Diane S. Lidke

The crosslinking of IgE-bound FcεRI by multivalent allergens initiates mast cell and basophil signaling underlying Type 1 allergy. Yet, how allergen properties and IgE occupancy impact receptor aggregation and downstream signaling remains unclear. We used Phl p 1-specific IgE and recombinant fusion proteins presenting a Phl p 1-derived peptide in defined valencies and positions (MB1N, MB1N1C, MB2N, and MB4N) to probe antigen-dependent signaling. Tetravalent MB4N evoked stronger degranulation and Ca2+ response than bivalent antigens MB1N1C and MB2N. MB4N was also capable of signaling at low IgE occupancy and in Lyn-deficient cells. Monte Carlo simulations predicted that MB4N forms larger, complex receptor aggregates, while MB1N1C and MB2N produce linear chains. Consistently, the addition of MB4N showed larger aggregates by electron microscopy and slower mobility by single-particle tracking, compared to bivalent antigens. Thus, allergen valency and epitope spatial arrangement dictate FcεRI aggregate organization and subsequent effector cell activation.

Tetraspanins are integral membrane proteins that play a crucial role in organizing and regulating cellular signaling by serving as scaffolds that compartmentalize receptors and other signaling molecules within membrane microdomains. Here, we report how the tetraspanin CD82 modulates the molecular organization and signaling of the EGF receptor (EGFR), a key molecule involved in cellular proliferation, differentiation, and survival. Combining multicolor super-resolution microscopy with advanced image reconstruction and analysis techniques, we demonstrate that CD82 selectively associates with EGFR, promotes receptor oligomerization, and acts as a regulator of ligand-independent receptor phosphorylation in a palmitoylation-dependent manner. Additionally, CD82 promotes a more compact molecular organization of EGFR, which correlates with altered endocytosis and downstream signaling outcomes. These findings underscore the importance of tetraspanins in the spatial and functional regulation of cell surface receptors, with implications for controlling aberrant signaling in disease and positions CD82 as a potential target for developing therapeutic strategies aimed at modulating EGFR signaling by influencing receptor organization.

While the majority of ovarian cancer (OC) patients respond to front-line carboplatin/paclitaxel chemotherapy and surgical debulking, nearly all patients will develop platinum-resistance and recur. Our study investigates how tumor-associated macrophages (TAMs) within the tumor microenvironment (TME) affect chemotherapy outcomes using OC patient-derived organoids and humanized patient-derived xenografts (huPDX). In vitro macrophage migration assays demonstrate the selective recruitment of M2 polarized macrophages to OC organoids. M2 macrophages, but not M1 macrophages, increase OC organoid viability and reduce their sensitivity to paclitaxel in co-culture assays. Furthermore, we identified BMS777607, a receptor tyrosine kinase inhibitor, that is capable of repolarizing M2 macrophages in vitro and reduces organoid viability by a macrophage-dependent mechanism. In a platinum-sensitive humanized patient-derived xenograft (huPDX) model, the presence of human immune cells increased between-mouse variability in response to paclitaxel with two of four mice demonstrating tumor regrowth after two weeks of treatment. A TAM-targeted CSF-1R inhibitor, BLZ945 significantly reduced the total number of human immune cells within the ascites fluid of huPDX3 mice, but did not reduce tumor burden. However BLZ945 in combination with paclitaxel reduced tumor burden with no sign of regrowth. Our study demonstrates that patient-derived OC organoids and huPDX, are useful for evaluating the immunomodulatory effects of therapies and the influence of TAMs on response. huPDX models could serve as a robust platform for preclinical testing of novel anti-cancer treatments, providing insights into the complex interplay between immune cells and cancer therapeutics.

Fc receptors containing immunoreceptor tyrosine-based activation motifs (ITAMs) are critical components of the innate immune system that bridge adaptive antibody recognition to cellular effector responses. In allergic responses, the high-affinity IgE receptor, FcεRI, is activated when multivalent antigens crosslink receptor-bound IgE, yet the molecular mechanisms linking antigen structure to signaling output remain incompletely understood. Here, we compare two antigens presenting identical IgE-binding haptens but differing in geometry: the high-valency, heterogeneous DNP-BSA and the defined trivalent antigen DF3. We find that these ligands elicit distinct patterns of degranulation and FcεRI γ-chain phosphorylation, correlating with differences in the recruitment of the inhibitory lipid phosphatase SHIP1. Monte Carlo simulations predicted that each antigen generates receptor aggregates with distinct size, complexity, and inter-receptor spacing. Using direct stochastic optical reconstruction microscopy (dSTORM) and Bayesian Grouping of Localizations (BaGoL) analysis, we directly visualized the nanoscale aggregate geometry and found that DF3 induced smaller, more linear aggregates with tighter receptor spacing than DNP–BSA. Together, our results show that antigen properties, including size, valency, and epitope spacing, modulate FcεRI aggregate architecture and tune the balance of positive and negative signaling to ultimately shape mast cell outcomes. Statement of Significance: Allergic immune responses are initiated when multivalent antigens aggregate IgE-bound FcεRI on mast cells, yet the relationship between antigen structure and signaling strength remains unclear. This study combines biochemical assays, Monte Carlo modeling, and super-resolution imaging to show that allergen properties, specifically valency and nanoscale epitope spacing, govern the geometry of FcεRI aggregates and the balance of activating and inhibitory signals. These findings establish a direct mechanistic link between antigen structure and immune receptor output, providing new insight into how physical antigen features encode mast cell responses.

Dysregulated cellular processes drive malignant transformation, tumor progression, and metastasis, and affect responses to therapies

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase (RTK) with important roles in many cellular processes as well as cancer and other diseases. EGF binding promotes EGFR dimerization and autophosphorylation through interactions that are well understood structurally. However, it is not clear how these dimers relate to higher-order EGFR oligomers detected at the cell surface. We used single-particle tracking (SPT) and Förster resonance energy transfer (FRET) imaging to examine how each domain within EGFR contributes to receptor dimerization and the rate of its diffusion in the cell membrane. We show that the EGFR extracellular region is sufficient to drive receptor dimerization, but that the EGF-induced EGFR slow-down seen by SPT requires formation of higher order oligomers, mediated in part by the intracellular tyrosine kinase domain – but only when in its active conformation. Our data thus provide important insight into higher-order EGFR interactions required for EGF signaling.