Liu, Yan

Abstract Obesity is a risk factor for Pancreatic Ductal Adenocarcinoma (PDAC), but the molecular mechanisms involved are unclear. Oncogenic mutation of K-Ras occurs early and nearly universally in patients with this disease. However, recent evidence indicates that oncogenic Ras is not fully active and for activity to surpass the threshold required to engage a Ras-inflammation feed-forward loop, it requires a stimulus. We hypothesized that high-fat intake acts as an inflammatory stimulus, increasing K-Ras activity and that cyclooxygenase -2 (COX2) expression is required in the inflammatory loop. LSL-K-Ras mice were crossed with elastase-CreER (acinar cell-specific) or Pdx1-Cre (pancreatic cell-specific) to “knock-in” expression of oncogenic K-Ras. Additionally, acinar cell-specific -Ras mice were crossed with COX2 conditional knockout mice. All mice were fed isocaloric diets with different amounts of fat and a COX2 inhibitor was administered to some acinar cell-specific -Ras mice. Pancreata were analyzed for Ras activity, Phospho-ERK levels, inflammation, fibrosis, PanIN and PDAC development. We observed that consumption of a high fat diet (HFD) led to increased K-Ras activity, PanIN formation, fibrotic stroma and PDAC development compared to a control diet. Additionally, we observed a significant reduction in the survival of mice fed a HFD. Genetic deletion of COX2 in acinar cells and COX2 systemic inhibition prevented the HFD-induced effects in acinar cell-specific -Ras mice. These findings indicated that a HFD stimulates activation of oncogenic K-Ras and initiates an inflammatory feed-forward loop requiring the expression of COX2 leading to pancreatic inflammation, fibrosis, PanINs and PDAC. This mechanism may explain the PDAC risks associated with consumption of a HFD. Citation Format: Bincy Philip, Christina L. Roland, Jarek Daniluk, Yan Liu, Deyali Chatterjee, Sobeyda Berenice Gomez, Baoan Ji, Huang Haojie, Huamin Wang, Jason B. Fleming, Craig D. Logsdon, Zobeida Cruz-Monserrate. High fat triggers oncogenic K-Ras activity and a COX2 dependent feed-forward loop to induce pancreatic ductal adenocarcinoma development. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr C61.

Abstract Increased Ras activity levels due to active mutations of Ras are critical for tumorigenesis. These oncogenic Ras mutations are considered to be locked in a permanent “On” state and “constitutively active”. Yet, surprisingly, expression of oncogenic Ras at physiologically levels in genetically engineered mice with “knock-in” mutant Ras has little effect on most cells. Here, we demonstrated that oncogenic K-Ras is not at all constitutively active. Rather, oncogenic K-Ras can be readily activated by upstream stimulants such as diet-induced hormones (eg. Cholecystokinin) and inflammatory stimuli (eg. PGE2 or LPS). However, unlike wild-type Ras, oncogenic K-Ras is very slow to inactivate. This effect on oncogenic K-Ras signaling kinetics leads to dramatically amplified levels of Ras activity initiated by physiologic stimuli. Sustained increase of Ras activity involves a feed-forward loop in which increased Ras activity generates more inflammatory mediators which act as Ras stimulants. High Ras activity led to acinar cell senescence and generated inflammation and fibrosis resembling the histological features of chronic inflammation with abundant precancerous lesions that spontaneously progressed to cancer only in animals expressing physiologic levels of oncogenic Ras. In summary, oncogenic Ras is not constitutively active but predisposes cells to pathological alterations dependent upon Ras activity levels. Since a large population of normal healthy humans harbors Ras mutations, in addition to targeting Ras downstream signaling pathways a reduction of factors that can activate Ras signaling may provide an important alternative cancer preventive value. These data also provide a mechanistic explanation for the link between inflammation, Ras and cancer and provide insights for cancer prevention. Citation Format: Ji Baoan, Huang Haojie, Liu Yan, Daniluk Jaroslaw, Logsdon Craig. Targeting oncogenic Ras activation for cancer prevention. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A31.

Abstract Elevated Ras activity is critical for Ras induced tumorigenesis. However, the underlying mechanisms that lead to pathological levels of Ras activity are unclear. Here, we found that stimulation of Ras signaling by typical inflammatory stimuli was transient and had no long term sequelae in wild-type mice. In contrast, these stimuli generated prolonged Ras signaling and led to chronic inflammation and precancerous lesions (PanINs) in mice expressing endogenous levels of oncogenic K-Ras. The effects of inflammatory stimuli on oncogenic Ras expressing mice were disrupted by deleting IKK2 or inhibiting Cox-2. Likewise, the expression of active IKK2 or Cox-2, or treatments with LPS generated chronic inflammation and PanINs only in mice expressing oncogenic Ras. The data support that in the presence of oncogenic Ras, inflammatory stimuli trigger an NF-κB mediated positive feedback mechanism involving Cox-2 that amplifies Ras activity to pathological levels. Because a large portion of the adult human population possesses Ras mutations in tissues including colon, pancreas, and lung, disruption of this positive feedback loop may be an important strategy for cancer prevention. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-425. doi:1538-7445.AM2012-LB-425