Reversible upregulation of tropomyosin-related kinase receptor B by geranylgeranoic acid in human neuroblastoma SH-SY5Y cells.

All-trans retinoic acid (ATRA) plays crucial roles in cell survival and differentiation of neuroblastoma cells. In the present study, we investigated the effects of geranylgeranoic acid (GGA), an acyclic retinoid, on differentiation and tropomyosin-related kinase receptor B (TrkB) gene expression in SH-SY5Y human neuroblastoma cells in comparison with ATRA. GGA induced growth suppression and neural differentiation to the same extent as ATRA. Two variants (145 and 95 kD) of the TrkB protein were dramatically increased by GGA treatment, comparable to the effect of ATRA. Following 6- to 8-day GGA treatment, the effect of GGA on TrkB was reversed after 2-4 days of its removal, whereas the effect of ATRA was irreversible under the same conditions. Both GGA and ATRA upregulated the cellular levels of three major TrkB messenger RNA splice variants in a time-dependent manner. Time-dependent induction of cell cycle-related genes, such as cyclin D1 and retinoblastoma protein, and amplification of the neural progenitor cell marker, brain lipid binding protein, were suppressed by GGA treatment and were completely abolished by ATRA. ATRA and GGA induced retinoic acid receptor β (RARβ) expression, whereas the time-dependent expression of both RARα and RARγ was abolished by ATRA, but not by GGA. Our results suggest that GGA may be able to restore neuronal properties of SH-SY5Y human neuroblastoma cells in a similar but not identical way to ATRA.