INDUCTION OF APOPTOSIS IN A NEUROBLASTOMA AND HEPATOCYTE COCULTURE MODEL

Background. The dysregulation of apoptosis may alter the progression o f tumor growth and explain the clinical dichotomy observed in children with neuroblastoma (NB). An overexpression of the bcl-2 proto-oncogen e induces resistance to apoptosis and has been observed in unfavorable NB. We hypothesized that alterations in apoptosis may be a result of the interactions between NB and the tissues surrounding it. Materials and Methods. Human Chang liver cells (HCL, 10(4) cells/cm(2)) were pla ted in two-chamber slides for 3 days. Human NB cells (10(5) cells/cm(2 )) were added to one of the chambers and incubated for 3 more days. Co ntrol NB were plated under identical conditions in its own medium and in the HCL medium with growth curves measured. DNA fragmentation was d etected via the TUNEL method (TdT-mediated nick end-labeling) and bcl- 2 expression was determined by immunostaining. Results. NB growth was unaltered by the change in medium. NB stained mildly positive for bcl- 2 when plated alone but became markedly positive in coculture. Histolo gically, HCL and NB appeared healthy when plated alone, but a halo of apoptotic HCL was seen around NB in the coculture, When plated alone, both NB and HCL demonstrated minimal apoptotic activity as detected vi a the TUNEL method. In the coculture, a halo of HCL surrounding the NB exhibited markedly increased DNA fragmentation and this intensity dim inished in cells distant from the NB. Conclusions. The regulation of a poptosis was altered in this coculture model of NB and HCL. HCL stimul ated NB to overexpress bcl-2 and presumably become resistant to apopto sis. Conversely, NB induced the surrounding HCL to undergo apoptosis. The interaction between the local tissue and NB induced alterations in apoptosis in both cell types and resulted in a survival advantage for NB. (C) 1998 Academic Press.