Interacts with EP300 and acts as a repressor of MYOD-dependent transcription and muscle differentiation. Inhibits EP300 histone acetyltransferase activity. Acts as a repressor of TGFB/SMAD transcriptional responses. May act as a repressor of the TGFB/SMAD3-dependent signaling by selectively blocking formation of TGFB-induced SMAD3-SMAD4 complex (By similarity). Heterodimer with EID2B. Interacts with the C-terminus of EP300. Interacts with HDAC1 and HDAC2. Interacts with SMAD2, SMAD4 and with the MH2 domain of SMAD3 (By similarity). The N-terminal portion of EID2 is required for nuclear localization.