Membrane Traffic and Pathogenesis

  MEMBERSDr CAMPANA Vincenza / CATINO Maria-Agata / Dr LEBRETON Stephanie / Dr MAIJANOVIC Zrinka
POCARD Thomas / SCHIFF Edwin / Dr VINATIER Jacqueline

  Annual Report


One of the most important properties of epithelia is cell polarity, which enable cells to perform their vectorial activities. We study the mechanism of apical sorting of GPI-anchored proteins (GPI-APs) focusing our attention on the role of membrane microdomains (or rafts), and protein and lipid segregation in this event. We are also studying the exocytic and endocytic transport of the prion protein, PrPC, and its infectious form PrPSc (scrapie), as well as pathological mutants associated with hereditary forms of TSEs. This will enable us to understand the role of intracellular trafficking and of association to rafts in the function and pathological conversion of this cellular GPI-AP.

1) Mechanism of GPI-anchored protein sorting to the plasma membrane

GPI-APs are sorted to the apical membrane in several epithelial cell lines and associate with rafts during their transport to the plasma membrane. Our knowledge of how this occurs is only rudimentary. In this project we are using both microscopic and biochemical approaches to analyze the role of raft domains in sorting and trafficking of GPI-anchored proteins and to characterize the molecular components of the machinery.

In the last two years we have shown that:

1. Rafts are not sufficient for sorting of GPI-APs, but oligomerization is required (Paladino, 2004)

2. Oligomerization is a specific requirement for GPI-AP sorting in different epithelia (Paladino, in press)

3. The lipid composition of AP and BL detergent resistant domains is similar (Tivodar, 2006)

4. GPI-APs are sorted via a direct pathway to the apical domain of living cells (Paladino, 2006)

5. GPI-APs are organized in homo clusters independent of cholesterol that can form choleseterol dependent hetero clusters (submitted)

2) Intracellular trafficking of PrPC and its mutants: correlation with TSE pathogenesis

Transmissible spongiform encephalopathies (TSE) are fatal neurodegenerative disorders of humans and animals of either infectious, genetic or sporadic origin. They result from a post-translational alteration in the conformation of a host-encoded GPI-AP called PrPinto to the scrapie isoform PrPSc. This conformational transition is thought to be catalyzed by a specific physical interaction between endogenous PrPC and PrPSc, which is the principal component of the transmissible agent (or prion). The intracellular compartment where PrPC - PrPSc conversion occurs and how this process leads to neurological dysfunction are still unknown. Analyzing the intracellular trafficking of PrPC will be critical to understand how and where it is converted to PrPSc. In this project we have analysed the biosynthethic/ degradative pathway, exocytic/endocytic trafficking of PrPC and of some mutants responsible for the hereditary diseases. We have shown that:

1) Raft-association of PrPC is necessary for its correct folding in the ER (Sarnataro, 2004)

2) The raft environment may protect PrP mutants from conversion (Campana, 2005 and 2006, Sarnataro, 2006)

3) The proteasome is not involved in the degradation of PrP mutants (Campana, 2006).

4) Both raft-dependent and clathrin-dependent pathways are involved in PrPC endocytosis (submitted)


Publications 2006 of the unit on Pasteur's references database

Activity Reports 2006 - Institut Pasteur
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