Abstract 4732: Repression of transcriptional activity by the retinoid target gene G0S2

Abstract

Abstract Acute promyelocytic leukemia (APL) cases that express the PML/RARα fusion protein block maturation of myeloid precursors. All-trans retinoic acid (RA)-based differentiation therapy of these APL cases causes clinical remissions. Yet, clinical use of RA is associated with toxicities and drug resistance. In the search for RA target genes that can serve as alternative therapeutic targets in APL, G0S2 was found as one of the most rapidly and prominently RA-induced species. G0S2 is a 103 amino acid protein without apparent homology domains to other species. It was recently shown to inhibit adipose triglyceride lipase (ATGL) activity, leading to repression of lipolysis. G0S2 is abundantly expressed in adipose tissues, which is consistent with its role in regulating lipolysis. It is also induced in response to inflammatory stimuli in other cell types, indicating it has additional roles beyond fat storage. Here, we report a new G0S2 function uncovered after its transient transfection that led to substantial repression of reporter activities of multiple constructs (including RA-regulated species RARα, UBE1L and G0S2 itself). This repression was antagonized by siRNA-mediated G0S2 knockdown. Notably, an engineered form of G0S2 that lacked the internal hydrophobic domain did not exhibit these repressive effects. Inhibitors of either the proteasomal or lysosomal pathways did not overcome this suppression by G0S2. Thus, these repressive activities were unlikely due to enhanced proteasome or lysosome activities. The reported inhibition of ATGL activity by G0S2 causes an increase in lipid droplet size, which can also be achieved by treating cells with the neutral lipid oleic acid. Yet, this treatment did not impact reporter activity, indicating that changes in lipid droplet size did not affect this transcriptional repression. Intriguingly, G0S2 expression did not reduce endogenous expression of RARα, UBE1L or G0S2 (each RA-regulated species), indicating that only exogenous genes were affected by G0S2 transient transfection. Subcellular localization of endogenous G0S2 was examined in RA-treated NB4 APL cells and G0S2 was markedly expressed in the cytosol and membranes of these cells. Transiently transfected G0S2 protein was also detected in the cytoplasm. In summary, we report a previously unrecognized function for the RA target gene G0S2: it repressed exogenous reporter activity, but not endogenous gene expression. Both endogenous and exogenous G0S2 proteins were detected in the cytoplasm. Mechanistic studies that engage this G0S2 repressive effect are now underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4732. doi:1538-7445.AM2012-4732