The KRAB-containing zinc-finger transcriptional regulator ZBRK1 activates SCA2 gene transcription through direct interaction with its gene product, ataxin-2

Abstract

Gene transcription is controlled by transcriptional regulators acting with specific co-regulators to allow gene activation and repression. Here, we report the identification of the KRAB-containing zinc-finger transcriptional regulator, ZBRK1, as an interaction partner of the SCA2 gene product ataxin-2. Furthermore, we discovered that an elevated ZBRK1 level resulted in increased ataxin-2 levels, whereas interference on transcriptional and protein levels of ZBRK1 yielded reduced ataxin-2 levels, suggesting that a complex comprising ZBRK1 and ataxin-2 regulates SCA2 gene transcription. A bioinformatic analysis utilizing the known ZBRK1 consensus DNA-binding motif revealed ZBRK1-binding sites in the SCA2 promoter. These predicted sites were experimentally validated by chromatin-immunoprecipitation experiments along with luciferase-based promoter analyses corroborating that SCA2 gene transcription is controlled by a ZBRK1/ataxin-2 complex. Finally, we demonstrate that SCA2 gene transcription is significantly reduced in colon tumors possessing low ZBRK1 transcripts. Thus, our results provide first evidence that ataxin-2 acts as a co-regulator of ZBRK1 activating its own transcription, thereby representing the first identified ZBRK1 co-activator.

Epigenetics DNA methylation in the core ataxin-2 gene promoter: novel physiological and pathological implications

“…The CpG sites situated close to the transcription start are predominantly targeted by methylation suggesting that these regions might be important in epigenetic control of ATXN2 expression. Recent findings on transcriptional activation of atxn2 gene by ATXN2 protein (through an interaction with ZBRK1) (Hallen et al 2011) and our data showing hypermethylation in this gene suggest that the self-activating function of ATXN2 may be modified by the methylation state of its own promoter and may influence the feedback loop for ATXN2 regulation during cellular stress (Hallen et al 2011). In this light, the reduced or enhanced ATXN2 expression by hyper-or hypomethylation leading to reduced ATXN2 levels or increased cellular burden of expanded polyQ protein, respectively, may lead to an maladaptive stress response.…”

“…The differential methylation of atxn2 might also have modifying effects in other pathological conditions connected with C27 CAG repeat expansions in atxn2, such as ALS (Elden et al 2010;Lee et al 2011), neuropsychiatry disorders (Rottnek et al 2008;Goyal et al 2010), and cancer (Wiedemeyer et al 2003;Hallen et al 2011) or as the causative mutant gene in autosomal dominant parkinsonism (Charles et al 2007;Payami et al 2003). An intuitive relationship between the methylation pattern in atxn2 promoter and phenotypes resulting from CAG expansions in the atxn2 locus would be based on the balance of the methylation pattern and consecutive expression levels of ATXN2 at given condition and cell types.…”

“…Recently, an interaction between the KRAB-containing zinc-finger transcriptional regulator (ZBRK1) and ATXN2 was reported. The ZBRK1/ATXN2 complex activates the atxn2 transcription, where ATXN2 acts as co-activator of ZBRK1 (Hallen et al 2011). Other modulating mechanism regulating the atxn2 expression was not found highlighting that regulation of ATXN2 expression is poorly understood.…”

“…Gaining insights in this mechanism is crucial, because pathogenic CAG expansions in the atxn2 gene are directly and/or indirectly linked to the development of devastating neurodegenerative disorders such as SCA2, Parkinson disease, ALS and frontotemporal lobar degeneration (Neumann et al 2006;Socal et al 2008;Elden et al 2010). In addition, the expression levels of ATXN2 have been found to be important in the development of some malignancies (Wiedemeyer et al 2003;Hallen et al 2011), suggesting a tumor suppressing activity for this gene. Cellular concentrations of ATXN2 were reported to be important in mRNA processing and translation under stress conditions through interaction with DEAD/H-box RNA helicase DDX6 and poly (A)-binding protein and consequent interference with the assembly of cellular P-body structures and stress granules (Nonhoff et al 2007).…”

Analysis of ZNF350/ZBRK1 promoter variants and breast cancer susceptibility in non-BRCA1/2 French Canadian breast cancer families

“…15 In particular, the co-repressor complex ZNF350/BRCA1/CtIP (CtTB-interacting protein) is implicated in the repression of highmobility group AT-hook 2 (HMGA2) and angiopoietin-1 (ANG1) genes, which are involved in increased proliferation, mammary acini formation, anchorage-independent growth and vascular formation in breast tumors. 16,17 In addition, the ZNF350 gene overexpression led to an increase of ataxin-2 (ATXN2) mRNA levels (spinocerebellar ataxia type 2: SCA2 gene), 18 which is involved in RNA metabolism and endocytic processes. [19][20][21][22][23] In breast cancer cells, ZNF350 was also identified as a transcriptional repressor of p21 when associated with the KRAB domain-associated protein 1.…”