12 - Other Features Concerning the Analogy “Stem Cells: Primitive Eukaryotes”: ABC Transporters’ Anaerobiosis/Stemness Link

Abstract

The ABC transporters, ancestral membrane ATP- (and calcium-) dependent mechanisms present from prokaryotes to the vertebrates, are among the most conserved functional cellular features throughout evolution. In the vertebrate tissues two types of cells overexpress these molecules responsible for “multidrug resistance phenomenon”: mature cells exhibiting a specific function related to the efflux or influx of molecules through the cell membrane and primitive stem/progenitor cell populations. Overexpression of ABC transporters (mainly ABCG2 and ABCB1) is responsible for the so-called “side population” phenotype. The cells with SP phenotype, capable of rejecting some drugs from an intracellular environment, were initially discovered in cancers, which influenced the terminology of ABC transporters involved in this phenomenon. The overexpression of these transporters is also a hallmark of some anaerobic protists. In view of anaerobic metabolic set-up of stem cells, in this chapter we present the facts, proofs, and cues associating ABC transporters with anaerobiosis in the most primitive eukaryotes and stem cells, and, hence, with the evolutionary prototype and modern stemness phenomenon.