Differential PARP cleavage: An indication for existence of multiple forms of cell death in human gliomas

Background: Gliomas represent a diverse range of clinical presentation, histological differentiation, and response to therapy. Altered cell proliferation and cell death signals in gliomas are of great interest to elucidate the key molecules involved and to find effective treatment modalities. By considering the role of different proteases in correlation with differential poly (ADP-ribose) polymerase (PARP) fragmentation we have studied the pattern of cell death in human glioma tissues. Materials and Methods: In our study, five different human glioma biopsies were collected and analyzed for the PARP cleavage pattern by using western immunoblotting. Samples were also analyzed for pro-caspase 3, calpain I (µ) and II (m), granzyme-B and apoptosis-inducing factor (AIF). Parallel sections of histologically confirmed astrocytoma and glioblastoma multiforme (GBM) were used for immunohistochemical analysis of cleaved caspase-3, granzyme B, AIF and cyclo-oxygenase -2 (cox-2). Results: We found PARP fragmentation, along with usual ~ 89 kDa and ~ 24 kDa fragments, into other fragments of different molecular weights. Caspase mediated cell death may lead to appearance of larger ~ 89 kDa fragment and smaller ~ 24 kDa fragment indicating existence of apoptosis in the tumors. However, other fragments corresponding to ~ 64 kDa, ~ 54 kDa, and ~ 40 kDa were observed concomitantly in all glial tumor tissues. Conclusions: These results may indicate, not only apoptosis and necrosis, but there occurs the co-existence of intermediate cell death pathways in human glial tumors.

Keywords
Caspase-3, human gliomas, multiple forms of cell death, poly (ADP-ribose) polymerase cleavage