Ras and Notch signaling have recently been shown to cooperate in the maintenance of neoplastic transformation. Here, we show that TGF alpha, a known activator of Ras signaling, can drive cell proliferation and at the same time induce the expression of the Notch target Hes-1 in the neuroblastoma cell line SK-N-BE(2)c. The up-regulation of Hes-1 occurred both at the transcriptional and protein levels and by use of EGFR and MEK inhibitors we could show that the Hes-1 response was dependent on activation of the MAP kinase ERK. Blocking Notch activation by gamma-secretase inhibition did not profoundly affect the Hes-1 levels, neither in untreated nor in TGF alpha treated cells. The upregulation of Hes-1 was associated with down-regulation of its pro-neuronal target gene Hash-1. Taken together, these results show that TGF alpha is a potent mitogen of neuroblastoma cells and suggest a connection between activation of ERK and Hes-1, thus providing a link between the Ras and Notch signaling pathways.
- TGF alpha
- Ras/MAPK signaling