The regulation of CHK2 in human cancer.
Exceptional progress has been made in the past two decades in mapping oncogenes and tumour suppressors, defining a function for these master switches, and identifying novel anti-cancer drug targets. The p53 tumour suppressor is a central component of a DNA-damage-inducible pathway controlled by the ataxia telangiectasia mutated (ATM) and CHK2 protein kinases that have a central role in cancer suppression. One limitation of current human cancer research is the difficulty in developing genetic models that reveal the post-translational regulation of a growth suppressor like CHK2 within the microenvironment of a human tumour. Gaining such insights is important since yeast models and human tissue culture cell lines do not necessarily predict how enzymes like CHK2 are regulated in vivo, and therefore what factors can affect CHK2 tumour suppressor function. Translational cancer research aims to link basic research methodologies and clinical biology by uncovering cancer-specific pathways not revealed by other approaches. This approach is exemplified by two studies in this edition of Oncogene: both use a set of well-characterized human cancers with the objective of identifying novel post-translational control of the tumour suppressor CHK2. The authors have revealed two unexpected epigenetic modifications of the CHK2 pathway in vivo: (1) constitutive phosphorylation of CHK2 at its ATM-activated site in the absence of exogenous DNA damage; and (2) the production of hyper-spliced and inactive isoforms of CHK2. These studies highlight the need to develop model systems to understand why CHK2-activating pathways are being triggered or suppressed in different human cancers and whether the splicing machinery can be manipulated to control the activity of CHK2 for therapeutic benefit.