Biology subjects

Lemmon, M. A.

Publications and source records attributed to Lemmon, M. A..

3 recordsLinked to original sources

bioRxiv2021

Phosphatidylserine binding regulates TIM-3 effects on T cell receptor signaling

Co-signaling receptors for the T cell receptor are important therapeutic targets, with blocking co-inhibitory receptors such as PD-1 now central in immuno-oncology. Advancing additional therapeutic immune modulation approaches requires understanding ligand regulation of other co-signaling receptors. One poorly understood therapeutic target is TIM-3 (T cell immunoglobulin and mucin domain containing-3). Which ligands are relevant for TIM-3 signaling is unclear, and different studies have reported it as co-inhibitory or co-stimulatory. Here, we show that TIM-3 promotes NF-{kappa}B signaling and IL-2 secretion following T cell receptor stimulation in Jurkat cells, and is regulated by phosphatidylserine (PS) binding. TIM-3 signaling is stimulated by PS exposed constitutively in cultured Jurkat cells, and can be blocked by mutating the PS-binding site or by occluding this site with an antibody. We also find that TIM-3 signaling alters CD28 phosphorylation. Our findings help clarify conflicting literature results with TIM-3, and inform its exploitation as a therapeutic target.

biochemistry↗

bioRxiv2021

Glioblastoma mutations impair ligand discrimination by EGFR

The epidermal growth factor receptor (EGFR) is frequently mutated in human cancer, and is an important therapeutic target. EGFR inhibitors have been successful in lung cancer, where the intracellular tyrosine kinase domain is mutated, but not in glioblastoma multiforme (GBM) - where mutations (or deletions) occur exclusively in the EGFR extracellular region. Wild-type EGFR is known to elicit distinct signals in response to different growth factor ligands, exhibiting biased agonism. We recently showed that individual ligands stabilize distinct receptor dimer structures, which signal with different kinetics to specify outcome. EGF induces strong symmetric dimers that signal transiently to promote proliferation. Epiregulin (EREG) induces weak asymmetric dimers that generate sustained signaling and differentiation. Intriguingly, several GBM mutation hotspots coincide with residues that define the asymmetric and symmetric dimer structures. Here, we show that common extracellular GBM mutations prevent EGFR from distinguishing between EGF and EREG based on dimer structure and stability - allowing strong dimers to form with both ligands. Crystal structures show that the R84K mutation symmetrizes EREG-driven dimers, whereas the A265V mutation remodels key dimerization sites. Our results suggest that modulating EGFRs biased agonism plays an important role in GBM, and suggest new approaches for correcting aberrant EGFR signaling in cancer.

biochemistry↗

bioRxiv2021

ROR and RYK extracellular region structures suggest that receptor tyrosine kinases have distinct WNT-recognition modes

SUMMARYWNTs play key roles in development and disease, by binding both Frizzled (FZD) seven-pass transmembrane receptors and numerous co-receptors that include the ROR and RYK receptor tyrosine kinases (RTKs). We describe crystal structures and WNT-binding characteristics of extracellular regions from the Drosophila ROR and RYK orthologs Nrk (neurospecific receptor tyrosine kinase) and Derailed-2 (Drl-2). RORs bind WNTs though a FZD-related cysteine-rich domain (CRD), and RYKs through a WNT-inhibitory factor (WIF) domain. Our structures suggest that neither the Nrk CRD nor the Drl-2 WIF domain can accommodate the acyl chain typically attached to WNTs. The Nrk CRD contains a deeply buried bound fatty acid, unlikely to be exchangeable with a WNT acyl chain. The Drl-2 WIF domain lacks the lipid-binding site seen in WIF-1. We also show that DWnt-5, which regulates Drosophila ROR and RYK orthologs, lacks an acyl chain. Together with analysis of WNT/receptor interaction sites, these structures provide new insight into how WNTs recruit their RTK co-receptors into signaling complexes.

biochemistry↗