L3MBTL2-mediated CGA transcriptional suppression promotes pancreatic cancer progression through modulating autophagy

RHOD mediates ATG9A trafficking to promote autophagosome formation during autophagy in cancer

ATG9A is a transmembrane protein essential for macroautophagy/autophagy that drives autophagosome formation by delivering essential proteins and lipids to the phagophore through vesicle trafficking. Here, we demonstrate that the atypical Rho GTPase RHOD is required for ATG9A trafficking and stimulates autophagosome formation. Upon starvation, RHOD interacted with ATG9A and accompanied ATG9A trafficking from the Golgi toward phagophores. In addition, starvation-induced high levels of RHOD resulted in Golgi fragmentation to further promote ATG9A vesicle export from the trans-Golgi network to the peripheral region. Loss of RHOD suppressed ATG9A trafficking and reduced the distribution of ATG9A on the phagophore. Moreover, WHAMM (WASP homolog associated with actin, golgi membranes and microtubules) forms a complex with RHOD and participates in this process in a RHOD-dependent manner. Importantly, RHOD mutants, which lack the exon II-containing effector region motif that is required for ATG9A binding or lack the CAAX box that is responsible for membrane targeting, fail to stimulate ATG9A trafficking and autophagosome formation. Furthermore, RHOD plays a distinct suppressor role in tumor development, partly associated with its regulatory effect on autophagy. These findings reveal the important roles of RHOD in autophagy and tumor development.Abbreviation: ATG9A: autophagy related 9A; BafA1: bafilomycin A1; BiFC: bimolecular fluorescence complementation; co-IP: co-immunoprecipitation; EBSS: Earle's balanced salt solution; FM: full culture medium; KO: knockout; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PUP-IT: pupylation-based interaction tagging; RHOD: ras homolog family member D; SQSTM1: sequestosome 1; TGN: trans-Golgi network; VC: Venus C-terminal; VN: Venus N-terminal; WHAMM: WASP homolog associated with actin, golgi membranes and microtubules; WIPI2: WD repeat domain, phosphoinositide interacting 2; WT: wild-type; 3-MA: phosphatidylinositol 3-kinase (PtdIns3K) inhibitor 3-methyladenine.

Novel susceptibility genes for sleep apnea revealed by a cross-tissue transcriptome-wide association study

Sleep apnea (SA) is a sleep disorder characterized by frequent interruptions in breathing during sleep and is widely recognized as a significant global public health concern. Although genome-wide association studies (GWAS) have identified several loci associated with SA susceptibility, the underlying genes and biological mechanisms remain largely unknown. A cross-tissue transcriptome-wide association study (TWAS) was performed to integrate SA GWAS summary statistics from 410,385 individuals (43,901 cases and 366,484 controls) and gene expression data from 49 distinct tissues and obtained from 838 post-mortem donors. Functional Summary-based Imputation was employed to validate these findings in whole blood tissue. Additionally, candidate susceptibility genes were further verified using Gene Analysis combined with Multi-marker Analysis of Genomic Annotation. Subsequent Mendelian randomization and colocalization analyses were conducted. In the cross-tissue TWAS analysis, 60 susceptibility genes were identified. Two novel susceptibility genes, GPD2 and L3MBTL2, were validated through both single tissue TWAS and MAGMA analysis. Mitochondrial glycerophosphate dehydrogenase (GPD2) may reduce the SA risk by regulating energy metabolism, while Lethal (3) malignant brain tumor-like protein 2 (L3MBTL2) may increase the risk of SA by disturbing DNA damage repair pathway and by regulating the process of the cell cycle. In summary, two novel biological macromolecules were identified in our study whose expression was predicted to be associated with SA risk, providing new insight into the genetic basis of this condition.

WHAMM Inhibits Type II Alveolar Epithelial Cell EMT by Mediating Autophagic Degradation of TGF-β1 in Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is one of the most prevalent complication in preterm infants, primarily characterized by arrested alveolar growth. The involvement of epithelial-mesenchymal transition (EMT) of AECII cells is proposed to have a crucial role in the pathogenesis of BPD; however, the underlying mechanism remains unclear. The present study reveals a significant reduction of WHAMM (WASP homolog associated with actin, membranes, and microtubules) in hyperoxia-induced BPD mice, highlighting its crucial role in suppressing the progression of BPD through the inhibition of EMT in AECIIs. We demonstrated that hyperoxia-induced downregulation of WHAMM leads to the accumulation of TGF-β1 primarily through its mediation of the autophagic degradation pathway. Mechanistically, WHAMM enhanced the autophagosomal localization of TGF-β1 and concurrently promoted the process of autophagy, thereby comprehensively facilitating the autophagic degradation of TGF-β1. These findings reveal the important role of WHAMM in the development of BPD, and the proposed WHAMM/autophagy/TGF-β1/EMT pathway may represent a potential therapeutic strategy for BPD treatment.

