Dataset Information

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

ABSTRACT: 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.

SUBMITTER: Buchberger E

PROVIDER: S-EPMC3795655 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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

Buchberger Elisabeth E El Harchi Miriam M Payrhuber Dietmar D Zommer Anna A Schauer Dominic D Simonitsch-Klupp Ingrid I Bilban Martin M Brostjan Christine C

PloS one 20131011 10

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 aggregate ...[more]

PMID: 24146931

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Project description:In the cell, misfolded proteins are processed by molecular chaperone-mediated refolding or through ubiquitin-mediated proteosome system. Dysregulation of these mechanisms facilitates the aggregation of misfolded proteins and forms aggresomes in the juxta nuclear position of the cell which are removed by lysosome-mediated autophagy pathway in the subsequent cell division. Accumulation of misfolded proteins in the cell is hallmark of several neurological disorders and other diseases including cancer. However, the exact mechanism of aggresome formation and clearance is not thoroughly understood. Reports have shown that several proteins including p300, p53, TAU, ?-synuclein, SOD, etc. contain intrinsically disordered region (IDR) which has the tendency to form aggresome. To study the nature of aggresome formation and stability of the aggresome, we have chosen Twist1 as a model protein since it has IDR regions. Twist1 is a bHLH transcription factor which plays a major role in epithelial mesenchymal transition (EMT) and shown to interact with HAT domain of p300 and p53. In the present study, we generated several deletion mutants of human Twist1 with different fluorescent tags and delineated the regions responsible for aggresome formation. The Twist1 protein contains two NLS motifs at the N-terminal region. We showed that the deletions of regions spanning the amino acids 30-46 (Twist1?30-46) which lacks the first NLS motif form larger and intense aggregates while the deletion of residues from 47 to 100 (Twist1?47-100) which lacks the second NLS motif generates smaller and less intense aggregates in the juxta nuclear position. This suggests that both the NLS motifs are needed for the proper nuclear localization of Twist1. The aggresome formation of the Twist1 deletion mutants was confirmed by counterstaining with known aggresome markers: Vimentin, HDAC6, and gamma tubulin and further validated by MG-132 treatment. In addition, it was found that the aggresomes generated by the Twist1?30-46 construct are more stable than the aggresome produced by the Twist1?47-100 construct as well as the wild-type Twist1 protein. Taken together, our data provide an important understanding on the role of IDR regions on the formation and stability of aggresomes.

Dataset Information

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

Publications

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

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