Phosphorylation of Arfaptin 2 at Ser260 by Akt Inhibits PolyQ-huntingtin-induced Toxicity by Rescuing Proteasome Impairment

Abstract

Huntington disease (HD) is caused by an abnormal expanded polyglutamine repeat in the huntingtin protein. Insulin-like growth factor-1 is of particular interest in HD because it strongly inhibits polyQ-huntingtin-induced neurotoxicity. This neuroprotective effect involves the phosphorylation of huntingtin at Ser421 by the prosurvival kinase Akt (Humbert, S., Bryson, E. A., Cordelières, F. P., Connors, N. C., Datta, S. R., Finkbeiner, S., Greenberg, M. E., and Saudou, F. (2002) Dev. Cell 2, 831–837). Here, we report that Akt inhibits polyQ-huntingtin-induced toxicity in the absence of phosphorylation of huntingtin at Ser421, suggesting that Akt also acts on other downstream effector(s) to prevent neuronal death in HD. We show that this survival effect involves the ADP-ribosylation factor-interacting protein arfaptin 2, the levels of which are increased in HD patients. Akt phosphorylated arfaptin 2 at Ser260. Lack of phosphorylation of arfaptin 2 at this site substantially modified its subcellular distribution and increased neuronal death and intranuclear inclusions caused by polyQ-huntingtin. In contrast, arfaptin 2 had a neuroprotective effect on striatal neurons when phosphorylated by Akt. This effect is mediated through the proteasome, as phosphorylated arfaptin 2 inhibited the blockade of the proteasome induced by polyQ-huntingtin. This study points out a new mechanism by which Akt promotes neuroprotection in HD, emphasizing the potential therapeutic interest of this pathway in the disease. Huntington disease (HD) is caused by an abnormal expanded polyglutamine repeat in the huntingtin protein. Insulin-like growth factor-1 is of particular interest in HD because it strongly inhibits polyQ-huntingtin-induced neurotoxicity. This neuroprotective effect involves the phosphorylation of huntingtin at Ser421 by the prosurvival kinase Akt (Humbert, S., Bryson, E. A., Cordelières, F. P., Connors, N. C., Datta, S. R., Finkbeiner, S., Greenberg, M. E., and Saudou, F. (2002) Dev. Cell 2, 831–837). Here, we report that Akt inhibits polyQ-huntingtin-induced toxicity in the absence of phosphorylation of huntingtin at Ser421, suggesting that Akt also acts on other downstream effector(s) to prevent neuronal death in HD. We show that this survival effect involves the ADP-ribosylation factor-interacting protein arfaptin 2, the levels of which are increased in HD patients. Akt phosphorylated arfaptin 2 at Ser260. Lack of phosphorylation of arfaptin 2 at this site substantially modified its subcellular distribution and increased neuronal death and intranuclear inclusions caused by polyQ-huntingtin. In contrast, arfaptin 2 had a neuroprotective effect on striatal neurons when phosphorylated by Akt. This effect is mediated through the proteasome, as phosphorylated arfaptin 2 inhibited the blockade of the proteasome induced by polyQ-huntingtin. This study points out a new mechanism by which Akt promotes neuroprotection in HD, emphasizing the potential therapeutic interest of this pathway in the disease. Huntington disease (HD) 1The abbreviations used are: HD, Huntington disease; IGF-1, insulin-like growth factor-1; GST, glutathione S-transferase; Akt-ca, constitutively activated Akt; SGK, serum- and glucocorticoid-induced kinase; GFP, green fluorescent protein; NIIs, neuronal intranuclear inclusions; MT, microtubule; UPS, ubiquitin/proteasome system; ANOVA, analysis of variance. is a fatal neurodegenerative disorder characterized by involuntary movements, personality changes, and dementia (1Young A.B. J. Clin. Investig. 