PPARs and Gastrointestinal Cancer

Since the discovery of the peroxisome proliferator-activated receptors (PPARs) in Xenopus frogs as receptors that induce the proliferation of peroxisomes in cells, the study of these factors has received widespread interest. After the characterization of the different isoforms (PPARα, PPARβ/δ, and PPARγ) of these nuclear receptors in the 90s, numerous ligands have been described. Although the responsibility of PPARs in cancer development and progression is still controversial , many scientists consider PPARs as potential bio-markers/targets for cancer prevention and therapy. Numerous mechanisms of PPARs action have been well reported; however the behaviour and function of PPARs differs within the context of different types of tissues and also depends on etiologic agents which could be one of the reasons to explain the conflicting literature. The aim of this SI was to assemble different studies in order to better establish the functions of PPARs in the context of different types of gastrointestinal cancer (GI). There are two research papers published by our group and nine reviews covering the main aspects of all types of GI cancer with the aim of elucidating the role of PPARs by confining their function to the different organs taken in consideration by the different authors. In our research article entitled " Time-qualified patterns of variation of PPARγ, DNMT1, and DNMT3B expression in pancreatic cancer cell lines, " we assessed the time-related patterns of variation of PPARγ and DNMTs in pancreatic cancer (PC) cell lines after synchronization in order to understand the circadian behaviour of these factors. Our data demonstrated the temporal influence (over 24 h) on PPARγ expression in PC cells. The circadian fluctuation of PPARγ expression is an important finding that could help to understand the many disagreeing studies. A temporal variation of PPARγ mRNA expression over the day has to be taken into account when performing an " in vitro " or " in vivo " study. In our study " Correlations among PPARγ, DNMT1, and DNMT3B expression levels and pancreatic cancer, " we sought to investigate the relationship among PPARγ and the DNA-methyltransferases in PC patients and in " in vitro " models of PC cell lines to better understand the role of PPAR in epige-netic modification. We demonstrated that PPARγ expression is positively associated with DNMT1 but not with DNMT3B whose higher expression, however, was significantly associated to a lower mortality in a cohort of PC patients. A. Stravodimou et al. described the …