Thioredoxin-independent Regulation of Metabolism by the α-Arrestin Proteins

Thioredoxin-interacting protein (Txnip), originally characterized as an inhibitor of thioredoxin, is now known to be a critical regulator of glucose metabolism in vivo. Txnip is a member of the α-arrestin protein family; the α-arrestins are related to the classical β-arrestins and visual arrestins. Txnip is the only α-arrestin known to bind thioredoxin, and it is not known whether the metabolic effects of Txnip are related to its ability to bind thioredoxin or related to conserved α-arrestin function. Here we show that wild type Txnip and Txnip C247S, a Txnip mutant that does not bind thioredoxin in vitro, both inhibit glucose uptake in mature adipocytes and in primary skin fibroblasts. Furthermore, we show that Txnip C247S does not bind thioredoxin in cells, using thiol alkylation to trap the Txnip-thioredoxin complex. Because Txnip function was independent of thioredoxin binding, we tested whether inhibition of glucose uptake was conserved in the related α-arrestins Arrdc4 and Arrdc3. Both Txnip and Arrdc4 inhibited glucose uptake and lactate output, while Arrdc3 had no effect. Structure-function analysis indicated that Txnip and Arrdc4 inhibit glucose uptake independent of the C-terminal WW-domain binding motifs, recently identified as important in yeast α-arrestins. Instead, regulation of glucose uptake was intrinsic to the arrestin domains themselves. These data demonstrate that Txnip regulates cellular metabolism independent of its binding to thioredoxin and reveal the arrestin domains as crucial structural elements in metabolic functions of α-arrestin proteins. Thioredoxin-interacting protein (Txnip), originally characterized as an inhibitor of thioredoxin, is now known to be a critical regulator of glucose metabolism in vivo. Txnip is a member of the α-arrestin protein family; the α-arrestins are related to the classical β-arrestins and visual arrestins. Txnip is the only α-arrestin known to bind thioredoxin, and it is not known whether the metabolic effects of Txnip are related to its ability to bind thioredoxin or related to conserved α-arrestin function. Here we show that wild type Txnip and Txnip C247S, a Txnip mutant that does not bind thioredoxin in vitro, both inhibit glucose uptake in mature adipocytes and in primary skin fibroblasts. Furthermore, we show that Txnip C247S does not bind thioredoxin in cells, using thiol alkylation to trap the Txnip-thioredoxin complex. Because Txnip function was independent of thioredoxin binding, we tested whether inhibition of glucose uptake was conserved in the related α-arrestins Arrdc4 and Arrdc3. Both Txnip and Arrdc4 inhibited glucose uptake and lactate output, while Arrdc3 had no effect. Structure-function analysis indicated that Txnip and Arrdc4 inhibit glucose uptake independent of the C-terminal WW-domain binding motifs, recently identified as important in yeast α-arrestins. Instead, regulation of glucose uptake was intrinsic to the arrestin domains themselves. These data demonstrate that Txnip regulates cellular metabolism independent of its binding to thioredoxin and reveal the arrestin domains as crucial structural elements in metabolic functions of α-arrestin proteins. Thioredoxin-interacting protein (Txnip), 3The abbreviations used are:Txnipthioredoxin-interacting proteinPBSphosphate-buffered salineAMS4-acetamido-4′-maleimidylstilbene- 2,2′-disulfonate. an inhibitor of thioredoxin disulfide reductase activity in vitro (1Nishiyama A. Matsui M. Iwata S. Hirota K. Masutani H. Nakamura H. Takagi Y. Sono H. Gon Y. Yodoi J. J. Biol. Chem. 1999; 274: 21645-21650Abstract Full Text Full Text PDF PubMed Scopus (594) Google Scholar, 2Yamanaka H. Maehira F. Oshiro M. Asato T. Yanagawa Y. Takei H. Nakashima Y. Biochem. Biophys. Res. Commun. 2000; 271: 796-800Crossref PubMed Scopus (102) Google Scholar, 3Junn E. Han S.H. Im J.Y. Yang Y. Cho E.W. Um H.D. Kim D.K. Lee K.W. Han P.L. Rhee S.G. Choi I. J. Immunol. 