The Aim of the project was to investigate cell senescence in basal cell carcinoma (BCC). Although the concept of oncogene-induced senescence (OIS) was originally confined to cultured cells, it is now well established that this mechanism has an important role in tumour biology. OIS represents a physiological response that restricts the progression of benign tumours into their malignant counterparts e.g. nevi to melanoma or adenoma to adenocarcinoma. Full malignancy is associated with the loss of important tumour suppressor genes including RETINOBLASTOMA and/or TP53. BCC of the skin is the most common skin tumour and is associated with mutational inactivation of the PTCH1 tumour suppressor gene (and less frequently oncogenic activation of SMOOTHENED). Although BCC does not appear to stem from precursor lesions - though mouse models of BCC display areas of basaloid hyperproliferation - and it is relatively stable at the genomic level, we sought to determine if these unique tumours display any characteristics of OIS. Human BCCs were positive for Senescence-associated β-galactosidase (SA-β-gal) activity (pH 6.0) and expressed known markers of senescence including DCR2, DEC1 (SHARP2) as well as the cell cycle inhibitors p15INK4b and p16INK4a. Interestingly, SA-β-gal activity was observed in stromal cells surrounding the tumour islands and this may account for why BCCs are difficult to culture in vitro as senescent cells are known to express increased levels of growth factors, cytokines and ECM proteins. To determine if OIS is associated with Hedgehog signalling in BCC, I employed a novel in vitro model of BCC created through PTCH1 suppression in human immortalised NEB1 keratinocytes. NEB1-shPTCH1 cells are viable and proliferative (albeit more slowly than control NEB1-shCON cells) and do not display SA-β-gal activity but they express higher levels of several senescent markers including DCR2 and p21WAF1. I also investigated senescence in a Mouse model of BCC in which one allele of Ptch1 is mutated and which on x-ray irradiation results in BCC formation. The expression of known markers of senescence including DCR2, DEC1 (SHARP2) as well as the cell cycle inhibitors p15INK4b, p16INK4a and p53 were all with the exception of p21WAF1 detected in these tumours. Together these data suggest that senescence is a characteristic of BCC and may explain why these tumours rarely metastasise.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:667064 |
| Date | January 2012 |
| Creators | Pirzado, Muhammad Suleman |
| Publisher | Queen Mary, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://qmro.qmul.ac.uk/xmlui/handle/123456789/8633 |
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