BETA-1B SUBUNIT OF VOLTAGE-DEPENDENT CA2-LINE IMR32( CHANNELS IS PREDOMINANT ISOFORM EXPRESSED IN HUMAN NEUROBLASTOMA CELL)

Human neuroblastoma cells (IMR32) respond to treatment with either dib utyryl-cAMP or nerve factor by acquiring a neuronal phenotype which is accompanied by a marked increase in the density of neuronal (N-type) VDCC currents, Using IMR32 cells as a model for neuronal differentiati on, we were interested in examining possible changes in the level of e xpression of the alpha 1B subunit of N-type calcium channels as well a s beta subunit isoforms, Upon differentiation with dibutyryl-cAMP and 5-bromo-2-deoxyuridine for 16 days, ne observed a dramatic increase in alpha 1B protein which initiated between day 8 and 10, Day 10 evidenc ed maximal expression of alpha 1B protein, which was followed by an in terval of relatively constant expression of alpha 1B (day 12 to day 16 ), Monitoring beta subunit expression using a pan specific anti-beta a ntibody (Ab CW20), we observed an increase in expression of a single 8 2 kDa beta subunit, The predominant 82 kDa beta subunit expressed thro ughout the course of differentiation was identified as tile beta 1b is oform using a panel of beta subunit specific antibodies, Of significan ce, neither the beta 2 nor beta 3 isoforms were detected in full diffe rentiated IMR32 cells, Contrary to a previous report on the absence of neurotypic expression of VDCC beta subunits in a second model for in vitro differentiation, NGF-treated rat pheochromocytoma cells (PC12 ce lls) [1], we report the regulated expression of the beta 1b protein in differentiated IMR32 cells suggesting a cell specific function for th is beta subunit which parallels the acquisition of the neuronal phenot ype. The restrictive expression of the beta 1b in IMR32 cells may refl ect a cell-type specific function that extends beyond its role as an a uxiliary subunit of VDCC complexes. (C) 1997 Federation of European Bi ochemical Societies.