[P83A]: PKCδ as a moelcular switch in the apoptosis and survival of glioma cells

Abstract

Poster abstracts / Int. J. Devl Neuroscience 24 (2006) 495-603 531 tion what happens if the cells with self-renewal capacity are exposed to viral oncogenes.We studied how oncogenes and tumor suppressors affect the differentiation capacity, proportion and characteristics of progenitor cells in a model tissue. For this we used neural progenitor cells (NPCs) transduced with modified retroviruses carrying Human Papilloma Virus E6, E7 or E6/E7 oncogenes. HPV 16 E6/E7 is a classical oncogene complex, which degrades tumor suppressors p53 and pRb/p107/p130 and interferes with several other cellular activities. To examine further p53 and pRb involvement in NPC maintenance, we used p53−/− and E7 and E6/E7− expressing NPCs with restored pRb expression, respectively. E6/E7 expressing or p53−/− NPCs were able to differentiate, but simultaneously retained high capacity for self-renewal, proliferation, ability to remain multipotent in conditions promoting differentiation, and showed delayed cell cycle exit. These functions were mediated through p53 and pRb family and involved MEK-ERK signaling. Low amount of p53 increased self-renewal and proliferation, where as pRb affected only proliferation.This suggests that the oncogenes increase, while p53 and pRb-family tumor suppressors decrease the number and proportion of progenitor cells. These findings provide one explanation how oncogenes and tumor suppressors control tissue homeostasis and highlight their importance in stem cell self-renewal, linked both to cancer and life-long tissue turnover.PKC␦ is a key enzyme in the regulation of cell apoptosis in various cellular systems. PKC␦ can act as a pro or anti-apoptotic kinase depending on the cell type and apoptotic stimuli, however the molecular mechanisms underlying its diverse effects are not understood. Gliomas are characterized by deregulation of cell apoptosis and hence by increased resistance to apoptotic stimuli. Studies in our lab indicate that the expression PKC␦ is inversely correlated with the malignancy of gliomas. Here, we studied the role of PKC␦ in the apoptosis of glioma cells stimulated with etoposide and TRAIL. Using PKC␦WT, PKC␦KD mutant and PKC␦␦siRNAs, we found that PKC␦ played opposite roles in the apoptosis induced by etoposide and TRAIL; PKC␦␦increased the apoptotic effect of etoposide, whereas it reduced cell apoptosis induced by TRAIL. Both etoposide and TRAIL induced tyrosine phosphorylation of PKC␦ albeit on different residues; etoposide on tyrosine 187 and TRAIL on tyrosine 155. Etopo-side and TRAIL also induced differential translocation of PKC␦; etoposide to the nucleus and TRAIL to the ER. Both stimuli induced cleavage of PKC␦ and accumulation of the catalytic fragment. Using PKC␦ single tyrosine mutants, we found that the phosphorylation of PKC␦ on tyrosine 187 was not required for the nuclear translocation of PKC␦, but the phosphorylation on tyrosine 155 was essential for the translocation of PKC␦ to the ER in response to TRAIL. Tyrosine phosphorylation of PKC␦ was also necessary for the act...