A role for miR-34 in colon cancer stem cell homeostasis

In recent years, cancer stem cells have taken center stage in studies involving cancer origins and metastasis (1). Unlike somatic cells, which often follow symmetric cell division yielding two identical daughter cells, stem cells often undergo asymmetric division leading to non-identical cell types such as progenitor cells of various tissue origins during embryogenesis (2). This unique asymmetric division feature helps stem cells maintain homeostasis, with a constant number of daughter stem cells and differentiated cells. Even though stem cells undergo asymmetric division in most cases, they do undergo symmetric division in some tissue contexts such as Lgr5⁺ crypt base columnar cells in intestine to stabilize the number of cells (3). Cancer stem cells, which are also known as tumor initiating cells, behave in a similar manner to stem cells and undergo asymmetric division in response to loss of tumor suppressors. Now a recent paper reveals an intriguing connection between colon cancer stem cells and a non-coding RNA called miR-34 (4).