Human melanocortin 1 receptor-mediated ubiquitination of nonvisual arrestins. Role of Mahogunin Ring Finger 1 E3 ligase
BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH
Authors: Abrisqueta, Marta; Olivares, Concepcion; Herraiz, Cecilia; Castejon-Grinan, Maria; Sires-Campos, Julia; Garcia-Borron, Jose C.; Jimenez-Cervantes, Celia
Abstract
Signaling from the melanocortin 1 receptor (MC1R), a Gs protein-coupled receptor (GPCR) crucial for melanocyte proliferation and differentiation, is regulated by cytosolic beta-arrestins (ARRBs). MC1R signaling is also negatively modulated by the E3-ubiquitin ligase Mahogunin Ring Finger-1 (MGRN1), whose mutation causes hyperpigmentation, congenital heart defects and neurodegeneration in mice. We showed previously that although MC1R interacts stably with human ARRB1 or ARRB2, only ARRB2 mediates receptor desensitization and internalization. We analyzed MC1R-dependent ARRB ubiquitination, and the possible role of MGRN1. ARRB1 expressed in heterologous cells or human melanoma cells migrated in SDS-PAGE as a 55 kDa protein whereas ARRB2 migrated as two major bands of apparent molecular weight near 45 and 55 kDa, with an intermediate mobility band occasionally detected. These forms were related by post-translational modification rather than by proteolysis. Presence of MC1R favored expression of the 45 kDa protein, the form that interacted preferentially with MC1R. MC1R also mediated poly- or multimonoubiquitination of ARRB2. Ubiquitination was agonist-independent, but required a native MC1R conformation and/or normal receptor trafficking to the plasma membrane, as it was not observed for loss-of-function MC1R variants. In a heterologous expression system, MC1R-dependent ARRB ubiquitination was enhanced by overexpression of MGRN1 and was impaired by siRNA-mediated MGRN1 knockdown thus pointing to MGRN1 as the responsible E3-ligase. Co-immunoprecipitation experiments demonstrated interaction of MGRN1 and ARRBs in the presence of MC1R, suggesting a scaffolding role for the GPCR that may determine the selectivity of E3-ubiquitin ligase engagement and the functional outcome of ARRB ubiquitination.
Differential requirements for clathrin endocytic pathway components in cellular entry by Ebola and Marburg glycoprotein pseudovirions
VIROLOGY
Authors: Bhattacharyya, Suchita; Hope, Thomas J.; Young, John A. T.
Abstract
Clathrin-mediated endocytosis was previously implicated as one of the cellular pathways involved in filoviral glycoprotein mediated viral entry into target cells. Here we have further dissected the requirements for different components of this pathway in Ebola versus Marburg virus glycoprotein (GP) mediated viral infection. Although a number of these components were involved in both cases; Ebola GP-dependent viral entry specifically required the cargo recognition proteins Eps15 and DAB2 as well as the clathrin adaptor protein AP-2. In contrast, Marburg GP-mediated infection was independent of these three proteins and instead required beta-arrestin 1 (ARRB1). These findings have revealed an unexpected difference between the clathrin pathway requirements for Ebola GP versus Marburg GP pseudovirion infection. Anthrax toxin also uses a clathrin-, and ARRB1-dependent pathway for cellular entry, indicating that the mechanism used by Marburg GP pseudovirions may be more generally important for pathogen entry. (C) 2011 Elsevier Inc. All rights reserved.