2003; 111: 299-302Crossref PubMed Scopus (92) Google Scholar). The dominantly inherited causal gene encodes the huntingtin protein, which contains an abnormal polyglutamine expansion (polyQ) in HD patients. HD develops when this expansion exceeds 35 glutamine residues. There is a strong inverse correlation between the number of glutamines and the age at onset of the disease. HD leads to the selective dysfunction and death of striatal neurons in the brain. The presence of neuritic and intranuclear inclusions in neurons is also characteristic of the disease. There is currently no effective treatment to prevent or to delay disease progression, and death usually occurs 10–20 years after the appearance of the first clinical symptoms. We recently reported that the insulin-like growth factor-1 (IGF-1)/Akt signaling pathway could have a beneficial effect in HD (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar). In striatal neurons, the most vulnerable neurons in HD, IGF-1 completely blocks polyQ-huntingtin-induced toxicity (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar). This effect is mediated by the serine/threonine kinase Akt, which directly phosphorylates polyQ-huntingtin at Ser421, inhibiting the toxic properties of polyQ-huntingtin. These findings reveal that the IGF-1/Akt signaling pathway is of particular interest in HD, as it directly affects the protein that causes the disease. We observed that Akt is altered in the brains of HD patients and particularly in the striatum, showing that this kinase plays an important role in HD (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar). Akt is a potent prosurvival kinase that exerts its effects by phosphorylating key substrates such as components of the cell death machinery (3Brazil D.P. Yang Z.Z. Hemmings B.A. Trends Biochem. Sci. 2004; 29: 233-242Abstract Full Text Full Text PDF PubMed Scopus (722) Google Scholar). Akt could be particularly important in HD, as it abrogates the toxicity of polyQ-huntingtin by phosphorylating Ser421. It also acts on other substrates that promote survival by general mechanisms or by mechanisms relevant to HD. The phosphorylation by Akt of substrates other than huntingtin may be important in the latter stages of the disease. During the pathological process in HD, huntingtin is cleaved by several proteases, including caspases, calpains, and other unidentified proteases (4Wellington C.L. Singaraja R. Ellerby L. Savill J. Roy S. Leavitt B. Cattaneo E. Hackam A. Sharp A. Thornberry N. Nicholson D.W. Bredesen D.E. Hayden M.R. J. Biol. Chem. 2000; 275: 19831-19838Abstract Full Text Full Text PDF PubMed Scopus (300) Google Scholar, 5Kim Y.J. Yi Y. Sapp E. Wang Y. Cuiffo B. Kegel K.B. Qin Z.H. Aronin N. DiFiglia M. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 12784-12789Crossref PubMed Scopus (327) Google Scholar, 6Gafni J. Ellerby L.M. J. Neurosci. 2002; 22: 4842-4849Crossref PubMed Google Scholar, 7Goffredo D. Rigamonti D. Tartari M. De Micheli A. Verderio C. Matteoli M. Zuccato C. Cattaneo E. J. Biol. Chem. 2002; 277: 39594-39598Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 8Lunkes A. Lindenberg K.S. Ben-Haiem L. Weber C. Devys D. Landwehrmeyer G.B. Mandel J.L. Trottier Y. Mol. Cell. 2002; 10: 259-269Abstract Full Text Full Text PDF PubMed Scopus (311) Google Scholar). This cleavage generates short N-terminal amino acid fragments that contain the pathological polyglutamine expansion and that are more toxic to neurons than full-length huntingtin (4Wellington C.L. Singaraja R. Ellerby L. Savill J. Roy S. Leavitt B. Cattaneo E. Hackam A. Sharp A. Thornberry N. Nicholson D.W. Bredesen D.E. Hayden M.R. J. Biol. Chem. 2000; 275: 19831-19838Abstract Full Text Full Text PDF PubMed Scopus (300) Google Scholar, 9Gafni J. Hermel E. Young J.E. Wellington C.L. Hayden M.R. Ellerby L.M. J. Biol. Chem. 2004; 279: 20211-20220Abstract Full Text Full Text PDF PubMed Scopus (235) Google Scholar). Some of these short N-terminal fragments do not contain the Ser421 phosphorylation site, suggesting that the direct neuroprotective effect of Akt on huntingtin is lost during proteolysis (10Li S.H. Li X.J. Trends Genet. 