Subcellular compartmentalization of TNF receptor-1 and CD95 signaling pathways.

Receptors that belong to the family of death-receptors including TNF receptor-1 (TNF-R1), CD95 (Fas, APO-1) and TRAIL receptors (TRAIL-R1, TRAIL R2/DR4/DR5) transduce signals resulting in entirely different biological outcomes: They promote cell death via apoptosis but are also capable of inducing anti-apoptotic signals through the transcription factor nuclear factor NF-κB or activation of the proliferative MAPK/ERK protein kinase cascade resulting in cell protection and tissue regeneration. Recent findings revealed a regulatory role of receptor internalization and its intracellular trafficking in selectively transmitting signals that lead either to apoptosis or to the survival of the cell, providing a clue to the understanding of these contradictory biological phenomena. In this chapter we review our data obtained during the Collaborative Research Center 415 (CRC 415) focusing on the compartmentalization of TNF-R1 and CD95 pro and anti-apoptotic signaling. We will address the role of internalization in determining the fate of the receptors. We suggest that fusion of internalized TNF-receptosomes with trans-Golgi vesicles is a novel mechanism to transduce death signals along the endosomal trafficking route. The roles of acid sphingomyelinase, the lipid second messenger ceramide, and the aspartate-protease cathepsin D as novel players in the cell death scenario is also highlighted. We report on the regulation of NF-κB signaling by recruitment of the endosomal E3-ubiquitin ligases CARP-2 and CARP-1 during TNF-receptosome trafficking. The biological significance of TNF receptor-1 compartmentalization is demonstrated by the strategy of adenoviruses to impede TNF-R1 internalization and by this preventing host cell apoptosis.