Coordinated Regulation of AIB1 Transcriptional Activity by Sumoylation and Phosphorylation

Abstract

AIB1, a member of the steroid receptor coactivator (SRC) family that participates in gene transcriptional activation by nuclear receptors and other transcription factors, is required for animal growth and reproductive development and implicated in breast carcinogenesis. The mechanisms underlying the AIB1 pleiotropic functions are not fully understood and neither is the regulation of its activity. Here, we showed that AIB1 was a sumoylated protein and the sumoylation attenuated the transactivation activity of AIB1, which is in contrast to the sumoylation of its paralogs, GRIP1 and SRC-1. The transactivation activity of AIB1 is enhanced by its phosphorylation by several kinases, including mitogen-activated protein kinase. We demonstrated in this report that estrogen treatment led to an increased phosphorylation and decreased sumoylation of AIB1 and that the sumoylation coordinated with phosphorylation in regulating the transcriptional activity of AIB1, providing a mechanism for post-translational modifications in regulating the transcriptional output of AIB1. AIB1, a member of the steroid receptor coactivator (SRC) family that participates in gene transcriptional activation by nuclear receptors and other transcription factors, is required for animal growth and reproductive development and implicated in breast carcinogenesis. The mechanisms underlying the AIB1 pleiotropic functions are not fully understood and neither is the regulation of its activity. Here, we showed that AIB1 was a sumoylated protein and the sumoylation attenuated the transactivation activity of AIB1, which is in contrast to the sumoylation of its paralogs, GRIP1 and SRC-1. The transactivation activity of AIB1 is enhanced by its phosphorylation by several kinases, including mitogen-activated protein kinase. We demonstrated in this report that estrogen treatment led to an increased phosphorylation and decreased sumoylation of AIB1 and that the sumoylation coordinated with phosphorylation in regulating the transcriptional activity of AIB1, providing a mechanism for post-translational modifications in regulating the transcriptional output of AIB1. Nuclear receptors play critical roles in animal development and homeostasis through their bimodal function as repressors or activators of gene transcription (1Glass C.K. Rosenfeld M.G. Genes Dev. 2000; 14: 121-141Crossref PubMed Google Scholar). The repression and activation activity of nuclear receptors are determined by their association with corepressors and coactivators, respectively. Among the coactivators, the steroid receptor coactivator (SRC) 2The abbreviations used are: SRC, steroid receptor coactivator; MAPK, mitogen-activated protein kinase; SUMO, small ubiquitin-like modifier; CREB, cAMP-response element-binding protein; E1, ubiquitin-activating enzyme; E2, ubiquitin carrier protein; E3, ubiquitin-protein isopeptide ligase; DBD, DNA-binding domain; ERK, extracellular signal-regulated kinase; HA, hemagglutinin; E2, 17β-estradiol; wt, wild type; aa, amino acid(s).2The abbreviations used are: SRC, steroid receptor coactivator; MAPK, mitogen-activated protein kinase; SUMO, small ubiquitin-like modifier; CREB, cAMP-response element-binding protein; E1, ubiquitin-activating enzyme; E2, ubiquitin carrier protein; E3, ubiquitin-protein isopeptide ligase; DBD, DNA-binding domain; ERK, extracellular signal-regulated kinase; HA, hemagglutinin; E2, 17β-estradiol; wt, wild type; aa, amino acid(s). family is both necessary and sufficient for nuclear receptor-mediated gene activation as we previously demonstrated (2Shang Y. Hu X. DiRenzo J. Lazar M.A. Brown M. Cell. 2000; 103: 843-852Abstract Full Text Full Text PDF PubMed Scopus (1444) Google Scholar). The SRC family of coactivators includes three distinct but related p160 members: SRC-1, GRIP1 (or SRC-2), and AIB1 (also named RAC3, ACTR, SRC-3, or p/CIP in mice) (3Anzick S.L. Kononen J. Walker R.L. Azorsa D.O. Tanner M.M. Guan X.Y. Sauter G. Kallioniemi O.P. Trent J.M. Meltzer P.S. Science. 