IntroductionThe transcription of inflammatory genes is rapidly induced by extracellular stimuli through coordinated actions of transcription factors and large coactivator complexes. However, the mechanistic interplay between specific chromatin remodelers and kinase modules in driving the transcriptional burst of early inflammatory genes remains poorly understood. This study investigates the roles of the PBAF chromatin remodeling complex and the Mediator kinase module (MKM) in activating NF-κB-dependent CXCL1, CXCL2, and CXCL3 chemokine genes.MethodsWe employed a combination of molecular and genomic techniques. Protein-protein interactions were analyzed via co-immunoprecipitation (co-IP). Transcriptional outputs of CXCL1-3 genes were measured by quantitative mRNA analysis. Chromatin immunoprecipitation (ChIP) was used to assess the occupancy of RNA polymerase II (Pol II), its elongating form (Pol II-S2P), the MKM subunit CDK8, and the PBAF complex (via its BAF200 subunit) at target gene promoters. Functional contributions of the complexes were dissected using siRNA-mediated knockdown of BAF200 (PBAF) and small-molecule inhibition of the MKM.ResultsPBAF and MKM physically interact with each other and with the NF-κB subunit RELA, and both complexes additively contribute to the transcriptional activation of CXCL1-3 genes. Knockdown of the PBAF-specific subunit BAF200 resulted in the loss of the entire PBAF complex from chromatin, a reduction in total Pol II and CDK8 promoter occupancy, and consequently, impaired gene induction. In contrast, MKM inhibition did not affect PBAF recruitment but specifically reduced the level of elongating Pol II-S2P and transcriptional activation. These data indicate non-redundant, stage-specific functions.DiscussionOur results demonstrate that the PBAF complex and the Mediator kinase module regulate distinct, sequential steps in the transcription cycle of CXCL1-3 genes. PBAF is critical for the initial promoter recruitment or stabilization of the transcription machinery, while MKM primarily facilitates the transition into productive elongation. Their additive positive effect and physical interaction suggest a coordinated mechanism where PBAF establishes a permissive chromatin context, enabling subsequent MKM-dependent phosphorylation events that drive the transcriptional burst of key inflammatory chemokines.

Background/Objectives: Currently, there is limited knowledge on the molecular mechanisms of the “non-canonical” Hippo signaling pathway in hematopoietic tumor cells. We have shown that targeting the MST1/2 kinases, which are the key molecules in this signaling pathway, may be an effective approach to the treatment of hematologic tumors. Methods: The methods used in this study include cell growth assays, caspase assays, Western blot hybridizations, flow cytometry, and whole-transcriptome analyses. These methods allowed us to better understand the molecular pathways at play. Results: Our results showed that XMU-MP-1, an inhibitor of MST1/2 kinase, specifically reduces the viability of hematopoietic cancer cells but not breast cancer cells. It effectively inhibits the growth of the tumor B- and T-cell lines by blocking cell cycle progression, mainly during the G2/M phase, inducing apoptosis and autophagy. XMU-MP-1 treatment led to increased caspase 3/7 activity and increased levels of the cleaved PARP protein. Levels of the LC3-II protein were also shown to be increased, while the level of p62 decreased. These changes are associated with apoptosis and autophagy, respectively. RNA-seq analysis has demonstrated that XMU-MP-1 suppressed the expression of cell cycle regulators, such as E2F, and cell division cycle genes CDC6,7,20,25,45; cyclins A2,B1,B2, and cyclin-dependent kinases. At the same time, it increased the expression of genes involved in apoptosis, autophagy, and necroptosis. Conclusions: Combinations of growth assays, caspase assays, Western blotting, and RNA-seq have shown that the dramatic reduction in the number of hematopoietic tumor cells after treatment with XMU-MP-1 is due to both cytostatic and cytotoxic effects. The use of MST1/2 kinase inhibitors could be highly promising for complex therapy of hematological tumors.

The MLE helicase of D. melanogaster, like its ortholog DHX9 in mammals, is involved in a wide range of processes related to the regulation of gene expression. In the present study, we investigated the impact of the mle[9] mutation on its own mRNA expression level. It was shown that in addition to the previously described deletion in the catalytic domain of the protein, which impairs its helicase activity, the mle[9] mutation contains an additional small deletion in the C-terminal domain. In the mle[9] mutation background, there was a threefold increase in the expression of the main transcript of the mle gene encoding the full-length protein. Binding of MLE to chromatin at the coding region and promoters of the mle gene and nearby enhancers was analyzed. To exclude the influence of dosage compensation, experiments were performed on females. The data obtained indicate the role of MLE in specific regulation of its own mRNA expression level in vivo at the adult stage.

