672 Dual role of the anaphase promoting complex/cyclosome in regulating stemness and differentiation in human primary keratinocytes

Abstract

Cdc20 and Cdh1 activate the Anaphase Promoting Complex/Cyclosome (APC/C), a master cell cycle regulator. Although cell cycle modifications occur during differentiation of stem cells, a role for the APC/C on stem cell fate has not been established in embryonic or adult human tissues. We found that differentiated human primary keratinocytes (HPKs) from the skin (paraclones) express extremely low levels of Cdc20 compared to HPK 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 is a cause rather than a consequence of terminal differentiation. By contrast, Cdh1 silencing induced the opposite cellular phenotype, which was characterised by an increase in stemness, cellular proliferation and loss of differentiation markers. These data pinpoint the APC/C as a key regulator of adult stem cell fate. They also demonstrate the critical and opposing roles of APC/CCdc20 and APC/CCdh1 in controlling the balance between HPK proliferation and differentiation, and therefore in regulating skin homeostasis.