Colorectal cancer (CRC) is a major cause of death from cancer worldwide. Several genes and pathways have been found mutated in CRC and most of them converge on the activation of MYC, thus making this oncogene an attractive therapeutic target. However, attempts to find direct MYC inhibitors have been disappointing, suggesting that alternative strategies, aimed at reducing MYC expression or activity are preferable options. One avenue is the inhibition of MYC translation, although the presence of an IRES region in its 5'UTR enables this oncogene to be translated also under non-permissive conditions and to escape from pharmacological inhibition. Thus, IRES-translation of MYC might represent a novel actionable target for CRC.
Our preliminary work has led to the identification of CNBP as a regulator of MYC IRES translation that is essential for the growth and survival of CRC.
The proposed project aims at elucidating the role of IRES-mediated translation of MYC and of its putative regulator CNBP in colorectal tumorigenesis and the therapeutic potential of their targeting.
We will address these issues with the following main tasks:
Task 1: We will define the pathophysiological relevance of IRES-dependent translation of MYC and the role of CNBP on colorectal tumorigenesis: we will delete by CRISPR-Cas9 approach the IRES region of MYC from CRC cells and study the consequences on tumor proliferation and viability in vitro and in vivo, in the presence or absence of CNBP.
Task 2: We will study the effect of CNBP ablation in the colorectal cancer mouse models APCMin/+: we will delete CNBP gene in the intestinal epithelium using our newly established CNBP loxP/loxP x villin CRE mouse model and cross these mice with APCMin/+.
Results of this project will inform us about an unprecedented mechanism of regulation of MYC translation and the consequences of its targeting in CRC.
Despite the significant efforts and advances in the understanding of the molecular basis of CRC, this tumor is still a major cause of death from cancer worldwide. In particular, the prognosis of the late stages of the disease is still poor and limited therapeutic options are available.
Systems-wide screenings of large cohorts of patients have identified recurrent gene mutations and pathway alterations, leading to novel molecular stratifications of patients. However, attempts to specifically inhibit one or more aberrantly activated pathways have not been successful so far, largely because of the occurrence of compensatory mechanisms, often able to bypass drug inhibitions and to restore the function of the downstream effectors.
Based on these considerations, a reasonable approach to overcome this problem appears to be the targeting of downstream transcription factors. In this regard, most of the pathways involved in colorectal tumorigenesis (WNT, Ras-MAPK, Pi3K, SMAD among the others) have the ability to upregulate MYC and this oncogene is found upregulated in nearly all CRCs. Hence, inhibition of this common effector would be a very appropriate strategy to fight CRC and other tumors where this oncogene plays a pivotal role. However, attempts to directly or indirectly target MYC expression or function have been quite disappointing because of the flat structure of the protein and presence of salvage mechanisms that prevent its complete downregulation. One of these salvage pathways is the IRES translation, a mechanism used by selected few targets to warrant proper levels of protein under unfavorable conditions, i.e. when the general translation is inhibited, such as during cellular stress or apoptosis. The present proposal aims at understanding how important is the IRES translation of MYC for the growth and survival of CRC, an issue that has not been fully understood and addressed at the physiological level yet. In particular, the main goal of this project is to establish whether in the absence of the endogenous IRES region of MYC, CRC cells have decreased tumorigenic potential and are more vulnerable to cellular stress and other treatments. Additionally, the project aims at determining whether and how the RNA binding protein CNBP plays a relevant role in this context, by regulating MYC IRES translation and contributing to tumor growth and survival. Elucidations of these issues will certainly provide critical information to better understand the function of MYC and its regulation in CRC and to establish if targeting these newly identified mechanisms and molecules could represent a novel and compelling approach to treat CRC.
References
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