Primary drug resistance of tumor cells or resistance acquired during treatment is among the main factors that significantly limit the efficacy of antitumor chemotherapy, along with severe side effects depending on the drug dose. To increase the efficacy, chemotherapeutics can be used in combination with substances that modulate the functions of cell signaling pathways. In this work, the substance XMU-MP-1, an inhibitor of key MST1/2 kinases of the Hippo signaling pathway, was shown to enhance the antitumor activity of two genotoxic chemotherapeutics, etoposide and cisplatin, against Namalwa Burkitt's B-cell lymphoma cells. XMU-MP-1 increased the cytotoxicity of the agents and significantly reduced their CTD50. The drug efficacy is therefore possible to increase significantly, and a therapeutic effect might be achieved at a lower drug concentration to reduce the likelihood of life-threatening side effects.

The PBAF chromatin remodeling complex of the SWI/SNF family plays a critical role in the regulation of gene expression during tissue differentiation and organism development. The subunits of the PBAF complex have domains responsible for binding to N-terminal histone sequences. It determines the specificity of binding of the complex to chromatin. PHF10, a specific subunit of the PBAF complex, contains a DPF domain, which is a unique chromatin interaction domain. A PHF10 isoform that lacks the DPF domain is also present in vertebrate cells. This work shows that during neuronal and muscle differentiation of human and mouse cells, the expression of PHF10 isoforms changes: the form that does not have DPF replaces the form in which it is present. Replacement of PHF10 isoforms in the PBAF complex may affect its selectivity in the regulation of genes in differentiating cells.

The TREX-2 complex of eukaryotes is responsible for the export of a wide range of mRNAs from the nucleus to the cytoplasm. Previously, we showed that a subunit of the D. melanogaster TREX-2 complex, the PCID2 protein, has a domain that specifically interacts with RNA. However, it remains unknown whether other components of the complex are involved in interaction with and recognition of the target mRNA. In the present study, we determined the role of Xmas-2, the core structural subunit of the complex, in the specific recognition of ras2 mRNA fragments. In this work, we showed that Xmas-2 interacts with ras2 mRNA independently of other subunits of the complex. We showed that RNA-binding domains are located in both the N-terminal domain and the C-terminal domain of Xmas-2. However, the interaction of the protein with ras2 mRNA fragments is independent of RNA sequence and structure and is nonspecific. Thus, the Xmas-2 subunit is not involved in the recognition of specific RNA sequences by the complex.

MLE of D. melanogaster is a conserved protein in higher eukaryotes, an ortholog of human DHX9 helicase. In mammals, this helicase has been shown to participate in different stages of gene expression. In D. melanogaster, the role of MLE as one of the components of the species-specific Dosage Compensation Complex has been extensively studied. However, the role of MLE in other processes has remained poorly understood. In this work, for the first time, the mle[9] mutation is mapped at the molecular level and shown to be caused by a deletion resulting in the loss of a highly conserved motif III in the catalytic core of the molecule. Thus, mle[9] specifically disrupts the helicase activity of the protein without affecting the function of other domains. The study of phenotypic manifestations of the mutation in females showed that in the homozygous state it has a pleiotropic effect. Without affecting survival, it significantly reduces fertility and lifespan. In addition, the duplication of scutellar macrochaetae was observed with high frequency. These results confirm that in D. melanogaster MLE helicase is involved in a wide range of gene expression regulation processes distinct from its role in dosage compensation.

The process of mRNA localization in the cytoplasm involves the directed transport of mRNP particles using the microtubule system. This transport is mediated and regulated by specific factors—adaptors between mRNA molecules and microtubule motor proteins. Adaptors are a key link in the mechanism of mRNA transport, but to date their identity and functioning are mostly unknown. In this review, we examine the features and importance of adaptor proteins in mRNA transport during oogenesis and in neuronal function. This article summarizes recent data on mRNA binding adaptors in the cytoplasm and the mechanisms of their interaction with microtubule motor proteins.

