The nucleolar PICT-1/GLTSCR2 protein forms homo-oligomers

The human "protein interacting with carboxyl terminus 1" (PICT-1), also designated as the "glioma tumor suppressor candidate region 2 gene product", GLTSCR2, is a nucleolar protein whose activity is, as yet, unknown. Contradictory results regarding the role of PICT-1 in cancer have been reported, and PICT-1 has been suggested to function either as a tumor suppressor protein or as an oncogene. In this study, we demonstrate self-association of PICT-1. Through yeast two-hybrid assay, we identified PICT-1 as its own interaction partner. We confirmed the interaction of PICT-1 with itself by direct yeast two-hybrid assay and also showed self-association of PICT-1 in mammalian cells by co-immunoprecipitation and fluorescence resonance energy transfer assays. Furthermore, we confirmed direct self-association of PICT-1 by using in vitro microfluidic affinity binding assays. The later assay also identified the carboxy-terminal domain as mediating self-interaction of PICT-1. Glutaraldehyde cross-linking and gel-filtration assays suggest that PICT-1 forms dimers, though it may form higher-order complexes as well. Our findings add another layer of complexity in understanding the different functions of PICT-1 and may help provide insights regarding the activities of this protein.