Ubiquitin recruiting chimera: more than just a PROTAC.

Ubiquitinylation of protein substrates results in various but distinct biological consequences, among which ubiquitin-mediated degradation is most well studied for its therapeutic application. Accordingly, artificially targeted ubiquitin-dependent degradation of various proteins has evolved into the therapeutically relevant PROTAC technology. This tethered ubiquitinylation of various targets coupled with a broad assortment of modifying E3 ubiquitin ligases has been made possible by rational design of bi-specific chimeric molecules that bring these proteins in proximity. However, forced ubiquitinylation inflicted by the binary warheads of a chimeric PROTAC molecule should not necessarily result in protein degradation but can be used to modulate other cellular functions. In this respect it should be noted that the ubiquitinylation of a diverse set of proteins is known to control their transport, transcriptional activity, and protein-protein interactions. This review provides examples of potential PROTAC usage based on non-degradable ubiquitinylation.

BRCA Mutations-The Achilles Heel of Breast, Ovarian and Other Epithelial Cancers.

Two related tumor suppressor genes, BRCA1 and BRCA2, attract a lot of attention from both fundamental and clinical points of view. Oncogenic hereditary mutations in these genes are firmly linked to the early onset of breast and ovarian cancers. However, the molecular mechanisms that drive extensive mutagenesis in these genes are not known. In this review, we hypothesize that one of the potential mechanisms behind this phenomenon can be mediated by Alu mobile genomic elements. Linking mutations in the BRCA1 and BRCA2 genes to the general mechanisms of genome stability and DNA repair is critical to ensure the rationalized choice of anti-cancer therapy. Accordingly, we review the literature available on the mechanisms of DNA damage repair where these proteins are involved, and how the inactivating mutations in these genes (BRCAness) can be exploited in anti-cancer therapy. We also discuss a hypothesis explaining why breast and ovarian epithelial tissues are preferentially susceptible to mutations in BRCA genes. Finally, we discuss prospective novel therapeutic approaches for treating BRCAness cancers.

Transglutaminase 2 Regulates Innate Immunity by Modulating the STING/TBK1/IRF3 Axis.

We have recently shown that type 2 transglutaminase (TG2) plays a key role in the host's inflammatory response during bacterial infections. In this study, we investigated whether the enzyme is involved in the regulation of the STING pathway, which is the main signaling activated in the presence of both self- and pathogen DNA in the cytoplasm, leading to type I IFN (IFN I) production. In this study, we demonstrated that TG2 negatively regulates STING signaling by impairing IRF3 phosphorylation in bone marrow-derived macrophages, isolated from wild-type and TG2 knockout mice. In the absence of TG2, we found an increase in the IFN-ß production and in the downstream JAK/STAT pathway activation. Interestingly, proteomic analysis revealed that TG2 interacts with TBK1, affecting its interactome composition. Indeed, TG2 ablation facilitates the TBK1-IRF3 interaction, thus indicating that the enzyme plays a negative regulatory effect on IRF3 recruitment in the STING/TBK1 complex. In keeping with these findings, we observed an increase in the IFNß production in bronchoalveolar lavage fluids from COVID-19-positive dead patients paralleled by a dramatic decrease of the TG2 expression in the lung pneumocytes. Taken together, these results suggest that TG2 plays a negative regulation on the IFN-ß production associated with the innate immunity response to the cytosolic presence of both self- and pathogen DNA.

Perspective on multi-target antiplatelet therapies: high content phenotypic screening as an unbiased source of novel polypharmacological strategies.

Platelets play an important role in cardiovascular thrombosis as well as in many other pathological conditions such as inflammation, atherosclerosis and cancer. While multi-target strategies to treat complex diseases are gaining considerable attention, current development of antiplatelet therapies is mostly oriented towards several single targets, arising from our present understanding of the regulation of platelet activation. Limited efforts to develop multi-target agents or multidrug therapies are mostly due to a lack of a systematic basis to define target combinations with synergistic effects. Here we discuss the perspective to use high content phenotypic screening of in vitro models as a potential source for inference of synergetic multi-target strategies to control platelet activation.

Polyclonal antibodies against human proteasome subunits PSMA3, PSMA5, and PSMB5.

