Biology subjects

Espinoza, C. A.

Publications and source records attributed to Espinoza, C. A..

4 recordsLinked to original sources

bioRxiv2025

Autoregulation of the MET Receptor Tyrosine Kinase by its Intracellular Juxtamembrane Domain

Receptor Tyrosine Kinases (RTKs) are single-pass transmembrane receptors whose activation is tightly regulated by intra-domain interactions within both their extracellular and intracellular regions. The intracellular juxtamembrane domain, which links the transmembrane and kinase domains, often plays a critical role in modulating kinase activity. The MET receptor, activated by Hepatocyte Growth Factor (HGF), requires precise regulation to support normal development and wound healing, but becomes a potent oncogene when overexpressed or mutated. A common oncogenic lesion in MET, caused by exon 14 skipping, leads to partial deletion of its unusually long intracellular juxtamembrane domain and is frequently detected in non-small cell lung cancer (NSCLC), as well as pancreatic, liver and brain cancers. Despite its length and abundance of post-translational modifications, the functional role of the MET juxtamembrane domain has remained poorly understood. We have uncovered that this segment regulates the kinetics of MET kinase activation. Specifically, we found that a membrane-proximal, N-terminal region of the juxtamembrane domain accelerates activation loop phosphorylation promoting kinase transition to an active state. This regulation does not depend on the oligomeric state of MET but likely acts allosterically to enhance autophosphorylation of the kinase domain. Notably, this function is absent in the closely related MST1R/RON RTK, suggesting it is a unique feature of the MET receptor. Together, these findings uncover a previously unrecognized layer of MET regulation with potential implications for the development of selective therapies targeting MET-driven cancers.

biochemistry↗

bioRxiv2024

Protein-protein interactions with G3BPs drive stress granule condensation and gene expression changes under cellular stress

Stress granules (SGs) are macromolecular assemblies that form under cellular stress. Formation of these condensates is driven by the condensation of RNA and RNA-binding proteins such as G3BPs. G3BPs condense into SGs following stress-induced translational arrest. Three G3BP paralogs (G3BP1, G3BP2A, and G3BP2B) have been identified in vertebrates. However, the contribution of different G3BP paralogs to stress granule formation and stress-induced gene expression changes is incompletely understood. Here, we identified key residues for G3BP condensation such as V11. This conserved amino acid is required for formation of the G3BP-Caprin-1 complex, hence promoting SG assembly. Total RNA sequencing and ribosome profiling revealed that disruption of G3BP condensation corresponds to changes in mRNA levels and ribosome engagement during the integrated stress response (ISR). Moreover, we found that G3BP2B preferentially condenses and promotes changes in mRNA expression under endoplasmic reticulum (ER) stress. Together, this work suggests that stress granule assembly promotes changes in gene expression under cellular stress, which is differentially regulated by G3BP paralogs.

cell biology↗

bioRxiv2023

A genome-wide CRISPR screen supported by human genetics identifies the TNRC18 gene locus as a novel regulator of inflammatory signaling

Interleukin-1{beta} (IL-1{beta}) is dysregulated in many chronic inflammatory diseases, yet the genetic factors influencing IL-1{beta} production and signaling remain largely unknown. Myeloid-derived cells are the primary producers of IL-1{beta}, prompting a genome-wide CRISPR knockout screen in the human myeloid-derived U937 cell model, treated with lipopolysaccharide (LPS) to mimic inflammatory conditions, and sorted for high and low intracellular IL-1{beta} levels. A total of 295 genes were identified as regulators of IL-1{beta} production, including known mediators, such as TLR4, JAK-STAT, IL-10 receptor, and the Cullin ring finger ligase complex. Notably, 57 out of the 295 genes overlapped with loci associated with human inflammatory diseases, including the TNRC18 gene on chromosome 7p22.1 associated with multiple diseases in the Finnish population. U937 cells engineered with the homozygous rs748670681 risk allele associated with inflammatory bowel disease, demonstrated decreased levels of mRNA for TNRC18 and an adjacent gene WIPI2, reduction in LPS-dependent gene activation and cytokine production, but elevation of interferon-responsive gene programs. Transcriptomic profiles for individual knockouts of TNRC18 and WIPI2 attributed the loss of LPS-dependent signaling primarily to TNRC18 while the exacerbation of interferon signaling is a hallmark of loss of WIPI2. Collectively, these findings delineate the global regulatory mechanisms of IL-1{beta} production and provide molecular insights to the role of the rs748670681 variant as a pleiotropic risk factor for inflammatory diseases.

genomics↗

bioRxiv2023

Conserved regulatory motifs in the juxtamembrane domain and kinase N-lobe revealed through deep mutational scanning of the MET receptor tyrosine kinase domain.

MET is a receptor tyrosine kinase (RTK) responsible for initiating signaling pathways involved in development and wound repair. MET activation relies on ligand binding to the extracellular receptor, which prompts dimerization, intracellular phosphorylation, and recruitment of associated signaling proteins. Mutations, which are predominantly observed clinically in the intracellular juxtamembrane and kinase domains, can disrupt typical MET regulatory mechanisms. Understanding how juxtamembrane variants, such as exon 14 skipping (MET{Delta}Ex14), and rare kinase domain mutations can increase signaling, often leading to cancer, remains a challenge. Here, we perform a parallel deep mutational scan (DMS) of the MET intracellular kinase domain in two fusion protein backgrounds: wild type and MET{Delta}Ex14. Our comparative approach has revealed a critical hydrophobic interaction between a juxtamembrane segment and the kinase C-helix, pointing to potential differences in regulatory mechanisms between MET and other RTKs. Additionally, we have uncovered a {beta}5 motif that acts as a structural pivot for the kinase domain in MET and other TAM family of kinases. We also describe a number of previously unknown activating mutations, aiding the effort to annotate driver, passenger, and drug resistance mutations in the MET kinase domain.

molecular biology↗