Mammalian Bcnt/Cfdp1, a potential epigenetic factor characterized by an acidic stretch in the disordered N-terminal and Ser250 phosphorylation in the conserved C-terminal regions

Cfdp1 Is Essential for Cardiac Development and Function

Cardiovascular diseases (CVDs) are the prevalent cause of mortality worldwide. A combination of environmental and genetic effectors modulates the risk of developing them. Thus, it is vital to identify candidate genes and elucidate their role in the manifestation of the disease. Large-scale human studies have revealed the implication of Craniofacial Development Protein 1 (CFDP1) in Coronary Artery Disease (CAD). CFDP1 belongs to the evolutionary conserved Bucentaur (BCNT) family, and to date, its function and mechanism of action in Cardiovascular Development are still unclear. We utilized zebrafish to investigate the role of cfdp1 in the developing heart due to the high genomic homology, similarity in heart physiology, and ease of experimental manipulations. We showed that cfdp1 was expressed during development, and we tested two morpholinos and generated a cfdp1 mutant line. The cfdp1-/- embryos developed arrhythmic hearts and exhibited defective cardiac performance, which led to a lethal phenotype. Findings from both knockdown and knockout experiments showed that abrogation of cfdp1 leads to downregulation of Wnt signaling in embryonic hearts during valve development but without affecting Notch activation in this process. The cfdp1 zebrafish mutant line provides a valuable tool for unveiling the novel mechanism of regulating cardiac physiology and function. cfdp1 is essential for cardiac development, a previously unreported phenotype most likely due to early lethality in mice. The detected phenotype of bradycardia and arrhythmias is an observation with potential clinical relevance for humans carrying heterozygous CFDP1 mutations and their risk of developing CAD.

Overcoming off-targets: assessing Western blot signals for Bcnt/Cfdp1, a tentative component of the chromatin remodeling complex

The Bucentaur (BCNT) protein family is characterized by a conserved amino acid sequence at the C-terminus (BCNT-C domain) and plays an essential role in gene expression and chromosomal maintenance in yeast and Drosophila. The mammalian Bucentaur/Craniofacial developmental protein 1 (Bcnt/Cfdp1) is also a tentative component of the SNF2-related CBP activator protein (Srcap) chromatin remodeling complex, but little is known about its properties, partly because few antibodies are available to examine the endogenous protein. In this paper, we assigned the Western blot signal against the mouse Bcnt/Cfdp1 as a doublet of approximately 45 kDa using anti-Bcnt/Cfdp1 antibodies, which were generated against either of two unrelated immunogens, BCNT-C domain or mouse N-terminal peptide, and in addition, the Cfdp1 knockdown mouse ES cell line and bovine tissue were used as potential negative controls. Moreover, LC-MS/MS analysis of the corresponding doublet to the Flag-tagged mouse Bcnt/Cfdp1 that was constitutively expressed in a HEK293 cell exhibited that the upper band was much more phosphorylated than the lower band with preferential Ser phosphorylation in the WESF motif of BCNT-C domain. Western blot analysis with these evaluated antibodies indicated a preferential expression of Bcnt/Cfdp1 in the early stages of brain development of mouse and rat, which is consistent with a data file of the expression of Bcnt/Cfdp1 mRNA.

A spatial similarity of stereochemical environments formed by amino acid residues defines a common epitope of two non-homologous proteins

It is critical for development of high-quality antibodies in research and diagnostics to predict accurately their cross-reactivities with "off-target" molecules, which potentially induce false results. Herein, we report a good example of such a cross-reactivity for an off-target due to a stereochemical environment of epitopes, which does not simply depend on amino acid sequences. We found that significant subpopulation of a polyclonal peptide antibody against Bcnt (Bucentaur) (anti-BCNT-C antibody) cross-reacted with a completely different protein, glutamine synthetase (GS), and identified four amino acids, GYFE, in its C-terminal region as the core amino acids for the cross-reaction. Consistent with this finding, the anti-BCNT-C antibody strongly recognized endogenously and exogenously expressed GS in tissues and cultured cells by Western blotting and immunohistochemistry. Furthermore, we elucidated that the cross-reaction is caused by a spatial similarity between the stereochemical environments formed by amino acid residues, including the GYFE of GS and the GYIE of Bcnt, rather than by their primary sequences. These results suggest it is critical to comprehensively analyze antibody interactions with target molecules including off-targets with special attention to the physicochemical environments of epitope-paratope interfaces to decrease the risk of false interpretations of results using antibodies in science and clinical applications.

