Tissue-specific downregulation of type VII collagen gene (COL7A1) transcription in cultured epidermal keratinocytes by ultraviolet A radiation (UVA) and UVA-inducible cytokines, with special reference to cutaneous photoaging

Abstract

Background

Type VII collagen is the major component of anchoring fibrils, which stabilize the attachment of the basement membrane zone to the dermis. Expression of type VII collagen in epidermal keratinocytes and formation of anchoring fibrils in the basement membrane zone are reduced in photoaged skin, suggesting their involvement in the pathophysiology of photoaging.

Objective

To investigate the effects of ultraviolet A radiation (UVA) and UVA-inducible cytokines, tumor necrosis factor (TNF)-α and interleukin (IL)-1β on type VII collagen gene (COL7A1) transcription in epidermal keratinocytes.

Methods

Cultured epidermal and HaCaT keratinocytes were transiently/stably transfected with plasmid constructs containing sequential 5′-end deletions of the COL7A1 promoter, linked to luciferase or the GFP gene. Twenty-four hours after treatment with either UVA, TNF-α or IL-1β, luciferase activity and GFP expression of TNF-α and IL-1β were detected by luminometer or fluorescence microscopy, respectively.

Results

UVA, TNF-α and IL-1β all decreased COL7A1 promoter activity in cultured epidermal keratinocytes as well as GFP expression in HaCaT keratinocytes. Deletion analysis revealed that the UVA- and cytokine-responsive region of COL7A1 lies between nucleotides −524 and −22.

Conclusion

UVA, TNF-α and IL-1β inhibit COL7A1 expression at the transcriptional level by acting on nucleotides −524 to −22 of the promoter region. These results suggest that UVA-induced downregulation of COL7A1 transcription in epidermal keratinocytes diminishes anchoring fibrils formation, resulting in skin fragility. Additional external factors including physical forces and UVB radiation in the sun-exposed areas may further promote deep wrinkle formation.