No abstract

In this study, we report that the Krüppel-like zinc finger transcription factor Gli-similar 3 (Glis3) is induced during the secondary transition of pancreatic development, a stage of cell lineage specification and extensive patterning, and that Glis3 zf/zf mutant mice develop neonatal diabetes, evidenced by hyperglycemia and hypoinsulinemia. The Glis3 zf/zf mutant mouse pancreas shows a dramatic loss of ␤ and ␦ cells, contrasting a smaller relative loss of ␣, PP, and cells. In addition, Glis3 zf/zf mutant mice develop ductal cysts, while no significant changes were observed in acini. Gene expression profiling and immunofluorescent staining demonstrated that the expression of pancreatic hormones and several transcription factors important in endocrine cell development, including Ngn3, MafA, and Pdx1, were significantly decreased in the developing pancreata of Glis3 zf/zf mutant mice. The population of pancreatic progenitors appears not to be greatly affected in Glis3 zf/zf mutant mice; however, the number of neurogenin 3 (Ngn3)-positive endocrine cell progenitors is significantly reduced. Our study indicates that Glis3 plays a key role in cell lineage specification, particularly in the development of mature pancreatic ␤ cells. In addition, we provide evidence that Glis3 regulates insulin gene expression through two Glis-binding sites in its proximal promoter, indicating that Glis3 also regulates ␤-cell function.

In this study, we examine the potential role of receptorassociated protein 80 (RAP80), a nuclear protein containing two ubiquitin-interacting motifs (UIM), in DNA damage response and double-strand break (DSB) repair. We show that following ionizing radiation and treatment with DNA-damaging agents, RAP80 translocates to discrete nuclear foci that colocalize with those of ;-H2AX. The UIMs and the region of amino acids 204 to 304 are critical for the relocalization of RAP80 to ionizing radiation-induced foci (IRIF). These observations suggest that RAP80 becomes part of a DNA repair complex at the sites of IRIF. We also show that RAP80 forms a complex with the tumor repressor BRCA1 and that this interaction is mediated through the BRCA1 COOH-terminal repeats of BRCA1. The UIMs are not required for the interaction of RAP80 with BRCA1. Knockdown of RAP80 in HEK293 cells significantly reduced DSB-induced homologydirected recombination (HDR). Moreover, inhibition of RAP80 expression by small interfering RNA increased radiosensitivity, whereas increased radioresistance was observed in human breast cancer MCF-7 cells with overexpression of RAP80. Taken together, our data suggest that RAP80 plays an important role in DNA damage response signaling and HDR-mediated DSB repair. We further show that RAP80 can function as a substrate of the ataxia-telangiectasia mutated protein kinase in vitro, which phosphorylates RAP80 at Ser 205 and Ser 402 . We show that this phosphorylation is not required for the migration of RAP80 to IRIF. [Cancer Res 2007;67(14):6647-56]

In this study, we describe the identification and characterization of a novel transcription factor GLI-similar 3 (GLIS3). GLIS3 is an 83.8 kDa nuclear protein containing five C2H2-type Krüppel-like zinc finger motifs that exhibit 93% identity with those of GLIS1, however, little homology exists outside their zinc finger domains. GLIS3 can function as a repressor and activator of transcription. Deletion mutant analysis determined that the N- and C-termini are required for optimal transcriptional activity. GLIS3 binds to the GLI-RE consensus sequence and is able to enhance GLI-RE-dependent transcription. GLIS3(DeltaC496), a dominant-negative mutant, inhibits transcriptional activation by GLIS3 and GLI1. Whole mount in situ hybridization on mouse embryos from stage E6.5 through E14.5 demonstrated that GLIS3 is expressed in specific regions in developing kidney and testis and in a highly dynamic pattern during neurulation. From E11.5 through E12.5 GLIS3 was strongly expressed in the interdigital regions, which are fated to undergo apoptosis. The temporal and spatial pattern of GLIS3 expression observed during embryonic development suggests that it may play a critical role in the regulation of a variety of cellular processes during development. Both the repressor and activation functions of GLIS3 may be involved in this control.