A proteasome is a multi-subunit protein complex, which plays a central role in ubiquitin-dependent protein degradation in all eukaryotic cells. The 26S proteasome is composed of a catalytic 20S core complex and one or two 19S regulatory complexes. The 20S core complex forms a cylinder consisting of four stacked rings of seven α (PSMA1-7) or ß (PSMB1-7) subunits. Target proteins are degraded in the cavity of the 20S complex due to proteolytic activities of three ß subunits having catalytic sites located on the inner surface of the cylinder. The aim of this study was the generation of polyclonal antibodies against human proteasome subunits PSMA3, PSMA5, and PSMB5 and characterization of their experimental applications. To construct GST-fusion proteins, DNA sequences encoding PSMA3, PSMA5, and PSMB5 were cloned into prokaryotic expression vectors pGEX-5X-1 or pGEX-4T-3. Recombinant proteins GST-PSMA3, GST-PSMA5, and GST-PSMB5 were highly expressed in E. coli BL21 (DE3) cells, purified by glutathione-affinity chromatography and further used for rabbit immunization. The activity and specificity of the obtained antibody-containing sera were evaluated using Western blot analysis and immunoprecipitation. We have shown by Western blot analysis that our anti-PSMA3, anti-PSMA5, and anti-PSMB5 antibodies recognized both recombinant and endogenous proteins from different human cell lines. We have also shown that anti-PSMA3 and anti-PSMA5 sera were able to recognize and immunoprecipitate native forms of both endogenous and overexpressed FLAG-tagged proteins PSMA3 and PSMA5, respectively. Thus, the antibodies generated against PSMA3, PSMA5, and PSMB5 can be used in various experimental applications, including the evaluation of cellular levels of proteasome subunits in cell extracts and affinity purification of the endogenous and/or overexpressed proteasome subunits, which facilitates subsequent analysis of their post-translational modifications as well as protein-protein interactions in vivo.

Lysine-specific demethylase 1 regulates the embryonic transcriptome and CoREST stability.

Lysine-specific demethylase 1 (LSD1), which demethylates mono- and dimethylated histone H3-Lys4 as part of a complex including CoREST and histone deacetylases (HDACs), is essential for embryonic development in the mouse beyond embryonic day 6.5 (e6.5). To determine the role of LSD1 during this early period of embryogenesis, we have generated loss-of-function gene trap mice and conditional knockout embryonic stem (ES) cells. Analysis of postimplantation gene trap embryos revealed that LSD1 expression, and therefore function, is restricted to the epiblast. Conditional deletion of LSD1 in mouse ES cells, the in vitro counterpart of the epiblast, revealed a reduction in CoREST protein and associated HDAC activity, resulting in a global increase in histone H3-Lys56 acetylation, but not H3-Lys4 methylation. Despite this biochemical perturbation, ES cells with LSD1 deleted proliferate normally and retain stem cell characteristics. Loss of LSD1 causes the aberrant expression of 588 genes, including those coding for transcription factors with roles in anterior/posterior patterning and limb development, such as brachyury, Hoxb7, Hoxd8, and retinoic acid receptor γ (RARγ). The gene coding for brachyury, a key regulator of mesodermal differentiation, is a direct target gene of LSD1 and is overexpressed in e6.5 Lsd1 gene trap embryos. Thus, LSD1 regulates the expression and appropriate timing of key developmental regulators, as part of the LSD1/CoREST/HDAC complex, during early embryonic development.

Lysine methylation goes global.

The process of post-translational covalent modifications of proteins represents a transcription-independent regulatory mechanism allowing rapid alteration of protein activity and function in response to various intra- and extracellular stimuli. Lysine methylation (KM) was deemed to be a constant covalent mark, providing long-term signaling, including the histone-dependent mechanism for transcriptional memory. Only recently has it become apparent that lysine methylation, similar to other covalent modifications, is transient and can be dynamically regulated by an opposing activity, de-methylation. These discoveries accelerated a systematic search for other nonhistone substrates of lysine methylation, especially among transcription factors. Recent findings suggest that KM affects gene expression not only at the level of chromatin, but also by modifying transcription factors.