Biology subjects

Mendoza, M. C.

Publications and source records attributed to Mendoza, M. C..

8 recordsLinked to original sources

bioRxiv2025

ERK builds a population of short-lived nascent adhesions that produce persistent edge protrusion and cell migration

Cell migration is realized through the fast and persistent protrusion of a leading edge in the direction of movement. The actin and adhesion structures that build edge protrusions are integrated such that pro-migration signaling pathways must control both assemblies to induce protrusion. Understanding the contribution of adhesion regulation has been complicated by the inability to selectively assay the nascent adhesions that promote edge protrusion. Here, we dissect how the core RAS[->]RAF[->]MEK[->]ERK pathways control of nascent adhesions contributes to edge protrusion and cell migration by targeting an ERK FRET biosensor to adhesions and quantifying ERKs spatial and temporal activity. We find that ERK is activated in the assembling, membrane-proximal region of nascent adhesions through adhesion scaffold paxillin, which interacts with the ERK activator MEK. Tracking nascent adhesion dynamics during cell migration showed that ERK promotes both nascent adhesion assembly and disassembly to create a population of nascent adhesions with short lifetimes. MEK inhibition is partially complemented by expression of a talin R8vvv mutant that increases the nascent adhesion population, demonstrating the significance of ERKs adhesion regulation for edge protrusion and migration persistence. These findings suggest that when new adhesions initiate, the ERK activation level dictates adhesion assembly and disassembly rates to specifically build nascent adhesions that rapidly turnover, an adhesion population that promotes protrusion persistence and migration. SignificanceCell migration is essential for development, healing, and cancer spread. To move, cells need to build and break tiny structures called nascent adhesions, specifically at their edge that protrudes in the direction of movement. We discovered that ERK, a key signaling protein activated during development and cancer, helps create a fast-turning-over population of these adhesions, which supports steady movement. Using new biosensors and adhesion tracking, we showed ERK is active in the assembling part of the adhesion, where it promotes both assembly and disassembly. Increasing the nascent adhesion population helps cells move when ERK is blocked. This work reveals how ERK controls cell movement by balancing adhesion dynamics and introduces tools to study similar processes in other signaling pathways.

cell biology↗

bioRxiv2025

Mechanism of ERK-mediated Rho Activation and Stress Fiber Assembly for Cell Migration

The growth factor-activated RAS/Extracellular Regulated Kinase (ERK) pathway is a fundamental regulatory pathway that induces cell migration. ERK supports protrusion of a leading edge and also activates the small GTPase Rho, which induces actin assembly into contractile stress fibers that pull the cell body forward. Yet, the mechanism behind ERKs induction of Rho in the cell body has remained elusive. We discover here that ERK controls Rho activity and contractile stress fibers by inhibiting Ezrin, a protein that physically links proximal actin filaments to the plasma membrane, but which also inhibits Rho by recruiting and activating ARHGAP18. ERK specifically reduces Ezrin activity in the cell body by phosphorylating the C-terminal tail of the Ezrin-activating kinase lymphocyte-oriented kinase (LOK). This phosphorylation inhibits LOKs activation of Ezrin, thereby releases Ezrins inhibition of Rho and stress fibers. The ERK-LOK-Ezrin-ARHGAP18-Rho signal provides key mechanistic insight into how ERK, activated during development, wound healing, and cancer, induces Rho activity and stress fibers for cell migration.

