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Surface receptor-induced apoptosis in transformed cells : defining the molecular events involved in TNF-R1 and Fas / APO-1 apoptotic signalling


Aim of the project is the definition of the molecular requirements for the generation and intracellular transmission of the apoptotic signal from surface receptors in transformed cells.

As surface receptor-mediated apoptosis induction is a key mechanism exploited by immune effect cells to eliminate cancer cells, understanding the biochemical nature of the apoptotic signal is of major relevance in cancer biology. The model we are using in the human system is represented by two highly related receptors, widely expressed on a variety of normal and transformed cells, the tumour necrosis factor receptor type 1 (TNF-R1) and the Fas/APO-1 receptor. Crosslinking of TNF-R1 and Fas/APO-1 by their specific ligands triggers a cascade of still largely undefined events, eventually leading to cellular apoptosis. TNF-R1 and Fas/APO-1 are trimeric receptors which share extended structural homology, including a cytoplasmic region which has been named 'death domain', as deletions or mutations within it result in the inability by the respective ligands to grigger apoptosis.

Structural similarities both in the extracellular and in the intracellular portion of the two receptors suggest similar mechanisms for the generation of the apoptotic signal, however differences may exist in the complexity of its fine regulation and control, which may be relevant for the specialisation of the death signal in different cell types. Our goal is to define the mechanisms for signal generation and propagation from the two receptors, identifying common central relays as well as unique control features of each apoptotic pathway. We will address receptor structural requirements for productive lingand/receptor interactions, with particular emphasis on the role of alternatively spliced isoforms of the Fas/APO-1 receptor in signal control. Moreover, the function of death domains in the generation of the apoptotic signal will be investigated, specifically by searching for cytosolic death domain-like molecules. Membrane modifications following TNF-R1 and Fas/APO-1 crosslinking and their relevance for the propagation of the death signal will be investigated by measuring different phospholipases and sphingomyelinases activities and identifying relevant downstream targets. We will therefore study how relevant diffusible second messengers can activate potential distal targets, like interleukin-1 converting enzyme (ICE) and homologues, as well as reactive oxygen intermediates (ROI), potentially involved in mediating the effector phase of the response. Finally, the role of bcl-2 family members, key players in the control of the apoptotic response, will be addressed.

Defining the molecular steps responsible for TNF-R1 and Fas/APO-1 induced apoptosis will reveal potential targets for anti-apoptotic strategies adopted by cancer cells to survive. Uncover such strategies has potential relevance for both diagnosis and selective therapy of tumours.

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Participants (5)