Cell-specific regulation of the stably expressed serotonin 5-HT1A receptor and altered ganglioside synthesis.

Neurotransmission is dependent on the presence of neuronal receptors at the synapses, and important cell surface molecules such as gangliosides are pivotal in the maintenance of synaptic contacts. To study the interrelationship between these two classes of molecules, we achieved stable expression of the hippocampus- and CNS-localized serotonin 1A receptor (5-HT1A-R) in three 5-HT1A-R-deficient neuronal cell lines and also the control, non-neural CHO cells. A strong passage dependence of 5-HT1A-R expression, as measured by mRNA levels as well as membrane binding to the selective agonist [3H]8-OH-DPAT, was observed only in the HN2 (hippocampal) and NCB-20 (CNS) cells which are derived from tissues of natural occurrence of the 5-HT1A-R. A paradigm of stress was obtained by carrying out continuous culture of cells without feeding. During this time a dramatic increase in 5-HT1A-R mRNA and [3H]8-OH-DPAT binding was observed only in the neuronal cells after confluence and during decreased cell viability (days 10/11). This was not due to differentiation, since deliberate serum deprivation and differentiation of cells did not result in any dramatic increase in 5-HT1A-R expression. Analysis of ganglioside synthesis by pulse labeling of the transfected cells produced striking results. In the dorsal root of the ganglion (DRG) derived F-11 cells which show low but significant levels of complex gangliosides before transfection, the mere presence of the serotonin 1A receptor resulted in a dramatic increase in synthesis of gangliosides comigrating with GM2, GD1a, GD1b, and GT1b (20-fold by densitometry). In contrast, there was only a 2-fold increase in the overall content of complex gangliosides in the presence of the 5-HT1A-R. In the NCB-20 cells which contain only GD1a but no GD1b or GT1b before transfection, a decrease in GD1a synthesis was observed following transfection. Also agonist (8-OH-DPAT) binding to the serotonin 1A receptor in NCB-20 cells produced a 3-fold increase in synthesis of a ganglioside comigrating with GM3. Thus, our neuroblastoma transfectants help demonstrate stress-induced regulation of the 5-HT1A-R, which in turn exerts a strong and cell type-specific control over such essential cell-surface determinants like gangliosides.