Sara Polletti

Genome-wide association studies investigating autoimmune disorders may reveal previously unrecognized regulators of immune cell functions. A Crohn’s disease risk allele was associated with increased expression in T lymphocytes of the adapter protein Src kinase–associated phosphoprotein 2 (SKAP2), whose functional role in these cells is unknown. By analyzing T cells from individuals homozygous for either allelic variant or engineered to modulate SKAP2 endogenous levels, we found that SKAP2 promotes T cell adhesion while restraining migration, acting nonredundantly with its homologue SKAP1. Consistent with such functional differences, SKAP1 and SKAP2 displayed distinct activation-induced regulation as well as unique protein interactomes. Prolonged TCR activation triggered caspase-mediated SKAP2 cleavage, leading to the disassembly of its interactome and enabling a migratory program. Together, these findings identify SKAP2 as a genetically regulated modulator of T cell function whose expression and activity control the balance between adhesion and migration.

Myelodysplastic syndromes (MDS) are heterogeneous myeloid neoplasms associated with an increased risk of progression to secondary acute myeloid leukemia (sAML). This study investigates the genomic correlates of disease progression in MDS by profiling active genomic regulatory regions and their transcriptional impact using H3K27ac chromatin immunoprecipitation–sequencing and RNA-sequencing analysis on CD34+ bone marrow progenitors cells isolated from a prospective cohort of 86 and 357 patients, respectively. Our analysis revealed distinct patterns of genomic region activation and transcriptional regulation across different disease stages such as low-risk MDS, high-risk MDS, and sAML. Unexpectedly, unsupervised clustering revealed a subset of patients with low-risk MDS displaying regulatory and transcriptional profiles similar to those of high-risk MDS and sAML, highlighting early molecular events that may predispose patients to disease progression. This subset is characterized by PU.1 genomic occupancy in regions linked to immune and inflammatory responses, increased T-cell and natural killer cell activation, and a higher frequency of SRSF2 mutations. Clinically, patients in this group exhibit greater susceptibility to infections and cardiovascular events, along with an elevated risk of disease progression, resulting in significantly reduced overall survival. Functional studies demonstrated that PU.1 inhibition suppresses MDS cell proliferation and clonogenicity, as impaired PU.1 binding inhibits the activation of key transcriptional programs involved in disease advancement. Collectively, these findings identify epigenetic factors that predispose patients with low-risk MDS to progression to high-risk MDS and, ultimately, sAML.

Genetic variants in the FCRL3 gene are linked to autoimmune disorders. However, the functional properties of FCRL3-expressing T lymphocytes, and the regulation and functional impact of FCRL3 expression remain understudied. Here, we performed a multiomic and functional analysis of human T lymphocytes expressing FCRL3. FCRL3 expression correlated with reduced capacity of T cells to undergo activation and was accompanied by functional specialization toward a cytotoxic phenotype, resembling cytotoxic CD4+ T lymphocytes and CD8+ effector memory TEMRA cells. FCRL3 expression was induced upon repetitive TCR engagement, and sufficed to attenuate T cell responses, indicating a role as a negative regulator of the activation of differentiated T cell subsets with high cytotoxic capacity. Mechanistically, the cytoplasmic domain of FCRL3 engaged inhibitory molecules, suggesting a direct role in limiting activating signals. Overall, our study establishes FCRL3 as a functional immunoregulatory receptor that restrains the activation of highly specialized human memory T cells.

More than 500 kinases are implicated in the control of most cellular process in mammals, and deregulation of their activity is linked to cancer and inflammatory disorders. 80 clinical kinase inhibitors (CKIs) have been approved for clinical use and hundreds are in various stages of development. However, CKIs inhibit other kinases in addition to the intended target(s), causing both enhanced clinical effects and undesired side effects that are only partially predictable based on in vitro selectivity profiling. Here, we report an integrative approach grounded on the use of chromatin modifications as unbiased, information-rich readouts of the functional effects of CKIs on macrophage activation. This approach exceeded the performance of transcriptome-based approaches and allowed us to identify similarities and differences among CKIs with identical intended targets, to recognize novel CKI specificities and to pinpoint CKIs that may be repurposed to control inflammation, thus supporting the utility of this strategy to improve selection and use of CKIs in clinical settings.

While pancreatic ductal adenocarcinomas (PDACs) are addicted to KRAS-activating mutations, inhibitors of downstream KRAS effectors, such as the MEK1/2 kinase inhibitor trametinib, are devoid of therapeutic effects. However, the extensive rewiring of regulatory circuits driven by the attenuation of the KRAS pathway may induce vulnerabilities of therapeutic relevance. An in-depth molecular analysis of the transcriptional and epigenomic alterations occurring in PDAC cells in the initial hours after MEK1/2 inhibition by trametinib unveiled the induction of endogenous retroviruses (ERVs) escaping epigenetic silencing, leading to the production of double-stranded RNAs and the increased expression of interferon (IFN) genes. We tracked ERV activation to the early induction of the transcription factor ELF3, which extensively bound and activated nonsilenced retroelements and synergized with IRF1 (interferon regulatory factor 1) in the activation of IFNs and IFN-stimulated genes. Trametinib-induced viral mimicry in PDAC may be exploited in the rational design of combination therapies in immuno-oncology.

