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RNA fingerprinting displays UVB-specific disruption of transcriptional control in human melanocytes
Abstract:
In mammalian cells, UV induces a limited set of early transcribed genes, which overlaps with the set of genes induced by tumor promoting drugs such as 12-O-tetradecanoyl phorbol-13-acetate (TPA). Among these are genes for transcription factors, the activation of which leads to complex secondary changes in expression of multiple target genes. How these delayed pleiotropic UV effects on transcription may contribute to initiation of melanoma skin cancer is poorly understood. We analyzed changes in the relative abundances of 1900 transcripts in newborn human melanocytes 8 h after treatment with UVB, TPA, and cycloheximide in all combinations, using RNA arbitrarily primed PCR for differential display. The relative abundances of 205 transcripts (11% of all transcripts surveyed) were altered by one or more of the treatment combinations. Fourteen of the 77 genes up-regulated by TPA were also up-regulated by UVB, but 60 of the TPA up-regulated genes were down-regulated by UVB, indicating both intersecting and independent signal transduction pathways for UVB and TPA. A number of UVB and TPA target genes were identified by cDNA cloning. Consistent with UVB induction of a partly transformed phenotype in mammalian cells, UVB antagonized the TPA-inducible expression of tumor-suppressive tropomyosin 3 mRNA. In addition, UVB may impair mitochondrial functioning and induce oxidative stress by strong down-regulation of mitochondrial transcription. Finally, increased expression of the dihydropteridine reductase gene, a major regulator of the cellular tetrahydrobiopterin pool, was linked to the UV pathway.
Insights
UV radiation and tumor promoters like TPA affect gene expression in human melanocytes, influencing pathways relevant to melanoma development. UVB and TPA share some targets but also have independent effects on gene regulation.
Area of Science:
- Molecular Biology
- Dermatology
- Cancer Research
Background:
- Ultraviolet (UV) radiation induces early transcribed genes in mammalian cells, some overlapping with those affected by tumor promoters like 12-O-tetradecanoyl phorbol-13-acetate (TPA).
- The delayed, complex effects of UV on gene expression and their role in melanoma initiation are not well understood.
- Transcription factors activated by UV contribute to secondary changes in gene expression.
Purpose of the Study:
- To analyze changes in transcript abundance in human melanocytes following UVB, TPA, and cycloheximide treatments.
- To identify UV and TPA target genes and understand their intersecting and independent signaling pathways.
- To investigate the contribution of UV-induced transcriptional changes to melanoma development.
Main Methods:
- Differential display using RNA arbitrarily primed PCR was employed.
- Newborn human melanocytes were treated with UVB, TPA, and cycloheximide in combination.
- Changes in the relative abundances of 1900 transcripts were analyzed 8 hours post-treatment.
- cDNA cloning was used to identify specific target genes.
Main Results:
- The relative abundances of 205 transcripts (11%) were altered by the treatments.
- UVB and TPA exhibited both overlapping and distinct effects on gene expression.
- UVB down-regulated tropomyosin 3 mRNA, antagonizing TPA's effect, and strongly down-regulated mitochondrial transcription.
- Increased expression of dihydropteridine reductase gene was linked to the UV pathway.
Conclusions:
- UVB and TPA modulate gene expression through both shared and independent signaling pathways.
- UVB may impair mitochondrial function and induce oxidative stress.
- UVB's effects on gene expression, including antagonism of tumor suppressor genes, may contribute to melanoma initiation.