Regulation of cancer cell growth involves activation of genes (oncogenes) that promote cell growth and survival, and the inactivation of other genes (tumour suppressors) that negatively regulate these critical cellular processes. The major focus of this CRS proposal is to evaluate the role of the RSK (pronounced "risk") family of proteins in breast cancer. This family includes four members, termed RSK1-4, which were found to be hyperactivated and overexpressed in breast cancer. The first objective of the proposal is to characterize the mechanisms by which RSK promotes cancer cell growth and proliferation. The second objective of the proposal will evaluate the role of each RSK family member (RSK1-4) in breast cancer cell proliferation and tumour growth. A better understanding of RSK will be required to determine if these proteins are important for breast cancer cell proliferation and whether they are valuable therapeutic targets for this prevalent disease.