Regulation of chromogranin biosynthesis by neurotrophic growth factors in neuroblastoma cells

Polypeptide growth factors secreted from the target tissue determine the choice of transmitter synthesis in the innervating nerves. We have investigated whether they also influence the expression of chromogranins and neuropeptide Y, components co-stored with the neurotransmitters within large dense-core vesicles. IMR-32 and SH-SY5Y human neuroblastoma cells were treated for up to six days with various neurotrophic growth and differentiation factors. For chromogranins A and B, no significant changes at the mRNA level were observed and for chromogranin A this was confirmed at the protein level. The expression of secretogranin II/pro-secretoneurin mRNA, however, was considerably enhanced in both cell lines after basic fibroblast growth factor treatment. In IMR-32 cells we determined a fast and continuous induction, whereas the up-regulation in SH-SY5Y cells was more delayed. A transient elevation of secretogranin II/pro-secretoneurin mRNA levels was seen in SH-SY5Y cells in response to epidermal growth factor. In these cells we also measured the amounts of secretogranin II/pro-secretoneurin protein which were increased by both growth factors. In addition to the above described changes in secretogranin II/pro-secretoneurin biosynthesis we extended and confirmed data available on neuropeptide Y. We found a qualitatively similar pattern of biosynthesis regulation as for secretogranin II/pro-secretoneurin, indicating that the ultimately increased expression of the two proteins may be characteristic of the phenotypic differentiation after growth factor treatment. Moreover, this finding of a concomitant regulation further emphasizes the concept of secretogranin II/pro-secretoneurin being a neuropeptide precursor from which the functional peptide secretoneurin is proteolytically liberated.