BMAL1 and CLOCK proteins in regulating UVB-induced apoptosis and DNA damage responses in human keratinocytes

Area of Science:

• Chronobiology
• Dermatology
• Molecular Biology

Background:

• Circadian rhythms influence numerous biological processes, including skin responses to ultraviolet radiation (UVR).
• Core clock proteins, such as BMAL1 and CLOCK, are known to regulate UVR-induced apoptosis and DNA damage responses in mouse skin.
• The specific roles of these clock proteins in human keratinocytes (HKCs) following UVB exposure remain to be fully elucidated.

Purpose of the Study:

• To investigate the function of circadian clock proteins, specifically BMAL1 and CLOCK, in regulating UVB responses in human keratinocytes.
• To determine the impact of BMAL1 and CLOCK depletion on UVB-induced DNA damage checkpoints, apoptosis, and cell cycle regulation in HKCs.

Main Methods:

• Utilized immortalized HaCat HKCs and primary HKCs.
• Assessed the effects of low-dose UVB irradiation (5 mJ/cm²) on gene expression of BMAL1 and CLOCK.
• Employed gene depletion techniques (siRNA) for BMAL1 and CLOCK.
• Analyzed DNA damage response pathways (Rad3-related protein kinases-checkpoint kinase 1-p53), apoptosis, DNA damage markers (γ-H2AX), cell cycle inhibitors (p21), and keratinocyte differentiation.

Main Results:

• UVB altered the mRNA expression of BMAL1 and CLOCK in HaCat cells.
• Depletion of BMAL1 or CLOCK suppressed UVB-stimulated apoptosis and downregulated UVB-induced γ-H2AX and p21 expression.
• CLOCK depletion reduced UVB-induced p53 protein accumulation.
• Both BMAL1 and CLOCK depletion led to premature keratinocyte differentiation in HKCs.
• Diminished apoptotic responses were observed in primary HKCs lacking BMAL1 or CLOCK post-UVB.

Conclusions:

• Circadian clock proteins BMAL1 and CLOCK play distinct roles in regulating UVB-induced apoptosis and DNA damage responses in human keratinocytes.
• These clock proteins influence UVB responses through different mechanisms in immortalized and primary HKCs.
• Understanding these circadian controls is crucial for addressing UVB-related skin aging and photocarcinogenesis.