The role of JNK phosphorylation as a molecular target to enhance adenovirus replication, oncolysis and cancer therapeutic efficacy

Oncolytic adenoviruses (Ads) are cancer selective tumoricidal agents; however their mechanism of Ad-mediated cancer cell lysis, or oncolysis, remains undefined. This report focuses upon the autophagy mediator c-JUN n-terminal kinase (JNK) and its effects upon Ad oncolysis and replication. Previously, E1b-deleted Ads have been used to treat several hundred cancer patients with limited clinical efficacy. We hypothesize that by studying the potential interactions between E1b and JNK, mechanisms to improve oncolytic Ad design and cancer therapeutic efficacy may be elucidated. To test this hypothesis, E1b was selectively deleted from the Ad genome. These studies indicated that Ads encoding E1b induced JNK phosphorylation predominately occurred via E1b-19K. The expression of another crucial Ad gene E1a was then overexpressed by the CMV promoter via the replication competent Ad vector Adhz69; these data indicated that E1A also induced JNK phosphorylation. To assess the effects of host cell JNK expression upon Ad oncolysis and replication, siRNA targeting JNK1 and JNK2 (JNK1/2) were utilized. The oncolysis and replication of the E1b-19K wild-type Ads Ad5 and Adhz63 were significantly attenuated following JNK1/2 siRNA transfection. However the oncolytic effects and replication of the E1b-19K deleted Ad Adhz60 were not altered by JNK1/2 siRNA transfection, further implicating the crucial role of E1b-19K for Ad oncolysis and replication via JNK phosphorylation. This study has demonstrated for the first time that JNK is an intriguing molecular marker associated with enhanced Ad virotherapy efficacy, influencing future Ad vector design.

Functional analysis of the cfdp1 gene in zebrafish provides evidence for its crucial role in craniofacial development and osteogenesis

The CFDP1 proteins have been linked to craniofacial development and osteogenesis in vertebrates, though specific human syndromes have not yet been identified. Alterations of craniofacial development represent the main cause of infant disability and mortality in humans. For this reason, it is crucial to understand the cellular functions and mechanism of action of the CFDP1 protein in model vertebrate organisms. Using a combination of genomic, molecular and cell biology approaches, we have performed a functional analysis of the cfdp1 gene and its encoded protein, zCFDP1, in the zebrafish model system. We found that zCFDP1 is present in the zygote, is rapidly produced after MTZ transition and is highly abundant in the head structures. Depletion of zCFDP1, induced by an ATG-blocking morpholino, produces considerable defects in craniofacial structures and bone mineralization. Together, our results show that zCFDP1 is an essential protein required for proper development and provide the first experimental evidence showing that in vertebrates it actively participates to the morphogenesis of craniofacial territories.

Dual function of Swc5 in SWR remodeling ATPase activation and histone H2A eviction

The chromatin remodeler SWR deposits histone H2A.Z at promoters and other regulatory sites via an ATP-driven histone exchange reaction that replaces nucleosomal H2A with H2A.Z. Simultaneous binding of SWR to both H2A nucleosome and free H2A.Z induces SWR ATPase activity and engages the histone exchange mechanism. Swc5 is a conserved subunit of the 14-polypeptide SWR complex that is required for the histone exchange reaction, but its molecular role is unknown. We found that Swc5, although not required for substrate binding, is required for SWR ATPase stimulation, suggesting that Swc5 is required to couple substrate recognition to ATPase activation. A biochemical complementation assay was developed to show that a unique, conserved domain at the C-terminus of Swc5, called Bucentaur (BCNT), is essential for the histone exchange activity of SWR, whereas an acidic region at the N-terminus is required for optimal SWR function. In vitro studies showed the acidic N-terminus of Swc5 preferentially binds to the H2A–H2B dimer and exhibits histone chaperone activity. We propose that an auxiliary function of Swc5 in SWR is to assist H2A ejection as H2A.Z is inserted into the nucleosome.