1997; 277: 965-968Crossref PubMed Scopus (1430) Google Scholar, 4Hong H. Kohli K. Trivedi A. Johnson D.L. Stallcup M.R. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 4948-4952Crossref PubMed Scopus (612) Google Scholar, 5Li H. Gomes P.J. Chen J.D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8479-8484Crossref PubMed Scopus (501) Google Scholar, 6Onate S.A. Tsai S.Y. Tsai M.J. O'Malley B.W. Science. 1995; 270: 1354-1357Crossref PubMed Scopus (2051) Google Scholar). They share 40% overall sequence similarity, and they all contain, in the N terminus, a basic helix-loop-helix domain that is known for protein dimerization-DNA interaction as well as a Per-Arnt-Sim domain, which is known to be involved in protein-protein interaction. Three LXXLL motifs, also known as nuclear receptor boxes (for nuclear receptor binding), are centrally located in all three proteins (7Heery D.M. Kalkhoven E. Hoare S. Parker M.G. Nature. 1997; 387: 733-736Crossref PubMed Scopus (1768) Google Scholar, 8Darimont B.D. Wagner R.L. Apriletti J.W. Stallcup M.R. Kushner P.J. Baxter J.D. Fletterick R.J. Yamamoto K.R. Genes Dev. 1998; 12: 3343-3356Crossref PubMed Scopus (827) Google Scholar, 9McInerney E.M. Rose D.W. Flynn S.E. Westin S. Mullen T.M. Krones A. Inostroza J. Torchia J. Nolte R.T. Assa-Munt N. Milburn M.V. Glass C.K. Rosenfeld M.G. Genes Dev. 1998; 12: 3357-3368Crossref PubMed Scopus (526) Google Scholar). In the C terminus, the SRC proteins contain two activation domains, AD1 and AD2, which are associated with histone acetyltransferases (CREB-binding protein/p300 and pCAF) and coactivator-associated arginine methyltransferase 1, respectively, and function to modify the configuration of the chromatin structure (10Sheppard H.M. Harries J.C. Hussain S. Bevan C. Heery D.M. Mol. Cell. Biol. 2001; 21: 39-50Crossref PubMed Scopus (93) Google Scholar, 11Stallcup M.R. Oncogene. 2001; 20: 3014-3020Crossref PubMed Scopus (151) Google Scholar). Despite the structural similarities among the members of the SRC family of coactivators, evidence has been accumulated to suggest different physiological functions for SRC-1, GRIP1, and AIB1. Genetic studies with gene ablation showed that, although both male and female SRC1-null mice are viable and fertile, they exhibit partial resistance to several hormones, including estrogen, progestin, androgen, and thyroid hormones (12Xu J. Qiu Y. DeMayo F.J. Tsai S.Y. Tsai M.J. O'Malley B.W. Science. 1998; 279: 1922-1925Crossref PubMed Scopus (591) Google Scholar, 13Weiss R.E. Xu J. Ning G. Pohlenz J. O'Malley B.W. Refetoff S. EMBO J. 1999; 18: 1900-1904Crossref PubMed Scopus (217) Google Scholar). Elimination of GRIP1 impairs fertility in both male and female mice (14Gehin M. Mark M. Dennefeld C. Dierich A. Gronemeyer H. Chambon P. Mol. Cell. Biol. 2002; 22: 5923-5937Crossref PubMed Scopus (221) Google Scholar), and GRIP-null mice are protected against obesity and display enhanced adaptive thermogenesis, whereas SRC-1 null mice are prone to obesity due to reduced energy expenditure (15Picard F. Gehin M. Annicotte J.S. Rocchi S. Champy M.F. O'Malley B.W. Chambon P. Auwerx J. Cell. 2002; 111: 931-941Abstract Full Text Full Text PDF PubMed Scopus (372) Google Scholar). It has been documented that, unlike SRC-1 and GRIP1, AIB1 is more promiscuous; it can enhance the transcriptional activity of a number of different activators (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar, 17Torres-Arzayus M.I. Font de Mora J. Yuan J. Vazquez F. Bronson R. Rue M. Sellers W.R. Brown M. Cancer Cell. 2004; 6: 263-274Abstract Full Text Full Text PDF PubMed Scopus (322) Google Scholar). Indeed, AIB1-null mice are not only abnormal in reproductive function but also small in animal size (18Xu J. Liao L. Ning G. Yoshida-Komiya H. Deng C. O'Malley B.W. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 6379-6384Crossref PubMed Scopus (454) Google Scholar, 19Wang Z. Rose D.W. Hermanson O. Liu F. Herman T. Wu W. Szeto D. Gleiberman A. Krones A. Pratt K. Rosenfeld R. Glass C.K. Rosenfeld M.G. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 13549-13554Crossref PubMed Scopus (170) Google Scholar). At the molecular level, we recently demonstrated SRC-1, GRIP1, and AIB1 are differentially implicated in steroid receptor-mediated gene transcription (20Zhang H. Yi X. Sun X. Yin N. Shi B. Wu H. Wang D. Wu G. Shang Y. Genes Dev. 2004; 18: 1753-1765Crossref PubMed Scopus (82) Google Scholar, 21Shang Y. Brown M. Science. 2002; 295: 2465-2468Crossref PubMed Scopus (990) Google Scholar, 22Wu H. Chen Y. Liang J. Shi B. Wu G. Zhang Y. Wang D. Li R. Yi X. Zhang H. Sun L. Shang Y. Nature. 2005; 438: 981-987Crossref PubMed Scopus (237) Google Scholar). The differential activity for SRC-1, GRIP1, and AIB1 is probably determined primarily by their intrinsic protein structures. Ultimately, the function of a protein is also regulated by additional mechanisms particularly post-translational modifications. It has been reported that the activity of the SRC proteins is regulated by phosphorylation. For example, SRC-1 has been shown to be phosphorylated by mitogen-activated protein kinase (MAPK) at Thr-1179 and Ser-1185. Mutations of these sites attenuated SRC-1 ability to coactivate progesterone receptor-dependent transcription (23Rowan B.G. Weigel N.L. O'Malley B.W. J. Biol. Chem. 2000; 275: 4475-4483Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar); MAPK also phosphorylates GRIP1 but at Ser-736, the integrity of which is required for a full GRIP1 transcriptional activation function (24Lopez G.N. Turck C.W. Schaufele F. Stallcup M.R. Kushner P.J. J. Biol. Chem. 2001; 276: 22177-22182Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar). Interestingly, these phosphorylation sites are not conserved in AIB1. AIB1 was shown to be phosphorylated by several different kinases, including MAPK, IκB kinase, and receptor tyrosine kinase HER2/neu (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar, 25Font de Mora J. Brown M. Mol. Cell. Biol. 2000; 20: 5041-5047Crossref PubMed Scopus (400) Google Scholar, 26Shou J. Massarweh S. Osborne C.K. Wakeling A.E. Ali S. Weiss H. Schiff R. J. Natl. Cancer Inst. 2004; 96: 926-935Crossref PubMed Scopus (985) Google Scholar), with Ser-505, Ser-543, Ser-860, and Ser-867 being identified as potential MAPK sites (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar). Sequence alignments for the SRC coactivators revealed that, whereas Ser-505 and Ser-543 of AIB1 are conserved in SRC-1 and GRIP1, Ser-860 and Ser-867 are unique for AIB1. Thus, different phosphorylation profiles may contribute, in part, to the differential activity of AIB1, GRIP1, and SRC-1. In addition to phosphorylation, recent studies have identified sumoylation as another important post-translational modification that regulates the biological functions of a protein. In sumoylation, SUMO (small ubiquitin-like modifier) is to a in a sequence is a and amino the nuclear a to in which a of and G. Genes Dev. 2004; 18: PubMed Scopus Google Scholar). to phosphorylation, sumoylation is a and is the function of is a nuclear that to a number of sumoylated proteins T. H. H. J. 2000; PubMed Scopus Google Scholar, J. Wang D. Wang Z. Mol. Cell. Biol. 2004; PubMed Scopus Google Scholar, L. S. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar, D. P. J. 2002; PubMed Scopus Google Scholar); is a nuclear that has an activity to that of J. M. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar, H. H. M.J. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar); in the T. H. H. J. 2000; PubMed Scopus Google Scholar, L. T. 2000; PubMed Scopus Google Scholar), and was primarily in the L. T. 2000; PubMed Scopus Google Scholar, S. T. S. N. H. K. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar). SUMO modification with an enhanced or attenuated activity of for example, as has been shown for nuclear receptors as receptor H. U. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: PubMed Scopus Google Scholar), receptor S. H. J. 2002; PubMed Scopus Google Scholar), progesterone receptor A. L. M. A. E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, H. L. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar), and estrogen receptor S. M. C. L. Mol. 2005; PubMed Scopus Google and their including SRC-1 A. L. M. A. E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), GRIP1 N. U. