bims-pimaco 2024-07-21 papers

Issue of 2024–07–21
four papers selected by
Lucas B. Zeiger

Mol Cell. 2024 Jul 09. pii: S1097-2765(24)00534-3. [Epub ahead of print]

Functional and structural insights into RAS effector proteins.

Alessandro M Mozzarelli, Dhirendra K Simanshu, Pau Castel.

RAS proteins are conserved guanosine triphosphate (GTP) hydrolases (GTPases) that act as molecular binary switches and play vital roles in numerous cellular processes. Upon GTP binding, RAS GTPases adopt an active conformation and interact with specific proteins termed RAS effectors that contain a conserved ubiquitin-like domain, thereby facilitating downstream signaling. Over 50 effector proteins have been identified in the human proteome, and many have been studied as potential mediators of RAS-dependent signaling pathways. Biochemical and structural analyses have provided mechanistic insights into these effectors, and studies using model organisms have complemented our understanding of their role in physiology and disease. Yet, many critical aspects regarding the dynamics and biological function of RAS-effector complexes remain to be elucidated. In this review, we discuss the mechanisms and functions of known RAS effector proteins, provide structural perspectives on RAS-effector interactions, evaluate their significance in RAS-mediated signaling, and explore their potential as therapeutic targets.

Keywords: GTPase; RAS; RAS-binding domain; RBD; effector

DOI: https://doi.org/10.1016/j.molcel.2024.06.027

Cancer Res. 2024 Jul 18.

Targeting Cholesterol Biosynthesis with Statins Synergizes with AKT Inhibitors in Triple-Negative Breast Cancer.

Alissandra L Hillis, Timothy D Martin, Haley E Manchester, Jenny Högström, Na Zhang, Emmalyn Lecky, Nina Kozlova, Jonah Lee, Nicole S Persky, David E Root, Myles Brown, Karen Cichowski, Stephen J Elledge, Taru Muranen, David A Fruman, Simon T Barry, John G Clohessy, Ralitsa R Madsen, Alex Toker.

Triple-negative breast cancer (TNBC) is responsible for a disproportionate number of breast cancer patient deaths due to extensive molecular heterogeneity, high recurrence rates and lack of targeted therapies. Dysregulation of the phosphoinositide 3-kinase (PI3K)/AKT pathway occurs in approximately 50% of TNBC patients. Here, we performed a genome-wide CRISPR/Cas9 screen with PI3Kα and AKT inhibitors to find targetable synthetic lethalities in TNBC. Cholesterol homeostasis was identified as a collateral vulnerability with AKT inhibition. Disruption of cholesterol homeostasis with pitavastatin synergized with AKT inhibition to induce TNBC cytotoxicity in vitro, in mouse TNBC xenografts and in patient-derived, estrogen receptor (ER)-negative breast cancer organoids. Neither ER-positive breast cancer cell lines nor ER-positive organoids were sensitive to combined AKT inhibitor and pitavastatin. Mechanistically, TNBC cells showed impaired sterol regulatory element-binding protein 2 (SREBP-2) activation in response to single agent or combination treatment with AKT inhibitor and pitavastatin, which was rescued by inhibition of the cholesterol trafficking protein Niemann-Pick C1 (NPC1). NPC1 loss caused lysosomal cholesterol accumulation, decreased endoplasmic reticulum cholesterol levels, and promoted SREBP-2 activation. Taken together, these data identify a TNBC-specific vulnerability to the combination of AKT inhibitors and pitavastatin mediated by dysregulated cholesterol trafficking. These findings support combining AKT inhibitors with pitavastatin as a therapeutic modality in TNBC. .

DOI: https://doi.org/10.1158/0008-5472.CAN-24-0970

Nat Commun. 2024 Jul 19. 15(1): 6076

Combined inhibition of KRASG12C and mTORC1 kinase is synergistic in non-small cell lung cancer.

Current KRASG12C (OFF) inhibitors that target inactive GDP-bound KRASG12C cause responses in less than half of patients and these responses are not durable. A class of RASG12C (ON) inhibitors that targets active GTP-bound KRASG12C blocks ERK signaling more potently than the inactive-state inhibitors. Sensitivity to either class of agents is strongly correlated with inhibition of mTORC1 activity. We have previously shown that PI3K/mTOR and ERK-signaling pathways converge on key cellular processes and that inhibition of both pathways is required for inhibition of these processes and for significant antitumor activity. We find here that the combination of a KRASG12C inhibitor with a selective mTORC1 kinase inhibitor causes synergistic inhibition of Cyclin D1 expression and cap-dependent translation. Moreover, BIM upregulation by KRASG12C inhibition and inhibition of MCL-1 expression by the mTORC1 inhibitor are both required to induce significant cell death. In vivo, this combination causes deep, durable tumor regressions and is well tolerated. This study suggests that the ERK and PI3K/mTOR pathways each mitigate the effects of inhibition of the other and that combinatorial inhibition is a potential strategy for treating KRASG12C-dependent lung cancer.

DOI: https://doi.org/10.1038/s41467-024-50063-z

Trends Cancer. 2024 Jul 16. pii: S2405-8033(24)00120-1. [Epub ahead of print]

Transcriptomic subtyping of gastrointestinal malignancies.

Tim R de Back, Sander R van Hooff, Dirkje W Sommeijer, Louis Vermeulen.

Gastrointestinal (GI) cancers are highly heterogeneous at multiple levels. Tumor heterogeneity can be captured by molecular profiling, such as genetic, epigenetic, proteomic, and transcriptomic classification. Transcriptomic subtyping has the advantage of combining genetic and epigenetic information, cancer cell-intrinsic properties, and the tumor microenvironment (TME). Unsupervised transcriptomic subtyping systems of different GI malignancies have gained interest because they reveal shared biological features across cancers and bear prognostic and predictive value. Importantly, transcriptomic subtypes accurately reflect complex phenotypic states varying not only per tumor region, but also throughout disease progression, with consequences for clinical management. Here, we discuss methodologies of transcriptomic subtyping, proposed taxonomies for GI malignancies, and the challenges posed to clinical implementation, highlighting opportunities for future transcriptomic profiling efforts to optimize clinical impact.

Keywords: colorectal cancer; gastric cancer; gastrointestinal malignancies; pancreatic ductal adenocarcinoma; personalized medicine; transcriptomic subtyping

DOI: https://doi.org/10.1016/j.trecan.2024.06.007