Differential modulation of nucleoside transport types in neuroblastoma cells by protein kinase activation

Nucleoside transport regulation in undifferentiated Neuro-2A cells has been studied and found to include Na+-dependent adenosine transport and facilit ated diffusion adenosine transport. The latter corresponded to nitro benzyl thioinosine-sensitive nucleoside transport. Short-term treatment of Neuro-2 A cells with physiologically relevant signals only modulated the facilitate d diffusion component. The stimulation of undifferentiated cells with forsk olin or other activators of the protein kinase A pathway, decreased NBTI-se nsitive adenosine transport. Treatment of cells with an inactive analogue o f forskolin, 1,9-dideoxi-forskolin, had no effect on NBTI-sensitive nucleos ide transport. Therefore, the inhibition of protein kinase A activity by pr e-incubation with H-89 or the cAMP antagonist, Rp-8-Br-cAMPS, completely pr evented the inhibitory effect of forskolin, Similarly, the activation of pr otein kinase C with phorbol 12,13-dibutyrate (PDBu) and the calcium ionopho re A-23187 decreased NBTI-sensitive adenosine transport. The effect of PDBu was reversed by pre-incubation of cells with staurosporine. Maximal transp ort inhibition was obtained by the simultaneous stimulation of cells with a phorbol ester and A-23187 or a phorbol eater and forskolin. The modulation of NBTI-sensitive nucleoside transport corresponded to changes in specific [H-3]NBTI binding to Neuro-2A cells. Maximal inhibition correlated well wi th a maximal enhancement of cAMP production. However, the Na (+)-dependent adenosine transport in Neuro-2A cells was not modulated by any of these sig nals. (C) 1999 Elsevier Science Ltd. All rights reserved.