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar), and D. D. A. E. R.T. Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). In this we demonstrated that is to AIB1 and in contrast to GRIP1 and SRC-1, SUMO modification the transactivation activity of AIB1. In sumoylation of AIB1 with a decreased of AIB1 phosphorylation by MAPK, whereas AIB1 phosphorylation by MAPK was with a of the SUMO phosphorylation and sumoylation to the transcriptional activity of AIB1. and and to the AIB1 and the and domain to and and of by of Cancer signal-regulated kinase and against and was was and breast and in with to the For or for and with to for by treatment with or or for The and and a and or in and in and with The and nuclear protein as previously E. J. P. A. A. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar). The was at for at for the was with for at protein at for the was in or and proteins the by for in and The was a and the enhanced to the AIB1 by has recently been identified as an important mechanism that regulates protein functions in biological as gene structure and the SRC family of coactivators, both GRIP1 N. U. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google and SRC-1 A. L. M. A. E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google have been reported to be the for of AIB1 and the mechanism of the regulation of AIB1 we to AIB1 is also a sumoylated protein in For this we of breast by with shown in AIB1 also be with an that AIB1 is a sumoylated protein. Interestingly, AIB1 sumoylation treatment of with sumoylated AIB1 was although the AIB1 was SUMO are nuclear and it is that of the functions of SUMO in the In AIB1 functions as a that estrogen receptor-mediated transcription in the the treatment of In of the that sumoylated AIB1 was only in the of we to the sumoylation of AIB1 in or in the For this we and nuclear protein in the of was with these two protein the and with the by shown in sumoylated AIB1 was only in nuclear of the protein that sumoylated AIB1 in the The for of nuclear and was by a nuclear protein and a protein of in AIB1 to proteins at which are in in a sequence In the amino for the SUMO modification motifs, we three potential and in the AIB1 The and in the nuclear receptor interaction The in the to the protein/p300 interaction Interestingly, the and sites are conserved that are sumoylated in the two other members of the SRC SRC-1 and and GRIP1 and A. L. M. A. E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, N. U. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). these sites as in AIB1 as well as to the of AIB1 sumoylation its transactivation we AIB1 in which these or or to arginine and the AIB1 to domain The AIB1 in with or of a The with an by with an shown in be in all three AIB1, or whereas in AIB1 was that and all be the for SUMO in AIB1. The of was in all the sumoylation in AIB1, we the AIB1 or and or and and or with the with the against and the the against shown in SUMO was in the or and but not in the or and In the SUMO was in the AIB1 but not that In of SRC-1 or GRIP1 not SUMO showed that and are all sumoylation sites in AIB1 and an additional sumoylation in AIB1 with SRC-1 and of AIB1 the of AIB1 sumoylation the transactivation activity of AIB1, we with a with the or and the activity was shown in whereas AIB1 a as AIB1 activity was increased in that with AIB1 or The activity was in that with AIB1 In the of these the activity was in with a by estrogen suggest that the sumoylation of AIB1 attenuated its transactivation is a and of SUMO is to be a function of of or and function in the whereas is a the that sumoylation of AIB1 attenuated its transactivation activity and to which be involved in regulating AIB1 we or with AIB1 and AIB1 shown in of or activity in of in in the activity in with AIB1 In AIB1 although the of the was that of of not the activity. In the of in was of an which that are to its not these that functions to AIB1. The of the AIB1 and was by of a of the which a its wild J. Wang D. Wang