rClca2 is associated with epidermal differentiation and is strongly downregulated by ultraviolet radiation.
BACKGROUND
Excessive skin exposure to solar radiation damages proteins and DNA, ultimately leading to skin ageing and cancers.


OBJECTIVE
To identify new ultraviolet B (UVB) target genes to understand the mechanisms behind the detrimental effects of UVB.


METHODS
Organotypic, stratified cultures of rat keratinocytes were exposed to UVB and analysed using a genome-wide expression array, quantitative real-time polymerase chain reaction and histology. The most downregulated gene, rClca2, was further characterized in rat keratinocytes and mouse skin models.


RESULTS
A single, 30 mJ cm(-2) dose of broadband UVB proved effective in the organotypic epidermal culture. The expression of 627 genes was changed 24 h postirradiation. In silico analysis of the data indicated activation of DNA repair, metabolism, cell cycle control and amino acid metabolism, but only limited inflammation under these conditions. We selected for further investigation the most downregulated gene, rClca2, previously suggested to regulate keratinocyte differentiation and adhesion, and found that UVB caused a long-lasting downregulation in its expression. Both the rClca2 full-length isoform (expressed in the differentiating cells) and the truncated isoform (expressed in the basal layers) were reduced by UVB. Immunohistochemistry of mouse skin samples with isoform-specific antibodies showed a similar, epidermal differentiation-related pattern. In mouse specimens exposed to chronic ultraviolet radiation (UVR) the staining intensities were reduced and the differentiation-related isoform was disturbed in the hyperplastic and carcinomatous areas induced by UVR.


CONCLUSIONS
The data show that rClca2 is a novel UVB target gene and suggest that it might play a role in epidermal differentiation and UV-dependent skin malignancies.
Institute of Biomedicine, University of Eastern Finland, P.O. Box 1627, FI-70211, Kuopio, Finland.
G
G
Bart
L
L
Hämäläinen
L
L
Rauhala
P
P
Salonen
M
M
Kokkonen
T W
TW
Dunlop
P
P
Pehkonen
T
T
Kumlin
M I
MI
Tammi
S
S
Pasonen-Seppänen
R H
RH
Tammi
D000818:Animals; D002454:Cell Differentiation / Q000528:radiation effects; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D015536:Down-Regulation; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism / Q000528:radiation effects*; D055106:Genome-Wide Association Study; D006801:Humans; D015603:Keratinocytes / Q000528:radiation effects; D051379:Mice; D012313:RNA / Q000378:metabolism; D051381:Rats; D014157:Transcription Factors / Q000528:radiation effects; D014466:Ultraviolet Rays
C574515:CLCA2 protein, rat; D018118:Chloride Channels; C492299:Clca2 protein, mouse; D014157:Transcription Factors; D012313:RNA