Investigation of the functions of Matrix Metalloproteinase-8 (MMP-8) in Mammary Carcinoma Cells

Abstract Breast cancer is the most common cancer in the UK today, with incidence rates rising steadily. Prognosis is improving but patients with metastatic disease only have a 15% chance of surviving 5 years beyond prognosis. Therefore, factors influencing the metastatic spread of breast cancer require better understanding. The matrix metalloproteinases (MMPs) are a family of proteases thought to promote metastasis due to their matrix degradation capabilities. MMP-8 however has been discovered to be anti-tumourigenic in many cancers, and anti-metastatic in breast cancer. This occurs through unknown mechanisms, so this work sought to gain further insight into the functional effects of MMP-8. In the literature it has been suggested that MMP-8 is tumour protective through its role in regulating innate immune responses and preventing chronic inflammation. This occurs through activational cleavage of a pro-inflammatory chemokine, Interleukin-8 (IL-8). Using an in vitro over-expression model it is shown in this thesis that MMP-8 reduced 2D random migration and scratch wound closure. It also increased cell adhesion and reduced colony formation and prevented primary tumour growth in mice. These data indicate an anti-tumourigenic role for MMP-8. Biochemically, MMP-8 induced expression of IL-8 in mammary carcinoma cells, and also the expression of a pro-inflammatory cytokine IL-6, dependent on its catalytic activity. This required NFĸB signalling and IL-6 also required Protease Activated receptor-2. This occurred following transient expression of MMP-8, and also in rare stably transfected clones that expressed MMP-8 long-term. However, wild-type MMP-8 was not tolerated by breast cancer cells and was epigenetically silenced, potentially as a mechanism to overcome growth inhibitory effects exerted by wild-type MMP-8. In these rare “long-term” MMP-8 expressing cells phenotypic alterations occurred, including elevated IL-6 and IL- 8 expression independent of MMP-8, and a self-reinforcing loop between MMP- 8, IL-6 and IL-8. 3 This pathway may contribute to the anti-tumourigenic and metastasis suppressive effects of MMP-8, or it may represent a cellular response to overcome the anti-tumour actions of the protease.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2013

Author dc:creator

• Thirkettle, Sally

Language dc:language

en