Distinct regulation of vasoactive intestinal peptide (VIP) expression at mRNA and peptide levels in human...

Neuronal differentiation was induced in cultures of the human neuroblastoma cell line subclone SH-SY5Y by 14-day treatment with dibutyryl cAMP (dBcAMP), retinoic acid, and phorbol 12-myristate 13-acetate (PMA). An approximate 4-fold increase in vasoactive intestinal peptide (VIP) mRNA concentration was observed after differentiation with retinoic acid, whereas no change in VIP mRNA concentration was observed after differentiation with dBcAMP or PMA. A short-term treatment of cells with PMA did however result in a 5-fold transient increase in VIP mRNA; prior differentiation with retinoic acid or dBcAMP diminished this effect. Observed increases in VIP mRNA were in all cases accompanied by increases in VIP immunoreactivity. Remarkably, however, long-term treatment of cells with dBcAMP, which caused no change in mRNA levels, resulted in a six-fold increase in VIP immunoreactivity. Acute (36-h) treatment with carbachol also caused an increase in VIP immunoreactivity (about 2-fold, and blocked by atropine) without an increase in VIP mRNA level. Thus, a quantitative change in gene transcription or mRNA stability appears not to be a prerequisite for increased VIP expression, indicating that regulation can occur at translational or post-translational steps.