The human Cranio Facial Development Protein 1 (Cfdp1) gene encodes a protein required for the maintenance of higher-order chromatin organization

The human Cranio Facial Development Protein 1 (Cfdp1) gene maps to chromosome 16q22.2-q22.3 and encodes the CFDP1 protein, which belongs to the evolutionarily conserved Bucentaur (BCNT) family. Craniofacial malformations are developmental disorders of particular biomedical and clinical interest, because they represent the main cause of infant mortality and disability in humans, thus it is important to understand the cellular functions and mechanism of action of the CFDP1 protein. We have carried out a multi-disciplinary study, combining cell biology, reverse genetics and biochemistry, to provide the first in vivo characterization of CFDP1 protein functions in human cells. We show that CFDP1 binds to chromatin and interacts with subunits of the SRCAP chromatin remodeling complex. An RNAi-mediated depletion of CFDP1 in HeLa cells affects chromosome organization, SMC2 condensin recruitment and cell cycle progression. Our findings provide new insight into the chromatin functions and mechanisms of the CFDP1 protein and contribute to our understanding of the link between epigenetic regulation and the onset of human complex developmental disorders.

Expression of human Cfdp1 gene in Drosophila reveals new insights into the function of the evolutionarily conserved BCNT protein family

The Bucentaur (BCNT) protein family is widely distributed in eukaryotes and is characterized by a highly conserved C-terminal domain. This family was identified two decades ago in ruminants, but its role(s) remained largely unknown. Investigating cellular functions and mechanism of action of BCNT proteins is challenging, because they have been implicated in human craniofacial development. Recently, we found that YETI, the D. melanogaster BCNT, is a chromatin factor that participates to H2A.V deposition. Here we report the effects of in vivo expression of CFDP1, the human BCNT protein, in Drosophila melanogaster. We show that CFDP1, similarly to YETI, binds to chromatin and its expression results in a wide range of abnormalities highly reminiscent of those observed in Yeti null mutants. This indicates that CFDP1 expressed in flies behaves in a dominant negative fashion disrupting the YETI function. Moreover, GST pull-down provides evidence indicating that 1) both YETI and CFDP1 undergo homodimerization and 2) YETI and CFDP1 physically interact each other by forming inactive heterodimers that would trigger the observed dominant-negative effect. Overall, our findings highlight unanticipated evidences suggesting that homodimerization mediated by the BCNT domain is integral to the chromatin functions of BCNT proteins.

Prospects and progress of antibody-drug conjugates in solid tumor therapies

INTRODUCTION

Antibody-drug conjugates (ADCs) for targeted chemotherapy have evolved in the past 2-3 decades to become a validated clinical cancer therapy modality. While considerable strides have been made in treating hematological tumors, challenges remain in the more difficult-to-treat solid cancers.

AREAS COVERED

The current model for a successful ADC uses a highly potent cytotoxic drug as the payload, with stringent linker requirements and limited substitutions. In solid tumor treatment, a number of ADCs have not progressed beyond Phase I clinical trials, indicating a need to optimize additional factors governing translational success. In this regard, insights from mathematical modeling provide a number of pointers relevant to target antigen and antibody selection. Together with the choice of targets, these can be expected to complement the gains made in ADC design towards the generation of better therapeutics.

EXPERT OPINION

While highly potent microtubule inhibitors continue to dominate the current ADC landscape, there are promising data with other drugs, linkers, and targets that suggest a more flexible model for a successful ADC is evolving. Such changes will undoubtedly lead to the consideration of new targets and constructs to overcome some of the unique natural barriers that impede the delivery of cytotoxic agents in solid tumor.