Characterizing Regulatory Mechanisms Underlying Drug Resistance in Breast Cancer Using Keratin 19

Catholic University Of America, Washington DC

Investigators

Linked publications & trials

Abstract

PROJECT SUMMARY Drug resistance continues to be the major limiting factor in achieving cures for cancer patients. In breast cancer, cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors have been approved recently to treat patients with advanced estrogen receptor-positive tumors. However, most patients exhibit resistance due to a lack of predictive biomarker. Understanding the molecular basis underlying drug resistance is required to provide a critical breakthrough in identifying a predictive biomarker and developing effective therapeutic strategies. Based on our previous work and preliminary data, we propose that a cytoskeletal protein keratin 19 (K19), which currently serves as one of the most reliable diagnostic and prognostic markers, regulates signaling events to impact resistance against CDK4/6 inhibitors. We found that K19 binds to and inhibits a multifunctional kinase GSK to stabilize a CDK4/6 partner cyclin D3 in breast cancer cells. K19-GSK3 interaction was associated with decreased accumulation of GSK3 in the nucleus that is crucial to GSK3 function. Moreover, K19 promoted proliferation and maintained the sensitivity of cells to CDK4/6 inhibitors. We hypothesize that cyclin D3 stabilized by K19-dependent inhibition of GSK3 causes tumors to become dependent on the CDK4/6 pathway for growth and sensitizes them to CDK4/6 inhibitors. At the molecular level, we surmise that K19 filaments serve as cytoplasmic scaffolds for GSK3 to prevent its entry into the nucleus where it phosphorylates cyclin D3 for degradation. To address our hypotheses, we propose to 1) determine K19 effects on the GSK3 signaling network, 2) characterize the interaction between K19 and GSK3, and 3) determine the impact of K19 on drug resistance and tumor growth. To this end, in Aim 1, we will identify upstream regulators of K19-GSK3 interaction as well as GSK3 targets whose activities affect K19- dependent phenotypes. In Aim 2, GSK3-binding deficient K19 mutant will be characterized to determine how K19 interacts with GSK3 and affects the nuclear entry of GSK3. In Aim 3, we will assess how K19 affects sensitivities of various breast cancer subtypes to CDK4/6 inhibitors and test the role of K19 and GSK3 on the sensitivity of tumors to a CDK4/6 inhibitor in vivo. Upon successful completion, the knowledge gained from the study can help design new drugs targeting K19-dependent signaling pathways, establish K19 as a predictive biomarker for response to CDK4/6 inhibitors, and develop effective therapeutic strategies to combat drug resistance.