T-cell proto-oncogene rhombotin-2 is a complex transcription regulator containing multiple activation and repression domains

The LIM domain protein rhombotin-2 (RBTN-2/TTG-2/LMO2) is involved in many processes, including leukemogenesis and erythropoiesis, It is thought that the principle role of RBTN-2 in these processes is to regulate transcription. To examine the potential for RBTN-8 to modulate transcription, we constructed RBTN-2/GAL4 DNA-binding domain fusion proteins and measured their ability to activate transcription of a reporter gene construct, From these studies we identified a transcription activation domain within the NH, terminus of RBTN-2, This activation domain was further localized within a proline-rich 19-amino acid region, A second activation domain of 11 amino acids was also identified. This domain was located within the COOH terminus of RBTN-8, and functioned in mammalian cells but not in yeast, Furthermore, the two LIM domains of RBTN-2 were shown to function as transcription repression domains. Each individual LIM domain acted as an independent transcription repression domain on a heterologous activation domain. However, in context of full-length RBTN-8, the LIM domains selectively repressed the NH2-terminal activation domain, but had no effect on the COOH-terminal domain, Overall, these results demonstrate that the T-cell oncogene RBTN-2 is a complex transcription factor possessing multiple transcription regulatory modules, including two activation domains and two repression domains.