MYC upstream region orchestrates resistance to PI3K inhibitors in cancer cells through FOXO3a-mediated autophagic adaptation.

The MYC oncogene is frequently overexpressed in tumors and inhibition of its translation is considered an attractive therapeutic opportunity. Despite numerous reports proposing an internal ribosome entry site (IRES) within the MYC Upstream Region (MYC UR) to sustain MYC translation during cellular stress or chemotherapy, conflicting evidence remains regarding the validity of such a mechanism. Through comprehensive investigations in MYC-driven Colorectal Cancer (CRC) and Burkitt Lymphoma (BL) cells, we demonstrate that MYC UR does not facilitate cap-independent translation, but instead orchestrates resistance to PI3K inhibitors. Genomic deletion of MYC UR neither impacts MYC protein levels nor viability in CRC cells, either untreated or exposed to cellular stress. However, in response to PI3K inhibitors, MYC UR drives a FOXO3a-dependent transcriptional upregulation of MYC, conferring drug resistance. This resistance is mediated by enhanced autophagic flux, governed by MYC, and blockade of autophagy sensitizes CRC cells to PI3K inhibition in vitro and in vivo. Remarkably, BL cells lacking the translocation of MYC UR exhibit sensitivity to PI3K inhibitors, whereas MYC UR-translocated cells respond to these drugs only when autophagy is inhibited. These findings challenge previous notions regarding IRES-mediated translation and highlight a promising strategy to overcome resistance to PI3K inhibitors in MYC-driven malignancies, offering potential clinical implications for CRC and BL treatment. In response to BKM120, the upstream region of MYC (UR) enhances MYC expression, via FOXO3a, leading to increased autophagic flux and resistance to PI3K inhibitors (left). Pharmacological blockade of autophagy (center) or lack of translocated MYC UR along with MYC CDS in BL (right) overcome resistance and induces cells death. Image created in BioRender.

WTAP and m6A-modified circRNAs modulation during stress response in acute myeloid leukemia progenitor cells.

N6-methyladenosine (m6A) is one of the most prevalent and conserved RNA modifications. It controls several biological processes, including the biogenesis and function of circular RNAs (circRNAs), which are a class of covalently closed-single stranded RNAs. Several studies have revealed that proteotoxic stress response induction could be a relevant anticancer therapy in Acute Myeloid Leukemia (AML). Furthermore, a strong molecular interaction between the m6A mRNA modification factors and the suppression of the proteotoxic stress response has emerged. Since the proteasome inhibition leading to the imbalance in protein homeostasis is strictly linked to the stress response induction, we investigated the role of Bortezomib (Btz) on m6A regulation and in particular its impact on the modulation of m6A-modified circRNAs expression. Here, we show that treating AML cells with Btz downregulated the expression of the m6A regulator WTAP at translational level, mainly because of increased oxidative stress. Indeed, Btz treatment promoted oxidative stress, with ROS generation and HMOX-1 activation and administration of the reducing agent N-acetylcysteine restored WTAP expression. Additionally, we identified m6A-modified circRNAs modulated by Btz treatment, including circHIPK3, which is implicated in protein folding and oxidative stress regulation. These results highlight the intricate molecular networks involved in oxidative and ER stress induction in AML cells following proteotoxic stress response, laying the groundwork for future therapeutic strategies targeting these pathways.

Combined inhibition of polyamine metabolism and eIF5A hypusination suppresses colorectal cancer growth through a converging effect on MYC translation.

A key mechanism driving colorectal cancer (CRC) development is the upregulation of MYC and its targets, including ornithine decarboxylase (ODC), a master regulator of polyamine metabolism. Elevated polyamines promote tumorigenesis in part by activating DHPS-mediated hypusination of the translation factor eIF5A, thereby inducing MYC biosynthesis. Thus, MYC, ODC and eIF5A orchestrate a positive feedback loop that represents an attractive therapeutic target for CRC therapy. Here we show that combined inhibition of ODC and eIF5A induces a synergistic antitumor response in CRC cells, leading to MYC suppression. We found that genes of the polyamine biosynthesis and hypusination pathways are significantly upregulated in colorectal cancer patients and that inhibition of ODC or DHPS alone limits CRC cell proliferation through a cytostatic mechanism, while combined ODC and DHPS/eIF5A blockade induces a synergistic inhibition, accompanied to apoptotic cell death in vitro and in mouse models of CRC and FAP. Mechanistically, we found that this dual treatment causes complete inhibition of MYC biosynthesis in a bimodal fashion, by preventing translational elongation and initiation. Together, these data illustrate a novel strategy for CRC treatment, based on the combined suppression of ODC and eIF5A, which holds promise for the treatment of CRC.

Regulation of Gene Expression by m6Am RNA Modification.

The field of RNA modification, also referred to as "epitranscriptomics," is gaining more and more interest from the scientific community. More than 160 chemical modifications have been identified in RNA molecules, but the functional significance of most of them still needs to be clarified. In this review, we discuss the role of N6,2'-O-dimethyladenosine (m6Am) in gene expression regulation. m6Am is present in the first transcribed nucleotide close to the cap in many mRNAs and snRNAs in mammals and as internal modification in the snRNA U2. The writer and eraser proteins for these modifications have been recently identified and their deletions have been utilized to understand their contributions in gene expression regulation. While the role of U2 snRNA-m6Am in splicing regulation has been reported by different independent studies, conflicting data were found for the role of cap-associated m6Am in mRNA stability and translation. However, despite the open debate on the role of m6Am in mRNA expression, the modulation of regulators produced promising results in cancer cells. We believe that the investigation on m6Am will continue to yield relevant results in the future.

Multiple Roles of m6A RNA Modification in Translational Regulation in Cancer.

Despite its discovery in the early 1970s, m6A modification within mRNA molecules has only powerfully entered the oncology field in recent years. This chemical modification can control all aspects of the maturation of mRNAs, both in the nucleus and in the cytoplasm. Thus, the alteration in expression levels of writers, erasers, and readers may significantly contribute to the alteration of gene expression observed in cancer. In particular, the activation of oncogenic pathways can lead to an alteration of the global rate of mRNA translation or the selective translation of specific mRNAs. In both cases, m6A can play an important role. In this review, we highlight the role of m6A in the regulation of translation by focusing on regulatory mechanisms and cancer-related functions of this novel but still controversial field.