expressed in 293 cells in proteolytic processing of this domain has been not shows that when treated with PNGase which from both full-length and fibrinogen-like domain of Angptl4 on However, of the N-terminal coiled-coil domain is not by PNGase These that Angptl4 protein is at the fibrinogen-like domain. In this report, we that a recently identified secreted protein, which is selectively expressed in adipose tissue, liver, and both as a full-length oligomerized protein as well as Oligomerized Angptl4 is by a protease activity to release its carboxyl fibrinogen-like domain, which circulates as a monomer. property has not been reported in other angiopoietins or angiopoietin-like proteins. The N-terminal coiled-coil domain of Angptl4 is sufficient to form structure. The fibrinogen-like domain is and its function has not been The processing of full-length Angptl4 is of that of In both proteolytic conversion is with of the of full-length proteins. In the of processing of full-length causes on and E. C. S. A. 2002; PubMed Scopus Google Scholar, J. S. D. S. A. 2001; PubMed Scopus Google Scholar). The of of is regulated by insulin and on of plasma levels are also under hormonal control and may play a role in insulin under the T. J. M. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, S. P. J.C. R.S. 2003; PubMed Scopus Google Scholar). is for of the in disulfide and the regulation of Angptl4 processing from to be report that Angptl4 causes by lipoprotein lipase activity (11.Yoshida K. Shimizugawa T. Ono M. Furukawa H. J. Lipid Res. 2002; 43: 1770-1772Abstract Full Text Full Text PDF PubMed Scopus (313) Google Scholar). circulating protein to angiopoietin-like protein also causes of plasma very low density lipoprotein by inhibition of R. Y. Ono M. M. H. T. H. Furukawa H. Nat. 2002; PubMed Scopus Google Scholar). to Angptl4 may be circulating of plasma The and Angptl4 also to regulation by is a target of liver receptor R. T. M. J. Lipid Res. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, T. M. M. N. N. Y. H. R. M. I. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar), Angptl4 is a target of PPARα and Because both and liver receptor with receptor for biological it is that both and are also regulated by the in vivo. In has also been reported to by to to the release of and glycerol M. M. S. Y. Ono M. R. Furukawa H. M. I. Biochem. Res. 2003; PubMed Scopus Google Scholar). However, is expressed by liver, Angptl4 is expressed selectively by adipose tissue, liver, and and other In the levels of expression are not regulated by nutritional The in and regulation of expression could tissue of and In we that a circulating protein primarily expressed by adipose tissue and liver, angiopoietin 1 in a higher order of (12.Davis S. Papadopoulos N. Aldrich T.H. Maisonpierre P.C. Huang T. Kovac L. Xu A. Leidich R. Radziejewska E. Rafique A. Goldberg J. Jain V. Bailey K. Karow M. Fandl J. Samuelsson S.J. Ioffe E. Rudge J.S. Daly T.J. Radziejewski C. Yancopoulos G.D. Nat. Struct. Biol. 2003; 10: 38-44Crossref PubMed Scopus (179) Google Scholar). In contrast to angiopoietin 1, however, oligomerized full-length Angptl4 undergoes regulated proteolysis an amino-terminal coiled-coil domain and a carboxyl fibrinogen-like domain, the first example among angiopoietins and angiopoietin-like proteins. is that proteolytic processing of full-length, oligomerized Angptl4 could as a of with domain having One is the of Angptl4 (11.Yoshida K. Shimizugawa T. Ono M. Furukawa H. J. Lipid Res. 2002; 43: 1770-1772Abstract Full Text Full Text PDF PubMed Scopus (313) Google Scholar), which could be mediated by domain. It is to that proteolytic conversion of Angptl4 in could be with of plasma as well as other conditions. We Research and for and of this