Biology subjects

Cho, K.-J.

Publications and source records attributed to Cho, K.-J..

5 recordsLinked to original sources

bioRxiv2026

The galectin-3 carbohydrate recognition domain maintains plasma membrane phosphatidylserine required for KRAS function

KRAS is a small GTPase essential for cellular proliferation, differentiation, and survival. It is predominantly localized to the plasma membrane (PM), where it forms nanoclusters essential for signal transduction. This PM binding and nanoclustering strictly depend on phosphatidylserine (PtdSer), an anionic phospholipid enriched in the inner PM leaflet. Galectin-3 (Gal-3), a {beta}-galactoside-binding lectin implicated in cell growth, migration and tumor progression, has been shown to regulate KRAS PM binding and nanoclustering. Here, we demonstrate that Gal-3 knockout (KO) or inhibition of its carbohydrate recognition domain (CRD) depletes KRAS and PtdSer from the PM. Exogenous PtdSer supplementation fully restores PM PtdSer and partially restores KRAS PM binding, indicating that Gal-3 promotes KRAS PM binding in part by maintaining PM PtdSer content. Total cellular PtdSer, PM PI4P, cholesterol and GM3 are unchanged, excluding these established regulators of PM PtdSer. Instead, Gal-3 CRD inhibition disrupts the cellular balance of sphingomyelin (SM) and ceramide, alters intracellular SM distribution, and impairs the endocytic and recycling transport of PtdSer, SM, and epidermal growth factor receptor (EGFR). Together, our findings demonstrate that Gal-3 CRD activity sustains PM PtdSer content through endocytic trafficking, providing the PM lipid composition required for KRAS PM spatial organization.

cell biology↗

bioRxiv2025

eIF2B Selectively Anchors and Activates Mutant KRAS

Much is known about how RAS oncoproteins regulate mRNA translation factors, but the reverse relationship, how translation factors influence RAS activity, has remained largely unexplored. At the plasma membrane (PM), Son of Sevenless (SOS) acts as the canonical guanine nucleotide exchange factor (GEF) for RAS proteins, yet mechanisms governing its specificity for individual RAS isoforms remain unknown. Here, we show that the translation initiation factor eIF2B, best known for its GEF function in translation initiation, forms a distinct complex with SOS and mutant KRAS at the PM, but not with other oncogenic RAS variants. Mechanistically, eIF2B acts as an allosteric regulator of SOS, selectively enhancing GDP-GTP exchange on mutant KRAS. This specificity arises from the translational activity of eIF2B, which upregulates glycosphingolipid (GSL) biosynthesis to remodel PM lipids and preferentially anchor mutant KRAS. Together, our results uncover an unexpected moonlighting function of eIF2B: acting both as a direct activator of SOS and as a regulator of GSL pathway that shapes the membrane landscape, both required for mutant KRAS activation. These insights redefine our understanding of eIF2B and mutant KRAS functions in cancer and have profound implications for KRAS-driven oncogenesis. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=161 SRC="FIGDIR/small/686860v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@1f50934org.highwire.dtl.DTLVardef@2f55b9org.highwire.dtl.DTLVardef@1a51e39org.highwire.dtl.DTLVardef@1634aac_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIeIF2B interacts with mutant KRAS and SOS at the plasma membrane (PM). C_LIO_LIThe eIF2B:SOS complex promotes the GTP-bound active state of mutant KRAS. C_LIO_LIeIF2B enhances the translation of B4GALT5 mRNA, encoding a key enzyme of glycosphingolipid (GSL) biosynthesis. C_LIO_LIUpregulation of the GSL metabolites, ganglioside GM3 and sulfatide SM4, remodels PM lipid composition to facilitate eIF2B:SOS:KRAS complex formation and mutant KRAS nanoclustering. C_LIO_LIThrough its interaction with SOS and stimulation of GSL synthesis, eIF2B selectively activates mutant KRAS at the PM among RAS isoforms. C_LIO_LIeIF2B is required for the development of mKRAS-driven lung adenocarcinoma in mice. C_LIO_LIeIF2B is a marker of poor prognosis in mutant KRAS-driven cancers. C_LI

cancer biology↗

bioRxiv2024

Myotubularin-related proteins regulate KRAS function by controlling plasma membrane levels of polyphosphoinositides and phosphatidylserine

