Towards development of new strategies for inhibiting skin cancer progression

Abstract

Skin cancers are the most common human malignancies, with rising incidence despite public health warnings into the dangers of excessive UV exposure. Skin cancers are divided in two major types: (i) keratinocyte or non-melanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), and (ii) melanoma.

Melanoma represents less than 5% of all skin cancers, however it has the highest mortality rates. Several factors are known to induce melanoma progression, such as the overexpression of serine protease inhibitors (serpins). Vaspin (also known as visceral adipose tissue-derived serpin; serpinA12) is the most recently identified serpin. Vaspin is expressed in the skin epidermis, its expression is dysregulated in psoriatic skin, but its potential role in melanoma has not been explored. In the current work, I investigated the expression and biological role of vaspin in melanoma. I observed that vaspin is overexpressed in melanoma cells compared to benign nevi or melanocytes. Additionally, I found that vaspin does not regulate proliferation, survival or migration, however it induces cell invasion. I further showed that vaspin-induced invasion is dependent on matrix metalloproteinases (MMPs).

Cutaneous SCC (cSCC) is the second most common skin cancer, comprising 20% of NMSC. cSCC arise from the aberrant proliferation of keratinocytes, although this process is also dysregulated in other skin diseases. Wingless-Type MMTV Integration Site Family (Wnt)/β-catenin signalling is upregulated in many cancers and is important for keratinocyte proliferation. Gene expression analysis has indicated that Wnt/β-catenin signalling is altered in cSCC. In the second part of this work, I investigated the Wnt/β-catenin signalling pathway as a possible driver of cSCC development. I demonstrated that β-catenin is expressed and active in human cSCC cell lines. However, stimulation with recombinant Wnt member 3 (Wnt3a) did not increase the levels of β-catenin in cSCC cells. Knockdown of β-catenin led to reduction in cSCC proliferation, without affecting cell viability and surprisingly, without affecting the classical β-catenin target genes. Two pharmacological inhibitors of the β-catenin interaction with TCF or LEF transcription factors, BC21 and PRI-724, respectively, reduced cSCC cell viability in a dose-dependent manner. Surprisingly, this effect was preserved in cells, in which β-catenin was knocked down, indicating that the observed reduction of cell viability by the compounds was independent of β-catenin. Subsequently, I found that BC21 and PRI-724 are reducing cell viability by altering the expression of cell cycle regulators, thereby inducing cell cycle arrest.

In summary, I describe for the first time the biological effect of vaspin in the context of melanoma. Additionally, I describe the role of β-catenin signalling in cSCC cells and the effect of BC21 and PRI-724 inhibitors.

Date of Award	2019
Original language	English
Sponsors	British Skin Foundation
Supervisor	Albena Dinkova-Kostova (Supervisor), Charlotte Proby (Supervisor), Victoria Sherwood (Supervisor) & Christopher Morris (Supervisor)