2004; 20: 146-154Abstract Full Text Full Text PDF PubMed Scopus (437) Google Scholar). We report here that Akt blocks the polyglutamine-dependent neuronal death and inclusion formation that are induced by an N-terminal fragment of huntingtin that does not contain Ser421. We demonstrate that this Ser421 huntingtin-independent mechanism involves the ADP-ribosylation factor-interacting protein arfaptin 2. Phosphorylation of arfaptin 2 at Ser260 by Akt promoted neuronal survival and decreased intranuclear inclusion formation in a neuronal model of HD. This demonstrates that arfaptin 2 is neuroprotective in HD. Finally, we show that phosphorylated arfaptin 2 inhibits the polyQ-huntingtin-induced blockade of the proteasome. Constructs—The vectors encoding β-galactosidase, hemagglutinin-tagged huntingtin N-terminal fragments 171-17 and 171-68, (exon 1 of huntingtin with 17 glutamines (exon 1-17) and 68 glutamines (exon 1-68), glutathione S-transferase (GST)-fused human huntingtin-(384–467), constitutively activated Akt (Akt-ca), inactivated Akt, and hemagglutinin-tagged Akt have been described previously (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar, 11Datta S.R. Dudek H. Tao X. Masters S. Fu H. Gotoh Y. Greenberg M.E. Cell. 1997; 91: 231-241Abstract Full Text Full Text PDF PubMed Scopus (4946) Google Scholar, 12Saudou F. Finkbeiner S. Devys D. Greenberg M.E. Cell. 1998; 95: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1371) Google Scholar). A bacterial expression plasmid encoding GST-fused arfaptin 2 (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar) was used as a template to generate plasmid encoding the C-terminal fragment of arfaptin 2. A mammalian expression plasmid (pcDNA3.1/GS) encoding full-length human arfaptin 2 fused to a His6 tag was purchased from Invitrogen (GeneStorm). The arfaptin 2 mutants for Akt phosphorylation sites were by the mammalian or bacterial plasmid of arfaptin 2 as a template and the for arfaptin 2 and for arfaptin 2 Cell and of striatal neurons were from 17 and at in by a modified F. Finkbeiner S. Devys D. Greenberg M.E. Cell. 1998; 95: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1371) Google Scholar). The human and the cell were in modified with when and and and by the were as described (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar, H. J. M.E. Saudou F. S. J. Neurosci. 2004; PubMed Scopus Google Scholar). were with protein were and was was GST-fused were in and with and substrates were for at with of The were by and with and were by in phosphorylation by Akt in the presence of of or arfaptin 2 was as described previously Hemmings J. Biol. Chem. Full Text PDF PubMed Google Scholar). GST-fused and arfaptin 2 were with the to the in phosphorylation by Akt, of or arfaptin 2 was Hemmings J. Biol. Chem. Full Text PDF PubMed Google Scholar). phosphorylated were and 2 was with in at for were and were in of acid and were from the and from the of a with was out at for at and was on in and for were with a 2 at was to and to the was and by the was and an of 1 to a of it was to a to the The was and to the was with Cell and were 2 with 2 1 2 1 and for at and were after at for at were from the were in and by at for at of were to to and as by the of was and is to were the by the of were to and with 2 (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google and were on with for and with the 2 (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google tag Cell and of were with a of 2 on in 2001; PubMed Scopus Google Scholar) were with of was in the at a were and in a A of fluorescent were for green fluorescent protein The levels of were to the The from are as of green of and of striatal neurons were with huntingtin or polyQ-huntingtin and to the be that also the huntingtin were by the modified with a of to (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar). these of the neurons also the huntingtin not neurons were by in a and Cell death the was as the in the number of neurons between the points and is as a of cell intranuclear inclusion striatal neurons were with vectors of interest and a plasmid encoding were and for the presence of intranuclear inclusions and at to in or in a to the of neurons in neuronal survival and to neurons for inclusion were to Akt a of Ser421 Phosphorylation in Akt could promote neuroprotection of Ser421 We used an in neuronal model of HD to Akt could the neuronal toxicity induced by an N-terminal fragment of huntingtin not Ser421. In of striatal