Down-regulation of Notch receptor signaling pathway induces caspase-dependent and caspase-independent apoptosis in lung squamous cell carcinoma cells

Cao H, Hu Y, Wang P, Zhou J, Deng Z, Wen J. Down‐regulation of Notch receptor signaling pathway induces caspase‐dependent and caspase‐independent apoptosis in lung squamous cell carcinoma cells. APMIS 2012; 120: 441–50. Notch receptor signaling pathway (NRSP) is increasingly linked to carcinogenesis. Non‐small cell lung cancer (NSCLC) appears to actively utilize this conserved developmental pathway. The aims of this study are to determine whether or not Notch 1–4 are overexpressed in NSCLC tissues compared with normal lung tissues and whether inhibiting NRSP could induce caspase‐dependent or caspase‐independent apoptosis. Immunohistochemistry was used to evaluate the expression of Notch 1–4 in 101 NSCLC tissue samples and 30 normal lung tissue samples. DAPT was used to repress NRSP in SK‐MES‐1 cells. Apoptosis was determined by Annexin V and PI staining. Cleaved poly ADP‐ribose polymerase (PARP) was measured by Western blot; X‐linked inhibitor of apoptosis protein (XIAP) and Survivin were assessed by qRT‐PCR and Western blot; the release of second mitochondria‐derived activator of caspase (Smac) from mitochondria to cytoplasm was evaluated by Western blot; the subcellular locations of endonuclease G (Endo G) and apoptosis inducing factor (AIF) were observed by Western blot and indirect immunofluorescence analysis. (Mech Dev, 98, 2000, 95) Notch 1–4 are up‐regulated in NSCLC tissues and Notch 1, 2 are positively correlated with lymph node metastasis, (Proc Natl Acad Sci U S A, 106, 2009, 22293) DAPT treatment could inhibit NRSP and induce apoptosis, with a marked increase in cleaved PARP, decreases in XIAP and Survivin proteins and concomitant release of Smac, EndoG, and AIF from mitochondria, indicating that inhibiting NRSP by DAPT triggers caspase‐dependent and caspase‐independent apoptosis.