The role of E-cadherin loss in transgenic mouse skin carcinogenesis

Zaweia, Rema (2025) The role of E-cadherin loss in transgenic mouse skin carcinogenesis. PhD thesis, University of Glasgow.

Abstract

The purpose of this study is to examine the role of E-cadherin in cell-cell adhesion failure and altered signalling within a transgenic mouse skin carcinogenesis model that models human carcinogenesis. The main aim is to understand how the loss of E-cadherin collaborates with the activation of ras and fos oncogenes, along with PTEN loss, in driving the transformation of benign tumours into malignancies and their subsequent progression to aggressive squamous cell carcinomas (SCC). These are considered the most critical events in the progression of carcinogenesis from a patient’s perspective.

E-cadherin is a highly conserved adhesion molecule essential for maintaining epithelial integrity through its interaction with β-catenin. Loss of E-cadherin disrupts adhesion, promoting invasion and progression. Although many studies support this view, emerging evidence, such as that from Padmanaban et al. (2019), suggests that E-cadherin may also be necessary for certain types of invasion, emphasising the complexity of its role and the importance of tissue context in carcinogenesis.

To address these challenges, the approach involved a well-characterised transgenic mouse skin carcinogenesis model that expresses a combination of ras and fos activation, via a modified human keratin 1 vector (HK1.ras; HK1.fos), ensuring that ras and fos oncogenes are exclusively expressed in the proliferative basal layers of the epidermis and in malignant tumours. This results in hyperplasia and papillomatogenesis but shows no evidence of spontaneous malignant conversion. The stability of this phenotype makes it ideal for investigating the roles of oncogene cooperation in the development of benign tumours and their progression to malignancy. To explore the specific roles of E-cadherin in skin carcinogenesis models, the RU486-inducible cre/lox method was utilised to exclusively knock out E-cadherin via exon 6-10 ablation (K14creP/Δ-6-10Ecadflx).

These transgenic mice expressed activated ras and/or fos oncogenes (HK1.ras, HK1.fos). Inducible mutation of PTEN-regulated AKT activation via exon 5 ablation (K14creP/Δ5PTENflx) was also incorporated into this model by using the RU486-inducible cre/loxP method. Previous analysis of endogenous E-cadherin expression in the HK1.ras.fos-K14creP Δ5PTENflx/flx transgenic skin mouse model showed a reduction in membranous E-cadherin expression at the invasive front of well-differentiated SCC (wdSCC) following p53 loss.

In bi-genic HK1.ras-K14creP/Δ6-10Ecadflx mice, the synergistic effect between E-cadherin loss and wound-promotion sensitive (ear tagging) HK1.ras1205 line was observed to induce malignant conversion. The results showed that reduced functional E-cadherin in HK1.ras-K14creP/Δ6-10Ecadflx/het mice led to hyperplasia and papillomas similar to HK1.ras mice, but with intercellular gaps in the basal keratinocytes and carcinoma in situ. Functional E cadherin ablation in HK1.ras-K14creP/Δ6-10Ecadflx/flx initially caused malignant transformation into well-differentiated squamous cell carcinoma (wdSCC) that invaded in a grouped, collective manner but rapidly progressed into poorly differentiated squamous cell carcinoma (pdSCC), consistent with cell-cell adhesion failures and invasion by the more aggressive individual mode. These tumours correlated with cell-cell adhesion failure associated with p53 loss and nuclear β-catenin expression.

The heterozygous HK1.fos-K14creP/Δ5PTENflx/flx/Δ6-10Ecadflx/het mice develop keratoacanthomas (KAs) similar to HK1.fos-K14creP/Δ5PTENflx/flxmice, exhibiting characteristic micro-cysts that indicate accelerated and premature differentiation. No malignant transformation was observed because of strong membranous basal E-cadherin and basal membranous β-catenin expression, which triggers nuclear p53 expression. However, functional ablation of E-cadherin in HK1.fos-K14creP/Δ5PTENflx/flx/Δ6-10Ecadflx/flx KAs led to malignant conversion into invasive wdSCC. The HK1.fos-K14creP/Δ5PTENflx/flx/Δ6-10Ecadflx/flx mice initially develop KA-like tumours, with minimal effects on early pre-KA hyperplasia stages, similar to observations in HK1.ras mice. Over time, these tumours progress to invasive wdSCC with scattered areas of SCC. This progression ultimately results in the development of aggressive SCC. The gradual loss of p53, combined with a decrease in membranous and an increase in nuclear β-catenin expression, along with the progressive loss of Δ6-10E-cadherin, indicates a shift towards a more advanced SCC phenotype. These molecular changes suggest an increased potential for invasion and highlight the crucial role of these factors in driving malignant transformation and progression.

The HK1.ras1276.fos-K14creP/Δ5PTENflx/flx/Δ6-10Ecadflx model was also utilised, and in this model, the tumours were independent of wound promotion. This was evident as tumours developed in both TGE and NTGE of RU486-treated HK1.ras1276.fos-K14creP/Δ5PTENflx/flx/Δ6-10Ecadflx mice. The emergence of these tumours demonstrated a synergic interaction, resulting in a rapid malignant conversion and progression to SCC/pdSCC soon after p53 loss, consistent with cell-cell adhesion failure and deregulated signalling to β-catenin. Interestingly, these tumours were associated with loss of β-catenin, suggesting a critical link between E-cadherin loss and the dysregulation of β-catenin signalling. The loss of E-cadherin, a key component of adherens junctions, might disrupt the normal Wnt/β-catenin signalling dynamics, particularly affecting its nuclear translocation. This disruption may lead to inadequate accumulation of nuclear β-catenin, promoting its degradation rather than facilitating its role in gene transcription regulation. The consequent reduction in β-catenin expression could further exacerbate the loss of cell-cell adhesion, thereby accelerating the malignant progression of these tumour models.

In summary, this study demonstrates that E-cadherin loss has a minimal impact on papillomatogenesis but promotes hyperplasia and, in cooperation with Ras activation and endogenous p53 loss, facilitates malignant conversion. Furthermore, in the context of ras and fos activation with PTEN loss, E-cadherin loss accelerated malignant progression, consistent with disruption of cell-cell adhesion. Altogether, these models recapitulate key features of human SCC progression and provide insight into the molecular mechanisms linking E-cadherin loss, β-catenin dysregulation, and tumour invasiveness. Understanding these interactions not only deepens the comprehension of SCC pathogenesis but also highlights potential therapeutic targets aimed at restoring adhesion or modulating Wnt/β-catenin signalling to delay or prevent malignant progression.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QR Microbiology; R Medicine > RC Internal medicine > RC0254 Neoplasms. Tumors. Oncology (including Cancer)
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
• Supervisor's Name: Greenhalgh, Dr. David and Quinn, Dr. Jean
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85493
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 02 Oct 2025 15:25
• Last Modified: 02 Oct 2025 15:28
• Thesis DOI: 10.5525/gla.thesis.85493
• URI: https://theses.gla.ac.uk/id/eprint/85493