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Lymphocyte activation gene 3 (Lag3) is an inhibitory co-receptor expressed on activated T cells and has been proposed to regulate regulatory T (Treg) cell function. However, its precise modality and mechanisms remain elusive. We generated Treg cell-specific Lag3-mutant mouse models and found that Lag3 was essential for Treg cell control of autoimmunity. RNA sequencing analysis revealed that Lag3 mutation altered genes associated with metabolic processes, especially Myc target genes. Myc expression in Lag3-mutant Treg cells was increased to the level seen in conventional T helper (Th)1-type effector cells and directly correlated with their metabolic profiles and in vivo suppressive functions. The phosphatidylinositol 3-kinase (PI3K)-Akt-Rictor pathway was activated in Lag3-mutant Treg cells, and inhibiting PI3K, Rictor, or lactate dehydrogenase A (Ldha), a key Myc target enzyme converting pyruvate to lactate, was sufficient to restore normal metabolism and suppressive function in Lag3-mutant Treg cells. These findings indicate that Lag3 supports Treg cell suppression partly by tuning Myc-dependent metabolic programming.

BACKGROUND: Selective Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6i) have revolutionized the treatment of breast cancer and have potential in other cancers, being manageable drugs yet with some bone marrow toxicity. Selective CDK9 inhibitors (CDK9i) never advanced into clinical use, partly due to side effects, including gastrointestinal toxicity, and a small window between activity and cytotoxicity, which results in a narrow therapeutic index (TI).
METHODS: To overcome the drawbacks of CDK4/6 and CDK9 inhibitors, we have developed myrtleciclib, a selective CDK4/6/9 inhibitor with few non-critical molecular off-targets.
RESULTS: Myrtleciclib appears to bind to an allosteric site, unlike all other CDK4/6i and CDK9i acting by an ATP-competitive mechanism, which supports target specificity. Myrtleciclib\'s anti-proliferative effects are greater and its Therapeutic Index (TI) is broader than CDK9 and CDK4/6-only inhibitors. This can be explained by a moderate target inhibition, resulting in limited cytotoxicity. Moreover, we documented a synergy between CDK9 and CDK4/6 pathways inhibition, justifying increased drug efficacy, yet such synergy can only be achieved when the inhibition of both CDK9 and CDK4/6 is embedded within the same molecule and balanced within a certain ratio, as it is the case with myrtleciclib. Unlike CDK4/6i, myrtleciclib also induces cell death and apoptosis selectively on cancer cell lines, not on bystander cells. Synergy between myrtleciclib and other drugs with complementary Mechanism of Action (MoA) has also been documented.
CONCLUSIONS: CDK4/6/9i might represent a new frontier in cancer treatment to overcome the limitations of CDK4/6i and CDK9i for the treatment of cancers, including aggressive cancers with high unmet needs.

BACKGROUND: Non-small cell lung cancer (NSCLC) is a malignant form of lung cancer, and its prognosis could be improved by identifying key therapeutic targets. Thus, this study investigates the potential role of F-box Only Protein 33 (FBXO33) in NSCLC.
METHODS: The expression levels of FBXO33 in NSCLC were determined using University of Alabama at Birmingham Cancer Data Analysis Portal (UALCAN) prediction, and its correlation with overall survival (OS) was analyzed via Kaplan-Meier survival analysis. These results were validated through quantitative polymerase chain reaction (qPCR), western blot (WB), and immunofluorescence (IF). We modulated FBXO33 expression by overexpression or knockdown and analyzed its effects on cell growth, proliferation, migration, invasion, and stemness characteristics in NSCLC cell lines. Additionally, the interaction between FBXO33 and Myelocytomatosis (Myc) and its impact on Myc ubiquitination were examined. An in vivo NSCLC xenograft model was used to corroborate the in vivo experimental results.
RESULTS: The study found an inverse correlation between FBXO33 expression in NSCLC and OS. Lower FBXO33 expression enhanced the growth, proliferation, migration, invasion, and stemness characteristics of NSCLC cell lines. FBXO33 interacted with Myc to promote its ubiquitination and subsequent degradation, which suppressed NSCLC development.
CONCLUSIONS: FBXO33 is expressed at low levels in NSCLC and correlates with lower OS. Overexpression of FBXO33 promotes Myc ubiquitination and degradation and inhibits tumor cell proliferation, migration and stemness characteristics, thereby impeding NSCLC progression.

