Abstract
BackgroundRepeated exposures to UVB of human keratinocytes lacking functional p16INK-4a and able to differentiate induce an alternative state of differentiation rather than stress-induced premature senescence.Methodology/Principal FindingsA 2D-DIGE proteomic profiling of this alternative state of differentiation was performed herein at various times after the exposures to UVB. Sixty-nine differentially abundant protein species were identified by mass spectrometry, many of which are involved in keratinocyte differentiation and survival. Among these protein species was TRIpartite Motif Protein 29 (TRIM29). Increased abundance of TRIM29 following UVB exposures was validated by Western blot using specific antibody and was also further analysed by immunochemistry and by RT-PCR. TRIM29 was found very abundant in keratinocytes and reconstructed epidermis. Knocking down the expression of TRIM29 by short-hairpin RNA interference decreased the viability of keratinocytes after UVB exposure. The abundance of involucrin mRNA, a marker of late differentiation, increased concomitantly. In TRIM29-knocked down reconstructed epidermis, the presence of picnotic cells revealed cell injury. Increased abundance of TRIM29 was also observed upon exposure to DNA damaging agents and PKC activation. The UVB-induced increase of TRIM29 abundance was dependent on a PKC signaling pathway, likely PKCδ.Conclusions/SignificanceThese findings suggest that TRIM29 allows keratinocytes to enter a protective alternative differentiation process rather than die massively after stress.
Highlights
Keratinocytes proliferate in the basal layer of the epidermis before moving upwards in the suprabasal layers through a differentiation program that culminates in fully differentiated dead cells of the cornified layer representing a protective barrier [1]
Eight exposures to 300 mJ/cm2 UVB doses inhibited cell proliferation without any sign of lethality when compared to keratinocytes analysed before any exposure to UVB
Similar dose-dependent profiles of cell death were observed in N-hTERT and primary keratinocytes
Summary
Keratinocytes proliferate in the basal layer of the epidermis before moving upwards in the suprabasal layers through a differentiation program that culminates in fully differentiated dead cells of the cornified layer representing a protective barrier [1]. DNA is the major chromophore for UVB, explaining their high mutagenicity [2,3]. UVB interact with cellular chromophores and photosensitizers, resulting in the generation of reactive oxygen species that cause oxidative damage and activate cellular signaling pathways related to growth, differentiation, senescence, connective tissue degradation and inflammation [3,4]. Repeated exposures to UV can lead to epidermal malignancies [2]. Repeated exposures to UVB of human keratinocytes lacking functional p16INK-4a and able to differentiate induce an alternative state of differentiation rather than stress-induced premature senescence
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