Highlights
- •Phagocytosis in keratinocytes is enhanced by UVB and by oxidative stress.
- •Oxidative stress causes keratinocytes to accumulate in S-phase of the cell cycle.
- •Phagocytosis is enhanced by synchronizing keratinocytes to S-phase.
- •Phagocytosis in S-phase keratinocytes is abolished by a calcium ion chelator.
Abstract
Background
Phagocytosis is an essential process that maintains cellular homeostasis. In the epidermis,
the phagocytosis of melanosomes into keratinocytes is important to protect their DNA
against damage from ultraviolet B (UVB) radiation. Furthermore, it is considered that
UVB activates the phagocytosis by keratinocytes but the detailed mechanism involved
is not fully understood.
Objective
To clarify the mechanism of UVB-enhanced phagocytosis in keratinocytes, we investigated
the relationship between the phagocytic ability of keratinocytes and the cell cycle
stage of keratinocytes.
Methods
The phagocytic ability of keratinocytes was evaluated using the incorporation of fluorescent
beads after exposure to UVB or oxidative stress. S-phase was evaluated by BrdU incorporation
and immunostaining of cyclin D1. Intracellular calcium levels of keratinocytes were
measured using the probe Fluo-4AM.
Results
The phagocytosis of fluorescent beads into keratinocytes was enhanced by UVB and also
by oxidative stress. We found that keratinocytes exposed to UVB or oxidative stress
were at S-phase of the cell cycle. Furthermore, keratinocytes synchronized to S-phase
showed a higher phagocytic ability according to the increased intracellular ROS level.
The UVB-enhanced phagocytosis and entrance into S-phase of keratinocytes was abolished
by ascorbic acid, a typical antioxidant. Keratinocytes synchronized to S-phase and
exposed to UVB or oxidative stress had increased levels of intracellular calcium and
their enhanced phagocytic abilities were diminished by the calcium ion chelator BAPTA-AM.
Conclusion
Taken together, intracellular oxidative stress induced by intracellular calcium influx
mediates the UVB-enhanced phagocytic ability of keratinocytes accumulating at S-phase
of the cell cycle.
Abbreviations:
UVB (ultraviolet B), ROS (reactive oxygen species), MSs (melanosomes), PAR-2 (protease-activated receptor-2), BSO (buthionine sulfoximine), H2O2 (hydrogen peroxide), AA-Na (ascorbic acid sodium salt), BAPTA-AM (12-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester), H2DCFDA (2′7′‐dichlorodihydrofluorescein diacetate), GSH (glutathione), IL-1α (interleukin-1α), NHEKs (normal human epidermal keratinocytes), BSA (bovine serum albumin), CDK (cyclin dependent kinase)Keywords
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Article info
Publication history
Published online: June 10, 2021
Accepted:
June 9,
2021
Received in revised form:
June 8,
2021
Received:
February 21,
2021
Identification
Copyright
© 2021 Japanese Society for Investigative Dermatology. Published by Elsevier B.V. All rights reserved.
