During apoptosis, caspase cleavage of ROCK1 removes an auto-inhibitory region yielding a constitutively active kinase fragment. This results in phosphorylation of downstream targets that promote contractile force generation leading to cell shrinkage, membrane blebbing and nuclear disintegration. To address fundamental questions regarding the purpose of ROCK1 cleavage and consequent apoptotic morphological features, a novel mouse model was generated that carries a single amino acid substitution in the caspase cleavage site (D1113A) that converts ROCK1 to a caspase-resistant non-cleavable (ROCK1nc) form. When apoptosis was induced in ROCK1nc cells, morphological features were significantly impaired, although the biochemical apoptotic program itself was unaffected. To understand the biological role of apoptotic morphological features in the maintenance of tissue homeostasis, acute liver damage was induced in mice with the liver-selective genotoxic compound diethylnitrosamine (DEN). Following DEN treatment, there were increased TUNEL-positive apoptotic cells and increased neutrophil infiltration in ROCK1nc mice. Histologically, ROCK1nc livers were more damaged, paralleled by higher serum alanine transaminase levels. We hypothesized that uncleared apoptotic debris undergoing secondary necrosis may release damage associated molecular patterns (DAMPs) that may aggravate liver damage by recruiting neutrophils to the liver. Indeed, inhibiting the cytokine activities of HMGB1 reduced neutrophil infiltration as well as liver damage in ROCK1nc mice. Furthermore, to determine whether defects in tissue damage responses in ROCK1nc mice would affect tumour development, the ROCK1nc mutation was introduced into two different cancer models, specifically the DEN-induced hepatocellular carcinoma and Eµ-myc lymphoma mouse models. Defective caspase cleavage of ROCK1 promoted increased infiltration of CD8+ T-cells in ROCK1nc liver tumours and had a protective effect against tumour development in both tumour models. Taken together, our results indicate that apoptotic morphological features suppress inflammation which helps to maintain tissue homeostasis but enables tumourigenesis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:676593 |
| Date | January 2015 |
| Creators | Julian, Linda |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/6998/ |
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