The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences Dissertations and Theses (Open Access)
Mitochondrial Unfolded Protein Response Regulator ATF5 in Mitochondrial Targeted Therapies in AML
Author ORCID Identifier
Date of Graduation
Masters of Science (MS)
Richard E. Davis
Mitochondrial unfolded protein response (UPRmt) is an adaptive transcriptional response induced by damaged proteins accumulated in mitochondria. UPRmt signaling involves induction of mitochondrial specific chaperones and proteases such as HSP60, LonP1 and ClpP, aiding in the restoration of mitochondrial protein pool homeostasis. However, the cell-protective roles of UPRmt in the context of mitochondrial stress-induced cell death in AML has not been well explored. We demonstrate that AML cells are susceptible to mitochondrial targeted agents such as ONC201, an agonist of the mitochondrial protease ClpP, and gamitrinib, an inhibitor of mitochondrial chaperone TRAP1, however, these agents also induce activating transcription factor 5 (ATF5), a primary mediator of UPRmt in mammals. Thus, we hypothesized that inactivating the cell-protective UPRmt pathway, by inhibiting ATF5, could potentially sensitize AML cells to mitochondrial stress. Consistently, flow cytometry-based apoptosis assays demonstrated that stable knockdown of ATF5 by short-hairpin RNA (shRNA) sensitized AML cells to single treatments of ONC201 and gamitrinib. In contrast, ATF5 knockdown did not further enhance AML cell killing when these agents were combined with the BCL2 inhibitor venetoclax, suggesting that venetoclax combination may overcome the cell-protective response of UPRmt. However, tetracycline-inducible shRNA against ATF5 did not sensitize AML cells to any of the above treatments. Similarly, pharmacological inhibition of ATF5 function by cell penetrating peptide Dpep was also unable to sensitize AML cells to mitochondrial targeted agents, suggesting that short-term inactivation of ATF5 is not sufficient to abrogate its cell-protective functions. Of note, while knockdown of ATF5 gene expression was confirmed in both stable and transient short hairpin models, canonical downstream genes of UPRmt (e.g., LONP1 and HSPD1) were not significantly affected in neither model, suggesting a disconnect between ATF5 expression and regulation of UPRmt gene expression, perhaps uniquely in AML cells.
Acute Myeloid Leukemia, AML, Mitochondria, Unfolded Protein Stress Response, ATF5