KRAS, a small GTPase involved in cell proliferation and differentiation, frequently gains activating mutations in human cancers. For KRAS to function, it must bind the plasma membrane (PM) via interactions between its membrane anchor and phosphatidylserine (PtdSer). Therefore, depleting PM PtdSer abrogates KRAS PM binding and activity. From a genome-wide siRNA screen to identify genes regulating KRAS PM localization, we identified a set of phosphatidylinositol (PI) 3-phosphatases: myotubularin-related proteins (MTMR) 2, 3, 4, and 7. Here, we show that silencing MTMR 2/3/4/7 disrupts KRAS PM interactions by reducing PM PI 4-phosphate (PI4P) levels, thereby disrupting the localization and operation of ORP5, a lipid transfer protein maintaining PM PtdSer enrichment. Concomitantly, silencing MTMR 2/3/4/7 elevates PM PI3P levels while reducing PM and total PtdSer levels. We also observed MTMR 2/3/4/7 expression is interdependent. We propose that the PI 3-phosphatase activity of MTMR is required for generating PM PI, necessary for PM PI4P synthesis, promoting the PM localization of PtdSer and KRAS. eTOC summaryWe discovered that silencing the phosphatidylinositol (PI) 3-phosphatase, MTMR, disrupts the PM localization of PtdSer and KRAS. We propose a model, where MTMR loss depletes PM PI needed for PM PI4P synthesis, an essential phospholipid for PM PtdSer enrichment, thereby impairing KRAS PM localization.

cell biology↗

bioRxiv2023

A new ferrocene derivative blocks KRAS localization and function by oxidative modification at His95.

Ras proteins are membrane-bound GTPases that regulate essential cellular processes at the plasma membrane (PM). Constitutively active mutations of K-Ras, one of the three Ras isoforms in mammalian cells, are frequently found in human cancers. Ferrocene derivatives, which elevate cellular reactive oxygen species (ROS), have shown to block the growth of non-small cell lung cancers (NSCLCs) harboring oncogenic mutant K-Ras. Here, we developed and tested a novel ferrocene derivative on the growth of human pancreatic ductal adenocarcinoma (PDAC) and NSCLC. Our compound inhibited the growth of K-Ras-dependent PDAC and NSCLC and abrogated the PM binding and signaling of K-Ras, but not other Ras isoforms. These effects were reversed upon antioxidant supplementation, suggesting a ROS-mediated mechanism. We further identified K-Ras His95 residue in the G-domain as being involved in the ferrocene-induced K-Ras PM dissociation via oxidative modification. Together, our studies demonstrate that the redox system directly regulates K-Ras PM binding and signaling via oxidative modification at the His95, and proposes a role of oncogenic mutant K-Ras in the recently described antioxidant-induced metastasis in K-Ras-driven lung cancers.

cell biology↗

bioRxiv2018

Discovery of allosteric non-covalent KRAS inhibitors that bind with sub micromolar affinity and disrupt effector binding

Approximately 15% of all human tumors harbor mutant KRAS, a membrane-associated small GTPase and a notorious oncogene. Somatic mutations that render KRAS constitutively active lead to uncontrolled cell growth, survival, proliferation, and eventually cancer. KRAS is thus a critical anticancer drug target. However, despite aggressive efforts in recent years, there is no drug on the market that directly targets KRAS. In the current work, we combined molecular simulation and high-throughput virtual screening with a battery of cell-based and biophysical assays to discover a novel, pyrazolopyrimidine-based allosteric KRAS inhibitor that exhibits promising biochemical properties. The compound selectively binds to active KRAS with sub-micromolar affinity, slightly modulates exchange factor activity, disrupts effector Raf binding, significantly reduces signal transduction through mutant KRAS and inhibits cancer cell growth. Moreover, by studying two of its analogues, we identified key chemical features of the compound that are critical for affinity, effect on effector binding and mode of action. We propose a set of specific interactions with key residues at the switch regions of KRAS as critical for abrogating effector binding and reducing the rate of nucleotide exchange. Together, these findings not only demonstrate the viability of direct KRAS inhibition and offer guidance for future optimization efforts, but also show that pyrazolopyrimidine-based compounds may represent a first-in-class lead toward a clinically relevant targeting of KRAS by allosteric non-covalent inhibitors.

biochemistry↗