The DNA damage response links human squamous proliferation with differentiation.

Area of Science:

• Cell Biology
• Developmental Biology
• Cancer Biology

Background:

• Understanding cell multiplication and differentiation is key to tissue development and homeostasis.
• Epidermoid epithelia are prone to mutations and cancer due to continuous mutagen exposure.
• Mechanisms linking rapid proliferation to terminal differentiation remain unclear.

Purpose of the Study:

• To investigate the role of DNA damage response (DDR) pathways in controlling keratinocyte proliferation and differentiation.
• To determine if DDR signaling influences the epidermoid phenotype independently of DNA damage.

Main Methods:

• Over-activated or inhibited endogenous DDR pathways using TopBP1, shRNAs, and chemical inhibitors (ATR, ATM, DNA-PK).
• Assessed the impact of DDR modulation on keratinocyte differentiation and proliferation.
• Investigated the role of H2AX, a DDR target, in maintaining the epidermoid phenotype.

Main Results:

• DDR signaling controls keratinocyte differentiation in proliferating cells, irrespective of actual DNA damage.
• The DDR limits keratinocyte proliferation when faced with hyperproliferative stimuli.
• Knocking down H2AX disrupts the epidermoid phenotype, indicating DDR's role.

Conclusions:

• The DNA damage response (DDR) is essential for balancing proliferation and differentiation in keratinocytes.
• DDR signaling is integral to the squamous differentiation program.
• A homeostatic model is proposed where cell-autonomous mechanisms continuously clear genetic damage.