cell biology↗

bioRxiv2025

On the Mechanism of Ezrin Activation

Ezrin is a peripheral membrane protein that contributes to the organization and stability of cellular membrane structures by reversibly linking the plasma membrane to actin filaments. The formation of this membrane-actin linkage has been experimentally shown to require ezrin N-terminal (FERM) domain binding to PI(4,5)P2 phospholipid-enriched membrane sites and the phosphorylation of the ezrin C-terminal domain (CTD) at residue T567. Collectively, membrane association and T567 phosphorylation are believed to promote separation of the FERM and CTD domains; however, the underlying molecular mechanism remains less clear. In this study, we investigate the mechanistic steps of ezrin activation and the thermodynamic free energy landscape of FERM-CTD dissociation using enhanced sampling molecular dynamics (MD). We find that upon ezrin attachment to a lipid membrane, PI(4,5)P2 molecules outcompete other phospholipids at the surface of the FERM F1 and F3 subdomains. This interaction triggers a major conformational rearrangement within the FERM domain that destabilizes the FERM F2-CTD interface and initiates dissociation between the FERM and CTD. By employing well-tempered metadynamics (WTMetaD) with a contact-map collective variable, we determine that the principal barrier to FERM-CTD dissociation comes from F3-CTD interactions and that this dissociation can happen spontaneously with a moderate free energy barrier. We also show that the FERM-CTD reassociation after ezrin T567 phosphorylation is impeded due to reduced dissociation energy barrier. The free energy profile of dissociation between FERM and the CTD-replacing EBP50 protein is similar to that of the FERM-CTD system with nonphosphorylated T567, which agrees well with an in vivo experimental observation that EBP50 competes with the CTD for F2-F3 binding after CTD is dissociated. Together, our results help establish a revised view on the ezrin activation mechanism where FERM binding to PI(4,5)P2 enables spontaneous dissociation of the nonphosphorylated CTD. SIGNIFICANCEEzrin and related ERM proteins control how cells link their plasma membrane to the actin cytoskeleton, a process fundamental to cell shape, signaling and motility. Despite decades of study, the molecular basis of ezrin activation - how it transitions from a self-inhibited to an active membrane-bound state - has remained unresolved. Using atomistic and enhanced sampling molecular dynamics together with biochemical validation, we show that binding of the FERM domain to PI(4,5)P2-enriched membranes alone is sufficient to trigger spontaneous dissociation of the nonphosphorylated C-terminal domain. Phosphorylation of T567 subsequently stabilizes the open conformation and prevents domain reassociation, enabling actin engagement and binding of FERM partners such as EBP50. Collectively, these findings advance a more integrated view of ezrin activation, highlighting how membrane interactions, conformational flexibility and phosphorylation act in concert to regulate membrane-cytoskeleton coupling.

biophysics↗

bioRxiv2024

Tenascin-C in the early lung cancer tumor microenvironment promotes progression through integrin activation and FAK

Pre-cancerous lung lesions are commonly initiated by activating mutations in the RAS pathway, but do not transition to lung adenocarcinomas (LUAD) without additional oncogenic signals. Here, we show that expression of the extracellular matrix protein Tenascin-C (TNC) is increased in and promotes the earliest stages of LUAD development in oncogenic KRAS-driven lung cancer mouse models and in human LUAD. TNC is initially expressed by fibroblasts and its expression extends to tumor cells as the tumor becomes invasive. Genetic deletion of TNC in the mouse models reduces early tumor burden and high-grade pathology and diminishes tumor cell proliferation, invasion, and focal adhesion kinase (FAK) activity. TNC stimulates cultured LUAD tumor cell proliferation and migration through engagement of v-containing integrins and subsequent FAK activation. Intringuingly, lung injury causes sustained TNC accumulation in mouse lungs, suggesting injury can induce additional TNC signaling for early tumor cell transition to invasive LUAD. Biospecimens from patients with stage I/II LUAD show TNC in regions of FAK activation and an association of TNC with tumor recurrence after primary tumor resection. These results suggest that exogenous insults that elevate TNC in the lung parenchyma interact with tumor-initiating mutations to drive early LUAD progression and local recurrence.

cancer biology↗

bioRxiv2022

Mechanics of lung cancer: A finite element model shows strain amplification during early tumorigenesis

Early lung cancer lesions develop within a unique microenvironment that undergoes constant cyclic stretch from respiration. While tumor stiffening is an established driver of tumor progression, the contribution of stress and strain to lung cancer is unknown. We developed tissue scale finite element models of lung tissue to test how early lesions alter respiration-induced strain. We found that an early tumor, represented as alveolar filling, amplified the strain experienced in the adjacent alveolar walls. Tumor stiffening further increased the amplitude of the strain in the adjacent alveolar walls and extended the strain amplification deeper into the normal lung. In contrast, the strain experienced in the tumor proper was less than the applied strain, although regions of amplification appeared at the tumor edge. Measurements of the alveolar wall thickness in clinical and mouse model samples of lung adenocarcinoma (LUAD) showed wall thickening adjacent to the tumors, consistent with cellular response to strain. Modeling alveolar wall thickening by encircling the tumor with thickened walls moved the strain amplification radially outward, to the next adjacent alveolus. Simulating iterative thickening in response to amplified strain produced tracks of thickened walls. We observed such tracks in early-stage clinical samples. The tracks were populated with invading tumor cells, suggesting that strain amplification in very early lung lesions could guide pro-invasive remodeling of the tumor microenvironment. The simulation results and tumor measurements suggest that cells at the edge of a lung tumor and in surrounding alveolar walls experience increased strain during respiration that could promote tumor progression. Author SummaryLung cancer is the leading cause of cancer-related death in the world. Efforts to identify and treat patients early are hampered by an incomplete understanding of the factors that drive early lesion progression to invasive cancer. We aimed to understand the role of mechanical strain in early lesion progression. The lung is unique in that it undergoes cyclic stretch, which creates strain across the alveolar walls. Computational models have provided fundamental insights into the stretch-strain relationship in the lung. In order to map the strain experienced in the alveolar walls near a tumor, we incorporated a tumor into a tissue scale model of the lung under stretch. We used finite element modeling to apply physiological material behavior to the lung and tumor tissue. Based on reported findings and our measurements, tumor progression was modeled as stiffening of the tumor and thickening of the tumor-adjacent alveolar walls. We found that early tumors amplified the strain in the tumor-adjacent alveolar walls. Strain amplification also arose at the tumor edges. Simulating strain-mediated wall stiffening generated tracks of thickened walls. We experimentally confirmed the presence of tracks of thickened extracellular matrix in clinical samples of LUAD. Our model is the first to interrogate the alterations in strain in and around a tumor during simulated respiration and suggests that lung mechanics and strain amplification play a role in early lung tumorigenesis.

