Notch-1 signaling facilitates survivin expression in human non-small cell lung cancer cells

The oncogenic potential of Notch activation is observed in many instances including lung tumorigenesis, but the associated molecular regulatory mechanism has not been thoroughly defined. It has been demonstrated that hypoxia can act as one of the major stimuli in the progression of many types of tumorigenesis. This study was designed to examine the activation of Notch-1 signaling by hypoxia and its contribution to survivin expression in human lung carcinomas. Western-blot and PCR analysis showed that Notch-1 signaling is activated by hypoxia in the human non-small cell lung cancer (NSCLC) cell line, A549, through the upregulation of Notch-1, along with its intracellular domain (N1ICD). The activity of Hes-1, a crucial target molecule of N1ICD, was also increased under hypoxia. Interestingly, blockade of the Notch-1 pathway by a gamma-secretase inhibitor or small interfering RNA (siRNA) inhibited survivin expression. Conversely, activation of Notch-1 signaling by N1ICD or stimulation with the Jagged1 ligand enhanced survivin levels in A549 cells. Notably, HIF-1 alpha cooperated with Notch-1 signaling to increase survivin expression through its direct association with N1ICD, consequently accelerating survivin transcription. Overall, our findings suggest that Notch-1 signaling is involved in the upregulation of survivin expression in lung cancer cells, which is synergized by HIF-1 alpha.