The RNA polymerase III repressor MAF1 is regulated by ubiquitin-dependent proteasome degradation and modulates cancer drug resistance and apoptosis

Feedback loop centered on MAF1 reduces blood-brain barrier damage in sepsis-associated encephalopathy

BACKGROUND

A previous study found that MAF1 homolog, a negative regulator of RNA polymerase III (MAF1), protects the blood-brain barrier (BBB) in sepsis-associated encephalopathy (SAE); however, the related molecular mechanisms remain unclear.

SUBJECTS AND METHODS

In this study, a rat sepsis model was constructed using the cecum ligation and puncture (CLP) method. In vitro, rat brain microvascular endothelial cells and astrocytes were stimulated with serum from the sepsis model rats. The loss of MAF1 protein levels and the molecular mechanisms leading to cell damage were investigated.

RESULTS

It was shown in the SAE models that MAF1 was expressed at low levels. Knockdown of Cullin 2 (CUL2) stimulated the accumulation of MAF1 protein, attenuated the RNA sensor RIG-I/interferon regulatory factor 3 (IRF3) signaling pathway, and reduced cell apoptosis. Furthermore, it increased phosphatase and tensin homolog (PTEN) expression and inactivated the serine/threonine kinase (AKT)/mechanistic target of the rapamycin kinase (mTOR) signaling pathway. Interference with forkhead box O1 (FOXO1) inhibited MAF1 expression and activated the RIG-I/IRF3 signaling pathway, while MAF1 overexpression promoted PTEN expression, decreased cell apoptosis, and normalized autophagy.

CONCLUSIONS

These findings demonstrate that CUL2 promoted MAF1 ubiquitination and caused BBB injury in SAE. Through the regulatory loop of PTEN/AKT/FOXO1/MAF1, CUL2 initiated the gradual downregulation of MAF1, which subsequently regulated polymerase III (Pol III)-dependent transcription and played essential roles in cell apoptosis in SAE.

CLINICAL TRIAL NUMBER

not applicable.

Maf1 Cooperates with Progesterone Receptor to Repress RNA Polymerase III Transcription of Select tRNAs

Progesterone receptors (PR) can regulate transcription by RNA Polymerase III (Pol III), which transcribes small non-coding RNAs, including all transfer RNAs (tRNAs). We have previously demonstrated that PR is associated with the Pol III complex at tRNA genes and that progestins downregulate tRNA transcripts in breast tumor models. To further elucidate the mechanism of PR-mediated regulation of Pol III, we studied the interplay between PR, the Pol III repressor Maf1, and TFIIIB, a core transcription component. ChIP-seq was performed for PR, the Pol III subunit POLR3A, the TFIIIB component Brf1, and Maf1 in breast cancer cells with or without progestin treatment. Upon progestin exposure, PR localized to approximately half of POLR3A-occupied tRNA genes, with Maf1 co-recruited to many of these PR-POLR3A sites. While progestin treatment did not significantly alter the number of tRNA genes occupied by Pol III or Brf1, Brf1 occupancy was stabilized, as indicated by increased peak amplitudes. Analysis of nascent tRNA transcription revealed a specific progestin-induced downregulation of approximately one-third of highly expressed tRNA genes. This repression was significantly reduced by Maf1 knockdown, indicating that Maf1 is necessary for PR-mediated tRNA transcription downregulation. Overall, these findings demonstrate a ligand-dependent PR-mediated repression of tRNA transcription through Maf1.

Transcriptome and proteome changes triggered by overexpression of the transcriptional regulator Maf1 in the human pathogen Leishmania major

Maf1, originally described as a repressor of RNA polymerase III (RNAP III) transcription in yeast, participates in multiple functions across eukaryotes. However, the knowledge about Maf1 in protozoan parasites is scarce. To initiate the study of Maf1 in Leishmania major, we generated a cell line that overexpresses this protein. Overexpression of Maf1 led to a significant reduction in the abundance of tRNAs, 5S rRNA, and U4 snRNA, demonstrating that Maf1 regulates RNAP III activity in L. major. To further explore the roles played by Maf1 in this microorganism, global transcriptomic and proteomic changes due to Maf1 overexpression were determined using RNA-sequencing and label-free quantitative mass spectrometry. Compared to wild-type cells, differential expression was observed for 1082 transcripts (615 down-regulated and 467 up-regulated) and 205 proteins (132 down-regulated and 73 up-regulated) in the overexpressing cells. A correlation of 44% was found between transcriptomic and proteomic results. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the differentially expressed genes and proteins are mainly involved in transcription, cell cycle regulation, lipid metabolism and transport, ribosomal biogenesis, carbohydrate metabolism, autophagy, and cytoskeleton modification. Thus, our results suggest the involvement of Maf1 in the regulation of all these processes in L. major, as reported in other species, indicating that the functions performed by Maf1 were established early in eukaryotic evolution. Notably, our data also suggest the participation of L. major Maf1 in mRNA post-transcriptional control, a role that, to the best of our knowledge, has not been described in other organisms.

