METTL3 orchestrates glycolysis by stabilizing the c-Myc/WDR5 complex in triple-negative breast cancer

BACKGROUND

The carcinogenic transcription factor c-Myc is the most aggressive oncogene, which drive malignant transformation and dissemination of triple-negative breast cancer (TNBC). Recruitment of many cofactors, especially WDR5, a protein that nucleates H3K4me chromatin modifying complexes, play a pivotal role in regulating c-Myc-dependent gene transcription, a critical process for c-Myc signaling to function in a variety of biological and pathological contexts. For this reason, interrupting the interaction between c-Myc and the transcription cofactor WDR5 may become the most promising new strategy for treating c-Myc driven TNBC.

METHODS

Immunoprecipitation and mass spectrometry (IP-MS) is used to screen proteins that bind c-Myc/WDR5 interactions. The interaction of METTL3 with c-Myc/WDR5 in breast cancer tissues and TNBC cells was detected by Co-IP and immunofluorescence. Subsequently, we further analyzed the influence of METTL3 expression on c-Myc/WDR5 protein expression and its interaction stability by Western blot and Co-IP. The correlation between METTL3 and c-Myc pathway was analyzed by ChIP-seq sequencing and METTL3 knockdown transcriptome data. The effect of METTL3 expression on c-Myc transcriptional activity was detected by ChIP-qPCR and Dual Luciferase Reporter. At the same time, the overexpression vector METTL3-MUT (m6A) was constructed, which mutated the methyltransferase active site (Aa395-398, DPPW/APPA), and further explored whether the interaction between METTL3 and c-Myc/WDR5 was independent of methyltransferase activity. In addition, we also detected the changes of METTL3 expression on TNBC's sensitivity to small molecule inhibitors such as JQ1 and OICR9429 by CCK8, Transwell and clonal formation assays. Finally, we further verified our conclusions in spontaneous tumor formation mouse MMTV-PyMT and nude mouse orthotopic transplantation tumor models.

RESULTS

METTL3 was found to bind mainly to c-Myc/WDR5 protein in the nucleus. It enhances the stability of c-Myc/WDR5 interaction through its methyltransferase independent mechanism, thereby enhancing the transcriptional activity of c-Myc on downstream glucose metabolism genes. Notably, the study also confirmed that METTL3 can directly participate in the transcription of glucose metabolism genes as a transcription factor, and knockdown METTL3 enhances the drug sensitivity of breast cancer cells to small molecule inhibitors JQ1 and OICR9429. The study was further confirmed by spontaneous tumor formation mouse MMTV-PyMT and nude mouse orthotopic transplantation tumor models.

CONCLUSION

METTL3 binds to the c-Myc/WDR5 protein complex and promotes glycolysis, which plays a powerful role in promoting TNBC progression. Our findings further broaden our understanding of the role and mechanism of action of METTL3, and may open up new therapeutic avenues for effective treatment of TNBC with high c-Myc expression.

Mettl3 synergistically regulates TGF-β/SMAD2/3 to promote proliferation and metastasis of gastric cancer

Transforming Growth factor-β (TGF-β)/Smad signaling is a complex regulatory network that both inhibits and promotes tumorigenesis. However, the mechanisms underlying the function of TGF-β/Smad signaling pathway remain to be fully elucidated. As a methyltransferase, METTL3 is closely related to tumor development, but the role of METTL3 in the proliferation and metastasis of TGF-β/Smad-activated gastric cancer (GC) is unclear. In this study, we identified TGF-β/Smad2/3 axis as an important carcinogenic pathway in GC, which significantly promoted the proliferation and metastasis of GC. Furthermore, we found that Smad3 mRNA could be modified by m6A, which was subsequently recognized and stabilized by IGF2BP2, thereby enhancing Smad3 protein expression and promoting the activation of TGF-β/Smad pathway. Importantly, we also found that METTL3 could combine with p-Smad3 to regulate the transcription of downstream target genes. Therefore, this study revealed a novel mechanism by which METTL3 synergistically regulates TGF-β/Smad2/3 signaling and provide a new potential therapeutic target for the treatment of GC.

