Resistance to etoposide-induced apoptosis in a Burkitt's lymphoma cell line.
Burkitt's lymphoma cells that vary in their phenotypic characteristics show significantly different degrees of susceptibility to radiation-induced apoptosis. Propensity to undergo apoptosis is reflected in the degradation of substrates such as DNA-dependent protein kinase but the status of bcl-2, c-myc and p53 has been uninformative. In this study, we have focused on 2 Epstein-Barr virus (EBV)-associated Burkitt's cell lines, one (WW2) susceptible and the other (BL29) resistant to etoposide-induced apoptosis. Differences in expression of BHRF1, an EBV gene that is homologous to the Bcl-2 proto-oncogene and known to inhibit apoptosis, or changes in apoptosis inhibitory proteins (IAPs), did not appear to account for the difference in susceptibility in the 2 cell lines. Cytoplasmic extracts from etoposide-treated WW2 cells caused apoptotic changes in nuclei isolated from either BL29 or WW2 cells, whereas extracts from BL29 cells failed to do so. In addition, extracts from etoposide-treated WW2 cells degraded the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), an important indicator of apoptosis, but this protein was resistant to degradation by BL29 extracts. It appears likely that caspase 3 (CPP32) is involved in this degradation since it was activated only in the apoptosis susceptible cells and the pattern of cleavage of DNA-PKcs was similar to that reported previously with recombinant caspase 3. As observed previously, addition of caspase 3 to nuclei failed to induce morphological changes indicative of apoptosis, but addition of caspase 3 to nuclei in the presence of extract from the resistant cells led to apoptotic changes. We conclude that resistance to apoptosis in BL29 cells is due to a failure of etoposide to activate upstream effectors of caspase activity.
Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Herston, Australia.
E G
EG
Zhao
Q
Q
Song
S
S
Cross
I
I
Misko
S P
SP
Lees-Miller
M F
MF
Lavin
D017209:Apoptosis / Q000187:drug effects*; D002051:Burkitt Lymphoma / Q000473:pathology* / Q000821:virology; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000473:pathology; D002474:Cell-Free System; D003593:Cytoplasm / Q000187:drug effects / Q000473:pathology; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000633:toxicity*; D004854:Herpesvirus 4, Human / Q000302:isolation & purification; D006801:Humans; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000090063:Proto-Oncogene Mas
D004268:DNA-Binding Proteins; C000715470:MAS1 protein, human; D009687:Nuclear Proteins; D000090063:Proto-Oncogene Mas; D005047:Etoposide; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases