Abstract
The homeostatic control of the cellular proteome steady-state is dependent either on the 26S proteasome activity or on the lysosome function. The sex hormone 17β-estradiol (E2) controls a plethora of biological functions by binding to the estrogen receptor α (ERα), which is both a nuclear ligand-activated transcription factor and also an extrinsic plasma membrane receptor. Regulation of E2-induced physiological functions (e.g., cell proliferation) requires the synergistic activation of both transcription of estrogen responsive element (ERE)-containing genes and rapid extra-nuclear phosphorylation of many different signalling kinases (e.g., ERK/MAPK; PI3K/AKT). Although E2 controls ERα intracellular content and activity via the 26S proteasome-mediated degradation, biochemical and microscopy-based evidence suggests a possible cross-talk among lysosomes and ERα activities. Here, we studied the putative localization of endogenous ERα to lysosomes and the role played by lysosomal function in ERα signalling. By using confocal microscopy and biochemical assays, we report that ERα localizes to lysosomes and to endosomes in an E2-dependent manner. Moreover, the inhibition of lysosomal function obtained by chloroquine demonstrates that, in addition to 26S proteasome-mediated receptor elimination, lysosome-based degradation also contributes to the E2-dependent ERα breakdown. Remarkably, the lysosome function is further involved in those ERα activities required for E2-dependent cell proliferation while it is dispensable for ERα-mediated ERE-containing gene transcription. Our discoveries reveal a novel lysosome-dependent degradation pathway for ERα and show a novel biological mechanism by which E2 regulates ERα cellular content and, as a consequence, cellular functions.
Highlights
The functions of the cellular proteome are controlled by a homeostatic steady-state, which is granted by the balance between protein synthesis and degradation
Mg-132 administration (1 and 10 mM) to MCF-7 cells effectively induced the accumulation of total cellular ubiquitinated species as well as the increase in the rapidly 26S proteasome turn-overed protein p53 (Fig. 1A and 1B’), demonstrating the 26S proteasome is inhibited by the drug treatment
Epidermal growth factor (EGF)-induced epidermal growth factor (EGF) receptor (EGF-R) degradation, which occurs in the lysosomes [18], was not affected by Mg-132 doses that were effective in increasing the total cellular ubiquitinated species in HeLa cells (Fig. 1B and 1B’)
Summary
The functions of the cellular proteome are controlled by a homeostatic steady-state, which is granted by the balance between protein synthesis and degradation (i.e., proteostasis). Degradation of intracellular proteins occurs via targeted (i.e., ubiquitindependent) 26S proteasome activation and extra-cellular proteins are eliminated through a vesicular system that addresses them to the lysosomes. The estrogen receptor a (ERa) is a ligand-activated transcription factor that belongs to the nuclear hormone receptor superfamily. It is clear that ERa membrane association is required for the E2-dependent activation of rapid kinase signalling pathways (e.g., ERK/MAPK; PI3K/AKT) (i.e., extra-nuclear activity) and the realization of the E2-induced cellular effects both in cell lines (e.g., cell proliferation) [5,6,7,8] and in mice (e.g., cell migration) [9]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
