Dual Role of the Anaphase Promoting Complex/Cyclosome in Regulating Stemness and Differentiation in Human Primary Keratinocytes.

Cdc20 and Cdh1 activate the anaphase-promoting complex/cyclosome, a master cell cycle regulator. Although cell cycle modifications occur during differentiation of stem cells, a role for the anaphase-promoting complex/cyclosome on stem cell fate has not been established in embryonic or adult human tissues. We found that differentiated human primary keratinocytes from the skin express extremely low levels of Cdc20 compared with human primary keratinocyte stem cells (holoclones). In agreement with this, staining of human skin biopsies showed that Cdc20 is expressed in occasional cells from the basal and epibasal layers of the epidermis and is absent from the differentiated layers. Conversely, Cdh1 is preferentially expressed in differentiated cells. Interestingly, partial silencing of Cdc20 enhanced differentiation, indicating that loss of Cdc20 might be a cause rather than a consequence of terminal differentiation. By contrast, Cdh1 silencing induced the opposite cellular phenotype, which was characterized by an increase in stemness, cellular proliferation, and loss of differentiation markers. These data pinpoint the anaphase-promoting complex/cyclosome as a key regulator of adult stem cell fate. They also demonstrate the critical and opposing roles of Cdc20 and Cdh1 in controlling the balance between human primary keratinocyte proliferation and differentiation, and therefore in regulating skin homeostasis.