Erythropoiesis is a multistep process of erythroid cell production that is controlled by multiple regulatory factors. Ribosome rescue factor PELO plays a crucial role in cell meiotic division and mice embryonic development. However, the function of PELO in erythroid differentiation remains unclear. Here, we showed that knockdown of PELO increased hemin-induced erythroid differentiation of K562 and HEL cells, exhibiting a higher number of benzidine-positive cells and increased mRNA levels of erythroid genes. PELO knockdown inhibited the proliferation and cell cycle progression and promoted apoptosis of K562 cells. Mechanistically, PELO could regulate the expression of KLF10 through interaction with MYC. Moreover, KLF10 knockdown also enhanced erythroid differentiation of K562 and HEL cells induced by hemin. Collectively, our results demonstrated that PELO regulates erythroid differentiation and increases KLF10 expression levels by interacting with MYC.

UNASSIGNED: Canine transmissible venereal tumor (CTVT), a unique transmissible cancer in dogs, affects the external genitalia and potentially spreads to other parts of the body. While somatic mutations in oncogenic and tumor-suppressing genes are linked to CTVT development, the impact of DNA methylation, which affects gene expression, remains unclear. This study explored whether DNA methylation in the promoter regions of the MYC oncogene and CDKN2B tumor suppressor genes in CTVTs is associated with their expression, both at the gene and protein levels.
UNASSIGNED: To investigate promoter DNA methylation of MYC and CDKN2B in CTVTs, we analyzed frozen tissue samples from genital CTVT (GTVTs) and extragenital CTVT (ETVTs). Genomic DNA was extracted, bisulfite-treated, and analyzed using bisulfite polymerase chain reaction (PCR) and sequencing. The messenger RNA and protein of MYC and CDKN2B were also extracted and assessed by real-time PCR and Western blotting. Matching formalin-fixed, paraffin-embedded blocks were used for immunohistochemical staining to visualize protein distribution in GTVT and ETVT tissues.
UNASSIGNED: Although both GTVT and ETVT samples showed MYC promoter methylation, the extent of methylation differed significantly. GTVTs displayed a much higher degree of methylation, potentially explaining the more pronounced downregulation of MYC gene expression and reduction in c-MYC protein levels observed in GTVTs compared with ETVTs. Our data revealed a prevalent hypermethylation pattern in the CDKN2B promoter across both sample types. However, DNA methylation, which was expected to have a suppressive effect, did not correlate with gene/protein expression. GTVTs displayed high protein levels despite significantly reduced CDKN2B expression. Conversely, ETVTs maintained regular CDKN2B expression but exhibited reduced protein production, suggesting a complex interplay between methylation and expression in these tumors.
UNASSIGNED: MYC demonstrated a clear association between its promoter methylation status, gene expression, and protein levels; however, CDKN2B lacked this correlation, implying the involvement of methylation-independent regulatory mechanisms and highlighting the need for further investigation.

Tumor initiation and progression rely on intricate cellular pathways that promote proliferation while suppressing differentiation, yet the importance of pathways inhibiting differentiation in cancer remains incompletely understood. Here, we reveal a novel mechanism centered on the repression of the neuronal-specific transcription factor ARNT2 by the MYC oncogene that governs the balance between proliferation and differentiation. We found that MYC coordinates the transcriptional repression of ARNT2 through the activity of polycomb repressive complex 2 (PRC2). Notably, ARNT2, highly and specifically expressed in the central nervous system, is diminished in glioblastoma, inversely correlating with patient survival. Utilizing in vitro and in vivo models, we demonstrate that ARNT2 knockout (KO) exerts no discernible effect on the in vitro proliferation of glioblastoma cells, but significantly enhances the growth of glioblastoma cells in vivo. Conversely, ARNT2 overexpression severely dampens the growth of fully transformed glioblastoma cells subcutaneously or orthotopically xenografted in mice. Mechanistically, ARNT2 depletion diminishes differentiation and enhances stemness of glioblastoma cells. Our findings provide new insights into the complex mechanisms used by oncogenes to limit differentiation in cancer cells and define ARNT2 as a tumor suppressor in glioblastoma.