PHF10 is a subunit of the PBAF complex, which regulates the expression of many genes in developing and maturing organisms. PHF10 has four isoforms that differ in domain structure. The PHF10A isoform, containing a DPF domain at the C-terminus and 46 amino acids at the N-terminus, is necessary for the expression of proliferation genes; the functions of the other isoforms are less studied. In this work, we have established that, upon contact inhibition of mouse and human cell proliferation caused by the establishment of a tight junction and adherence junction between cells, the expression of the PHF10A isoform stops and instead the PHF10D isoform is expressed, which does not contain DPF-domain and N-terminal sequence. The function of the PHF10D isoform may be associated with the establishment of intercellular contacts.

The TREX-2-ORC protein complex of D. melanogaster is necessary for the export of the bulk of synthesized poly(A)-containing mRNA molecules from the nucleus to the cytoplasm through the nuclear pores. However, the role of this complex in the export of other types of RNA remains unknown. We have shown that TREX-2-ORC participates in the nuclear export of histone mRNAs: it associates with histone mRNPs, binds to histone H3 mRNA at the 3'-terminal part of the coding region, and participates in the export of histone mRNAs from the nucleus to the cytoplasm.

PCID2 protein is a component of the eukaryotic TREX-2 complex responsible for mRNA export from the nucleus to the cytoplasm. Previously, we showed that PCID2 of D. melanogaster is involved in specific mRNA recognition and identified key amino acids responsible for interaction with the RNA of the ras2 gene. In this work, we show that point mutations of these amino acids disrupt the interaction of the protein with cellular RNA and the export of polyA-containing mRNA from the nucleus to the cytoplasm in Drosophila cells.

The PCID2 protein is a component of the eukaryotic TREX-2 complex, which is responsible for mRNA export from the nucleus into the cytoplasm. We have previously shown that Drosophila melanogaster PCID2 is involved in specific mRNA recognition and identified the key amino acids responsible for its interaction with the ras2 RNA. In this work, point mutations of the amino acids were shown to disrupt the PCID2 interaction with cell RNAs and to distort the export of polyA-containing mRNAs from the nucleus into the cytoplasm in Drosophila cells.

ENY2 is an evolutionarily conserved multifunctional protein and is a member of several complexes that regulate various stages of gene expression. ENY2 is a subunit of the TREX-2 complex, which is necessary for the export of bulk mRNA from the nucleus to the cytoplasm through the nuclear pores in many eukaryotes. The wide range of ENY2 functions suggests that it can also associate with other protein factors or complexes. In a search for proteins that interact with ENY2 of Drosophila melanogaster, a cDNA library was screened in a yeast two-hybrid system. ENY2 was thus found to interact with the RNA-binding protein Paip2. Paip2 directly bound ENY2 in vitro and interacted with ENY2 in vivo at the molecular and genetic levels. Paip2 was capable of association with the ENY2-containing TREX-2 complex. Paip2 was present at the locus of the histone gene cluster. Both Paip2 and ENY2 were detected at histone locus body (HLBs), nuclear structure where coordinated histone mRNA transcription and processing take place. Paip2 and subunits of the TREX-2 complex were shown to associate with histone mRNP particles. A Paip2 knockdown via RNA interference resulted in decreased binding of TREX-2 subunits to histone mRNPs. Thus, Paip2 was identified as a new partner protein of ENY2 within the TREX-2 complex and suggested to participate in TREX-2 binding to histone mRNPs.

The TREX-2 protein complex is the key complex involved in the export of mRNA from the nucleus to the cytoplasm through the nuclear pores. Previously, a joint protein complex of TREX-2 with ORC was isolated in D. melanogaster . It was shown that the interaction of TREX-2 with ORC is necessary for efficient mRNA export from the nucleus to the cytoplasm. In this work, we showed that the TREX-2-ORC joint complex is also formed in human cells.

In mammals, a large number of proteins are expressed as more than one isoform, resulting in the increased diversity of their proteome. Understanding the functions of isoforms is very important, since individual isoforms of the same protein can have oncogenic or pathogenic properties, or serve as disease markers. The high homology of isoforms with ubiquitous expression makes it difficult to study them. In this work, we propose a new approach for the study of protein isoforms in mammalian cells, which makes it possible to individually detect and investigate the functions of an individual isoform. The approach was developed to study the functions of isoforms of the PHF10 protein, a chromatin subunit of the PBAF remodeling complex. We demonstrated the possibility of induced simultaneous suppression of all endogenous PHF10 isoforms and the expression of a single recombinant FLAG-tagged isoform. For this purpose, we created constructs based on the pSLIK plasmid with a cloned cassette containing the recombinant gene of interest and miR30 with the corresponding shRNAs. The doxycycline-induced activation of the cassette allows on and off switching. Using this construct, we achieved the preferential expression of only one recombinant PHF10 isoform with a simultaneously reduced number of all endogenous isoforms. Our approach can be used to study the role of point mutations, the functions of individual domains and important sites, or to individually detect untagged isoforms with knockdown of all endogenous isoforms.