IGF2BP2-modified UBE2D1 interacts with Smad2/3 to promote the progression of breast cancer

Recent studies have suggested that ubiquitin-conjugating enzyme E2D1 (UBE2D1) is involved in tumor progression. In this study, we found that UBE2D1 expression was upregulated in breast cancer (BC) and was related to the prognosis of BC patients. Through in vitro and in vivo experiments, we demonstrated the aberrant expression of UBE2D1 promoted the proliferation and migration of BC cells, and the IGF2BP2-mediated N6-methyladenosine (m6A) modification increased the stability of UBE2D1 mRNA. Mechanistically, UBE2D1 expression regulated the activity of TGF-β signaling through modulating the expression and the phosphorylation level of Smad2/3. Furthermore, UBE2D1 directly bound to Smad2/3 and affected the subsequent binding of Smad2 and Smad3, which is a necessary step for TGF-β signaling activation. Thus, our study reveals a pro-oncogenic role of UBE2D1 in the progression of BC and may provide novel strategies for BC treatment.

Pseudomonas exit-site infections in CAPD patients: evolution and outcome of treatment

OBJECTIVE

To examine the natural history of Pseudomonas aeruginosa (PSA) exit-site infections (ESI) in patients treated with antibiotics with or without surgical interventions.

DESIGN

Retrospective record review from May 1994 to April 1997.

SETTING

A single dialysis unit in a district hospital.

PATIENTS

The review included 353 patients who had undergone continuous ambulatory peritoneal dialysis (CAPD).

OUTCOME MEASURES

The prevalence and etiology of ESI, the treatment regimen for PSA ESI, and the outcome of treatment.

RESULTS

The prevalence of ESI was 55%. A total of 131 episodes (range 1-5) of PSA ESI occurred in 78 (40.2%) of the 194 patients who experienced ESI. Among these 78 patients, 4 groups with different outcomes were identified. In group I, 35 patients (44.9%) were treated successfully with antibiotic therapy alone. Among these 35 patients, 4 developed PSA peritonitis at a mean of 5 months (range 2-10 mth) after apparent clinical resolution of PSA ESI. Two of the 4 patients switched to long-term hemodialysis (HD) because of peritoneal failure. In group II, 8 patients (10.3%) responded to a combination of antibiotics and shaving of the external cuff. In group III, 21 patients (26.9%) with recurrent ESI underwent elective Tenckhoff catheter removal and reinsertion. One of the 21 patients had relapse of PSA ESI 14 months after the operation. In group IV, 14 patients (17.9%) had recurrent PSA ESI that failed to respond to multiple courses of antibiotics and shaving of the external cuff. Consent for Tenckhoff catheter removal was not obtained and 4 of these 14 patients subsequently developed PSA peritonitis. One of the 4 patients changed to permanent HD due to peritoneal failure.

CONCLUSIONS

Considering the increased risk and the poor outcome of PSA peritonitis in patients with persistent PSA ESI, early Tenckhoff catheter removal is recommended if the patient fails to respond to antibiotics with or without externalization of the external cuff.

Biliary sludge-cast formation following liver transplantation

The development of biliary sludge, in the absence of anastomotic obstruction in the common bile duct, has become a very rare complication following orthotopic liver transplantation since the adoption of modern techniques of biliary reconstruction and routine biliary flushing before cold preservation. We describe the successful treatment of this serious complication in an 18-year-old woman whose biliary sludge aggregated into firm casts occupying the extrahepatic and intrahepatic bile ducts causing obstruction and cholangitis necessitating operative intervention followed by interventional radiological approaches to treat the intrahepatic bile duct strictures. Postoperative choledochofiberscopy was also used to remove the retained biliary casts. The pathogenesis of biliary sludge appeared to be multifactorial, but cold ischemic damage to the bile duct wall seemed to play an important role in this case.