2000; 164: 6287-6295Crossref PubMed Scopus (400) Google Scholar), is robustly induced by glucose (4Schulze P.C. Yoshioka J. Takahashi T. He Z. King G.L. Lee R.T. J. Biol. Chem. 2004; 279: 30369-30374Abstract Full Text Full Text PDF PubMed Scopus (302) Google Scholar, 5Minn A.H. Hafele C. Shalev A. Endocrinology. 2005; 146: 2397-2405Crossref PubMed Scopus (290) Google Scholar, 6Stoltzman C.A. Peterson C.W. Breen K.T. Muoio D.M. Billin A.N. Ayer D.E. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 6912-6917Crossref PubMed Scopus (191) Google Scholar) and a critical regulator of metabolism in vivo (7Parikh H. Carlsson E. Chutkow W.A. Johansson L.E. Storgaard H. Poulsen P. Saxena R. Ladd C. Schulze P.C. Mazzini M.J. Jensen C.B. Krook A. Björnholm M. Tornqvist H. Zierath J.R. Riddersträle M. Altshuler D. Lee R.T. Vaag A. Groop L.C. Mootha V.K. PLoS Med. 2007; 4: e158Crossref PubMed Scopus (367) Google Scholar, 8Chutkow W.A. Patwari P. Yoshioka J. Lee R.T. J. Biol. Chem. 2008; 283: 2397-2406Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 9Hui S.T. Andres A.M. Miller A.K. Spann N.J. Potter D.W. Post N.M. Chen A.Z. Sachithanantham S. Jung D.Y. Kim J.K. Davis R.A. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 3921-3926Crossref PubMed Scopus (177) Google Scholar, 10Bodnar J.S. Chatterjee A. Castellani L.W. Ross D.A. Ohmen J. Cavalcoli J. Wu C. Dains K.M. Catanese J. Chu M. Sheth S.S. Charugundla K. Demant P. West D.B. de Jong P. Lusis A.J. Nat. Genet. 2002; 30: 110-116Crossref PubMed Scopus (180) Google Scholar). In humans, Txnip expression is suppressed by insulin and strongly up-regulated in diabetes (7Parikh H. Carlsson E. Chutkow W.A. Johansson L.E. Storgaard H. Poulsen P. Saxena R. Ladd C. Schulze P.C. Mazzini M.J. Jensen C.B. Krook A. Björnholm M. Tornqvist H. Zierath J.R. Riddersträle M. Altshuler D. Lee R.T. Vaag A. Groop L.C. Mootha V.K. PLoS Med. 2007; 4: e158Crossref PubMed Scopus (367) Google Scholar). Txnip-deficient mice have fasting hypoglycemia and ketosis (8Chutkow W.A. Patwari P. Yoshioka J. Lee R.T. J. Biol. Chem. 2008; 283: 2397-2406Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 9Hui S.T. Andres A.M. Miller A.K. Spann N.J. Potter D.W. Post N.M. Chen A.Z. Sachithanantham S. Jung D.Y. Kim J.K. Davis R.A. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 3921-3926Crossref PubMed Scopus (177) Google Scholar, 11Oka S. Liu W. Masutani H. Hirata H. Shinkai Y. Yamada S. Yoshida T. Nakamura H. Yodoi J. FASEB J. 2006; 20: 121-123Crossref PubMed Scopus (102) Google Scholar, 12Hui T.Y. Sheth S.S. Diffley J.M. Potter D.W. Lusis A.J. Attie A.D. Davis R.A. J. Biol. Chem. 2004; 279: 24387-24393Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar) with a striking enhancement of glucose uptake by peripheral tissues (8Chutkow W.A. Patwari P. Yoshioka J. Lee R.T. J. Biol. Chem. 2008; 283: 2397-2406Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 9Hui S.T. Andres A.M. Miller A.K. Spann N.J. Potter D.W. Post N.M. Chen A.Z. Sachithanantham S. Jung D.Y. Kim J.K. Davis R.A. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 3921-3926Crossref PubMed Scopus (177) Google Scholar). We have proposed that Txnip inhibits thioredoxin by forming a mixed disulfide with thioredoxin at its catalytic active site cysteines in a disulfide exchange reaction (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar). However, it is not known how Txnip metabolic functions relate to its ability to bind thioredoxin. thioredoxin-interacting protein phosphate-buffered saline 4-acetamido-4′-maleimidylstilbene- 2,2′-disulfonate. Structurally, Txnip belongs to the arrestin superfamily of proteins (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar). The prototypical arrestins (the visual arrestins and the β-arrestins) are key regulators of receptor signaling. The β-arrestins, named for their interaction with the β-adrenergic receptor, are now known to control signaling through the multiple families of receptors (15Lefkowitz R.J. Rajagopal K. Whalen E.J. Mol. Cell. 2006; 24: 643-652Abstract Full Text Full Text PDF PubMed Scopus (249) Google Scholar). These arrestin proteins have two wing-like arrestin domains arranged around a central core that detects and binds selectively to the charged phosphates of activated receptors (16Gurevich V.V. Gurevich E.V. Pharmacol. Ther. 2006; 110: 465-502Crossref PubMed Scopus (363) Google Scholar). The arrestin domains then act as multifunctional scaffolds that cannot only quench receptor signals by recruiting endocytotic machinery and ubiquitin ligases, but also start new signal cascades (15Lefkowitz R.J. Rajagopal K. Whalen E.J. Mol. Cell. 2006; 24: 643-652Abstract Full Text Full Text PDF PubMed Scopus (249) Google Scholar). Recently, arrestin-β2 has also been shown to play a key role in metabolism as a controller of insulin receptor signaling that is deficient in diabetes (17Luan B. Zhao J. Wu H. Duan B. Shu G. Wang X. Li D. Jia W. Kang J. Pei G. Nature. 2009; 457: 1146-1149Crossref PubMed Scopus (196) Google Scholar). In addition to the classical visual/β-arrestins, a large number of arrestins more closely related to Txnip are present throughout multicellular evolution. These proteins have been termed the “α-arrestins,” as they are of more ancient origin than the visual/β family (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar). Although no structures are known of the α-arrestins to date, they appear highly likely to share the overall fold: two β-sheet sandwich arrestin domains connected by a short linker sequence (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar, 18Mittal R. McMahon H.T. EMBO Rep. 2009; 10: 41-43Crossref PubMed Scopus (14) Google Scholar). Confidence in this prediction has been enhanced by the surprising finding that the vps26 family of proteins, even more distantly related to the classical arrestins than Txnip, also share the arrestin fold (19Shi H. Rojas R. Bonifacino J.S. Hurley J.H. Nat. Struct. Mol. Biol. 2006; 13: 540-548Crossref PubMed Scopus (139) Google Scholar). The vps26 proteins are a component of the retromer complex that controls retrograde transport of recycling endosomes to the trans-Golgi network. This functional overlap with visual/β-arrestin regulation of endocytosis suggests that control of endosome formation and transport may be a conserved function of the arrestin superfamily fold. The functions of the mammalian α-arrestins remain unclear. Humans have six α-arrestins: Txnip and five other proteins, which have been assigned the names Arrdc1–5 (arrestin domain-containing 1–5) (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar). Very little is known about these other α-arrestins; thioredoxin binding is not conserved beyond Txnip (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar, 20Oka S. Masutani H. Liu W. Horita H. Wang D. Kizaka-Kondoh S. Yodoi J. Endocrinology. 2006; 147: 733-743Crossref PubMed Scopus (56) Google Scholar). More is known in that α-arrestins function in regulation of endocytosis and protein through in their C-terminal T. Hirata Y. A. 2002; PubMed Scopus Google Scholar, J.M. Mol. 2004; PubMed Scopus Google Scholar, S. J.M. Proc. Natl. Acad. Sci. U.S.A. 2005; PubMed Scopus Google Scholar, Chu T. Cell. 2008; Full Text Full Text PDF PubMed Scopus (367) Google Scholar, E. EMBO Rep. 2008; PubMed Scopus Google Scholar). However, as the α-arrestins have the α-arrestins (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar), their may yeast α-arrestins. that other α-arrestins are not proteins, we that Txnip metabolic functions may be conserved in mammalian α-arrestins and independent of its interaction with thioredoxin. of Txnip in vitro of thioredoxin and of (1Nishiyama A. Matsui M. Iwata S. Hirota K. Masutani H. Nakamura H. Takagi Y. Sono H. Gon Y. Yodoi J. J. Biol. Chem. 1999; 274: 21645-21650Abstract Full Text Full Text PDF PubMed Scopus (594) Google Scholar, 3Junn E. Han S.H. Im J.Y. Yang Y. Cho E.W. Um H.D. Kim D.K. Lee K.W. Han P.L. Rhee S.G. Choi I. J. Immunol. 2000; 164: 6287-6295Crossref PubMed Scopus (400) Google Scholar, Y. Lee R.T. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). However, in vivo of two Txnip-deficient no in thioredoxin (8Chutkow W.A. Patwari P. Yoshioka J. Lee R.T. J. Biol. Chem. 2008; 283: 2397-2406Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, S.S. Castellani L.W. S. C. J.S. P. Attie A.D. Lusis A.J. J. Res. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). Txnip binds to other proteins J.H. Lee Choi I. Res. 2005; PubMed Scopus Google Scholar) and T. Liu T. P. Chen W. Li H. J. Cell. 2008; Full Text Full Text PDF PubMed Scopus Google Scholar), but it is not to these are independent of a Txnip-thioredoxin complex Kim S.S. 2004; PubMed Scopus Google Scholar). of a mutant Txnip that does not bind thioredoxin, we show that a metabolic function of Txnip, its inhibition of glucose does not interaction with thioredoxin. Instead, we show that inhibition of glucose uptake is a conserved function of of Txnip and α-arrestins that the metabolic functions of Txnip and Arrdc4 are intrinsic to the arrestin Txnip in and α-arrestins as (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar). of Txnip in by by of with as in Txnip and Txnip C247S as (8Chutkow W.A. Patwari P. Yoshioka J. Lee R.T. J. Biol. Chem. 2008; 283: 2397-2406Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar). Txnip and in as J. K. Chutkow W.A. J. Schulze P.C. C. E. Lee R.T. Res. 2007; PubMed Scopus Google Scholar). R. of at was the and of using the and to Arrdc4 and P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar) was at to the sequence for Arrdc4 was then the and of using the and to Arrdc3 was with and and the sequence by overlap H.D. J.K. PubMed Scopus Google Scholar). The and for and and for Arrdc3. The as in The then the and of and by as skin for and in with and and in with and and J. K. Chutkow W.A. J. Schulze P.C. C. E. Lee R.T. Res. 2007; PubMed Scopus Google Scholar) is was thioredoxin was the Txnip-thioredoxin we disulfide exchange by with T. S. M. H. T. K. Proc. Natl. Acad. Sci. U.S.A. PubMed Scopus Google Scholar). with Txnip wild type and mutant in and proteins with in for then at for at The with then at for at The then in and at with for and the proteins to and in by in in with expression was by to was to glucose to Txnip then in addition of and for was by in with in then with The in the was by and was with no was by a lactate with with with a by at and are as by We have that a for the ability of Txnip to bind in an in vitro binding (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar). We used the Txnip C247S mutant to whether the interaction of thioredoxin with Txnip is for Txnip metabolic we to the inhibition of glucose uptake by Txnip it is as an important Txnip function in vivo (7Parikh H. Carlsson E. Chutkow W.A. Johansson L.E. Storgaard H. Poulsen P. Saxena R. Ladd C. Schulze P.C. Mazzini M.J. Jensen C.B. Krook A. Björnholm M. Tornqvist H. Zierath J.R. Riddersträle M. Altshuler D. Lee R.T. Vaag A. Groop L.C. Mootha V.K. PLoS Med. 2007; 4: e158Crossref PubMed Scopus (367) Google Scholar, 8Chutkow W.A. Patwari P. Yoshioka J. Lee R.T. J. Biol. Chem. 2008; 283: 2397-2406Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar). We wild type and C247S Txnip in mature adipocytes by and glucose uptake by of was to the uptake of the with the control with (7Parikh H. Carlsson E. Chutkow W.A. Johansson L.E. Storgaard H. Poulsen P. Saxena R. Ladd C. Schulze P.C. Mazzini M.J. Jensen C.B. Krook A. Björnholm M. Tornqvist H. Zierath J.R. Riddersträle M. Altshuler D. Lee R.T. Vaag A. Groop L.C. Mootha V.K. PLoS Med. 2007; 4: e158Crossref PubMed Scopus (367) Google Scholar), wild type Txnip inhibited glucose uptake with an control both and we that of mutant Txnip C247S also inhibited glucose uptake and that this function of Txnip is independent of binding to thioredoxin. that this was to primary cells, we the with primary skin fibroblasts. of wild type inhibited glucose uptake with and of Txnip also inhibited glucose uptake with analysis of both wild type and mutant that the C247S the interaction of Txnip and thioredoxin in cells, we a new for Txnip-thioredoxin Because Txnip and thioredoxin may a complex (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar), alkylation of of the complex by disulfide or as the we that reaction of of Txnip-thioredoxin We then tested whether Txnip and C247S with thioredoxin in an we also Txnip a of a highly conserved that does not binding to thioredoxin (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar). The