OBJECTIVE: Accurately predicting which patients diagnosed with non-small cell lung cancer (NSCLC) will respond to immunotherapy remains a clinical challenge. This study aims to determine the associations between MYC immunoreactivity, MYC copy number gain (CNG), driver mutations and survival following immunotherapy treatment, to provide insight into whether clinical MYC assessment may have predictive value.
METHODS: MYC copy number status was determined in 82 patients with NSCLC treated with immunotherapy, and MYC immunohistochemistry (IHC) was performed on 80 of these cases. MYC staining in ≥ 40 % of tumor cells was considered positive. Driver gene alterations, PD-L1 status and survival outcomes were assessed through retrospective chart review. Overall survival (OS) and progression free survival (PFS) were calculated from the date of immunotherapy initiation.
RESULTS: Nine (11 %) of 82 cases had MYC CNG and 56 (70 %) of the 80 immunostained cases were positive for MYC. MYC CNG was significantly associated with STK11 mutation (P=0.023), whereas positive MYC IHC was significantly associated with KRAS mutation (P=0.0076) and current/former smoking (P=0.0007). MYC CNG and positive MYC IHC were not significantly associated with each other (P=0.42), or with PD-L1 ≥ 1 % (MYC CNG: P=0.10; MYC IHC: P=0.09). Positive MYC IHC and PD-L1 ≥ 1 % were both significant predictors of OS (MYC: HR 2.7, 95 % CI 1.1-6.4, P=0.026; PD-L1: HR 0.33, 95 % CI 0.15-0.72, P=0.0055). MYC IHC positive/PD-L1 < 1 % cases had the shortest OS (median 230 versus 918 days, P=0.00069) and PFS (median 84 versus 254 days, P=0.0087). MYC CNG was not associated with OS or PFS.
CONCLUSIONS: We find that positive MYC IHC is an independent predictor of shorter OS after immunotherapy treatment, with MYC positive/PD-L1 < 1 % status predictive of particularly poor immunotherapy response. We identify positive MYC IHC as a feature of possible relevance to NSCLC treatment selection and of interest for future therapy development.

The SAGA complex is an evolutionarily conserved histone acetyltransferase complex and transcription coactivator essential for development and disease. Dysregulation of SAGA is implicated in various human diseases, including cancer. In this issue of Genes & Development, Chen et al. (doi/10.1101/gad.351789.124) uncover a critical role for SAGA in multiple myeloma wherein SAGA\'s ADA2B component is required for the expression of mTORC1 pathway genes and targets of the MYC, E2F, and MAF (musculoaponeurotic fibrosarcoma) transcription factors. SAGA cooperates with MYC and MAF to sustain oncogenic gene expression programs vital for multiple myeloma survival and thus may serve as a therapeutic target for future cancer therapies.

Despite recent advances in therapeutic treatments, multiple myeloma (MM) remains an incurable malignancy. Epigenetic factors contribute to the initiation, progression, relapse, and clonal heterogeneity in MM, but our knowledge on epigenetic mechanisms underlying MM development is far from complete. The SAGA complex serves as a coactivator in transcription and catalyzes acetylation and deubiquitylation. Analyses of data sets in the Cancer Dependency Map Project revealed that many SAGA components are selective dependencies in MM. To define SAGA-specific functions, we focused on ADA2B, the only subunit in the lysine acetyltransferase (KAT) module that specifically functions in SAGA. Integration of RNA sequencing (RNA-seq), assay for transposase-accessible chromatin with sequencing (ATAC-seq), and cleavage under targets and release using nuclease assay (CUT&RUN) results identified pathways directly regulated by ADA2B including MTORC1 signaling and oncogenic programs driven by MYC, E2F, and MM-specific MAF. We discovered that ADA2B is recruited to MAF and MYC gene targets, and that MAF shares a majority of its targets with MYC in MM cells. Furthermore, we found that the SANT domain of ADA2B is required for interaction with both GCN5 and PCAF acetyltransferases, incorporation into SAGA, and ADA2B protein stability. Our findings uncover previously unknown SAGA KAT module-dependent mechanisms controlling MM cell growth, revealing a vulnerability that might be exploited for future development of MM therapy.