High inorganic phosphate intake promotes tumorigenesis at early stages in a mouse model of lung cancer

© 2015 Lee et al. Inorganic phosphate (Pi) is required by all living organisms for the development of organs such as bone, muscle, brain, and lungs, regulating the expression of several critical genes as well as signal transduction. However, little is known about the effects of prolonged dietary Pi consumption on lung cancer progression. This study investigated the effects of a highphosphate diet (HPD) in a mouse model of adenocarcinoma. K-rasLA1 mice were fed a normal diet (0.3% Pi) or an HPD (1% Pi) for 1, 2, or 4 months. Mice were then sacrificed and subjected to inductively coupled plasma mass/optical emission spectrometry and laser ablation inductively coupled plasma mass-spectrometry analyses, western blot analysis, histopathological, immunohistochemical, and immunocytochemical analyses to evaluate tumor formation and progression (including cell proliferation, angiogenesis, and apoptosis), changes in ion levels and metabolism, autophagy, epithelial-to-mesenchymal transition, and protein translation in the lungs. An HPD accelerated tumorigenesis, as evidenced by increased adenoma and adenocarcinoma rates as well as tumor size. However, after 4 months of the HPD, cell proliferation was arrested, and marked increases in liver and lung ion levels and in energy production via the tricarboxylic acid cycle in the liver were observed, which were accompanied by increased autophagy and decreased angiogenesis and apoptosis. These results indicate that an HPD initially promotes but later inhibits lung cancer progression because of metabolic adaptation leading to tumor cell quiescence. Moreover, the results suggest that carefully regulated Pi consumption are effective in lung cancer prevention

Caspase involvement in autophagy

Caspases are a family of cysteine proteases widely known as the principal mediators of the apoptotic cell death response, but considerably less so as the contributors to the regulation of pathways outside cellular demise. In regards to autophagy, the modulatory roles of caspases have only recently begun to be adequately described. In contrast to apoptosis, autophagy promotes cell survival by providing energy and nutrients through the lysosomal degradation of cytoplasmic constituents. Under basal conditions autophagy and apoptosis cross-regulate each other through an elaborate network of interconnections which also includes the interplay between autophagyrelated proteins (ATGs) and caspases. In this review we focus on the effects of this crosstalk at the cellular level, as we aim to concentrate the main observations from research conducted so far on the fine-tuning of autophagy by caspases. Several members of this protease-family have been found to directly interact with key ATGs involved in different tiers across the autophagic cascade. Therefore, we firstly outline the core mechanism of macroautophagy in brief. In an effort to emphasize the importance of the intricate cross-regulation of ATGs and caspases, we also present examples drawn from Drosophila and plant models regarding the contribution of autophagy to apoptotic cell death during normal development