in cells, which have Txnip protein with and analysis was a at the of a Txnip and thioredoxin complex with wild type Txnip as as Txnip and Txnip no was with Txnip C247S with that the was a Txnip-thioredoxin complex. In no Txnip-thioredoxin complex was with of Txnip C247S, expression of Txnip mutant proteins. These data demonstrate that of Txnip to of interaction with thioredoxin in and that inhibition of glucose uptake by Txnip is not by the C247S of ability to bind to thioredoxin. Txnip to be the α-arrestins in its ability to bind we and have shown that the α-arrestins closely related to Txnip and in of not bind thioredoxin (13Patwari P. Higgins L.J. Chutkow W.A. Yoshioka J. Lee R.T. J. Biol. Chem. 2006; 281: 21884-21891Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar, 20Oka S. Masutani H. Liu W. Horita H. Wang D. Kizaka-Kondoh S. Yodoi J. Endocrinology. 2006; 147: 733-743Crossref PubMed Scopus (56) Google Scholar). Because thioredoxin binding was not for regulation of glucose uptake by Txnip, we that regulation of glucose metabolism be a function conserved in other α-arrestins. we for the with C-terminal and we characterized the of the proteins by of Txnip to the Y. Masutani H. S. Y. Y. K. Y. Yodoi J. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar). Arrdc3 to the and to in the with an of Arrdc3 with endocytotic as by S. Masutani H. Liu W. Horita H. Wang D. Kizaka-Kondoh S. Yodoi J. Endocrinology. 2006; 147: 733-743Crossref PubMed Scopus (56) Google Scholar). of Arrdc4 was to that of to both the and was in the only of Arrdc4 Y. M. G. K. M. S. Res. Google Scholar), which may be to type or to the of of both Arrdc4 and Arrdc3 is of a conserved in endocytosis and for the mammalian α-arrestins. of the α-arrestins cells, we a striking in the of the while the of with and Arrdc3 as the of with Txnip and Arrdc4 an glucose uptake or metabolism the to In with glucose as the primary is by lactate H. S. M. Schulze J. Biol. Chem. Full Text PDF PubMed Google Scholar). is the of glucose uptake in in L.J. D. J. Biol. Chem. Full Text PDF PubMed Google Scholar) and is to the by Biochem. J. 1999; PubMed Scopus Google Scholar). We the lactate in the with Txnip had lactate of the α-arrestin Arrdc4 also strongly inhibited lactate to the In of Arrdc3 had no lactate of a also had no lactate show that Arrdc4 inhibits glucose we the of of α-arrestins in primary skin fibroblasts. uptake was by protein of the to uptake of then to the of the of Txnip glucose uptake to of control of Arrdc4 also strongly glucose to of control while of Arrdc3 had no These data that Txnip and share the ability to glucose In to the β-arrestins, no is for the α-arrestins (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar, Chu T. Cell. 2008; Full Text Full Text PDF PubMed Scopus (367) Google Scholar). Because Txnip and Arrdc4 had metabolic effects while Arrdc3 we that conserved in Txnip and Arrdc4 but not Arrdc3 or that control α-arrestin function. of Txnip, and only of more than they of a a known binding for proteins T. Li Li S.S. 2008; 13: PubMed Scopus Google Scholar). We in five by the conserved Txnip with the in Arrdc3 or in a was used as the to of expression and for the effects of the metabolic we tested whether mutant inhibited lactate with Txnip inhibited lactate to the of mutant also inhibited lactate to with of the to have a role in lactate However, we that of Txnip of the of The not but enhanced of the Txnip in the by interaction with an Y. Masutani H. S. Y. Y. K. Y. Yodoi J. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar), and Txnip has two classical and is not in primary to the the to may be a functional with a binding to enhanced of this in not Txnip inhibition of lactate the of Txnip cysteines for its interaction with thioredoxin, we also whether to Txnip and Both cysteines in thioredoxin binding and are present only in the Txnip are conserved the and we identified that is present in Txnip and Arrdc4 but not Txnip whether Txnip is important for Txnip we Txnip in and lactate to the wild type Txnip inhibited lactate with the Txnip with other also inhibited lactate and of Txnip