Inducible MDM2 Ablation Increases p53 Expression to Block Papillomatogenesis in HK1.ras Transgenic Mice

Gutierrez Crispini, A., Slosarska, A. and Greenhalgh, D. (2023) Inducible MDM2 Ablation Increases p53 Expression to Block Papillomatogenesis in HK1.ras Transgenic Mice. British Journal of Dermatology 189(1):e16. Meeting Abstract: British Society for Investigative Dermatology (BSID) Annual Meeting, Technology & Innovation Centre, University of Strathclyde, Glasgow, Scotland, 20–21 March 2023. (doi: 10.1093/bjd/ljad174.027)

Abstract

Previously, p53 loss was a consistent theme in skin carcinogenesis driven by activated rasHa/fos expression (HK1.ras/fos) and ablation of phosphatase and tensin homolog (PTEN)-mediated Akt regulation (K14.creP/Δ5PTENflx), leading to well-differentiated squamous cell carcinoma. Given that MDM2 is a ubiquitin ligase that targets p53 for degradation, the potential efficacy of MDM2 functional knockout to protect p53 levels and thus inhibit tumour formation was investigated. Initial experiments investigated the inhibition of benign papilloma formation in HK1.ras mice as analysis of endogenous MDM2 status showed that activated p-MDM2166 activity was confined to suprabasal layers, resulting in strong nuclear p53 expression in basal layers that inhibited conversion. Yet, earlier hyperplasia expressed only sporadic p53/MDM2, suggesting that should MDM2 activity be inhibited, increased p53 in hyperplasia may inhibit papilloma formation. Therefore, loss of MDM2-mediated p53 degradation was investigated via inducible ablation of MDM2 exons 5 and 6, which bind p53 and chaperone for ubiquitination, employing K14-driven Cre/lox-P and treatment with topical RU486 (K14cre-Δ5/6MDM2flx/flx). In control, RU486-treated K14cre-Δ5/6MDM2flx/flx littermates, surprisingly few effects were observed, as normal epidermis expressed only sporadic p53/MDM2 as keratinocytes divided. Similarly, early HK1.ras hyperplasia displayed sporadic p53/MDM2 coexpression, suggesting an epidermis was relatively tolerant of Ras-mediated proliferation, where p53 overexpression risks problems of barrier maintenance due to excess apoptosis. With time, HK1.ras papillomas increased nuclear basal layer p53; p-MDM2166 also increased but remained suprabasal – alongside p-Akt1473 – possibly geared to maintain barrier functions from potential p53-mediated apoptosis. Conversely, in RU486-treated HK1.ras-Δ5/6MDM2flx/flx littermates, while hyperplasia histotype appeared unaffected, expression analysis found strong, elevated p53 expression in all compartments, consistent with loss of MDM2 inhibition. Moreover, this level of basal layer p53 in early hyperplasia apparently blocked papilloma formation and fed back to inhibit p-Akt1, whereas heterozygous MDM2 HK1.ras-Δ5/6MDM2flx/wt littermates exhibited a papillomatogenesis identical to wild-type HK1.ras littermates, with suprabasal p-MDM2166 and p-Akt1473. These findings suggest that MDM2 inhibition can inhibit benign tumour formation via maintaining p53 levels; however, with time (> 20 weeks), small papillomas did appear, showing that this inhibition can be circumvented.

• Item Type: Conference or Workshop Item
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Greenhalgh, Dr David and Gutierrez Crispini, Miss Ana
• Authors: Gutierrez Crispini, A., Slosarska, A., and Greenhalgh, D.
• College/School: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• ISSN: 0007-0963