Sumoylation of corepressor scaffold attachment factor b1-mechanism of action and biological relevance in breast cancer.

Abstract #3046

Scaffold attachment factor B1 (SAFB1) was originally isolated due to its ability to bind Scaffold/Matrix attachment regions of genomic DNA. Subsequently, SAFB1 has also been shown to be involved in RNA processing, chromatin organization and stress response. Work from our laboratory has shown that SAFB1 can bind and modulate transcription of the HSP-27 promoter and repress activity of ERα. Repression of ERα occurs through an independent and transferable c-terminal repression domain. Further work has indicated that SAFB1 can interact with and repress transactivation of a host of nuclear receptors suggesting a general role for SAFB1 in transcriptional repression. Many proteins associated with transcriptional regulation are post translationally modified by small ubiquitin like modifier (SUMO). SUMO is a 98 amino acid mature polypeptide that is added post translationally to target proteins usually within a consensus sumoylation motif, YKXE (where Y is a large hydrophobic residue, K-lysine of modification and X any residue). SUMO modification of proteins associated with transcription has generally been associated with transcriptional repression. The mechanism by which this modification leads to transcriptional repression has yet to be defined. Work by our laboratory has indicated that SAFB1 is modified by sumoylation. Immunoprecpitation studies indicated modification of SAFB1 by SUMO1. To better understand the potential role sumoylation plays in SAFB1's function we mutated both lysines within the two consensus sumoylation sites to arginine creating a SAFB1 K2R mutant. Mutation of these sumoylation sites lead to loss of interaction between SAFB1 and SUMO1 by co-immunoprecipitation. Mutation of the sumoylation sites also lead to loss of transcriptional repression. Transient transfection ERE-Tk-Luciferase assays showed a loss of repression with overexpression of SAFB1 K2R compared to SAFB1 WT. To examine the effect of SAFB1 sumoylation on its intrinsic repressive capability transient transfection Gal4-DBD assays were performed. Loss of transcriptional repression was seen with SAFB1 K2R compared to SAFB1 WT indicating an effect of sumoylation on SAFB1's intrinsic repressive function. The mechanism by which SAFB1 is sumoylated and the extent of the functional consequences of this sumoylation has yet to be determined. Ongoing studies within the lab are aimed at addressing this question. Studies are focused to the conjugating and deconjugating enzymes responsible for SAFB1 sumoylation. Other work is aimed at determining possible changes in protein-protein interaction or subcellular localization with sumoylation of SAFB1. In relation to the potential role of SAFB1 sumoylation in breast cancer, DNA from clinical breast cancer specimens is going to be sequenced to examine possible mutation present within the SAFB1 sumoylatyion sites that may be important in clinical breast cancer specimens.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3046.