Tubulation of Class II MHC Compartments Is Microtubule Dependent and Involves Multiple Endolysosomal Membrane Proteins in Primary Dendritic Cells

Abstract

Immature dendritic cells (DCs) capture exogenous Ags in the periphery for eventual processing in endolysosomes. Upon maturation by TLR agonists, DCs deliver peptide-loaded class II MHC molecules from these compartments to the cell surface via long tubular structures (endolysosomal tubules). The nature and rules that govern the movement of these DC compartments are unknown. In this study, we demonstrate that the tubules contain multiple proteins including the class II MHC molecules and LAMP1, a lysosomal resident protein, as well as CD63 and CD82, members of the tetraspanin family. Endolysosomal tubules can be stained with acidotropic dyes, indicating that they are extensions of lysosomes. However, the proper trafficking of class II MHC molecules themselves is not necessary for endolysosomal tubule formation. DCs lacking MyD88 can also form endolysosomal tubules, demonstrating that MyD88-dependent TLR activation is not necessary for the formation of this compartment. Endolysosomal tubules in DCs exhibit dynamic and saltatory movement, including bidirectional travel. Measured velocities are consistent with motor-based movement along microtubules. Indeed, nocodazole causes the collapse of endolysosomal tubules. In addition to its association with microtubules, endolysosomal tubules follow the plus ends of microtubules as visualized in primary DCs expressing end binding protein 1 (EB1)-enhanced GFP.

The Adjuvanticity of a Mannosylated Antigen Reveals TLR4 Functionality Essential for Subset Specialization and Functional Maturation of Mouse Dendritic Cells

“…This finding is consistent with previous studies (4,5). Activation of DCs with TLR agonists such as LPS has been shown to transform MHC class II compartments from intracellular endosomes into endolysosomal tubules that move toward the cell surface in a microfilament-dependent manner (32,33). Maturation of DCs enhances the lysosomal function and Ag proteolysis (5,21).…”

Metastasis Suppressor Tetraspanin CD82/KAI1 Regulates Ubiquitylation of Epidermal Growth Factor Receptor

“…Previously described modulatory activities of CD82 were directed toward the cell surface pool of the associated receptors. Indeed, until recently, the intracellular distribution of CD82 has been studied mainly in hematopoetic cells, where it was shown to be abundant in multivesicular bodies in B lymphocytes (13) and in endolysosomal tubules in dendritic cells (14). In their recent report Xu et al (15) confirmed that in prostate epithelial cells CD82 is localized to various endocytic organelles including late endosomes and lysosomes.…”

MHC Class II Antigen Presentation by Dendritic Cells Regulated through Endosomal Sorting

“…In this case, a pathway should exist for pMHCII to travel back from ILVs to the endosomal-delimiting membrane from where it could then reach the plasma membrane. Such a pathway, also referred to as "back-fusion" or retrofusion of ILVs, was also proposed to explain the disappearance of the MVB during DC maturation (Kleijmeer et al 2001) and to provide a source of membrane needed for the formation of MIIC-associated tubules in maturing DCs (Boes et al 2002(Boes et al , 2003Chow et al 2002;Vyas et al 2007). More recently, however, it was shown that such membrane tubules can be generated as a consequence of homotypic endosome fusion (Skjeldal et al 2012), which is accelerated in maturing DCs (van Nispen tot Pannerden et al 2010).…”

“…In maturing DCs, transport of MHCII is mediated via membrane tubules that radiate out from the MIIC toward the plasma membrane, and this pathway depends on an intact microtubule network (Kleijmeer et al 2001;Boes et al 2002Boes et al , 2003Chow et al 2002;Vyas et al 2007;van Nispen tot Pannerden et al 2010). MHCII, DM, and LAMP1 are not enriched in these tubules relative to the vacuolar endosomes from which they derive, suggesting that this pathway may not require active recruitment but is entered by default (Kleijmeer et al 2001).…”