Dendritic cells (DCs) have the unique ability to pick up dead cells carrying antigens in tissue and migrate to the lymph nodes where they can cross-present cell-associated antigens by MHC class I to CD8+ T cells. There is strong in vivo evidence that the mouse XCR1+ DCs subset acts as a key player in this process. The intracellular processes underlying cross-presentation remain controversial and several pathways have been proposed. Indeed, a wide number of studies have addressed the cellular process of cross-presentation in vitro using a variety of sources of antigen and antigen-presenting cells. Here, we review the in vivo and in vitro evidence supporting the current mechanistic models and disscuss their physiological relevance to the cross-presentation of cell-associated antigens by DCs subsets.

7 Abstract The organization, assembly and remodeling of 8 the actin cytoskeleton provide force and tracks for a variety 9 of (endo)membrane-associated events such as membrane 10 trafficking. This review illustrates in different cellular 11 models how actin and many of its numerous binding and 12 regulatory proteins (actin and co-workers) participate in the 13 structural organization of the Golgi apparatus and in traf-14 ficking-associated processes such as sorting, biogenesis and 15 motion of Golgi-derived transport carriers. 16 17 Keywords Golgi apparatus Á Cytoskeleton Á Actin Á 18 Spectrin Á Myosin Á Rho GTPases Introduction 20The function of the Golgi apparatus is the result of a 21 complex interaction between the molecules that establish 22 its architecture, those that determine protein transport and 23 those that integrate signals from either outside or inside the 24 cell. Cytoskeletal elements (microtubules, actin filaments 25 or microfilaments and intermediate filaments) integrate 26 these processes. Association and coordination between 27 them as well as their respective binding and regulatory 28 proteins are present in the majority of endomembrane 29 systems, including the Golgi apparatus. While its basic 30 function is highly conserved, the Golgi varies greatly in 31 shape and number from one organism to another. Briefly, it 32 ranges from dispersed cisternae or isolated tubular net-33 works as occurs in algae, protozoa and the yeast Saccha-34 romyces cerevisiae, to a pile of flattened cisternae aligned 35 in parallel and known as the Golgi stack. This, depending 36 on the organism examined, could be present in a single 37 (fungi and the yeast Pichia pastoris) or multiple copies, the 38 latter being scattered throughout the cytoplasm (plants and 39 Drosophila) or organized as a ribbon around centrioles 40 (vertebrates) (daSilva et al. 2004; Hawes and Satiat-Je-41 unemaitre 2005; He et al. 2004;He2007; Henderson et al. 42 2007; Kondylis and Rabouille 2003; Ladinsky et al. 1999; 43 Lowe 2011; Mogelsvang et al. 2003; Pelletier et al. 2002; 44 Preuss et al. 1992;Rambourg and Clermont 1986; Ram-45 bourg et al. 2001;Ramírez and Lowe 2009; Rios and 46 Bornens 2003; Rossanese et al. 1999). The cytoskeleton 47 determines the location of the Golgi, and depending on the 48 cellular model, either microtubules or actin filaments have 49 the greater influence (Egea and Rios 2008), the impact of 50 intermediate filaments being very limited (Gao and Sztul 51 2001; Gao et al. 2002;Styers et al. 2006; Toivola et al. 52 2005). Historically, microtubules were the first cytoskele-53 ton element to be linked to the Golgi structure and function 54 (Thyberg and Moskalewski 1999), and only later was it 55 firmly established that actin and associated proteins (actin 56 et al.) also played a significant role (for recent reviews see 44Histochem Cell Biol DOI 10.1007/s00418-013-1115 Author Proof U N C O R R E C T E D P R O O F63 between the actin-based cytoskeleton and the Golgi in a 64 variety of cellular models ...

Cross-presentation, in which exogenous antigens are presented via MHC I complexes, is involved both in the generation of anti-infectious and anti-tumoral cytotoxic CD8+ T cells and in the maintenance of immune tolerance. While cross-presentation was described almost four decades ago and while it is now established that some dendritic cell (DC) subsets are better than others in processing and cross-presenting internalized antigens, the involved molecular mechanisms remain only partially understood. Some of the least explored molecular mechanisms in cross-presentation concern the origin of cross-presenting MHC I molecules and the cellular compartments where antigenic peptide loading occurs. This review focuses on MHC I molecules and their intracellular trafficking. We discuss the source of cross-presenting MHC I in DCs as well as the role of the endocytic pathway in their recycling from the cell surface. Next, we describe the importance of the TAP peptide transporter for delivering peptides to MHC I during cross-presentation. Finally, we highlight the impact of innate immunity mechanisms on specific antigen cross-presentation mechanisms in which TLR activation modulates MHC I trafficking and TAP localization.

SummaryThe inhibition of phosphatidic acid phosphatase (PAP) activity by propanolol indicates that diacylglycerol (DAG) is required for the formation of transport carriers at the Golgi and for retrograde trafficking to the ER. Here we report that the PAP2 family member lipid phosphate phosphatase 3 (LPP3, also known as PAP2b) localizes in compartments of the secretory pathway from ER export sites to the Golgi complex. The depletion of human LPP3: (i) reduces the number of tubules generated from the ER-Golgi intermediate compartment and the Golgi, with those formed from the Golgi being longer in LPP3-silenced cells than in control cells; (ii) impairs the Rab6-dependent retrograde transport of Shiga toxin subunit B from the Golgi to the ER, but not the anterograde transport of VSV-G or ssDsRed; and (iii) induces a high accumulation of Golgi-associated membrane buds. LPP3 depletion also reduces levels of de novo synthesized DAG and the Golgi-associated DAG contents. Remarkably, overexpression of a catalytically inactive form of LPP3 mimics the effects of LPP3 knockdown on Rab6-dependent retrograde transport. We conclude that LPP3 participates in the formation of retrograde transport carriers at the ER-Golgi interface, where it transitorily cycles, and during its route to the plasma membrane.