A NUMB–EFA6B–ARF6 recycling route controls apically restricted cell protrusions and mesenchymal motility

International audienceThe endocytic protein NUMB has been implicated in the control of various polarized cellular processes, including the acquisition of mesenchymal migratory traits through molecular mechanisms that have only been partially defined. Here, we report that NUMB is a negative regulator of a specialized set of understudied, apically restricted, actin-based protrusions, the circular dorsal ruffles (CDRs), induced by either PDGF or HGF stimulation. Through its PTB domain, NUMB binds directly to an N-terminal NPLF motif of the ARF6 guanine nucleotide exchange factor, EFA6B, and promotes its exchange activity in vitro. In cells, a NUMB-EFA6B-ARF6 axis regulates the recycling of the actin regulatory cargo RAC1 and is critical for the formation of CDRs that mark the acquisition of a mesenchymal mode of motility. Consistently, loss of NUMB promotes HGF-induced cell migration and invasion. Thus, NUMB negatively controls membrane protrusions and the acquisition of mesenchymal migratory traits by modulating EFA6B-ARF6 activity

Molecularly Distinct Clathrin-Coated Pits Differentially Impact EGFR Fate and Signaling

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Faciogenital dysplasia protein Fgd1 regulates invadopodia biogenesis and extracellular matrix degradation and is up-regulated in prostate and breast cancer.

Invadopodia are proteolytically active membrane protrusions that extend from the ventral surface of invasive tumoral cells grown on an extracellular matrix (ECM). The core machinery controlling invadopodia biogenesis is regulated by the Rho GTPase Cdc42. To understand the upstream events regulating invadopodia biogenesis, we investigated the role of Fgd1, a Cdc42-specific guanine nucleotide exchange factor. Loss of Fgd1 causes the rare inherited human developmental disease faciogenital dysplasia. Here, we show that Fgd1 is required for invadopodia biogenesis and ECM degradation in an invasive cell model and functions by modulation of Cdc42 activation. We also find that Fgd1 is expressed in human prostate and breast cancer as opposed to normal tissue and that expression levels matched tumor aggressiveness. Our findings suggest a central role for Fgd1 in the focal degradation of the ECM in vitro and, for the first time, show a connection between Fgd1 and cancer progression, proposing that it might function during tumorigenesis

Reticulon 3-dependent ER-PM contact sites control EGFR nonclathrin endocytosis

The integration of endocytic routes is critical to regulate receptor signaling. A nonclathrin endocytic (NCE) pathway of the epidermal growth factor receptor (EGFR) is activated at high ligand concentrations and targets receptors to degradation, attenuating signaling. Here we performed an unbiased molecular characterization of EGFR-NCE. We identified NCE-specific regulators, including the endoplasmic reticulum (ER)-resident protein reticulon 3 (RTN3) and a specific cargo, CD147. RTN3 was critical for EGFR/CD147-NCE, promoting the creation of plasma membrane (PM)-ER contact sites that were required for the formation and/or maturation of NCE invaginations. Ca2+release at these sites, triggered by inositol 1,4,5-trisphosphate (IP3)-dependent activation of ER Ca2+channels, was needed for the completion of EGFR internalization. Thus, we identified a mechanism of EGFR endocytosis that relies on ER-PM contact sites and local Ca2+signaling

A self-sustaining endocytic-based loop promotes breast cancer plasticity leading to aggressiveness and pro-metastatic behavior

It is unclear if genetic alterations in endocytic proteins play a causal role in high incidence human cancers. Here, the authors report the oncogenic role of Epsin3 (EPN3) in breast cancer, and show EPN3 to drive tumorigenesis through induction of a partial epithelial mesenchymal transition state and a TGFβ-dependent regulatory loop that promotes cellular plasticity and invasive behaviour