The integration of distinct internalization routes is crucial to determine the fate of plasma membrane (PM) receptors and the output of their signalling pathways. Contact sites between cellular organelles adds a further layer of regulation by creating microdomains that favour different signalling and metabolic pathways. These regulatory mechanisms are relevant to the epidermal growth factor receptor (EGFR). We found that EGFR internalization through non-clathrin endocytosis (NCE) leads primarily to receptor degradation and signal extinction, while clathrin-mediated endocytosis (CME) is mainly involved in EGFR recycling and sustaining signalling. Notably, internalization via NCE involves the formation of contact sites between the PM, the endoplasmic reticulum (ER) and the mitochondria, where EGF-dependent localized Ca2+ signalling occurs.
The founding hypothesis of this proposal is that the PM-ER-mitochondrial interface could represent a functional unit where direct cross-communication between EGFR signalling and mitochondria takes place. To investigate this hypothesis, we will use a three-tiered strategy aimed at elucidating:
1. the EGFR-dependent signalling that leads to NCE-ER-mitochondrial contact site formation and to local Ca2+ release, and the role of these contacts in EGFR endocytosis, signalling and fate;
2. the crosstalk between EGFR signalling and mitochondrial function at the PM-ER-mitochondrial interface by analysing the impact of EGFR-NCE on mitochondrial physiology and metabolism;
3. the relevance of NCE-ER-mitochondrial crosstalk to EGF-dependent cell physiological responses, e.g. migration, proliferation and differentiation, by exploiting isogenic cell derivatives from embryonic/pluripotent stem cells or ex vivo organoid cultures.
The verification of this hypothesis will expand our understanding of the impact of EGFR signalling on cellular functions not previously linked to this pathway and possibly impinging on cellular energetics and metabolism.
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