Axonogenesis in neuro-2a cells correlates with GM1 upregulation in the nuclear and plasma membranes

Abstract

GM1 ganglioside was previously shown to occur in the nuclear membrane, as well as the plasma membrane, of central nervous system (CNS) and peripheral nervous system (PNS) neurons undergoing morphological differentiation in culture. NG108-15 neuroblastoma cells showed the same phenomenon when induced to extend axon-like but not dendrite-like processes, although in both cases terminal differentiation was evidenced by failure of extended neurites to retract following washout of neuritogenic agent. The present study of Neuro-2a neuroblastoma cells subjected to similar treatments has revealed both similarities and differences compared to NG108-15 cells. Similar to the latter, Neuro-2a cells responded to neuraminidase and ionomycin with axon-like outgrowth together with upregulation of nuclear GM1, and to three other agents (retinoic acid, dibutyryl cyclic AMP, exogenous GM1) with dendrite-like outgrowth that was unaccompanied by nuclear GM1 increase. Although both cell types responded to low serum by extending neurites of mixed axonal-dendritic properties, Neuro-2a, in keeping with its greater tendency to extend some neurites of axonal character in low serum, showed elevated nuclear GM1 in a significant number of such differentiated cells. All three axonogenic agents induced parallel upregulation of GM1 in plasma-, nuclear-, and Golgi membranes, and these increases were stable to washout. Neurites generated in Neuro-2a cells by the three dendritogenic agents lacked stability, unlike those produced by the same agents in NG108-15 cells. This study also amplified the differences in response triggered by exogenous GM1 compared to that resulting from enzyme-mediated elevation of endogenous GM1.