cancer biology↗

bioRxiv2021

Nascent adhesions differentially regulate lamellipodium velocity and persistence

Cell migration is essential to physiological and pathological biology. Migration is driven by the motion of a leading edge, in which actin polymerization pushes against the edge and adhesions transmit traction to the substrate while membrane tension increases. How the actin and adhesions synergistically control edge protrusion remains elusive. We addressed this question by developing a computational model in which the Brownian ratchet mechanism governs actin filament polymerization against the membrane and the molecular clutch mechanism governs adhesion to the substrate (BR-MC model). Our model predicted that actin polymerization is the most significant driver of protrusion, as actin had a greater effect on protrusion than adhesion assembly. Increasing the lifetime of nascent adhesions also enhanced velocity, but decreased the protrusions motional persistence, because filaments maintained against the cell edge ceased polymerizing as membrane tension increased. We confirmed the model predictions with measurement of adhesion lifetime and edge motion in migrating cells. Adhesions with longer lifetime were associated with faster protrusion velocity and shorter persistence. Experimentally increasing adhesion lifetime increased velocity but decreased persistence. We propose a mechanism for actin polymerization-driven, adhesion-dependent protrusion in which balanced nascent adhesion assembly and lifetime generates protrusions with the power and persistence to drive migration.

cell biology↗

bioRxiv2021

NKX2-1 controls lung cancer progression by inducing DUSP6 to dampen ERK activity

Lung cancer remains a leading cause of cancer death, with unclear mechanisms driving the transition to aggressive cancer with poor prognosis. The RAS[->]RAF[->]MEK[->]ERK pathway is hyper-activated in [~]50% of human lung adenocarcinoma (LUAD). An initial activating mutation induces homeostatic feedback mechanisms that limit ERK activity. Additional, undefined genetic hits overcome the feedback, leading to high ERK activity that drives malignant progression. At detection, the majority of LUADs express the homeobox transcription factor NKX2-1, which also limits malignant progression. NKX2-1 constrains LUAD, in part, by maintaining a well-differentiated state with features of pulmonary identity. We asked if loss of NKX2-1 might also contribute to the release of ERK activity that drives tumor progression. Using human tissue samples and cell lines, xenografts, and genetic mouse models, we show that NKX2-1 induces the ERK phosphatase DUSP6. In tumor cells from late-stage LUAD with silenced NKX2-1, re-introduction of NKX2-1 induces DUSP6 and inhibits cell proliferation and migration and tumor growth and metastasis. CRISPR knockout studies show that DUSP6 is necessary for NKX2-1-mediated inhibition of tumor progression in vivo. Further, DUSP6 expression is sufficient to inhibit RAS-driven LUAD. We conclude that NKX2-1 silencing, and thereby DUSP6 downregulation, is a mechanism by which early LUAD can unleash ERK hyperactivation for tumor progression.

cancer biology↗

bioRxiv2020

An NKX2-1/ERK/WNT feedback loop modulates gastric identity and response to targeted therapy in lung adenocarcinoma

Cancer cells undergo lineage switching during natural progression and in response to therapy. NKX2-1 loss in human and murine lung adenocarcinoma leads to invasive mucinous adenocarcinoma (IMA), a lung cancer subtype that exhibits gastric differentiation and harbors a distinct spectrum of driver oncogenes. NKX2-1 is required for optimal tumor initiation, but dispensable for growth of established tumors, in BRAFV600E driven disease. NKX2-1-deficient, BRAFV600E driven tumors resemble human IMA and exhibit a distinct response to BRAF/MEK inhibitors. Whereas BRAF/MEK inhibitors drive NKX2-1-positive tumor cells into quiescence, NKX2-1-negative cells fail to exit the cell cycle after the same therapy. BRAF/MEK inhibitors also induce cell identity switching in NKX2-1-negative lung tumors within the gastric lineage, which is driven in part by WNT signaling and FoxA1/2. These data elucidate a complex, reciprocal relationship between lineage specifiers and oncogenic signaling pathways in the regulation of lung adenocarcinoma identity that is likely to impact lineage-specific therapeutic strategies.

cancer biology↗