had no lactate analysis of of Txnip mutant These demonstrate that while a is for interaction with thioredoxin, a conserved but not is for Txnip metabolic function in this that Txnip bind to thioredoxin, we the binding with of Txnip wild type and in analysis the of a Txnip complex The of Txnip is for its to the linker or sequence that the two arrestin domains (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar). In the β-arrestins, the of the sequence is to be important for a binding to a receptor (16Gurevich V.V. Gurevich E.V. Pharmacol. Ther. 2006; 110: 465-502Crossref PubMed Scopus (363) Google Scholar). α-arrestin to Txnip are also for a short of in cysteines in We that the Arrdc4 also in Arrdc4 metabolic function. However, of both wild type and Arrdc4 in inhibited lactate to the with controls the Txnip to be a critical regulator of Txnip metabolic function but does not the of function Txnip and Because in primary sequence not appear to the of function Txnip and we whether α-arrestin domains for metabolic function. the β-arrestins, the α-arrestins have two arrestin domains and a C-terminal However, the α-arrestin C-terminal is with highly conserved motifs, a the β-arrestins (14Alvarez C.E. BMC Evol. Biol. 2008; 8: 222Crossref PubMed Scopus (177) Google Scholar). with domain-containing proteins, which ubiquitin have recently shown that yeast α-arrestins receptor endocytosis and through the in the C-terminal E. EMBO Rep. 2008; PubMed Scopus Google Scholar, Chu T. Cell. 2008; Full Text Full Text PDF PubMed Scopus (367) Google Scholar). is whether the C-terminal to α-arrestin metabolic function. We tested C-terminal of Txnip for ability to inhibit lactate Txnip and and was Txnip inhibited lactate with the Txnip at the start of the C-terminal the ability to inhibit lactate In the C-terminal arrestin the lactate Txnip analysis of with of Txnip proteins. These demonstrate that the α-arrestin C-terminal is not for metabolic they that this function is intrinsic to the arrestin domains themselves. may function by with we used a to whether or both arrestin domains are for metabolic with β-arrestins suggests that the arrestin domains and that the have V.V. J. Kim R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). to their lactate no of with while inhibited lactate the Arrdc3 with a Txnip had no while Txnip with an Arrdc3 inhibited lactate The with the arrestin domains had no Txnip with an Arrdc3 arrestin lactate These that Txnip inhibits lactate the for its C-terminal its arrestin domains are important for this function. We then tested the effects of the glucose uptake in primary skin fibroblasts. uptake was to protein and as a of the of the control wild type Arrdc3 had no glucose uptake with wild type Txnip strongly inhibited glucose uptake The for the was Arrdc3 with a Txnip had no Txnip with an Arrdc3 strongly inhibited glucose uptake In of the arrestin both inhibited glucose uptake in addition to regulation of lactate output, Txnip also inhibits cellular glucose uptake for its C-terminal However, of the arrestin that at a glucose uptake is with of the Txnip arrestin Because only a inhibited lactate was with of the it is that the proteins are in their function. the other inhibition of glucose uptake was a and for function. These the that conserved of the arrestin domains beyond primary sequence to the metabolic functions of Txnip and Furthermore, even Arrdc3 does not inhibit glucose proteins with only Txnip arrestin appear that the arrestin domains of Arrdc3 as Txnip and Although little is known of Arrdc3 it has been to the of in the of the G. J. G. J. J. E. Scholar), it may also have a role in regulation of These show that Txnip inhibits glucose uptake and lactate independent of thioredoxin This suggests while to function as an inhibitor of thioredoxin, Txnip may function as an α-arrestin that is by thioredoxin. of both Txnip and the related α-arrestin Arrdc4 as of glucose uptake that the α-arrestins are a new family of metabolic the mammalian α-arrestin functions are we that Txnip may be in its ability to metabolism in to both glucose and as it with but not thioredoxin. with