Colon Cancer is one of the most prevalent forms of cancer in Australia, resulting in 15 000 cases and 4000 deaths per year. Late presentation of the disease is associated with poor prognosis and a 5-year survival rate as low as 5%.
Approximately 80% of colon cancers are caused by aberrant activation of the Wnt/β-Catenin pathway. This is primarily a consequence of homozygous loss or inactivation of the tumour suppressor gene APC. However inhibition of the Wnt/β-Catenin pathway is likely to result in on-target toxicity. Interestingly, APC-mutant intestinal epithelium, but not normal epithelium, requires continuous signalling through the gp130-Jak-STAT3 pathway. This suggests that the gp130-Jak-STAT3 pathway can be rate-limiting for the proliferation of the intestinal epithelium in the presence of excessive Wnt/β-Catenin signalling. Pro-inflammatory cytokines Interleukin 6/11 (IL-6/-11) activate the gp130-Jak-STAT3 pathway. Excessive secretion of these cytokines results in increased activity of the Signal Transducer and Activator of Transcription (STAT). Janus Kinases (JAKs) are important upstream tyrosine kinases that phosphorylate STAT3. Therapeutic inhibition of JAKs can limit STAT3 activation and therefore reduce the role it plays in proliferation, survival and invasion.
We have used in vitro techniques to analyse the role JAKs play in colon cancer. Firstly we determined which JAKs are expressed in a panel of colon cancer cell lines and then determined the role they play in STAT3 activation and colony formation using a system of inducible shRNA-mediated downregulation of specific members of the JAK family. In addition we have developed guide RNAs for CRISPR/Cas9 system to knockout members of the JAK family, to investigate the role that these play in colon cancer and to determine whether there are compensatory mechanisms associated with single JAK knockouts.
The future directions of this project include the use of a CDX2-Cre inducible mouse model of colon cancer to investigate the efficacy and effectiveness of several JAK inhibitors including the clinically approved Ruxolitinib, as well as several other experimental inhibitors.