Ebf1 as a nuclear matrix protein

Abstract

EBF1 is a highly conserved transcription factor that plays pivotal roles in the development of normal and malignant B cells. In mice, homozygous loss of Ebf1 completely suppresses normal B-cell development, while heterozygosity results in decreased pro-B cell numbers and increased DNA damage accumulation upon UV light exposure. In man, EBF1 deletions are typically heterozygous and frequently occur in B-cell precursor acute lymphoblastic leukaemia. In contrast to EBF1 deletions, EBF1 mutations are found in mature B cell malignancies. Both mutations and deletions are thought to function via loss of EBF1’s transcriptional activities.Here, I show that Ebf1 depletion in Abelson transformed murine pro-B cells resulted in rapid cell cycle arrest associated with nuclear collapse and heterochromatin accumulation at the periphery of the nuclei. Using in situ fractionation, I was able to show that a fraction of EBF1 was detected in the isolated nuclear matrix fraction, suggesting that EBF1 might be involved in nuclear matrix regulation of pro-B cells. Preliminary proteomics data suggested that EBF1 might interact with nuclear structural proteins including SRSF2, RPL14 LGALS9 and MTDH; loss of function of these proteins might play a role in the nuclear collapse upon EBF1 depletion. EBF1 depletion also resulted in pro-B cell arrest at the G1 phase and rapid CCND3 protein degradation. CCND3 was previously shown to localize on the nuclear structural matrix in pro-B cells. Therefore, it was hypothesized that CCND3 might interact with EBF1 at the nuclear matrix. Here I show that EBF1 does not interact with CCND3, and they do not have a potential common structural binding partners. Conclusion: My data suggest that EBF1 may have functions within the nuclear matrix independent of its transcriptional activities.