Blood最新文献

Circular RNAs are a novel class of RNA transcripts, which regulate important cellular functions in health and disease. Herein, we report on the functional relevance of circPCMTD1 in BCR/ABL1-positive myeloid leukemias. In screening experiments, we found that circPCMTD1 depletion strongly inhibited the proliferative capacity of leukemic cells with BCR/ABL1 translocations. RNA sequencing and mass cytometry experiments identified aberrant activation of the DNA damage response (DDR) pathway as a downstream effect of circPCMTD1 depletion. DNA fiber assays, Comet assays and profiling of DDR markers (phospho-H2AX, phospho-CHK1, etc.) further underscored the pronounced effect of circPCMTD1 depletion in increasing genotoxic stress and inhibiting leukemic cell growth. circPCMTD1 targeting also led to aberrant DDR activation in leukemia patient blasts with BCR/ABL1 translocations. In in vivo experiments, circPCMTD1 knock-down prolonged the survival of mice engrafted with BCR/ABL1-positive leukemia cells. Mechanistically, we found that circPCMTD1 is enriched in the cytoplasm and associates with the ribosomes of leukemic blasts. We detected a cryptic open reading frame within the circPCMTD1 sequence and found that circPCMTD1 generates a 127 amino-acid peptide product (cPCMTD1-127aa). Using a custom-produced antibody, we found that the cPCMTD1-127aa interacts with the BCR/ABL1 oncoprotein, as well as with the BLM, TOP3A and RMI1 proteins, which form the BTR complex and regulate DNA repair and genome stability. cPCMTD1-127aa enhanced BTR complex formation, thereby increasing cellular tolerance to genotoxic stress. In summary, we identify and characterize circPCMTD1 as a molecular vulnerability and potential therapeutic target in BCR/ABL1-positive leukemias.

Abstract: Oncogenic growth places great strain and dependence on protein homeostasis (proteostasis). This has made proteostasis pathways attractive therapeutic targets in cancer, but efforts to drug these pathways have yielded disappointing clinical outcomes. One exception is proteasome inhibitors, which are approved for the frontline treatment of multiple myeloma. However, proteasome inhibitors are largely ineffective for the treatment of other cancers at tolerable doses, including acute myeloid leukemia (AML), although reasons for these differences are unknown. Here, we determined that proteasome inhibitors are ineffective in AML due to their inability to disrupt proteostasis. In response to proteasome inhibition, AML cells activated HSF1 and increased autophagic flux to preserve proteostasis. Genetic inactivation of HSF1 sensitized AML cells to proteasome inhibition, marked by accumulation of unfolded protein, activation of the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK)-mediated integrated stress response, severe reductions in protein synthesis, proliferation and cell survival, and significant slowing of disease progression and extension of survival in vivo. Similarly, combined autophagy and proteasome inhibition suppressed proliferation, synergistically killed human AML cells, and significantly reduced AML burden and extended survival in vivo. Furthermore, autophagy and proteasome inhibition preferentially suppressed protein synthesis and colony formation and induced apoptosis in cells from patients with primary AML, including AML stem/progenitor cells, compared with normal hematopoietic stem/progenitor cells. Combined autophagy and proteasome inhibition activated a terminal integrated stress response, which was surprisingly PKR. These studies unravel how proteostasis pathways are coopted to promote AML growth, progression and drug resistance and reveal that disabling the proteostasis network is a promising strategy to therapeutically target AML.