BTB domain mutations perturbing KCTD15 oligomerisation cause a distinctive frontonasal dysplasia syndrome

INTRODUCTION

KCTD15 encodes an oligomeric BTB domain protein reported to inhibit neural crest formation through repression of Wnt/beta-catenin signalling, as well as transactivation by TFAP2. Heterozygous missense variants in the closely related paralogue KCTD1 cause scalp-ear-nipple syndrome.

METHODS

Exome sequencing was performed on a two-generation family affected by a distinctive phenotype comprising a lipomatous frontonasal malformation, anosmia, cutis aplasia of the scalp and/or sparse hair, and congenital heart disease. Identification of a de novo missense substitution within KCTD15 led to targeted sequencing of DNA from a similarly affected sporadic patient, revealing a different missense mutation. Structural and biophysical analyses were performed to assess the effects of both amino acid substitutions on the KCTD15 protein.

RESULTS

A heterozygous c.310G>C variant encoding p.(Asp104His) within the BTB domain of KCTD15 was identified in an affected father and daughter and segregated with the phenotype. In the sporadically affected patient, a de novo heterozygous c.263G>A variant encoding p.(Gly88Asp) was present in KCTD15. Both substitutions were found to perturb the pentameric assembly of the BTB domain. A crystal structure of the BTB domain variant p.(Gly88Asp) revealed a closed hexameric assembly, whereas biophysical analyses showed that the p.(Asp104His) substitution resulted in a monomeric BTB domain likely to be partially unfolded at physiological temperatures.

CONCLUSION

BTB domain substitutions in KCTD1 and KCTD15 cause clinically overlapping phenotypes involving craniofacial abnormalities and cutis aplasia. The structural analyses demonstrate that missense substitutions act through a dominant negative mechanism by disrupting the higher order structure of the KCTD15 protein complex.

Zinc Finger and BTB Domain-Containing 20: A Newly Emerging Player in Pathogenesis and Development of Human Cancers

Zinc finger and BTB domain-containing 20 (ZBTB20), which was initially identified in human dendritic cells, belongs to a family of transcription factors (TFs) with an N-terminal BTB domain and one or more C-terminal DNA-binding zinc finger domains. Under physiological conditions, ZBTB20 acts as a transcriptional repressor in cellular development and differentiation, metabolism, and innate immunity. Interestingly, multiple lines of evidence from mice and human systems have revealed the importance of ZBTB20 in the pathogenesis and development of cancers. ZBTB20 is not only a hotspot of genetic variation or fusion in many types of human cancers, but also a key TF or intermediator involving in the dysregulation of cancer cells. Given the diverse functions of ZBTB20 in both health and disease, we herein summarize the structure and physiological roles of ZBTB20, with an emphasis on the latest findings on tumorigenesis and cancer progression.

Hepatic Zbtb18 (Zinc Finger and BTB Domain Containing 18) alleviates hepatic steatohepatitis via FXR (Farnesoid X Receptor)

A lasting imbalance between fatty acid synthesis and consumption leads to non-alcoholic fatty liver disease (NAFLD), coupled with hepatitis and insulin resistance. Yet the details of the underlying mechanisms are not fully understood. Here, we unraveled that the expression of the transcription factor Zbtb18 is markedly decreased in the livers of both patients and murine models of NAFLD. Hepatic Zbtb18 knockout promoted NAFLD features like impaired energy expenditure and fatty acid oxidation (FAO), and induced insulin resistance. Conversely, hepatic Zbtb18 overexpression alleviated hepato-steatosis, insulin resistance, and hyperglycemia in mice fed on a high-fat diet (HFD) or in diabetic mice. Notably, in vitro and in vivo mechanistic studies revealed that Zbtb18 transcriptional activation of Farnesoid X receptor (FXR) mediated FAO and Clathrin Heavy Chain (CLTC) protein hinders NLRP3 inflammasome activity. This key mechanism by which hepatocyte's Zbtb18 expression alleviates NAFLD and consequent liver fibrosis was further verified by FXR's deletion and forced expression in mice and cultured mouse primary hepatocytes (MPHs). Moreover, CLTC deletion significantly abrogated the hepatic Zbtb18 overexpression-driven inhibition of NLRP3 inflammasome activity in macrophages. Altogether, Zbtb18 transcriptionally activates the FXR-mediated FAO and CLTC expression, which inhibits NLRP3 inflammasome's activity alleviating inflammatory stress and insulin resistance, representing an attractive remedy for hepatic steatosis and fibrosis.

