fig1

Figure 1. Aldehyde dehydrogenases (ALDHs) expression and function in the tumour microenvironment. ALDH expression in cancer stem cells (CSCs) and differentiated cells have been linked with several cellular processes including glycolysis/glucogenesis and amino acid metabolism, which are likely to be affected by the local microenvironment including impact by hypoxia (A, B). Various ALDH isoforms have been shown to be regulated by e.g. tumour suppressor genes, oncogenes and microRNAs, however a well-documented functional role is linked with the retinoic acid (RA) pathway resulting in transcriptional activation of a number of genes important in cell differentiation (C). High ALDH expression is frequently used as an endogenous marker that in combination with cell surface markers can be used to isolate CSCs (D). More research is required to understand how ALDH activity may contribute to signaling pathways, maintenance of CSCs and contribute to tumour aggresiveness (D, E)