L3MBTL2 maintains MYCN-amplified neuroblastoma cell proliferation through silencing NRIP3 and BRME1 genes

Epigenetic alterations critically affect tumor development. Polycomb-group complexes constitute an evolutionarily conserved epigenetic machinery that regulates stem cell fate and development. They are implicated in tumorigenesis, primarily via histone modification. Polycomb repressive complex 1 (PRC1) complexes 1-6 (PRC1.1-6) mediate the ubiquitination of histone H2A on lysine 119 (H2AK119ub). Here, we studied the functional roles of a PRC1.6 molecule, L3MBTL2, in neuroblastoma (NB) cells. L3MBTL2-knockout and knockdown revealed that L3MBTL2 depletion suppressed NB cell proliferation via cell-cycle arrest and gamma-H2A.X upregulation. L3MBTL2-knockout profoundly suppressed xenograft tumor formation. Transcriptome analysis revealed suppressed cell-cycle-related and activated differentiation-related pathways. Break repair meiotic recombinase recruitment factor 1 (BRME1) and nuclear receptor interacting protein 3 (NRIP3) were notably de-repressed by L3MBTL2-knockout. The deletion of L3MBTL2 reduced enrichment of H2AK119ub and PCGF6 at transcriptional start site proximal regions of the targets. Add-back studies unveiled the importance of L3MBTL2-BRME1 and -NRIP3 axes for NB cell proliferation. We further manifested the association of MYCN with de-repression of NRIP3 in an L3MBTL2-deficient context. Therefore, this study first revealed the significance of L3MBTL2-mediated gene silencing in MYCN-amplified NB cells.

UBTF mediates activation of L3MBTL2 to suppress NISCH expression through histone H2AK119 monoubiquitination modification in breast cancer

Lethal(3)malignant brain tumor-like protein 2 (L3MBTL2) has been related to transcriptional inhibition and chromatin compaction. Nevertheless, the biological functions and mechanisms of L3MBTL2 are undefined in breast cancer (BRCA). Here, we revealed that L3MBTL2 is responsible for the decline of Nischarin (NISCH), a well-known tumor suppressor, in BRCA, and explored the detailed mechanism. Knockdown of L3MBTL2 reduced monoubiquitination of histone H2A at lysine-119 (H2AK119ub), leading to reduced binding to the NISCH promoter and increased expression of NISCH. Meanwhile, the knockdown of L3MBTL2 decreased proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) of BRCA cells, and increased apoptosis, which were abated by NISCH knockdown. Nucleolar transcription factor 1 (UBTF) induced the transcription of L3MBTL2 in BRCA, and the suppressing effects of UBTF silencing on EMT in BRCA cells were also reversed by NISCH knockdown. Knockdown of UBTF slowed tumor progression and attenuated lung tumor infiltration, whereas simultaneous knockdown of NISCH accelerated EMT and increased tumor lung metastasis. Taken together, our results show that L3MBTL2, transcriptionally activated by UBTF, exerts oncogenic functions in BRCA, by catalyzing H2AK119Ub and reducing expression of NISCH.

Research advances of polycomb group proteins in regulating mammalian development

Polycomb group (PcG) proteins are a subset of epigenetic factors that are highly conserved throughout evolution. In mammals, PcG proteins can be classified into two muti-proteins complexes: Polycomb repressive complex 1 (PRC1) and PRC2. Increasing evidence has demonstrated that PcG complexes play critical roles in the regulation of gene expression, genomic imprinting, chromosome X-inactivation, and chromatin structure. Accordingly, the dysfunction of PcG proteins is tightly orchestrated with abnormal developmental processes. Here, we summarized and discussed the current knowledge of the biochemical and molecular functions of PcG complexes, especially the PRC1 and PRC2 in mammalian development including embryonic development and tissue development, which will shed further light on the deep understanding of the basic knowledge of PcGs and their functions for reproductive health and developmental disorders.

Augmenting L3MBTL2-induced condensates suppresses tumor growth in osteosarcoma

Osteosarcoma is a highly aggressive cancer and lacks effective therapeutic targets. We found that L3MBTL2 acts as a tumor suppressor by transcriptionally repressing IFIT2 in osteosarcoma. L3MBTL2 recruits the components of Polycomb repressive complex 1.6 to form condensates via both Pho-binding pockets and polybasic regions within carboxyl-terminal intrinsically disordered regions; the L3MBTL2-induced condensates are required for its tumor suppression. Multi-monoubiquitination of L3MBTL2 by UBE2O results in its proteasomal degradation, and the UBE2O/L3MBTL2 axis was crucial for osteosarcoma growth. There is a reverse correlation between L3MBTL2 and UBE2O in osteosarcoma tissues, and higher UBE2O and lower L3MBTL2 are associated with poorer prognosis in osteosarcoma. Pharmacological blockage of UBE2O by arsenic trioxide can enhance L3MBTL2-induced condensates and consequently suppress osteosarcoma growth. Our findings unveil a crucial biological function of L3MBTL2-induced condensates in mediating tumor suppression, proposing the UBE2O-L3MBTL2 axis as a potential cancer therapeutic target in osteosarcoma.

Cytoplasmic Expression of TP53INP2 Modulated by Demethylase FTO and Mutant NPM1 Promotes Autophagy in Leukemia Cells

Acute myeloid leukemia (AML) with a nucleophosmin 1 (NPM1) mutation is a unique subtype of adult leukemia. Recent studies show that NPM1-mutated AML has high autophagy activity. However, the mechanism for upholding the high autophagic level is still not fully elucidated. In this study, we first identified that tumor protein p53 inducible nuclear protein 2 (TP53INP2) was highly expressed and cytoplasmically localized in NPM1-mutated AML cells. Subsequent data showed that the expression of TP53INP2 was upregulated by fat mass and obesity-associated protein (FTO)-mediated m⁶A modification. Meanwhile, TP53INP2 was delocalized to the cytoplasm by interacting with NPM1 mutants. Functionally, cytoplasmic TP53INP2 enhanced autophagy activity by promoting the interaction of microtubule-associated protein 1 light chain 3 (LC3) - autophagy-related 7 (ATG7) and further facilitated the survival of leukemia cells. Taken together, our study indicates that TP53INP2 plays an oncogenic role in maintaining the high autophagy activity of NPM1-mutated AML and provides further insight into autophagy-targeted therapy of this leukemia subtype.