Miz-1 and Max compete to engage c-Myc: implication for the mechanism of inhibition of c-Myc transcriptional activity by Miz-1

MYCN in human development and diseases

Somatic mutations in MYCN have been identified across various tumors, playing pivotal roles in tumorigenesis, tumor progression, and unfavorable prognoses. Despite its established notoriety as an oncogenic driver, there is a growing interest in exploring the involvement of MYCN in human development. While MYCN variants have traditionally been associated with Feingold syndrome type 1, recent discoveries highlight gain-of-function variants, specifically p.(Thr58Met) and p.(Pro60Leu), as the cause for megalencephaly-polydactyly syndrome. The elucidation of cellular and murine analytical data from both loss-of-function (Feingold syndrome model) and gain-of-function models (megalencephaly-polydactyly syndrome model) is significantly contributing to a comprehensive understanding of the physiological role of MYCN in human development and pathogenesis. This review discusses the MYCN's functional implications for human development by reviewing the clinical characteristics of these distinct syndromes, Feingold syndrome, and megalencephaly-polydactyly syndrome, providing valuable insights into the understanding of pathophysiological backgrounds of other syndromes associated with the MYCN pathway and the overall comprehension of MYCN's role in human development.

Collaborating single-cell and bulk RNA sequencing for comprehensive characterization of the intratumor heterogeneity and prognostic model development for bladder cancer

INTRODUCTION

Gaining a deeper insight into the single-cell RNA sequencing (scRNA-seq) results of bladder cancer (BLCA) provides a transcriptomic profiling of individual cancer cells, which may disclose the molecular mechanisms involved in BLCA carcinogenesis.

METHODS

scRNA data were obtained from GSE169379 dataset. We used the InferCNV software to determine the copy number variant (CNV) with normal epithelial cells serving as the reference, and performed the pseudo-timing analysis on subsets of epithelial cell using Monocle3 software. Transcription factor analysis was conducted using the Dorothea software. Intercellular communication analysis was performed using the Liana software. Cox analysis and LASSO regression were applied to establish a prognostic model.

RESULTS

We investigated the heterogeneity of tumors in four distinct cell types of BLCA cancer, namely immune cells, endothelial cells, epithelial cells, and fibroblasts. We evaluated the transcription factor activity of different immune cells in BLCA and identified significant enrichment of TCF7 and TBX21 in CD8+ T cells. Additionally, we identified two distinct subtypes of cancer-associated fibroblasts (CAFs), namely iCAFs and myoCAFs, which exhibited distinct communication patterns. Using sub-cluster and cell trajectory analyses, we identified different states of normal-to-malignant cell transformation in epithelial cells. TF analysis further revealed high activation of MYC and SOX2 in tumor cells. Finally, we identified five model genes (SLCO3A1, ANXA1, TENM3, EHBP1, LSAMP) for the development of a prognostic model, which demonstrated high effectiveness in stratifying patients across seven different cohorts.

CONCLUSIONS

We have developed a prognostic model that has demonstrated significant efficacy in stratifying patients with BLCA.

RUNX3 inactivates oncogenic MYC through disruption of MYC/MAX complex and subsequent recruitment of GSK3β-FBXW7 cascade

MYC is one of the most commonly dysregulated proto-oncogenes in cancer. MYC promotes cancer initiation and maintenance by regulating multiple biological processes, such as proliferation and stem cell function. Here, we show that developmental regulator RUNX3 targets MYC protein for rapid degradation through the glycogen synthase kinase-3 beta-F-box/WD repeat-containing protein 7 (GSK3β-FBXW7) proteolytic pathway. The evolutionarily conserved Runt domain of RUNX3 interacts directly with the basic helix-loop-helix leucine zipper of MYC, resulting in the disruption of MYC/MAX and MYC/MIZ-1 interactions, enhanced GSK3β-mediated phosphorylation of MYC protein at threonine-58 and its subsequent degradation via the ubiquitin-proteasomal pathway. We therefore uncover a previously unknown mode of MYC destabilization by RUNX3 and provide an explanation as to why RUNX3 inhibits early-stage cancer development in gastrointestinal and lung mouse cancer models.

Targeting Myc-driven stress addiction in colorectal cancer

MYC is a proto-oncogene that encodes a powerful regulator of transcription and cellular programs essential for normal development, as well as the growth and survival of various types of cancer cells. MYC rearrangement and amplification is a common cause of hematologic malignancies. In epithelial cancers such as colorectal cancer, genetic alterations in MYC are rare. Activation of Wnt, ERK/MAPK, and PI3K/mTOR pathways dramatically increases Myc levels through enhanced transcription, translation, and protein stability. Elevated Myc promotes stress adaptation, metabolic reprogramming, and immune evasion to drive cancer development and therapeutic resistance through broad changes in transcriptional and translational landscapes. Despite intense interest and effort, Myc remains a difficult drug target. Deregulation of Myc and its targets has profound effects that vary depending on the type of cancer and the context. Here, we summarize recent advances in the mechanistic understanding of Myc-driven oncogenesis centered around mRNA translation and proteostress. Promising strategies and agents under development to target Myc are also discussed with a focus on colorectal cancer.

