Synergy of activin and ciliary neurotrophic factor signaling pathways in the induction of vasoactive intestinal peptide gene expression

Activin, a member of the transforming growth factor-beta superfamily, can r egulate neuropeptide gene expression in the nervous system and in neuroblas toma cells. Among the neuropeptide genes whose expression can be regulated by activin is the gene encoding the neuropeptide vasoactive intestinal pept ide (VIP). To investigate the molecular mechanisms by which activin regulat es neuronal gene expression, we have examined activin's regulation of VIP g ene expression in NBFL neuroblastoma cells. We report here that NBFL cells respond to activin by increasing expression of VIP mRNA. Activin regulates VIP gene transcription in NBFL cells through a 130-bp element in the VIP pr omoter that was previously characterized to be necessary and sufficient to mediate the induction of VIP by the neuropoietic cytokines and termed the c ytokine response element (CyRE). We find that the VIP CyRE is necessary and sufficient to mediate the transcriptional response to activin. In addition , ciliary neurotrophic factor (CNTF), a neuropoietic cytokine, synergizes w ith activin to increase VIP mRNA expression and transcription through the V IP CyRE. Mutations in either the Stat (signal transducer and activator of t ranscription) or AP-1 sites within the CyRE that reduce the response to CNT F, also reduce the response to activin. However, mutating both the Stat and AP-1 sites within the wild-type CyRE, while reducing the separate response s to either activin or CNTF, eliminates the synergy between them. These dat a suggest that activin and CNTF, two factors that appear to signal though d istinct pathways, activate VIP gene transcription through a common transcri ptional element, the VIP CyRE.