The TREX-2 complex integrates several stages of gene expression, such as transcriptional activation and mRNA export. In D. melanogaster, TREX-2 consists of four major proteins: Xmas-2, ENY2, PCID2, and Sem1p. The Xmas-2 protein is the core subunit of the complex, with which other TREX-2 subunits interact. Xmas-2 homologues were found in all higher eukaryotes. Previously, it was shown that the human Xmas-2 homologue, GANP protein, can undergo cleavage into two parts, probably during apoptosis. We showed that the Xmas-2 protein of D. melanogaster can also split into two fragments. The resulting fragments of the protein correspond to the two large Xmas-2 domains. Protein splitting is observed both in vivo and in vitro. However, Xmas-2 cleavage in D. melanogaster is observed under normal conditions and is probably a part of the mechanism of transcription and mRNA export regulation in D. melanogaster.

The Drosophila melanogaster Maleless (MLE) protein is a conserved helicase involved in a wide range of gene expression regulation processes. A MLE ortholog, named DHX9, was found in many higher eukaryotes, including humans. DHX9 is involved in diverse processes, such as genome stability maintenance, replication, transcription, splicing, editing and transport of cellular and viral RNAs, and translation regulation. Some of these functions are understood in detail today, while most of them remain uncharacterized. Study of the functions of the MLE ortholog in mammals in vivo is limited by the fact that the loss of function of this protein is lethal at the embryonic stage. In D. melanogaster, helicase MLE was originally discovered and studied for a long time as a participant in dosage compensation. Recent evidence indicates that helicase MLE is involved in the same cell processes in D. melanogaster and mammals and that many of its functions are evolutionarily conserved. Experiments in D. melanogaster revealed new important MLE functions, such as a role in hormone-dependent regulation of transcription and interactions with the SAGA transcription complex, other transcriptional cofactors, and chromatin remodeling complexes. Unlike in mammals, MLE mutations do not cause embryonic lethality in D. melanogaster, and the MLE functions are possible to study in vivo throughout ontogenesis in females and up to the pupal stage in males. The human MLE ortholog is a potential target for anticancer and antiviral therapies. Further investigation of the MLE functions in D. melanogaster is therefore of both basic and applied importance. The review discusses the systematic position, domain structure, and conserved and specific functions of MLE helicase in D. melanogaster.

The Polybromo-associated BAF (BRG1- or BRM-associated factors) (PBAF) chromatin-remodeling complex is essential for transcription in mammalian cells. In this study, we describe a novel variant of the PBAF complex from differentiated neuronal cells, called dcPBAF, that differs from the canonical PBAF existing in proliferating neuroblasts. We describe that in differentiated adult neurons, a specific subunit of PBAF, PHF10, is replaced by a PHF10 isoform that lacks N- and C-terminal domains (called PHF10D). In addition, dcPBAF does not contain the canonical BRD7 subunit. dcPBAF binds promoters of the actively transcribed neuron-specific and housekeeping genes in terminally differentiated neurons of adult mice. Furthermore, in differentiated human neuronal cells, PHF10D-containing dcPBAF maintains a high transcriptional level at several neuron-specific genes.

The PBAF chromatin remodeling complex regulates chromatin state and gene transcription in higher eukaryotes. In this work, we studied the role of PBAF in the regulation of NF-κB-and JAK/STAT-dependent activation of inflammatory genes. We performed knockdown of specific module subunit BAF200, which resulted in destruction of the entire PBAF specific module and changed the level of the genes transcription of both pathways. PBAF can be both an activator and a repressor of inflammatory genes. Thus, PBAF is an important regulator of inflammatory gene expression.

Following the transcription step, the newly synthesized mRNA is exported from the nucleus to the cytoplasm and further to the translation site. The TREX-2 complex is involved in the step of mRNA export from the nucleus to the cytoplasm. This complex in Drosophila melanogaster consists of four proteins: Xmas-2, PCID2, ENY2, and Sem1p. In our work, we have shown that deletion of the C-terminal sequence of PCID2 leads to a decrease in the interaction of the protein with RNA and to impaired mRNA export from the nucleus to the cytoplasm in D. melanogaster .