Title

 

Authors

C. Perrotta¹, Emma Assi¹, L. Bizzozero¹, D. Cazzato¹, L. Campana², P. Rovere-Querini², E. Gulbins³, E. Clementi<sup>1,2,4

1</sup>Unit of Clinical Pharmacology, Department of Clinical Science, Luigi Sacco Hospital, Università di Milano, ²H^. San Raffaele Scientific Institute, 20132 Milano, Italy, Milano, Italy , ³Inst. für Molekularbiologie Universitätsklinikum Essen, Germany; ⁴E. Medea Scientific Institute, Bosisio Parini, Lecco Italy.

 

Abstract

Brain tumours are one of the most devastating diseases because they are so difficult to treat, much less cure. Most brain tumours developed from glial cells are called gliomas.In the last few years, the attention of researchers has been focused on the interplay between cancer cells and stromal cells. Among these tumor-associated macrophages (TAM) represent the largest population of infiltrating inflammatory cells in malignant glioma. They promote the growth, invasion and immune evasion of tumoral cells through the activation of different pathways and the generation of several signaling molecules. Among these messengers Nitric Oxide (NO) plays an important role because of its anti-apoptotic action when generated at low levels. Here we demonstrate, for the first time, in vivo and in vitro that NO generated by TAM is able to protect glioma cells from apoptosis induced by the chemotherapeutic drug cisplatin. NO target is the ceramide-generating enzyme Acid sphingomyelinase (A.SMase), fundamental player in the recently described mechanism of action of cisplatin involving the activation of the death receptor CD95. NO,through the generation of cyclic GMP and the activation of protein G-kinase (PKG), inhibits A-SMase translocation and activity. This effect depend on the phosphorylation by PKG of the SNARE protein syntaxin 4, that we have already demonstrated to be involved in ASMase exocytosis, on serine 78. Phosphorylation on this residue induces the poli-ubiquitination of syntaxin 4 and triggers its degradation by proteasome. The direct consequence of the reduction of syntaxin 4 level is the inhibition ofA-SMase translocation and of its main biological effect, the triggering of death receptor induced apoptosis. The novel actions of syntaxin 4 and of NO in sphingolipid metabolism and exocytosis we describe here define signalling mechanisms of broad relevance in cancer pathophysiology and in resistance to chemotherapy.