neurons, fragments of huntingtin the abnormal polyglutamine expansion neuronal death and the formation of neuronal intranuclear inclusions F. Finkbeiner S. Devys D. Greenberg M.E. Cell. 1998; 95: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1371) Google Scholar). We striatal neurons with encoding the first amino of huntingtin 17 glutamine or 68 glutamine and with a encoding and neuronal survival induced a in neuronal survival with Akt completely inhibited neuronal death induced by huntingtin fragment We the effect of Akt on the formation of neuronal intranuclear inclusions We that Akt decreased the of neurons In phosphorylation that fragment 171-17 fragment was phosphorylated by not This that the effects of Akt are not to phosphorylation between amino 1 and of We have previously that of the neuroprotective effect of IGF-1 is mediated through the phosphorylation of huntingtin at Ser421 (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar). We show here that Akt striatal neurons from polyQ-huntingtin-induced toxicity not by directly phosphorylating also by phosphorylating other substrates that in polyQ-huntingtin-induced This effect of Akt to of the death of striatal neurons and the formation of intranuclear inclusions Akt may on a that directly polyQ-huntingtin-induced such an Akt we for an Akt phosphorylation site B. Biochem. J. 2000; PubMed Scopus Google Scholar). We arfaptin 2, which been to polyQ-huntingtin (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar). 2 in is the most in HD. arfaptin 2 is modified in the pathological we the levels of arfaptin 2 in human striatal from HD and HD patients were and as a for protein levels 2 levels were in from HD patients than in from This with on HD brains showing of arfaptin 2 (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar) and its in HD. 2 a of 2 a Akt phosphorylation site at Ser260 Akt phosphorylates arfaptin 2 in we GST-fused arfaptin 2 with or inactivated Akt in the presence of phosphorylated arfaptin 2, inactivated Akt not demonstrate that Ser260 is phosphorylated by Akt-ca, we a GST-fused C-terminal fragment of arfaptin 2 with Ser260 or a at this The C-terminal fragment of arfaptin 2 was no phosphorylated by when Ser260 was with the of the GST-fused protein was We out of full-length and arfaptin 2 to Ser260 as a site of phosphorylation of arfaptin 2 The observed in arfaptin 2 was not when Ser260 was to suggesting Ser260 as the site of phosphorylation of arfaptin 2 by Akt. Ser260 as an Akt phosphorylation site, we a that arfaptin 2 phosphorylated at Ser260. in the arfaptin 2 phosphorylated at Ser260 arfaptin 2 when with Akt-ca, to the protein with the These show that Akt phosphorylates arfaptin 2 at Ser260 in and that arfaptin 2 is a of Akt. We phosphorylates arfaptin 2 because this kinase a effect by phosphorylating huntingtin at Ser421 after IGF-1 H. J. M.E. Saudou F. S. J. Neurosci. 2004; PubMed Scopus Google Scholar). arfaptin 2 was not phosphorylated by SGK, that Akt phosphorylates arfaptin 2 at Ser260 Phosphorylation of 2 2 is in the of in particular the and in (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar). phosphorylation the distribution of arfaptin 2, we with or arfaptin 2. We used to the distribution of arfaptin 2 and the protein The and arfaptin 2 in the as and with in the the distribution of arfaptin 2 was The protein was to in the and was no in or that this effect was to of phosphorylation at we the effect of phosphorylation of Ser260 by it with arfaptin 2 had the subcellular as arfaptin 2 in and in striatal neurons not arfaptin 2 also in neuritic of striatal neurons of formation in and neurons that it was with of phosphorylation at as and arfaptin 2 In contrast, were observed in of and neurons arfaptin 2 2 on the that with when in M. Mol. Biol. Cell. 2003; PubMed Scopus Google Scholar). formation induced by of phosphorylation of arfaptin 2 at Ser260 with the of arfaptin 2 the to the effect of phosphorylation on the distribution of arfaptin 2 in to the the which is for the of the that arfaptin 2, the arfaptin 2 was the in a as described previously (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google in arfaptin 2, the was that the of arfaptin 2 and its by phosphorylation on we with an We that and arfaptin 2 were with the in the These show that arfaptin 2 on the of the and that of phosphorylation of arfaptin 2 leads to an of the We the effect of phosphorylation on arfaptin 2 distribution in We arfaptin 2 in cell and in and from with arfaptin 2 and arfaptin 2 were in the protein arfaptin 2 was strongly in the protein we have by and that of phosphorylation of arfaptin 2 at Ser260 the distribution of arfaptin 2. This in its and to the of the 2 of Phosphorylation by the of arfaptin 2 expression and phosphorylation of Ser260 on polyQ-huntingtin-induced toxicity in of striatal neurons We striatal neurons with 171-17 or and of arfaptin 2 and cell and arfaptin 2 neurons from neuronal arfaptin 2 neuronal We striatal neurons with the for the presence of arfaptin 2 decreased the of neurons arfaptin 2 In contrast, arfaptin 2 increased this These show that arfaptin 2 phosphorylated at Ser260 a neuroprotective effect on polyQ-huntingtin-induced toxicity by neuronal death and We of striatal neurons with arfaptin 2, and to the toxicity of arfaptin 2 is to phosphorylation by Akt at this site and we have inhibited neuronal death induced by In the presence of arfaptin 2, Akt a neuroprotective effect and polyQ-huntingtin-induced neuronal death when arfaptin 2 was in neurons, polyQ-huntingtin-induced neuronal death the neuroprotective effect of Akt is at mediated through phosphorylation of arfaptin 2. 171-68, Akt, and arfaptin 2 were in striatal neurons, a in formation of was observed This effect is to phosphorylation of Ser260 by Akt-ca, as this was not observed in the absence of Akt and was when Ser260 was to phosphorylated arfaptin 2 exerts a effect in HD that is mediated phosphorylation of Ser260 by Akt. 2 Phosphorylation of arfaptin 2 in and the toxicity of this protein with increased formation of to phosphorylation of arfaptin 2 could proteasome the of arfaptin is not arfaptin 2 been to proteasome (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar). We used a short fused to such that the protein is for 2001; PubMed Scopus Google Scholar). was by the in an in of protein We with or expanded polyglutamine N-terminal fragments to 1 of huntingtin (exon or and or arfaptin 2. The levels of were by cell were more fluorescent than 2001; PubMed Scopus Google Scholar, K. Mol. Genet. 2002; PubMed Google that abnormal polyglutamine expansion in huntingtin the proteasome. The was in with arfaptin 2 and This that arfaptin 2 inhibits the proteasome blockade induced by polyQ-huntingtin. In contrast, arfaptin 2 was to prevent polyQ-huntingtin-induced of protein by the proteasome. arfaptin 2 inhibits the proteasome protein This beneficial is lost in the absence of Ser260 We have that arfaptin 2 is neuroprotective in a neuronal model that that are observed in HD such as intranuclear inclusions of polyQ-huntingtin and neuronal We have that arfaptin 2 is a of Akt and that phosphorylation of arfaptin 2 by Akt at Ser260 promotes survival of striatal This that arfaptin 2 is in the neuroprotective effect of Akt in HD We have also that arfaptin 2 phosphorylation proteasome that is inhibited by the presence of polyQ-huntingtin in are with the study of (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar) that arfaptin 2 formation of Here, we have that this is on the phosphorylation of arfaptin 2. arfaptin 2 was constitutively phosphorylated it the formation of inclusions in of striatal of phosphorylation of arfaptin 2 at Ser260 of C-terminal mutants of arfaptin 2 that the Ser260 phosphorylation site polyQ-huntingtin in (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar). In contrast, we have that arfaptin 2 does not This may be to described or in the phosphorylation of arfaptin 2 in of the cell In it is that arfaptin 2 was as arfaptin 2 and arfaptin 2 had the in and We have that arfaptin 2 levels are increased in the brains of HD which is with in HD (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar). We have that arfaptin 