patic fibrosis, glaucoma, and mild mental retardation depending on the nature of the mutation. A similar phenotype, including neonatal diabetes, polycystic kidney disease, and hypothyroidism, is observed in mice lacking functional Glis3. Moreover, a number of genome-wide-association studies have implicated GLIS3 as a risk locus for the development of type 1 and type 2 diabetes. Additional evidence suggests that Glis3 directly regulates insulin transcription in mature beta cells by binding two GlisBS located within the proximal Amezinium metilsulfate biological activity PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/1974422 promoter of the preproinsulin gene. While the ZFD is involved in DNA binding, transcriptional activation of gene expression by Glis3 is mediated through a transactivation domain located within its C-terminus. To better understand Glis3 function and its roles in disease it is imperative to identify the proteins that regulate or mediate its transcriptional activity. With the exception of a recent report demonstrating that the co-activator, CBP, interacts with Glis3 as part of a transcriptional activation complex that regulates PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19740312 insulin gene transcription, little is currently known about the proteins mediating Glis3 transcriptional activity. Posttranslational modifications, including phosphorylation, ubiquitination, and acetylation, are also critical in the regulation of the activity and function of many proteins. Ubiquitination of target proteins, which is mediated through a multi-enzyme cascade involving activating, conjugating, and ligating enzymes, is implicated in the regulation of many physiological processes and in the onset and progression of several pathologies. 
Ubiquitination has multiple functions that include proteolytic and nonproteolytic roles. The role of ubiquitination in proteolytic degradation by the 26S proteasome is the best studied and provides an important mechanism to regulate protein levels and protein activity, including transcriptional regulation. To obtain greater insights into the mechanisms of action of Glis3, it is important to identify the posttranslational modifications that regulate Glis3 activity and function as well as the proteins that catalyze these changes. In addition to the centrally positioned ZFD and the activation domain at the C-terminus, Glis3 contains a relatively large N-terminus, the function of which is predominately unknown. Previous reports identified a highly conserved region of ~100 amino acids within Glis3 termed the N-terminal conserved region that shares extensive homology with a corresponding region of the downstream effectors of hedgehog signaling, Gli1-3. In order to obtain further insights into the role of the N-terminus of Glis3 in the regulation of its activity and function, we used two different strategies to identify proteins interacting with the Glis3 Nterminus. In the first strategy, the Glis3 N-terminus was isolated by affinity coimmunoprecipitation and analyzed by gel-enhanced liquid chromatography mass spectrometry. In the second strategy, we performed yeast two-hybrid analysis using the N-terminus of Glis3 as bait to identify interacting protein partners. The two methods identified several WW-domain containing proteins homologous to the E6 AP carboxyl terminus E3 ubiquitin ligase, including members of the Nedd4-family of E3 ligases, Nedd4, Smurf1-2, and Itch/AIP4. Follow up studies demonstrated that Itch, Smurf2, and NEDD4 interacted with Glis3 through their WW-domains and that interaction with Itch resulted in 2 / 22 Regulation of Glis3 Activity by