Maf1 loss regulates spinogenesis and attenuates cognitive impairment in Alzheimer's disease

Alzheimer's disease is neurodegenerative and characterized by progressive cognitive impairment. Synaptic dysfunction appears in the early stage of Alzheimer's disease and is significantly correlated with cognitive impairment. However, the specific regulatory mechanism remains unclear. Here, we found the transcription factor Maf1 to be upregulated in Alzheimer's disease and determined that conditional knockout of Maf1 in a transgenic mouse model of Alzheimer's disease restored learning and memory function; the downregulation of Maf1 reduced the intraneuronal calcium concentration and restored neuronal synaptic morphology. We also demonstrated that Maf1 regulated the expression of NMDAR1 by binding to the promoter region of Grin1, further regulating calcium homeostasis and synaptic remodelling in neurons. Our results clarify the important role and mechanism of the Maf1-NMDAR1 signalling pathway in stabilizing synaptic structure, neuronal function and behaviour during Alzheimer's disease pathogenesis. This therefore serves as a potential diagnostic and therapeutic target for the early stage of Alzheimer's disease.

Comprehensive prognostic and immunological analysis of Cullin2 in pan-cancer and its identification in hepatocellular carcinoma

BACKGROUND

As a member of the Cullin family, Cullin2 (CUL2) is involved in the development and spread of different types of cancers. However, the precise role of CUL2 in human cancer remains largely elusive.

METHODS

In this study, various databases were applied to observe the CUL2 expression. Kaplan-Meier and Spearman correlation analyses were employed to investigate the potential links between CUL2 level, patient prognosis, and the infiltration of immune cells. In addition, the association between CUL2 and the efficacy of immunotherapy in an immunotherapy cohort was investigated. Moreover, the expression and distribution of CUL2 in cells were observed using the Human Protein Atlas (THPA) database. Finally, clinical tissue specimens and in vitro function assays were conducted to validate the expressions and effects of CUL2 on the biological functions in hepatocellular carcinoma (HCC) cells.

RESULTS

While there are variations in CUL2 expression across different organs and cell types, it is notably upregulated in a majority of tumor tissues. In addition, CUL2 gene mutations are common in multiple cancers with low mutation rates and CUL2 is closely related to the prognosis of some cancer's patients, some immune regulatory factors, TMB, MSI, MMR genes, and DNA methylation. Further, our results found that downregulating CUL2 inhibits the proliferation, and migration abilities.

CONCLUSIONS

The expression of CUL2 has an impact on the prognosis of various tumors, and this correlation is particularly noteworthy due to its significant association with the infiltration of immune cells within tumors. CUL2 was an oncogene contributing to the progression of HCC.

LWJ-M30, a conjugate of DM1 and B6, for the targeted therapy of colorectal cancer with improved therapeutic effects†

Colorectal cancer (CRC) is one of the most prevalent cancers worldwide as well as a significant cause of mortality. The conventional treatment could cause serious side effects and induce drug resistance, recurrence and metastasis of cancers. Hence, specific targeting of cancer cells without affecting the normal tissues is currently an urgent necessity in cancer therapy. The emerging of peptide–drug conjugates (PDC) is regarded as a promising approach to address malignant tumors. LWJ-M30, a conjugate of DM1 and B6 peptide, targeted transferrin receptors (TfRs) on the surface of the CRC cells, showing a powerful anti-cancer effect. LWJ-M30 significantly inhibited the HCT116 cells proliferation and migration in vitro. LWJ-M30 also dramatically decreased the level of polymeric tubulin, while the disruption of microtubules caused the cell cycle to be arrested in the G2/M phase. LWJ-M30 induced the HCT116 cells apoptosis both in vivo and in vitro. The results in vivo demonstrated that LWJ-M30 could inhibit the HCT116 growth without affecting the mouse body weight. Taking these results together, our data indicated that LWJ-M30 could improve the therapeutic effects of DM1 while reducing the systemic toxicity in normal tissues.

LWJ-M30 targeted TfR, dramatically decreased the level of polymeric tubulin, while the disruption of microtubules meant the cell cycle was arrested in the G2/M phase and thus caused cells apoptosis.

The roles of E3 ligases in Hepatocellular carcinoma

Hepatocarcinogenesis is a complex multistep biological process involving genetic and epigenetic alterations that are accompanied by activation of oncoproteins and inactivation of tumor suppressors, which in turn results in Hepatocellular carcinoma (HCC), one of the common tumors with high morbidity and mortality worldwide. The ubiquitin-proteasome system (UPS) is the key to protein degradation and regulation of physiological and pathological processes, and E3 ligases are key enzymes in the UPS that contain a variety of subfamily proteins involved in the regulation of some common signal pathways in HCC. There is growing evidence that many structural or functional dysfunctions of E3 are engaged in the development and progression of HCC. Herein, we review recent research advances in HCC-associated E3 ligases, describe their structure, classification, functional roles, and discuss some mechanisms of the abnormal activation or inactivation of the HCC-associated signal pathway due to the binding of E3 to known substrates. In addition, given the success of proteasome inhibitors in the treatment of malignant cancers, we characterize the current knowledge and future prospects for targeted therapies against aberrant E3 in HCC.

