Molecular Mechanisms of Nanoliposomal C6-ceramide-induced Cell Death in Chronic Lymphocytic Leukemia
Open Access
- Author:
- Doshi, Ushma Atul
- Graduate Program:
- Molecular Medicine
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 31, 2015
- Committee Members:
- Dr Mark Kester, Dissertation Advisor/Co-Advisor
Charles H Lang, Committee Chair/Co-Chair
Dr Thomas Loughran, Committee Member
Hong Gang Wang, Committee Member
David F Claxton, Special Member
Jin Yang, Committee Member
Richard Robert Young, Committee Member - Keywords:
- chronic lymphocytic leukemia
ceramide
Warburg effect
STAT3
cell death - Abstract:
- Chronic lymphocytic leukemia (CLL) is the most prevalent form of adult leukemia in Western countries. Despite a high incidence, its pathogenesis is still poorly understood, hence limiting treatment strategies. Furthermore, since CLL is predominantly a disease of the elderly, numerous therapeutic strategies are unsuitable due to limited physical fitness of the patient. Therefore, the CLL remains incurable for most patients. Further research is needed to develop novel therapeutic strategies. Ceramide is a ‘tumor suppressor’ sphingolipid known to regulate differentiation, senescence and cell cycle arrest. While a large body of work reveals the mechanism of nanoliposomal ceramide (CNL)-induced cell death in several types of cancers, the effect in CLL remains unclear. This study investigates the effect of CNL in CLL and deciphers the key signaling mechanisms mediating CNL-induced cell death. We have shown that CNL selectively induces cell death in CLL cells by targeting the Warburg effect through reducing levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), with no detrimental effects on normal peripheral blood mononuclear cells. Additionally, CNL treatment results in tumor regression in an in vivo murine model of CLL. Several reports in the literature have shown that signal transducer and activator of transcription 3 (STAT3) is constitutively phosphorylated on serine-727 in CLL and that STAT3 might be a therapeutic target in this disease. We demonstrate that CNL suppresses STAT3 phosphorylation at both tyrosine-705 and serine-727 by inhibiting multiple upstream kinases that include Bruton’s tyrosine kinase, mitogen-activated protein kinase kinase and protein kinase C. This suppression in STAT3 phosphorylation and the subsequent downregulation of STAT3 transcriptional activity mediates CNL-induced cell death in CLL. Recent work in the literature has uncovered that STAT3 phosphorylated at serine-727 associates with mitochondrial components and regulates the respiratory chain. Overactivation of mitochondrial STAT3 phosphorylated at serine-727 confers viability and stress protection to CLL cells. Our initial results demonstrate that CNL treatment reduces mitochondrial STAT3 levels, which might also be critical to the cell death induction. Taken together, our results suggest that inhibition of glycolytic respiration and inhibition of STAT3 transcriptional activity are key signaling mechanisms of CNL-induced cell death in CLL cells. Additionally, we also speculate that inhibition of STAT3-dependent mitochondrial respiration is also critical for induction of cell death by CNL treatment. We conclude that CNL could potentially be an effective therapy for CLL. Overall, this work emphasizes targeting the sphingolipid pathway and development of sphingolipids-based therapeutics for cancer.