Formononetin enhances the chemosensitivity of triple negative breast cancer via BTB domain and CNC homolog 1-mediated mitophagy pathways

This study aimed to investigate the effects of formononetin on triple negative breast cancer (TNBC). Clinical samples were collected from patients with TNBC. Overall survival rates were evaluated using the Kaplan-Meier method. Gene expression was determined using immunohistochemistry, immunofluorescence and western blot. Cellular functions were determined using CCK-8, colony formation and propidium iodide (PI) staining. Xenograft assay was performed to further verify the effects of formononetin (FM) on TNBC. We found that FM combined therapy suppressed the metastasis of TNBC and increased the overall survival rates of TNBC patients. Moreover, FM suppressed the proliferation and induced mitochondrial damage and apoptosis of TNBC cells. FM increased the expression of the BTB domain and CNC homolog 1 (BACH1) in TNBC tissues as well as cells. However, BACH1 knockdown antagonized the effects of FM and promoted the survival of TNBC cells. FM suppressed the tumor growth of TNBC. Taken together, FM suppressed the aggressiveness of TNBC via BACH1/p53 signaling. Therefore, FM may be an alternative strategy for TNBC.

Optimizing Shape Complementarity Enables the Discovery of Potent Tricyclic BCL6 Inhibitors

To identify new chemical series with enhanced binding affinity to the BTB domain of B-cell lymphoma 6 protein, we targeted a subpocket adjacent to Val18. With no opportunities for strong polar interactions, we focused on attaining close shape complementarity by ring fusion onto our quinolinone lead series. Following exploration of different sized rings, we identified a conformationally restricted core which optimally filled the available space, leading to potent BCL6 inhibitors. Through X-ray structure-guided design, combined with efficient synthetic chemistry to make the resulting novel core structures, a >300-fold improvement in activity was obtained by the addition of seven heavy atoms.

A BTB/POZ domain-containing protein negatively regulates plant immunity in Nicotiana benthamiana

Plants have evolved immune systems to fight against pathogens. However, it is still largely unknown how the plant immunity is finely regulated. Here we identified a BTB/POZ domain-containing protein, namely NbBTB, which is predicted to be a member of the ubiquitin E3 ligase complex. The NbBTB expression is downregulated upon the oomycete pathogen Phytophthora parasitica infection. Overexpression of NbBTB in Nicotiana benthamiana promoted plant susceptibility to P. parasitica infection, and silencing NbBTB increased plant resistance to P. parasitica, indicating that NbBTB negatively modulates plant basal defense. Interestingly, overexpressing or silencing NbBTB did not affect plant resistance to two bacterial pathogens Ralstonia solanacearum and Pseudomonas syringae, suggesting that NbBTB is specifically involved in basal defense against oomycete pathogen. Expression of NbBTB suppressed hypersensitive response (HR) triggered by avirulence proteins from both R. sonanacearum and P. infestans, and silencing NbBTB showed the opposite effect, indicating that NbBTB negatively regulates effector-triggered immunity (ETI). Protein accumulation of avirulence effectors in NbBTB-silenced plants was significantly enhanced, suggesting that NbBTB is likely to negatively modulate ETI by affecting effector protein accumulation. Together, our results demonstrated that NbBTB is a negative regulator in both plant basal defense and ETI.

