Allosteric activation of preformed EGF receptor dimers by a single ligand binding event

Biochemical Pathways Delivering Distinct Glycosphingolipid Patterns in MDA-MB-231 and MCF-7 Breast Cancer Cells

The complex structure of glycosphingolipids (GSLs) supports their important role in cell function as modulators of growth factor receptors and glutamine transporters in plasma membranes. The aberrant composition of clustered GSLs within signaling platforms, so-called lipid rafts, inevitably leads to tumorigenesis due to disturbed growth factor signal transduction and excessive uptake of glutamine and other molecules needed for increased energy and structural molecule cell supply. GSLs are also involved in plasma membrane processes such as cell adhesion, and their transition converts cells from epithelial to mesenchymal with features required for cell migration and metastasis. Glutamine activates the mechanistic target of rapamycin complex 1 (mTORC1), resulting in nucleotide synthesis and proliferation. In addition, glutamine contributes to the cancer stem cell GD2 ganglioside-positive phenotype in the triple-negative breast cancer cell line MDA-MB-231. Thieno[2,3-b]pyridine derivative possesses higher cytotoxicity against MDA-MB-231 than against MCF-7 cells and induces a shift to aerobic metabolism and a decrease in S(6)nLc4Cer GSL-positive cancer stem cells in the MDA-MB-231 cell line. In this review, we discuss findings in MDA-MB-231, MCF-7, and other breast cancer cell lines concerning their differences in growth factor receptors and recent knowledge of the main biochemical pathways delivering distinct glycosphingolipid patterns during tumorigenesis and therapy.

Self-inhibition of HER2 and HER3 at fever temperatures may prevent their hetero-dimerization

HER2 and HER3 receptors dimerize into potent pro-oncogenic complexes involved in various aggressive and recurrent tumors. The role of febrile temperatures on the formation of HER2:HER3 complexes is unknown. To this end, molecular dynamics simulations of HER2 and HER3 were performed in the 37 °C-40 °C range. HER2 and ligand-free HER32 display inactive conformers that cannot form complexes at 40 °C, while maintaining their extended conformations able to dimerize in the 37 °C-39 °C range. Thermal therapy at particular fever points may complement existing therapy options for HER2-relevant cancers.Communicated by Ramaswamy H. Sarma.

Different EGF-induced receptor dimer conformations for signaling and internalization

The structural basis of the activation and internalization of EGF receptors (EGFR) is still a matter of debate despite the importance of this target in cancer treatment. Whether agonists induce dimer formation or act on preformed dimers remains discussed. Here, we provide direct evidence that EGF-induced EGFR dimer formation as best illustrated by the very large increase in FRET between snap-tagged EGFR subunits induced by agonists. We confirm that Erlotinib-related TK (tyrosine kinase) inhibitors also induce dimer formation despite the inactive state of the binding domain. Surprisingly, TK inhibitors do not inhibit EGF-induced EGFR internalization despite their ability to fully block EGFR signaling. Only Erlotinib-related TK inhibitors promoting asymmetric dimers could slow down this process while the lapatinib-related ones have almost no effect. These results reveal that the conformation of the intracellular TK dimer, rather than the known EGFR signaling, is critical for EGFR internalization. These results also illustrate clear differences in the mode of action of TK inhibitors on the EGFR and open novel possibilities to control EGFR signaling for cancer treatment.

Cryo-electron microscopy of IgM-VAR2CSA complex reveals IgM inhibits binding of Plasmodium falciparum to Chondroitin Sulfate A

Placental malaria is caused by Plasmodium falciparum-infected erythrocytes (IEs) adhering to chondroitin sulfate proteoglycans in placenta via VAR2CSA-type PfEMP1. Human pentameric immunoglobulin M (IgM) binds to several types of PfEMP1, including VAR2CSA via its Fc domain. Here, a 3.6 Å cryo-electron microscopy map of the IgM-VAR2CSA complex reveals that two molecules of VAR2CSA bind to the Cµ4 of IgM through their DBL3X and DBL5ε domains. The clockwise and anti-clockwise rotation of the two VAR2CSA molecules on opposite faces of IgM juxtaposes C-termini of both VAR2CSA near the J chain, where IgM creates a wall between both VAR2CSA molecules and hinders its interaction with its receptor. To support this, we show when VAR2CSA is bound to IgM, its staining on IEs as well as binding of IEs to chondroitin sulfate A in vitro is severely compromised.

Extracellular Vesicles and Epidermal Growth Factor Receptor Activation: Interplay of Drivers in Cancer Progression

Extracellular vesicles (EVs) are of great interest to study the cellular mechanisms of cancer development and to diagnose and monitor cancer progression. EVs are a highly heterogeneous population of cell derived particles, which include microvesicles (MVs) and exosomes (EXOs). EVs deliver intercellular messages transferring proteins, lipids, nucleic acids, and metabolites with implications for tumour progression, invasiveness, and metastasis. Epidermal Growth Factor Receptor (EGFR) is a major driver of cancer. Tumour cells with activated EGFR could produce EVs disseminating EGFR itself or its ligands. This review provides an overview of EVs (mainly EXOs and MVs) and their cargo, with a subsequent focus on their production and effects related to EGFR activation. In particular, in vitro studies performed in EGFR-dependent solid tumours and/or cell cultures will be explored, thus shedding light on the interplay between EGFR and EVs production in promoting cancer progression, metastases, and resistance to therapies. Finally, an overview of liquid biopsy approaches involving EGFR and EVs in the blood/plasma of EGFR-dependent tumour patients will also be discussed to evaluate their possible application as candidate biomarkers.