Serum depletion increases the neurofilament protein mRNA levels in a neuroblastoma cell line, GOTO.

A human neuroblastoma cell line, GOTO, extends neurite-like processes upon withdrawal of serum from culture medium. This morphological change was accompanied by a 5-fold increase in the neurofilament (NF)-L and a 10-fold increase in the NF-M mRNA levels after 24 h. The addition of a protein kinase inhibitor, H-7 (1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride) also induced the extension of neurite-like processes; however, it did not increase the NF mRNA levels. Thrombin inhibited the extension of neurite-like processes in serum-free culture without affecting the increase in the NF mRNA levels. There was no difference in the number of cells progressing through the S phase between serum-containing and -free cultures at 24 h. This indicates that the increase in the NF mRNA levels upon withdrawal of serum was not preceded by the growth arrest. Treatment with actinomycin D and cycloheximide inhibited the increase in the NF mRNA levels. The half life of the NF gene transcripts was prolonged in the serum-free condition. These results indicate that the serum depletion-induced increase in the NF-L and -M mRNA levels was regulated by both transcriptional and post-transcriptional mechanisms, and the increase in the expression of the NF genes was not simply mediated by growth arrest but controlled by unknown regulator proteins.