bims-pimaco 2021-12-19 papers

Issue of 2021‒12‒19
five papers selected by
Lucas B. Zeiger
Beatson Institute for Cancer Research

Elife. 2021 Dec 13. pii: e69729. [Epub ahead of print]10

Rpl24Bst mutation suppresses colorectal cancer by promoting eEF2 phosphorylation via eEF2K.

John Rp Knight, Nikola Vlahov, David M Gay, Rachel A Ridgway, William James Faller, Christopher Proud, Giovanna R Mallucci, Tobias von der Haar, Christopher Mark Smales, Anne E Willis, Owen J Sansom.

Increased protein synthesis supports the rapid cell proliferation associated with cancer. The Rpl24Bst mutant mouse reduces the expression of the ribosomal protein RPL24 and has been used to suppress translation and limit tumorigenesis in multiple mouse models of cancer. Here, we show that Rpl24Bst also suppresses tumorigenesis and proliferation in a model of colorectal cancer (CRC) with two common patient mutations, Apc and Kras. In contrast to previous reports, Rpl24Bst mutation has no effect on ribosomal subunit abundance but suppresses translation elongation through phosphorylation of eEF2, reducing protein synthesis by 40% in tumour cells. Ablating eEF2 phosphorylation in Rpl24Bst mutant mice by inactivating its kinase, eEF2K, completely restores the rates of elongation and protein synthesis. Furthermore, eEF2K activity is required for the Rpl24Bst mutant to suppress tumorigenesis. This work demonstrates that elevation of eEF2 phosphorylation is an effective means to suppress colorectal tumorigenesis with two driver mutations. This positions translation elongation as a therapeutic target in CRC, as well as in other cancers where the Rpl24Bst mutation has a tumour suppressive effect in mouse models.

Keywords: RPL24; cancer biology; cell biology; eEF2K; in vivo models; intestinal cancer; mouse; protein sythesis; translation

DOI: https://doi.org/10.7554/eLife.69729

Oncogene. 2021 Dec 14.

p53-mediated AKT and mTOR inhibition requires RFX7 and DDIT4 and depends on nutrient abundance.

Luis Coronel, David Häckes, Katjana Schwab, Konstantin Riege, Steve Hoffmann, Martin Fischer.

In recent years the tumor suppressor p53 has been increasingly recognized as a potent regulator of the cell metabolism and for its ability to inhibit the critical pro-survival kinases AKT and mTOR. The mechanisms through which p53 controls AKT and mTOR, however, are largely unclear. Here, we demonstrate that p53 activates the metabolic regulator DDIT4 indirectly through the regulatory factor X 7 (RFX7). We provide evidence that DDIT4 is required for p53 to inhibit mTOR complex 2 (mTORC2)-dependent AKT activation. Most strikingly, we also find that the DDIT4 regulator RFX7 is required for p53-mediated inhibition of mTORC1 and AKT. Our results suggest that AMPK activation plays no role and p53-mediated AKT inhibition is not critical for p53-mediated mTORC1 inhibition. Moreover, using recently developed physiological cell culture media we uncover that basal p53 and RFX7 activity can play a critical role in restricting mTORC1 activity under physiological nutrient conditions, and we propose a nutrient-dependent model for p53-RFX7-mediated mTORC1 inhibition. These results establish RFX7 and its downstream target DDIT4 as essential effectors in metabolic control elicited by p53.

DOI: https://doi.org/10.1038/s41388-021-02147-z

Mol Oncol. 2021 Dec 17.

KRAS mutation-independent downregulation of MAPK/PI3K signaling in colorectal cancer.

Kuen Kuen Lam, Choong Leong Tang, Emile Tan, Siew Heng Wong, Peh Yean Cheah.

KRAS is a gatekeeper gene in human colorectal tumorigenesis. KRAS is "undruggable", hence efforts have been diverted to inhibit downstream RAF/MEK/ERK and PI3K/Akt signaling. Nevertheless, none of these inhibitors has progressed to clinical use despite extensive trials. We examined levels of phospho-ERK1/2(T202/Y204) and phospho-Akt1/2/3(S473) in human colorectal tumor compared to matched mucosa with semi-quantitative near-infrared western blot and confocal fluorescence immunohistochemistry imaging. Surprisingly, 75.5% (25/33) of tumors had lower or equivalent phospho-ERK1/2 and 96.9% (31/32) of tumors had lower phospho-Akt1/2/3 compared to matched mucosa, irrespective of KRAS mutation status. In contrast, we discovered KRAS-dependent SOX9 upregulation in 28 of the 31 (90.3%) tumors. These observations were substantiated by analysis of the public domain transcriptomics The Cancer Genome Atlas (TCGA) and NCBI Gene Expression Omnibus (GEO) datasets and proteomics Clinical Proteomic Tumor Analysis Consortium (CPTAC) dataset. These data suggest that RAF/MEK/ERK and PI3K/Akt signaling are unlikely to be activated in most human colorectal cancer.

Keywords: CPTAC; KRAS signaling; MAPK/PI3K; SOX9; TCGA; colorectal tumorigenesis

DOI: https://doi.org/10.1002/1878-0261.13163

iScience. 2021 Dec 17. 24(12): 103528

Smurf1 silencing restores PTEN expression that ameliorates progression of human glioblastoma and sensitizes tumor cells to mTORC1/C2 inhibitor Torin1.

Qin Xia, Wenxuan Li, Sakhawat Ali, Mengchuan Xu, Yang Li, Shengzhen Li, Xinyi Meng, Liqun Liu, Lei Dong.

Amplification of ubiquitin E3 ligase Smurf1 promotes degradation of PTEN leading to hyperactivation of the Akt/mTORC1 pathway. However, inhibitors of this pathway have not hitherto yielded promising results in clinical studies because of strong drug resistance. Here, we investigated Smurf1 expression in various glioblastoma (GB) cell lines and patient tissues. The therapeutic efficacy of Smurf1 silencing and Torin1 treatment was assessed in GB cells and orthotopic mouse model. We found Smurf1 loss elevates PTEN levels that interrupt the epidermal growth factor receptor pathway activity. Cotreatment with Smurf1 silencing and mTORC1/C2 inhibitor Torin1 remarkably decreased phosphorylation of Akt, and mTORC1 downstream targets 4EBP1 and S6K resulting in synergistic inhibitory effects. Smurf1 knockdown in orthotopic GB mouse model impaired tumor growth and enhanced cytotoxicity of Torin1. Together, these findings suggest a rational combination of Smurf1 inhibition and Torin1 as a promising new avenue to circumvent PI3K/Akt pathway-driven tumor progression and drug resistance.

Keywords: Molecular biology; Oncology

DOI: https://doi.org/10.1016/j.isci.2021.103528