Transcription termination pathways mitigate the detrimental consequences of unscheduled promiscuous initiation occurring at hundreds of thousands of genomiccis-regulatory elements. The Restrictor complex, composed of the Pol II-interacting protein WDR82 and the RNA-binding protein ZC3H4, suppresses processive transcription at thousands of extragenic sites in mammalian genomes. Restrictor-driven termination does not involve nascent RNA cleavage, and its interplay with other termination machineries is unclear. Here we show that efficient termination at Restrictor-controlled extragenic transcription units involves the recruitment of the protein phosphatase 1 (PP1) regulatory subunit PNUTS, a negative regulator of the SPT5 elongation factor, and Symplekin, a protein associated with RNA cleavage complexes but also involved in cleavage-independent and phosphatase-dependent termination of noncoding RNAs in yeast. PNUTS and Symplekin act synergistically with, but independently from, Restrictor to dampen processive extragenic transcription. Moreover, the presence of limiting nuclear levels of Symplekin imposes a competition for its recruitment among multiple transcription termination machineries, resulting in mutual regulatory interactions. Hence, by synergizing with Restrictor, Symplekin and PNUTS enable efficient termination of processive, long-range extragenic transcription.

Objective Pancreatic ductal adenocarcinomas (PDACs) include heterogeneous mixtures of low-grade cells forming pseudoglandular structures and compact nests of high-grade cells organised in non-glandular patterns. We previously reported that low-grade PDAC cells display high expression of interferon regulatory factor 1 (IRF1), a pivotal transcription factor of the interferon (IFN) system, suggesting grade-specific, cell-intrinsic activation of IFN responses. Here, we set out to determine the molecular bases and the functional impact of the activation of IFN-regulated responses in human PDACs. Design We first confirmed the correlation between glandular differentiation and molecular subtypes of PDAC on the one hand, and the expression of IRF1 and IFN-stimulated genes on the other. We next used unbiased omics approaches to systematically analyse basal and IFN-regulated responses in low-grade and high-grade PDAC cells, as well as the impact of IRF1 on gene expression programmes and metabolic profiles of PDAC cells. Results High-level expression of IRF1 in low-grade PDAC cells was controlled by endodermal lineage-determining transcription factors. IRF1-regulated gene expression equipped low-grade PDAC cells with distinctive properties related to antigen presentation and processing as well as responsiveness to IFN stimulation. Notably, IRF1 also controlled the characteristic metabolic profile of low-grade PDAC cells, suppressing both mitochondrial respiration and fatty acid synthesis, which may in part explain its growth-inhibiting activity. Conclusion IRF1 links endodermal differentiation to the expression of genes controlling antigen presentation and processing as well as to the specification of the metabolic profile characteristic of classical PDAC cells.

Interactions between the splicing machinery and RNA polymerase II increase protein-coding gene transcription. Similarly, exons and splicing signals of enhancer-generated long noncoding RNAs (elncRNAs) augment enhancer activity. However, elncRNAs are inefficiently spliced, suggesting that, compared with protein-coding genes, they contain qualitatively different exons with a limited ability to drive splicing. We show here that the inefficiently spliced first exons of elncRNAs as well as promoter-antisense long noncoding RNAs (pa-lncRNAs) in human and mouse cells trigger a transcription termination checkpoint that requires WDR82, an RNA polymerase II–binding protein, and its RNA-binding partner of previously unknown function, ZC3H4. We propose that the first exons of elncRNAs and pa-lncRNAs are an intrinsic component of a regulatory mechanism that, on the one hand, maximizes the activity of these cis-regulatory elements by recruiting the splicing machinery and, on the other, contains elements that suppress pervasive extragenic transcription.

The commitment of mesenchymal stem cells to preadipocytes is stimulated by hormonal induction. Preadipocytes induced to differentiate repress protein synthesis, remodel their cytoskeleton, and increase mitochondrial function to support anabolic pathways. These changes enable differentiation into mature adipocytes. Our understanding of the factors that coordinately regulate the early events of adipocyte differentiation remains incomplete. Here, by using multipronged approaches, we have identified zinc finger CCCH-type containing 10 (Zc3h10) as a critical regulator of the early stages of adipogenesis. Zc3h10 depletion in preadipocytes resulted in increased protein translation and impaired filamentous (F)-actin remodeling, with the latter detrimental effect leading to mitochondrial and metabolic dysfunction. These defects negatively affected differentiation to mature adipocytes. In contrast, Zc3h10 overexpression yielded mature adipocytes with remarkably increased lipid droplet size. Overall, our study establishes Zc3h10 as a fundamental proadipogenic transcription factor that represses protein synthesis and promotes F-actin/mitochondria dynamics to ensure proper energy metabolism and favor lipid accumulation.

In response to starvation, cells tune protein synthesis to promote autophagy, thus ensuring nutrient recycling and survival.