High levels of nerve growth factor (NGF) are found in sera from individuals infected with human herpesvirus 8 (HHV-8). BC-1 and BCBL-1 cells are primary effusion lymphoma–derived B-cell lines; BC-1 cells are infected by HHV-8 and the Epstein-Barr virus (EBV), and BCBL-1 cells are infected only by HHV-8. Both cells express NGF receptors and produce NGF, whereas RAMOS cells (a B-cell line that is negative for HHV-8 and EBV) express NGF receptors but do not produce detectable NGF. Neutralization of endogenous NGF results in cell growth inhibition and apoptosis in BCBL-1 cells and, to a minor extent, in BC-1 cells. When the HHV-8 lytic cycle is induced in BCBL-1 cells by tetradecanoyl phorbol acetate (TPA), an initial reduction of endogenous NGF production is observed, and many cells undergo apoptosis. However, at 48 hours, TPA-treated cells produce significantly more NGF than untreated controls, and a subsequent recovery of cell viability is observed. Consistent with this finding, the addition of exogenous NGF or anti-NGF antibodies to TPA-treated cells reduces or increases, respectively, the rate of apoptosis in response to TPA. Finally, electron microscopy of TPA-treated BCBL-1 cells shows that the addition of exogenous NGF increases the number of cells producing and releasing complete virions as compared with the controls (25% versus 5%). On the contrary, NGF neutralization leads to the production of defective viral progeny in about 2% of cells. These data indicate that NGF is essential for both cell survival and virus maturation in HHV-8–infected cell lines.
Fast and slow nerve growth factor binding sites in human neuroblastoma and rat pheochromocytoma cell lines: relationship of sites to each other and to neurite formation