Signaling and Regulation Notch Signaling Contributes to Lung Cancer Clonogenic Capacity In Vitro but May Be Circumvented in

TheNotch signaling pathway is a critical embryonic developmental regulatory pathway that has been implicated in oncogenesis. In non–small cell lung cancer (NSCLC), recent evidence suggests that Notch signaling may contribute to maintenance of a cancer stem or progenitor cell compartment required for tumorigenesis. We explored whether intact Notch signaling is required for NSCLC clonogenic and tumorigenic potential in vitro and in vivo using a series of genetically modified model systems. In keeping with previous observations, we find that Notch3 in particular is upregulated in human lung cancer lines and that downregulation of Notch signaling using a selective g-secretase inhibitor (MRK-003) is associatedwith decreased proliferation and clonogenic capacity in vitro. We show that this phenotype is rescued with the expression of NICD3, a constitutively active cleaved form of Notch3 not affected by g-secretase inhibition. Using an inducible LSL-KRASG12Dmodel of lung cancer in vivo, we show a transient upregulation ofNotch pathway activity in early tumor precursor lesions. However, amore rigorous test of the requirement for Notch signaling in lung oncogenesis, crossing the LSL-KRASG12D mouse model with a transgenic with a similarly inducible global dominant-negative suppressor of Notch activity, LSL-DNMAML (dominant-negativemastermind-like), reveals no evidence ofNotch pathway requirement for lung tumor initiation or growth in vivo. Distinct Notch family members may have different and potentially opposing activities in oncogenesis, and targeted inhibition of individual Notch family members may be a more effective anticancer strategy than global pathway suppression. Mol Cancer Res; 9(12); 1746–54. 2011 AACR