The Hippo signaling pathway provides novel anti-cancer drug targets The Hippo signaling pathway provides novel anti-cancer drug targets

Park MK, et al. Lab Anim Res. 2018 Dec;34(4):160-165. https://doi.org/10.5625/lar.2018.34.4.160

Glycolysis is known as the main pathway for ATP production in cancer cells. However, in cancer cells, glucose deprivation for 24 h does not reduce ATP levels, whereas it does suppress lactate production. In this study, metabolic pathways were blocked to identify the main pathway of ATP production in pancreatic ductal adenocarcinoma (PDAC). Blocking fatty acid oxidation (FAO) decreased ATP production by 40% in cancer cells with no effect on normal cells. The effects of calorie balanced high- or low-fat diets were tested to determine whether cancer growth is modulated by fatty acids instead of calories. A low-fat diet caused a 70% decrease in pancreatic preneoplastic lesions compared with the control, whereas a high-fat diet caused a two-fold increase in preneoplastic lesions accompanied with increase of ATP production in the Kras (G12D)/Pdx1-cre PDAC model. The present results suggest that ATP production in cancer cells is dependent on FAO rather than on glycolysis, which can be a therapeutic approach by targeting cancer energy metabolism.

TopBP1 plays important roles in chromosome replication, DNA damage response, and other cellular regulatory functions in vertebrates. Although the roles of TopBP1 have been studied mostly in cancer cell lines, its physiological function remains unclear in mice and untransformed cells. We generated conditional knock-out mice in which exons 5 and 6 of the TopBP1 gene are flanked by loxP sequences. Although TopBP1-deficient embryos developed to the blastocyst stage, no homozygous mutant embryos were recovered at E8.5 or beyond, and completely resorbed embryos were frequent at E7.5, indicating that mutant embryos tend to die at the peri-implantation stage. This finding indicated that TopBP1 is essential for cell proliferation during early embryogenesis. Ablation of TopBP1 in TopBP1^flox/flox mouse embryonic fibroblasts and 3T3 cells using Cre recombinase-expressing retrovirus arrests cell cycle progression at the G₁, S, and G₂/M phases. The TopBP1-ablated mouse cells exhibit phosphorylation of H2AX and Chk2, indicating that the cells contain DNA breaks. The TopBP1-ablated mouse cells enter cellular senescence. Although RNA interference-mediated knockdown of TopBP1 induced cellular senescence in human primary cells, it induced apoptosis in cancer cells. Therefore, TopBP1 deficiency in untransformed mouse and human primary cells induces cellular senescence rather than apoptosis. These results indicate that TopBP1 is essential for cell proliferation and maintenance of chromosomal integrity.

Lung-resident neutrophils need to be tightly regulated to avoid degranulation- and cytokine-associated damage to fragile alveolar structures that can lead to fatal outcomes. Here we show that lung neutrophils (LNs) express distinct surface proteins and genes that distinguish LNs from bone marrow and blood neutrophils. Functionally, LNs show impaired migratory activity toward chemoattractants and produce high levels of interleukin-6 (IL-6) at steady state and low levels of tumor necrosis factor-α in response to lipopolysaccharide (LPS) challenge. Treating bone marrow neutrophils with bronchoalveolar lavage fluid or prostaglandin E2 induces LN-associated characteristics, including the expression of transglutaminase 2 (Tgm2) and reduced production of inflammatory cytokines upon LPS challenge. Neutrophils from Tgm2−/− mice release high levels of inflammatory cytokines in response to LPS. Lung damage is significantly exacerbated in Tgm2−/− mice in an LPS-induced acute respiratory distress syndrome model. Collectively, we demonstrate that prostaglandin E2 is a key factor for the generation of LNs with unique immune suppressive characteristics, acting through protein kinase A and Tgm2, and LNs play essential roles in protection of the lungs against pathogenic inflammation.