Ecm29-dependent proteasome localization regulates cytoskeleton remodeling at the immune synapse

Abstract

The formation of an immune synapse (IS) enables B cells to capture membrane-tethered antigens, where cortical actin cytoskeleton remodeling regulates cell spreading and depletion of F-actin at the centrosome promotes the recruitment of lysosomes to facilitate antigen extraction. How B cells regulate both pools of actin, remains poorly understood. We report here that decreased F-actin at the centrosome and IS relies on the distribution of the proteasome, regulated by Ecm29. Silencing Ecm29 decreases the proteasome pool associated to the centrosome of B cells and shifts its accumulation to the cell cortex and IS. Accordingly, Ecm29-silenced B cells display increased F-actin at the centrosome, impaired centrosome and lysosome repositioning to the IS and defective antigen extraction and presentation. Ecm29-silenced B cells, which accumulate higher levels of proteasome at the cell cortex, display decreased actin retrograde flow in lamellipodia and enhanced spreading responses. Our findings support a model where B the asymmetric distribution of the proteasome, mediated by Ecm29, coordinates actin dynamics at the centrosome and the IS, promoting lysosome recruitment and cell spreading.

Centrosomal Enrichment and Proteasomal Degradation of SYS-1/β-catenin Requires the Microtubule Motor Dynein

“…To circumvent this issue, we assayed for centrosomal proteasome activity indirectly by functionally testing an additional centrosomal target of the RPT-4 containing proteasome, the centriole duplicating kinase ZYG-1 (O’Connell, White et al 2001; Peel, O’Connell et al 2012). In addition, we assayed the centrosomal role of the C. elegans homolog of mammalian ECM29, ECPS-1, which is an adaptor protein that enhances local proteolytic activity of proteasomes via its function linking the dynein motor complex and the proteasome and regulating 26S proteasome distribution (Gorbea, Rechsteiner et al 2004; Gorbea, Rechsteiner et al 2010; Hsu, Cheng et al 2015; Ibañez-Vega, Yuseff et al 2021).…”