The BTB/POZ domain protein GmBTB/POZ promotes the ubiquitination and degradation of the soybean AP2/ERF-like transcription factor GmAP2 to regulate the defense response to Phytophthora sojae

Phytophthora root and stem rot in soybean (Glycine max) is a destructive disease worldwide, and hence improving crop resistance to the causal pathogen, P. sojae, is a major target for breeders. However, it remains largely unclear how the pathogen regulates the various affected signaling pathways in the host, which consist of complex networks including key transcription factors and their targets. We have previously demonstrated that GmBTB/POZ enhances soybean resistance to P. sojae and the associated defense response. Here, we demonstrate that GmBTB/POZ interacts with the transcription factor GmAP2 and promotes its ubiquitination. GmAP2-RNAi transgenic soybean hairy roots exhibited enhanced resistance to P. sojae, whereas roots overexpressing GmAP2 showed hypersensitivity. GmWRKY33 was identified as a target of GmAP2, which represses its expression by directly binding to the promoter. GmWRKY33 acts as a positive regulator in the response of soybean to P. sojae. Overexpression of GmBTB/POZ released the GmAP2-regulated suppression of GmWRKY33 in hairy roots overexpressing GmAP2 and increased their resistance to P. sojae. Taken together, our results indicate that GmBTB/POZ-GmAP2 modulation of the P. sojae resistance response forms a novel regulatory mechanism, which putatively regulates the downstream target gene GmWRKY33 in soybean.

The highly interactive BTB domain targeting other functional domains to diversify the function of BTB proteins in rice growth and development

The BTB (broad-complex, tram track, and bric-abrac) proteins are involved in developmental processes, biotic, and abiotic stress responses in various plants, but the molecular basis of protein interactions is yet to be investiagted in rice. In this study, the identified BTB proteins were divided into BTB-TAZ, MATH-BTB, BTB-NPH, BTB-ANK, BTB-Skp, BTB-DUF, and BTB-TPR subfamilies based on the additional functional domains found together with the BTB domain at N- and C-terminal as well. This suggesting that the extension region at both terminal sites could play a vital role in the BTB gene family expansion in plants. The yeast two-hybrid system, firefly luciferase complementation imaging (LCI) assay and bimolecular fluorescence complementation (BiFC) assay further confirmed that BTB proteins interact with several other proteins to perform a certain developmental process in plants. The overexpression of BTB genes of each subfamily in Arabidopsis revealed that BTB genes including OsBTB4, OsBTB8, OsBTB64, OsBTB62, OsBTB138, and OsBTB147, containing certain additional functional domains, could play a potential role in the early flowering, branching, leaf, and silique development. Thus we concluded that the presence of other functional domains such as TAZ, SKP, DUF, ANK, NPH, BACK, PQQ, and MATH could be the factor driving the diverse functions of BTB proteins in plant biology.

Elevated expression of sepiapterin reductase, regulator of G protein signaling 1, hypothetical protein CXorf58 homolog, and zinc finger and BTB domain-containing protein 21 isoform X2 is associated with progression of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers associated with high mortality rate. Understanding of events leading to HCC pathophysiology is essential for its better management. We earlier reported development of a novel rodent model by administrating chemical carcinogens, DEN, and 2-AAF for study of HCC at very early stage. 2D-Electrophoresis analysis of total serum proteins identified several differentially expressed proteins in animals undergoing tumorigenesis. MALDI-TOF-MS/MS analyses were performed to characterize the differentially expressed proteins. Further real-time PCR analyses were taken place to quantify the transcript expression for the identified proteins at HCC initiation and tumor stages. Considering protein-protein interactions among the experimentally identified proteins and their interacting neighbors, a protein network has been analyzed that provided further insight into molecular events taking place during HCC development. Histological changes confirmed HCC initiation and hepatotumorigenesis at 1 and 4 months post carcinogen treatment, respectively. Four differentially expressed proteins were identified which were further characterized as regulator of G protein signaling 1 (RGS1), sepiapterin reductase (SPR), similar to zinc finger and BTB domain-containing protein 21 isoform X2 (ZNF295), and a hypothetical protein CXorf58 homolog. Quantification of transcripts for these proteins revealed elevation in their expression both at initiation and tumorigenesis stages. The study deciphers the regulatory role of these proteins during HCC progression.

