Lyn regulates drug resistance mechanisms in chronic myelogenous leukemia (CML)

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  • March 21, 2019
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  • Okumu, Denis
    • Affiliation: School of Medicine, Department of Pharmacology
Abstract
  • Acquired resistance to anti-cancer therapy presents a critical challenge to effective clinical management of chronic myelogenous leukemia (CML). Drug-resistant CML cells devise diverse molecular adaptations to evade therapy. Examples of such adaptations include: target (Bcr-Abl) mutations that eliminate drug binding, target amplification, up-regulation of drug exporter proteins, and activation of alternative kinase(s). The CML cell (Myl-R) model described in this dissertation is a classic example of how CML cells can activate alternative kinase(s) to promote cell survival. Herein, I discuss two molecular adaptations regulated by Lyn in Myl-R cells. In the first project, I showed that increased Lyn expression and activity in Myl-R cells up-regulated the expression and stability of BIRC6, a member of the inhibitor of apoptosis proteins (IAP) family known to bind and inactivate active caspases. BIRC6’s role in promoting imatinib resistance was confirmed by the 15-fold increase in imatinib sensitivity upon BIRC6 shRNA knockdown. Pharmacological or genetic inhibition of Lyn reduced BIRC6 expression and stability. Further, BIRC6 stability was increased via Lyn-dependent phosphorylation of serine residues in a region that overlapped with caspase cleavage motifs. Pharmacological inhibition of Lyn resulted in caspase-mediated degradation of BIRC6. In the second project, I am investigating Lyn’s role in regulating creatine uptake by Myl-R cells. Our lab previously showed that total intracellular creatine pool was 5-fold higher in Myl-R than Myl cells. Our unpublished data show that the increased intracellular creatine comes from uptake from the cell culture media and not de novo synthesis. I, therefore, investigated the role of creatine in Myl-R cells by incubating the cells in normal growth media into which competitive inhibitors of creatine uptake were added. Our data show that reduction in total intracellular creatine pool lowered cell viability. Others previously showed that the Na+/K+-ATPase pump activity was critical for creatine uptake. Our data show that Lyn inhibition or shRNA knockdown reduced Na+/K+-ATPase activity and total intracellular creatine pool, suggesting a tripartite signaling cascade that supports Myl-R cell survival. Taken together, these studies enrich our understanding of the diverse therapy-survival mechanisms utilized by CML cells, and provide insights into novel targets for effective cure of CML.
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Advisor
  • Zhang, Yanping
  • Graves, Lee
  • Yeh, Jen Jen
  • Baines, Antonio
  • Johnson, Gary
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2018
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