2 is neuroprotective and that this may reveal a mechanism in In we have previously that Akt is altered in the latter stages of the disease (2Humbert S. Bryson E.A. Cordelières F.P. Connors N.C. Datta S.R. Finkbeiner S. Greenberg M.E. Saudou F. Dev. Cell. 2002; 2: 831-837Abstract Full Text Full Text PDF PubMed Scopus (410) Google Scholar). We not phosphorylated of arfaptin 2 in the not and the of Akt the phosphorylation of arfaptin 2 at Ser260 in the disease. This of may be to study a of Akt and points out a new neuroprotective mechanism in HD. Akt phosphorylates arfaptin 2, which the proteasome It been previously that Akt and of Akt and of M. S. Wang J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar, J. R. Yang D.P. A. D. Hemmings B.A. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar). This mechanism involves the phosphorylation of and by Akt, which leads to the of and inhibits by the proteasome. The prosurvival effect of Akt also be mediated by the of of cell growth and Akt also promotes of and a by a mechanism Thompson J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). The ubiquitin/proteasome is in several neurodegenerative including HD and other polyglutamine A. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). In polyglutamine may the of toxic to by the proteasome F. Finkbeiner S. Devys D. Greenberg M.E. Cell. 1998; 95: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1371) Google Scholar). In with this to the and the proteasome show and F. Finkbeiner S. Devys D. Greenberg M.E. Cell. 1998; 95: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1371) Google Scholar, E. Y. B. Y. A. Full Text Full Text PDF PubMed Scopus Google Scholar, E. A. F. R. J. J. Neurosci. 2001; PubMed Google Scholar, Genet. Dev. 2003; PubMed Scopus Google Scholar). have that the is during disease the and to the of in 2001; PubMed Scopus Google Scholar, K. Mol. Genet. 2002; PubMed Google Scholar). In are not by the This in the of expanded short These are to and the of the R. M. N. Mol. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). Finally, the in proteasome also to the of short fragments of polyQ-huntingtin H. F. Wang J. Li S.H. Li X.J. J. Cell Biol. 2003; PubMed Scopus Google Scholar). are of the and the of 2001; PubMed Scopus Google Scholar, 2003; PubMed Scopus Google Scholar). the of or that the is of potential therapeutic study that phosphorylated arfaptin 2 leads to from the proteasome induced by polyQ-huntingtin. does arfaptin 2 proteasome arfaptin 2 with and its C. Boshans R.L. M. L. J. 1997; PubMed Scopus Google Scholar, L. D. J. PubMed Scopus Google Scholar, Biochem. 2001; PubMed Scopus Google Scholar). The of the that with arfaptin 2 and its subcellular (13Peters P.J. Ning K. Palacios F. Boshans R.L. Kazantsev A. Thompson L.M. Woodman B. Bates G.P. D'Souza-Schorey C. Nat. Cell Biol. 2002; 4: 240-245Crossref PubMed Scopus (43) Google Scholar) that arfaptin 2 may the This is by that of phosphorylation of arfaptin 2 at Ser260 the in and for C.L. J. Cell Biol. 1998; PubMed Scopus Google an is for This that in the of and in by the proteasome P.J. Ning K. D'Souza-Schorey C. S. Proc. Natl. Acad. Sci. U. S. A. 2002; PubMed Scopus Google Scholar). 2 may be a of this a proteasome is in several neurodegenerative it be of interest to this mechanism in We have previously IGF-1 phosphorylates polyQ-huntingtin at Ser421 and abrogates its toxicity H. J. M.E. Saudou F. S. J. Neurosci. 2004; PubMed Scopus Google Scholar). This kinase does not arfaptin 2. These the of Akt in HD because Akt to neurons polyQ-huntingtin Akt the toxicity of full-length which contains Ser421. Akt also phosphorylates arfaptin 2 at protein This effect on proteasome is of particular During the of the polyQ-huntingtin is cleaved by several proteases, and more toxic N-terminal fragments that do not contain Ser421. The phosphorylation of substrates by Akt may be a process during the of the suggesting that the Akt pathway is of therapeutic in HD. We for C. D'Souza-Schorey for the GST-fused arfaptin 2 and for the 2 R. R. for and J. the F. Cordelières, and of the for We the for human