Zinc finger and BTB domain-containing protein 20 aggravates angiotensin II-induced cardiac remodeling via the EGFR-AKT pathway

Zinc finger and BTB domain-containing protein 20 (ZBTB20) play an important role in glucose and lipid homeostasis. ZBTB20 was shown to be a crucial protein for the maintenance of cardiac contractile function. However, the role of ZBTB20 in cardiac response remodeling has not been elucidated. Thus, this study aimed to explore the role of ZBTB20 in cardiac remodeling following angiotensin II insult. Mice were subjected to angiotensin II infusion to induce a cardiac adverse remodeling model. An adeno-associated virus (AAV) 9 system was used to deliver ZBTB20 to the mouse heart. Here, we demonstrate that ZBTB20 expression is elevated in angiotensin II-induced cardiac remodeling and in response to cardiomyocyte insults. Furthermore, AAV9-mediated overexpression of ZBTB20 caused cardiac wall hypertrophy, chamber dilation, increased fibrosis, and reduced ejection fraction. Additionally, ZBTB20 siRNA protected cardiomyocytes from angiotensin II-induced hypertrophy. Mechanistically, ZBTB20 interferes with EGFR and Akt signaling and modulates the remodeling response. Overexpression of constitutively active Akt counteracts ZBTB20 knockdown-mediated protection of adverse cardiac remodeling. These findings illustrate the role of ZBTB20 in the transition of adverse cardiac remodeling toward heart failure and provide evidence for the molecular programs inducing adverse cardiac remodeling. KEY MESSAGES: ZBTB20 is a transcription factor from the POK family. ZBTB20 is upregulated in heart tissue treated with angiotensin II. ZBTB20 influences cardiomyocyte hypertrophy via the EGFR-Akt pathway. Akt continuous activation leads to similar results to ZBTB20 overexpression.

GmBTB/POZ promotes the ubiquitination and degradation of LHP1 to regulate the response of soybean to Phytophthora sojae

Phytophthora sojae is a pathogen that causes stem and root rot in soybean (Glycine max [L.] Merr.). We previously demonstrated that GmBTB/POZ, a BTB/POZ domain-containing nuclear protein, enhances resistance to P. sojae in soybean, via a process that depends on salicylic acid (SA). Here, we demonstrate that GmBTB/POZ associates directly with soybean LIKE HETEROCHROMATIN PROTEIN1 (GmLHP1) in vitro and in vivo and promotes its ubiquitination and degradation. Both overexpression and RNA interference analysis of transgenic lines demonstrate that GmLHP1 negatively regulates the response of soybean to P. sojae by reducing SA levels and repressing GmPR1 expression. The WRKY transcription factor gene, GmWRKY40, a SA-induced gene in the SA signaling pathway, is targeted by GmLHP1, which represses its expression via at least two mechanisms (directly binding to its promoter and impairing SA accumulation). Furthermore, the nuclear localization of GmLHP1 is required for the GmLHP1-mediated negative regulation of immunity, SA levels and the suppression of GmWRKY40 expression. Finally, GmBTB/POZ releases GmLHP1-regulated GmWRKY40 suppression and increases resistance to P. sojae in GmLHP1-OE hairy roots. These findings uncover a regulatory mechanism by which GmBTB/POZ-GmLHP1 modulates resistance to P. sojae in soybean, likely by regulating the expression of downstream target gene GmWRKY40.