E3 Ubiquitin Ligase in Anticancer Drugdsla Resistance: Recent Advances and Future Potential

Drug therapy is the primary treatment for patients with advanced cancer. The use of anticancer drugs will inevitably lead to drug resistance, which manifests as tumor recurrence. Overcoming chemoresistance may enable cancer patients to have better therapeutic effects. However, the mechanisms underlying drug resistance are poorly understood. E3 ubiquitin ligases (E3s) are a large class of proteins, and there are over 800 putative functional E3s. E3s play a crucial role in substrate recognition and catalyze the final step of ubiquitin transfer to specific substrate proteins. The diversity of the set of substrates contributes to the diverse functions of E3s, indicating that E3s could be desirable drug targets. The E3s MDM2, FBWX7, and SKP2 have been well studied and have shown a relationship with drug resistance. Strategies targeting E3s to combat drug resistance include interfering with their activators, degrading the E3s themselves and influencing the interaction between E3s and their substrates. Research on E3s has led to the discovery of possible therapeutic methods to overcome the challenging clinical situation imposed by drug resistance. In this article, we summarize the role of E3s in cancer drug resistance from the perspective of drug class.

Maf1 suppression of ATF5-dependent mitochondrial unfolded protein response contributes to rapamycin-induced radio-sensitivity in lung cancer cell line A549

mTOR is well known to promote tumor growth but its roles in enhancing chemotherapy and radiotherapy have not been well studied. mTOR inhibition by rapamycin can sensitize cancer cells to radiotherapy. Here we show that Maf1 is required for rapamycin to increase radio-sensitivity in A549 lung cancer cells. In response to ionizing radiation (IR), Maf1 is inhibited by Akt-dependent re-phosphorylation, which activates mitochondrial unfolded protein response (UPR^mt) through ATF5. Rapamycin suppresses IR-induced Maf1 re-phosphorylation and UPR^mt activation in A549 cells, resulting in increased sensitivity to IR-mediated cytotoxicity. Consistently, Maf1 knockdown activates ATF5-transcription of mtHSP70 and HSP60, enhances mitochondrial membrane potential, reduces intracellular ROS levels and dampens rapamycin's effect on increasing IR-mediated cytotoxicity. In addition, Maf1 overexpression suppresses ethidium bromide-induced UPR^mt and enhances IR-mediated cytotoxicity. Supporting our cell-based studies, elevated expression of UPR^mt makers (mtHSP70 and HSP60) are associated with poor prognosis in patients with lung adenocarcinoma (LAUD). Together, our study reveals a novel role of Maf1-UPR^mt axis in mediating rapamycin's enhancing effect on IR sensitivity in A549 lung cancer cells.

Plasma Exosomal miRNA Expression Profile as Oxaliplatin-Based Chemoresistant Biomarkers in Colorectal Adenocarcinoma

Background: Chemotherapy is one of the most common therapies used in the treatment of colorectal cancer (CRC), but chemoresistance inevitably occurs. It is challenging to obtain an immediate and accurate diagnosis of chemoresistance. The potential of circulating exosomal miRNAs as oxaliplatin-based chemoresistant biomarkers in CRC patients was investigated in this study.

Methods: Plasma exosomal miRNAs in sensitive and resistant patients were analyzed by miRNA microarray analysis, followed by verification with a quantitative reverse-transcription polymerase chain reaction (RT-qPCR) assay in two independent cohorts. The diagnostic accuracy was determined by ROC curve analysis. Logistic regression analysis and Spearman's rank correlation test were also performed. Finally, bioinformatics was used to preliminarily explore the potential molecular mechanism of the selected miRNAs in chemoresistance.

Results: miRNA microarray analysis identified four upregulated miRNAs and 20 downregulated miRNAs in chemoresistant patients compared to chemosensitive patients. Twelve markedly dysregulated miRNAs were selected for further investigation, of which six (miR-100, miR-92a, miR-16, miR-30e, miR-144-5p, and let-7i) were verified to be significantly and consistently dysregulated (>1.5-fold, P < 0.05). The combination of the six miRNAs had the highest AUC (0.825, 95% CI, 0.753–0.897). The expression level of these 6 miRNAs was not correlated with tumor location, stage, or chemotherapy program. Only miR-100 was significantly upregulated in low histological grade. GO analysis and KEGG pathway analysis showed that miRNAs were related to RNA polymerase II transcription and enriched in the PI3K-AKT signaling pathway, AMPK signaling pathway, and FoxO signaling pathway.

Conclusions: We identified a panel of plasma exosomal miRNAs, containing miR-100, miR-92a, miR-16, miR-30e, miR-144-5p, and let-7i, that could significantly distinguish chemoresistant patients from chemosensitive patients. The detection of circulating exosomal miRNAs may serve as an effective way to monitor CRC patient responses to chemotherapy. Targeting these miRNAs may also be a promising strategy for CRC treatment.