The relationship between BCL6 bodies and nuclear sites of normal and halogenated DNA and RNA synthesis

Multi-SUMOylation of NAC1 is essential for the growth of prostate cancer cells

Nucleus accumbens-associated 1 (NAC1) is a member of pox virus and zinc finger/bric-a-brac tramtrack broad complex (BTB/POZ) gene family. Overexpression of NAC1 is implicated in cancer development, recurrence and chemotherapy resistance. In our previous study, we found NAC1 was a potential small ubiquitin-like modifier (SUMO) substrate in prostate cancer cells. However, there was still lack of evidences to further support and validate the result. In this work, we found that NAC1 is a multi-SUMO-sites acceptor. The SUMO acceptor lysines were K167, K318, K368, K483 and K498. SUMOylation didn't alter the localization of NAC1, but facilitated the formation of NAC1 nuclear bodies. Compared with NAC1 wild type (NAC1 WT), the SUMO-sites mutant of NAC1 (NAC1 SM) suppressed cell proliferation and tumor growth in cellular and animal levels. This work uncovered the function of SUMOylation of NAC1 in prostate cancer cells.

Overexpression of the transcriptional repressor complex BCL-6/BCoR leads to nuclear aggregates distinct from classical aggresomes

Nuclear inclusions of aggregated proteins have primarily been characterized for molecules with aberrant poly-glutamine repeats and for mutated or structurally altered proteins. They were termed “nuclear aggresomes” and misfolding was shown to promote association with molecular chaperones and proteasomes. Here, we report that two components of a transcriptional repressor complex (BCL-6 and BCoR) of wildtype amino acid sequence can independently or jointly induce the formation of nuclear aggregates when overexpressed. The observation that the majority of cells rapidly downregulate BCL-6/BCoR levels, supports the notion that expression of these proteins is under tight control. The inclusions occur when BCL-6/BCoR expression exceeds 150-fold of endogenous levels. They preferentially develop in the nucleus by a gradual increase in aggregate size to form large, spheroid structures which are not associated with heat shock proteins or marked by ubiquitin. In contrast, we find the close association of BCL-6/BCoR inclusions with PML bodies and a reduction in aggregation upon the concomitant overexpression of histone deacetylases or heat shock protein 70. In summary, our data offer a perspective on nuclear aggregates distinct from classical “nuclear aggresomes”: Large complexes of spheroid structure can evolve in the nucleus without being marked by the cellular machinery for protein refolding and degradation. However, nuclear proteostasis can be restored by balancing the levels of chaperones.

The zinc finger transcription factor ZXDC activates CCL2 gene expression by opposing BCL6-mediated repression

The zinc finger X-linked duplicated (ZXD) family of transcription factors has been implicated in regulating transcription of major histocompatibility complex class II genes in antigen presenting cells; roles beyond this function are not yet known. The expression of one gene in this family, ZXD family zinc finger C (ZXDC), is enriched in myeloid lineages and therefore we hypothesized that ZXDC may regulate myeloid-specific gene expression. Here we demonstrate that ZXDC regulates genes involved in myeloid cell differentiation and inflammation. Overexpression of the larger isoform of ZXDC, ZXDC1, activates expression of monocyte-specific markers of differentiation and synergizes with phorbol 12-myristate 13-acetate (which causes differentiation) in the human leukemic monoblast cell line U937. To identify additional gene targets of ZXDC1, we performed gene expression profiling which revealed multiple inflammatory gene clusters regulated by ZXDC1. Using a combination of approaches we show that ZXDC1 activates transcription of a gene within one of the regulated clusters, chemokine (C-C motif) ligand 2 (CCL2; monocyte chemoattractant protein 1; MCP1) via a previously defined distal regulatory element. Further, ZXDC1-dependent up-regulation of the gene involves eviction of the transcriptional repressor B-cell CLL/lymphoma 6 (BCL6), a factor known to be important in resolving inflammatory responses, from this region of the promoter. Collectively, our data show that ZXDC1 is a regulator in the process of myeloid function and that ZXDC1 is responsible for Ccl2 gene de-repression by BCL6.

Functional studies of BCL11A: characterization of the conserved BCL11A-XL splice variant and its interaction with BCL6 in nuclear paraspeckles of germinal center B cells

Background

Chromosomal aberrations of BCL11A at 2p16.1 have been reported in a variety of B-cell malignancies and its deficiency in mice leads to a profound block in B-cell development.

Results

Alternative pre-mRNA splicing of BCL11A produces multiple isoforms sharing a common N-terminus. The most abundant isoform we have identified in human lymphoid samples is BCL11A-XL, the longest transcript produced at this locus, and here we report the conservation of this major isoform and its functional characterization. We show that BCL11A-XL is a DNA-sequence-specific transcriptional repressor that associates with itself and with other BCL11A isoforms, as well as with the BCL6 proto-oncogene. Western blot data for BCL11A-XL expression coupled with data previously published for BCL6 indicates that these genes are expressed abundantly in germinal-center-derived B cells but that expression is extinguished upon terminal differentiation to the plasma cell stage. Although BCL11A-XL/BCL6 interaction can modulate BCL6 DNA binding in vitro, their heteromeric association does not alter the homomeric transcriptional properties of either on model reporter activity. BCL11A-XL partitions into the nuclear matrix and colocalizes with BCL6 in nuclear paraspeckles.

Conclusion

We propose that the conserved N-terminus of BCL11A defines a superfamily of C2HC zinc-finger transcription factors involved in hematopoietic malignancies.