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Discordant transforming growth factor beta 1 RNA and protein localization during chemical carcinogenesis of the skin
D J Fowlis1, K C Flanders, E Duffie
1Duncan Guthrie Institute of Medical Genetics, University of Glasgow, Yorkhill Hospitals, United Kingdom.
Abstract:
Transforming growth factor beta (TGF-beta) inhibits proliferation of normal keratinocytes, and this response is retained, to variable extents, in benign tumors of the skin (S. Haddow, D. J. Fowlis, K. Parkinson, R. J. Akhurst, and A. Balmain, Oncogene, 6: 1465-1470, 1991). To investigate the profile of TGF-beta biosynthesis during various stages of chemical carcinogenesis of the skin, we used a combination of ribonuclease protection assay, in situ hybridization with gene-specific probes for TGF-beta 1, -beta 2, and -beta 3, and immunohistochemistry with isoform-specific antibodies against TGF-beta 1. Following 12-O-tetradecanoylphorbol-13-acetate treatment of adult mouse skin, there was a rapid induction of TGF-beta 1 protein. Intracellular TGF-beta 1 protein was localized to suprabasal keratinocytes, and the extracellular form was localized predominantly to the dermis. Despite ubiquitous induction of TGF-beta 1 protein by 12-O-tetradecanoylphorbol-13-acetate in various mouse strains, we noted strain-specific differences in the quantitative induction of TGF-beta 1 RNA. Papillomas and carcinomas induced in vivo had elevated levels of TGF-beta 1 RNA within the basal keratinocyte compartment but did not contain significant levels of TGF-beta 1 protein within the tumor. We postulate that the tumor evades TGF-beta 1-controlled negative growth regulation by altered translational and/or posttranslational processing mechanisms of this growth factor. Levels of TGF-beta 2 and -beta 3 RNA were not elevated at any stage of chemical carcinogenesis of the skin.
Insights
Transforming growth factor beta 1 (TGF-beta 1) protein is rapidly induced in mouse skin during chemical carcinogenesis. Tumors show elevated TGF-beta 1 RNA but lack protein, suggesting altered processing evades growth regulation.
Area of Science:
- Dermatology
- Molecular Biology
- Oncology
Background:
- Transforming growth factor beta (TGF-beta) normally inhibits keratinocyte proliferation.
- This inhibitory response is often retained in benign skin tumors.
- Understanding TGF-beta biosynthesis during skin carcinogenesis is crucial.
Purpose of the Study:
- To investigate TGF-beta (isoforms 1, 2, and 3) biosynthesis during chemical skin carcinogenesis.
- To analyze TGF-beta 1 protein and RNA localization and expression levels.
- To explore potential mechanisms of tumor evasion of TGF-beta-mediated growth inhibition.
Main Methods:
- Ribonuclease protection assay for RNA analysis.
- In situ hybridization with gene-specific probes for TGF-beta 1, -beta 2, and -beta 3.
- Immunohistochemistry with isoform-specific antibodies for TGF-beta 1 protein.
Main Results:
- 12-O-tetradecanoylphorbol-13-acetate treatment rapidly induced TGF-beta 1 protein in suprabasal keratinocytes and dermis.
- Strain-specific differences in TGF-beta 1 RNA induction were observed.
- Papillomas and carcinomas showed elevated TGF-beta 1 RNA in basal keratinocytes but not significant protein within the tumor.
- TGF-beta 2 and -beta 3 RNA levels remained unchanged during carcinogenesis.
Conclusions:
- Tumors may evade TGF-beta 1 growth regulation through altered translational and/or posttranslational processing.
- TGF-beta 1 plays a complex role in skin carcinogenesis, with potential dysregulation in tumors.
- TGF-beta 2 and -beta 3 are not implicated in this model of skin carcinogenesis.