Structural analysis of the PATZ1 BTB domain homodimer

PATZ1 is a ubiquitously expressed transcriptional repressor belonging to the ZBTB family that is functionally expressed in T lymphocytes. PATZ1 targets the CD8 gene in lymphocyte development and interacts with the p53 protein to control genes that are important in proliferation and in the DNA-damage response. PATZ1 exerts its activity through an N-terminal BTB domain that mediates dimerization and co-repressor interactions and a C-terminal zinc-finger motif-containing domain that mediates DNA binding. Here, the crystal structures of the murine and zebrafish PATZ1 BTB domains are reported at 2.3 and 1.8 Å resolution, respectively. The structures revealed that the PATZ1 BTB domain forms a stable homodimer with a lateral surface groove, as in other ZBTB structures. Analysis of the lateral groove revealed a large acidic patch in this region, which contrasts with the previously resolved basic co-repressor binding interface of BCL6. A large 30-amino-acid glycine- and alanine-rich central loop, which is unique to mammalian PATZ1 amongst all ZBTB proteins, could not be resolved, probably owing to its flexibility. Molecular-dynamics simulations suggest a contribution of this loop to modulation of the mammalian BTB dimerization interface.

GmBTB/POZ, a novel BTB/POZ domain-containing nuclear protein, positively regulates the response of soybean to Phytophthora sojae infection

Phytophthora sojae is a destructive pathogen of soybean [Glycine max (L.) Merr.] which causes stem and root rot on soybean plants worldwide. However, the pathogenesis and molecular mechanism of plant defence responses against P. sojae are largely unclear. Herein, we document the underlying mechanisms and function of a novel BTB/POZ protein, GmBTB/POZ, which contains a BTB/POZ domain found in certain animal transcriptional regulators, in host soybean plants in response to P. sojae. It is located in the cell nucleus and is transcriptionally up-regulated by P. sojae. Overexpression of GmBTB/POZ in soybean resulted in enhanced resistance to P. sojae. The activities and expression levels of enzymatic superoxide dismutase (SOD) and peroxidase (POD) antioxidants were significantly higher in GmBTB/POZ-overexpressing (GmBTB/POZ-OE) transgenic soybean plants than in wild-type (WT) plants treated with sterile water or infected with P. sojae. The transcript levels of defence-associated genes were also higher in overexpressing plants than in WT on infection. Moreover, salicylic acid (SA) levels and the transcript levels of SA biosynthesis-related genes were markedly higher in GmBTB/POZ-OE transgenic soybean than in WT, but there were almost no differences in jasmonic acid (JA) levels or JA biosynthesis-related gene expression between GmBTB/POZ-OE and WT soybean lines. Furthermore, exogenous SA application induced the expression of GmBTB/POZ and inhibited the increase in P. sojae biomass in both WT and GmBTB/POZ-OE transgenic soybean plants. Taken together, these results suggest that GmBTB/POZ plays a positive role in P. sojae resistance and the defence response in soybean via a process that might be dependent on SA.

Backbone resonance assignment of the BCL6-BTB/POZ domain

BCL6 is a transcriptional repressor. Two domains of the protein, the N-terminal BTB-POZ domain and the RD2 domain are responsible for recruitment of co-repressor molecules and histone deacetylases. The BTB-POZ domain is found in a large and diverse range of proteins that play important roles in development, homeostasis and neoplasia. Crystal structures of several BTB-POZ domains, including BCL6 have been determined. The BTB-POZ domain of BCL6 not only mediates dimerisation but is also responsible for recruitment of co-repressors such as SMRT, NCOR and BCOR. Interestingly both SMRT and BCOR bind to the same site within the BCL6 BTB-POZ domain despite having very different primary sequences. Since both peptides and small molecules have been shown to bind to the co-repressor binding site it would suggest that the BTB_POZ domain is a suitable target for drug discovery. Here we report near complete backbone ¹⁵N, ¹³C and ¹H assignments for the BTB-POZ domain of BCL6 to assist in the analysis of binding modes for small molecules.