Z. Mol. Cell. Biol. 2004; PubMed Scopus Google Scholar), enhanced transcription not these the that sumoylation of AIB1 its transcriptional and is for the SUMO AIB1 protein. AIB1 by and has been documented that AIB1 is regulated by phosphorylation, and the transcriptional activity of AIB1 is enhanced by MAPK activation (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar, 25Font de Mora J. Brown M. Mol. Cell. Biol. 2000; 20: 5041-5047Crossref PubMed Scopus (400) Google Scholar). MAPK can AIB1 Ser-505, Ser-543, Ser-860, and Ser-867 (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar). the mechanism of sumoylation and phosphorylation in to AIB1 transcriptional we MAPK activation and AIB1 phosphorylation in with for different of and protein for of MAPK activation and AIB1 phosphorylation. shown in treatment in increased of phosphorylated in the was more of the with against showed that the of was not In the with by with an showed phosphorylation of AIB1 the phosphorylation and sumoylation of AIB1, with E2, a or an and the proteins and with AIB1 by of the with or shown in treatment was associated with an increased AIB1 phosphorylation and decreased AIB1 sumoylation, whereas both and increased AIB1 sumoylation but decreased AIB1 phosphorylation, that the sumoylation and phosphorylation of AIB1 may in a coordinated of AIB1 by and a the coordinated sumoylation and phosphorylation of AIB1, we the of SUMO and MAPK the transactivation potential of AIB1. The SUMO AIB1 and as well as phosphorylation AIB1 used in to the of these AIB1 the of the activity including treatment with E2, or or with in shown in treatment with or which was associated with an increased sumoylation and a decreased phosphorylation of AIB1 as demonstrated in decreased treatment with or of led to an increased activity. The activity was with AIB1 all sumoylation whereas the activity was with AIB1 all phosphorylation these suggest a coordinated of sumoylation and phosphorylation in regulating AIB1 transcriptional activity. the coordinated of sumoylation and phosphorylation of AIB1, with the AIB1 or the AIB1 all sumoylation treatment or treatment with E2, and with the against and with The of the that phosphorylation was in sumoylation AIB1 treatment of with AIB1 or the AIB1 all phosphorylation The of these revealed the of sumoylation in phosphorylation AIB1 the treatment of a coordinated phosphorylation and sumoylation in regulating AIB1 activity. these may also to the of activity in and the overall activation of the activity in in and AIB1 is in the and R. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google and is in of breast as well as in of (3Anzick S.L. Kononen J. Walker R.L. Azorsa D.O. Tanner M.M. Guan X.Y. Sauter G. Kallioniemi O.P. Trent J.M. Meltzer P.S. Science. 1997; 277: 965-968Crossref PubMed Scopus (1430) Google Scholar, S. H. Walker R.L. S. R. Meltzer P. C. Cancer 1998; Google Scholar); AIB1 has important physiological and At the molecular level, AIB1, with the other two members of the SRC family of coactivators, GRIP1 and SRC-1, gene transcription by nuclear receptors as well as by other transcription factors, as and activators of and R.C. O'Malley B.W. 2005; PubMed Scopus Google Scholar, N. Wang D. Zhang H. Yi X. Sun X. Shi B. Wu H. Wu G. Wang X. Shang Y. Cancer 2004; PubMed Scopus Google Scholar). AIB1, GRIP1, and SRC-1 exhibit differential functions that are in animal as well as in transcriptional we demonstrated that SRC coactivator proteins function in in which AIB1 is the for GRIP1 and SRC-1 (20Zhang H. Yi X. Sun X. Yin N. Shi B. Wu H. Wang D. Wu G. Shang Y. Genes Dev. 2004; 18: 1753-1765Crossref PubMed Scopus (82) Google Scholar). The basic mechanisms underlying transcription by nuclear receptors a of an of of coactivators have been identified in recent and both and studies have demonstrated that these coactivators are differentially used by transcription factors, including nuclear in a and the molecular underlying this In the both nuclear receptors and have been shown to be for post-translational modifications by It is that post-translational modifications of these proteins the for a required for gene activation by nuclear receptors and coactivators and that this also coactivators to the activity of other of transcription R.C. O'Malley B.W. 2005; PubMed Scopus Google Scholar). is a mechanism of post-translational modifications implicated in of AIB1 has been shown to different kinases, as MAPK, IκB kinase, and receptor tyrosine kinase HER2/neu (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar, 19Wang Z. Rose D.W. Hermanson O. Liu F. Herman T. Wu W. Szeto D. Gleiberman A. Krones A. Pratt K. Rosenfeld R. Glass C.K. Rosenfeld M.G. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 13549-13554Crossref PubMed Scopus (170) Google Scholar, G.N. Turck C.W. Schaufele F. Stallcup M.R. Kushner P.J. J. Biol. Chem. 2001; 276: 22177-22182Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar, 25Font de Mora J. Brown M. Mol. Cell. Biol. 2000; 20: 5041-5047Crossref PubMed Scopus (400) Google Scholar, 26Shou J. Massarweh S. Osborne C.K. Wakeling A.E. Ali S. Weiss H. Schiff R. J. Natl. Cancer Inst. 2004; 96: 926-935Crossref PubMed Scopus (985) Google Scholar, R.C. Qin J. Y. Wong J. Xu J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar). It has been shown that different differentially AIB1 at different of sites and that these phosphorylated profiles of AIB1 for distinct physiological functions (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar). In studies in recent have identified another important post-translational SUMO has been shown to modify a number of proteins with important roles in including gene chromatin and of the to this two members of the SRC family of coactivators, GRIP1 and SRC-1, have been shown to be by SUMO A. L. M. A. E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, N. U. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). In sumoylated GRIP1 and SRC-1 are associated with their enhanced transactivation activity. In this we showed that the AIB1 is also a sumoylated protein. sumoylation attenuated AIB1 transactivation activity. are molecular for the mechanism by which SUMO addition regulates transcription activity. modification with SUMO the of the protein and or at critical the ability of the protein to with its is that sumoylation or protein-protein and regulates the of transcriptional sumoylation other modifications as or of sumoylated transcription of transcription to protein nuclear sites nuclear regulating their or In sumoylation the transcription activity of its protein an for that sumoylation AIB1 to its GRIP1 and SRC-1 is more these proteins are We reported a sumoylation in AIB1 of the nuclear receptor which has not been reported for GRIP1 and SRC-1. Interestingly, AIB1 was also shown to unique MAPK phosphorylation sites that are not conserved in SRC-1 and among Ser-505, Ser-543, Ser-860, and Ser-867 of AIB1, Ser-505 and Ser-543 are conserved in SRC-1 and GRIP1, and Ser-860 and Ser-867 are unique for AIB1 (16Wu R.C. Qin J. Yi P. Wong J. Tsai S.Y. Tsai M.J. O'Malley B.W. Mol. Cell. 2004; 15: 937-949Abstract Full Text Full Text PDF PubMed Scopus (265) Google Scholar). or not these unique modifications in AIB1 in to AIB1 be a of it is that of a protein is determined by the of the of the as AIB1, GRIP1, and SRC-1 exhibit differential that may be of differential post-translational modifications. by different post-translational modifications are important for of The phosphorylation and sumoylation has also been reported for transcription E. R.T. Mol. Cell. 12: Full Text Full Text PDF PubMed Scopus Google Scholar). that a phosphorylation and sumoylation may play important roles in regulating AIB1 activity. The overall transactivation potential of AIB1 be enhanced by activation of the MAPK a of SUMO in AIB1. the other the transcription activation potential of AIB1 is its sumoylation, which is with its Thus, it is to that a phosphorylation and sumoylation is critical in the of the AIB1 activity. In it is not treatment to of AIB1. the of treatment the sumoylation of AIB1 a for It is that, to the activation of MAPK estrogen treatment that for SUMO studies the of the molecular that the phosphorylation and