Twist1 Suppresses Senescence Programs and Thereby Accelerates and Maintains Mutant Kras-Induced Lung Tumorigenesis

KRAS mutant lung cancers are generally refractory to chemotherapy as well targeted agents. To date, the identification of drugs to therapeutically inhibit K-RAS have been unsuccessful, suggesting that other approaches are required. We demonstrate in both a novel transgenic mutant Kras lung cancer mouse model and in human lung tumors that the inhibition of Twist1 restores a senescence program inducing the loss of a neoplastic phenotype. The Twist1 gene encodes for a transcription factor that is essential during embryogenesis. Twist1 has been suggested to play an important role during tumor progression. However, there is no in vivo evidence that Twist1 plays a role in autochthonous tumorigenesis. Through two novel transgenic mouse models, we show that Twist1 cooperates with KrasG12D to markedly accelerate lung tumorigenesis by abrogating cellular senescence programs and promoting the progression from benign adenomas to adenocarcinomas. Moreover, the suppression of Twist1 to physiological levels is sufficient to cause Kras mutant lung tumors to undergo senescence and lose their neoplastic features. Finally, we analyzed more than 500 human tumors to demonstrate that TWIST1 is frequently overexpressed in primary human lung tumors. The suppression of TWIST1 in human lung cancer cells also induced cellular senescence. Hence, TWIST1 is a critical regulator of cellular senescence programs, and the suppression of TWIST1 in human tumors may be an effective example of pro-senescence therapy

Erk1 and Erk2 regulate endothelial cell proliferation and migration during mouse embryonic angiogenesis.

Angiogenesis is a complex process orchestrated by both growth factors and cell adhesion and is initiated by focal degradation of the vascular basement membrane with subsequent migration and proliferation of endothelial cells. The Ras/Raf/MEK/ERK pathway is required for EC function during angiogenesis. Although in vitro studies implicate ERK1 and ERK2 in endothelial cell survival, their precise role in angiogenesis in vivo remains poorly defined. Cre/loxP technology was used to inactivate Erk1 and Erk2 in endothelial cells during murine development, resulting in embryonic lethality due to severely reduced angiogenesis. Deletion of Erk1 and Erk2 in primary endothelial cells resulted in decreased cell proliferation and migration, but not in increased apoptosis. Expression of key cell cycle regulators was diminished in the double knockout cells, and decreased DNA synthesis could be observed in endothelial cells during embryogenesis. Interestingly, both Paxillin and Focal Adhesion Kinase were expressed at lower levels in endothelial cells lacking Erk1 and Erk2 both in vivo and in vitro, leading to defects in the organization of the cytoskeleton and in cell motility. The regulation of Paxillin and Focal Adhesion Kinase expression occurred post-transcriptionally. These results demonstrate that ERK1 and ERK2 coordinate endothelial cell proliferation and migration during angiogenesis

Characterization of MYC-Induced Tumorigenesis by in Situ Lipid Profiling

We apply desorption electrospray ionization mass spectrometry imaging (DESI-MSI) to provide an in situ lipidomic profile of genetically modified tissues from a conditional transgenic mouse model of MYC-induced hepatocellular carcinoma (HCC). This unique, label-free approach of combining DESI-MSI with the ability to turn specific genes on and off has led to the discovery of highly specific lipid molecules associated with MYC-induced tumor onset. We are able to distinguish normal from MYC-induced malignant cells. Our approach provides a strategy to define a precise molecular picture at a resolution of about 200 μm that may be useful in identifying lipid molecules that define how the MYC oncogene initiates and maintains tumorigenesis

<i>Twist1</i> accelerates <i>Kras^G12D</i>-induced lung tumorigenesis and promotes progression to adenocarcinoma.

<p>(A) Kaplan-Meier tumor free survival using serial microCT of <i>CCSP-rtTA</i>/<i>Twist1-tetO₇-luc</i> (CT), <i>CCSP-rtTA</i>/<i>tetO-Kras^G12D</i> (CR) and <i>CCSP-rtTA</i>/<i>tetO-Kras^G12D</i>/<i>Twist1-tetO₇-luc</i> (CRT) mice. The double inducible oncogene animals (CRT) developed multiple tumors at a median tumor latency that was significantly shorter than the single CR animals, 15 weeks, by log-rank analysis (<i>p</i><0.0001). A syngenic control cohort consisting of wildtype mice, those with <i>tetO-Kras^G12D</i>/<i>Twist1-tetO₇-luc</i> (without <i>CCSP-rtTA</i>), <i>CCSP-rtTA</i> alone, or single oncogenes alone (n = 15 total) never developed lung tumors before 12 months of age. (B) Lung tumors from a CRT mouse at necropsy and H&E sections. Black bars equal 200 and 50 µm. H – heart; and L – liver. (C) Immunohistochemical (IHC) phenotyping of CRT tumors using antibodies against CCSP and proSpC. (D) Lung tumor burden is increased at 6 months in CRT <i>versus</i> CR mice qualitatively by microCT and H&E histology. Blue arrowheads denote lung tumors. (Lower panel) Lung tumors were quantified for CR <i>versus</i> CRT mice by microCT (n = 4 mice each). S – spine. Black bar equals 2 mm (E) Ki-67 IHC of CR <i>versus</i> CRT lung tumors (n = 3 mice each). Low - <5%; Med – 5–25%; and High - >25%. Histologic examination of lung tumors for numbers of benign lesions (hyperplasia, atypical adenomatous hyperplasia and adenomas) <i>versus</i> adenocarcinomas (AdenoCA) for CR and CRT mice (n = 2 mice each).</p