The disordered MAX N-terminus modulates DNA binding of the transcription factor MYC:MAX

The intrinsically disordered protein MYC belongs to the family of basic helix-loop-helix leucine zipper (bHLH-LZ) transcription factors (TFs). In complex with its cognate binding partner MAX, MYC preferentially binds to E-Box promotor sequences where it controls fundamental cellular processes such as cell cycle progression, metabolism, and apoptosis. Intramolecular regulation of MYC:MAX has not yet been investigated in detail. In this work, we use Nuclear Magnetic Resonance (NMR) spectroscopy to identify and map interactions between the disordered MAX N-terminus and the MYC:MAX DNA binding domain (DBD). We find that this binding event is mainly driven by electrostatic interactions and that it is competitive with DNA binding. Using Nuclear Magnetic resonance (NMR) spectroscopy and Surface Plasmon Resonance (SPR), we demonstrate that the MAX N-terminus serves to accelerate DNA binding kinetics of MYC:MAX and MAX:MAX dimers, while it simultaneously provides specificity for E-Box DNA. We also establish that these effects are further enhanced by Casein Kinase 2-mediated phosphorylation of two serine residues in the MAX N-terminus. Our work provides new insights how bHLH-LZ TFs are regulated by intramolecular interactions between disordered regions and the folded DNA binding domain.

Therapeutic targeting of "undruggable" MYC

c-MYC controls global gene expression and regulates cell proliferation, cell differentiation, cell cycle, metabolism and apoptosis. According to some estimates, MYC is dysregulated in ≈70% of human cancers and strong evidence implicates aberrantly expressed MYC in both tumor initiation and maintenance. In vivo studies show that MYC inhibition elicits a prominent anti-proliferative effect and sustained tumor regression while any alteration on healthy tissue remains reversible. This opens an exploitable window for treatment that makes MYC one of the most appealing therapeutic targets for cancer drug development. This review describes the main functional and structural features of the protein structure of MYC and provides a general overview of the most relevant or recently identified interactors that modulate MYC oncogenic activity. This review also summarizes the different approaches aiming to abrogate MYC oncogenic function, with a particular focus on the prototype inhibitors designed for the direct and indirect targeting of MYC.

Zinc Fingers 10 and 11 of Miz-1 undergo conformational exchange to achieve specific DNA binding

Miz-1 (ZBTB17) is a poly-zinc finger BTB/POZ transcription factor with 12 consecutive C2H2 zinc fingers (ZFs) that binds transcriptional start sites (TSSs) to regulate the expression of genes involved in cell development and proliferation. As of now, it is not known which of the 12 consecutive ZFs are responsible for the recognition of the 24 base pair consensus sequence found at these TSSs. Evidence suggests ZFs 7-12 plays this role. We provide validation for this and describe the structural and dynamical characterization of unprecedented conformational exchange in the linker between ZFs 10 and 11. This conformational exchange uncouples ZFs 7-10 from 11 and 12 and promotes a scanning-recognition mechanism through which the two segments cooperate to bind two sub-sites at both ends of the consensus. We further show that this can result in the coiling of TSSs as part of Miz-1's mechanism of transcriptional transactivation.

Targeting Myc Interacting Proteins as a Winding Path in Cancer Therapy

MYC, as a well-known oncogene, plays essential roles in promoting tumor occurrence, development, invasion and metastasis in many kinds of solid tumors and hematologic neoplasms. In tumors, the low expression and the short half-life of Myc are reversed, cause tumorigenesis. And proteins that directly interact with different Myc domains have exerted a significant impact in the process of Myc-driven carcinogenesis. Apart from affecting the transcription of Myc target genes, Myc interaction proteins also regulate the stability of Myc through acetylation, methylation, phosphorylation and other post-translational modifications, as well as competitive combination with Myc. In this review, we summarize a series of Myc interacting proteins and recent advances in the related inhibitors, hoping that can provide new opportunities for Myc-driven cancer treatment.

Radiosensitizing effects of c‑myc gene knockdown‑induced G2/M phase arrest by intrinsic stimuli via the mitochondrial signaling pathway

Osteosarcoma is the most common primary malignant bone tumor in children and adolescents and its long‑term survival rate has stagnated in the past decades. Previous studies have shown that tumors in the G2/M phase are more sensitive to radiotherapy. The proto‑oncogene c‑myc is a transformed member of the myc family and c‑myc‑interacting zinc finger protein‑1 (Miz‑1) is a poly‑Cys2His2 zinc finger (ZF) activator of cell cycle regulator genes, such as the cyclin‑dependent kinase inhibitor p21. C‑myc can repress the expression of p21 by binding to Miz‑1 and abolishing the interaction between Miz‑1 and its co‑activators, which induces G2/M phase arrest. Therefore, the present study investigated the radiosensitizing effects of the c‑myc gene and the sensitizing apoptosis pathway, aiming to identify a more effective combination radiotherapy treatment for osteosarcoma. The present study demonstrated that the c‑myc gene was overexpressed in osteosarcoma cells compared to osteoblasts. Following inhibition of c‑myc gene expression in osteosarcoma cells, tumor proliferation was significantly hindered after inducing G2/M phase arrest via regulating G2/M phase‑associated proteins. Additionally, it was revealed that inhibiting c‑myc gene expression combined with radiotherapy could significantly increase the apoptosis rate of osteosarcoma cells via the mitochondrial signaling pathway. In summary, the present study verified the radiosensitizing effects of c‑myc gene knockdown‑induced G2/M phase arrest, which was achieved by intrinsic stimuli through the mitochondrial signaling pathway.

Blocking Myc to Treat Cancer: Reflecting on Two Decades of Omomyc

First designed and published in 1998 as a laboratory tool to study Myc perturbation, Omomyc has come a long way in the past 22 years. This dominant negative has contributed to our understanding of Myc biology when expressed, first, in normal and cancer cells, and later in genetically-engineered mice, and has shown remarkable anti-cancer properties in a wide range of tumor types. The recently described therapeutic effect of purified Omomyc mini-protein—following the surprising discovery of its cell-penetrating capacity—constitutes a paradigm shift. Now, much more than a proof of concept, the most characterized Myc inhibitor to date is advancing in its drug development pipeline, pushing Myc inhibition into the clinic.