Function of the C. elegans T-box Transcription Factor TBX-2 Depends on SUMOylation and Groucho

T-box transcription factors are critical regulators of development in all animals, and reduction of their function underlies a number of known diseases. Overexpression of T-box factors has been identified in several cancers, indicating their actions must be tightly regulated for normal function, however relatively little is known about the molecular mechanisms of their activity. In this work we show that the C. elegans T-box transcription factor TBX-2 depends on SUMOylation and interaction with a Groucho corepressor for its function in pharyngeal development. tbx-2 is required for a subset of cells in the anterior pharynx, those which give rise to pharyngeal muscle from the ABa lineage. Complete loss of tbx-2 results in a loss of anterior pharyngeal muscles and larval lethality. In a yeast two-hybrid screen we identified the SUMO-conjugating enzyme UBC-9 and the Groucho like corepressor UNC-37 as interactors of TBX-2, and reduction of their function in vivo also leads to a loss of anterior pharyngeal muscles. Furthermore, tbx-2 interacts genetically with both ubc-9 and unc-37, as partial reduction of tbx-2 and ubc-9 or tbx-2 and unc-37 causes a tbx-2 null-like phenotype. TBX-2 is a transcriptional repressor which regulates its own expression via a negative autoregulatory loop, and tbx-2 is the only direct TBX-2 target known to date. Knockdown of tbx-2, ubc-9, or unc-37 by RNA interference similarly leads to deregulation of tbx-2. Taken together, these results suggest TBX-2 may function in a repressor complex with SUMO and UNC-37 during pharyngeal development, and because we show TBX-2 and its mammalian orthologs can be SUMOylated, we propose this as a novel mechanism to regulate T-box factor activity.