Distinct Dasatinib-Induced Mechanisms of Apoptotic Response and Exosome Release in Imatinib-Resistant Human Chronic Myeloid Leukemia Cells

Abstract

Although dasatinib is effective in most imatinib mesylate (IMT)-resistant chronic myeloid leukemia (CML) patients, the underlying mechanism of its effectiveness in eliminating imatinib-resistant cells is only partially understood. This study investigated the effects of dasatinib on signaling mechanisms driving-resistance in imatinib-resistant CML cell line K562 (K562RIMT). Compared with K562 control cells, exsomal release, the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/ mammalian target of rapamycin (mTOR) signaling and autophagic activity were increased significantly in K562RIMT cells and mTOR-independent beclin-1/Vps34 signaling was shown to be involved in exosomal release in these cells. We found that Notch1 activation-mediated reduction of phosphatase and tensin homolog (PTEN) was responsible for the increased Akt/mTOR activities in K562RIMT cells and treatment with Notch1 γ-secretase inhibitor prevented activation of Akt/mTOR. In addition, suppression of mTOR activity by rapamycin decreased the level of activity of p70S6K, induced upregulation of p53 and caspase 3, and led to increase of apoptosis in K562RIMT cells. Inhibition of autophagy by spautin-1 or beclin-1 knockdown decreased exosomal release, but did not affect apoptosis in K562RIMT cells. In summary, in K562RIMT cells dasatinib promoted apoptosis through downregulation of Akt/mTOR activities, while preventing exosomal release and inhibiting autophagy by downregulating expression of beclin-1 and Vps34. Our findings reveal distinct dasatinib-induced mechanisms of apoptotic response and exosomal release in imatinib-resistant CML cells.

Differences of basic and induced autophagic activity between K562 and K562/ADM cells

“…Similar results are also obtained in a multiple myeloma cell line, Pan et al (37) reported that expression level of LC3-Ⅱ was higher in DOX-resistant RPMI8226/DOX cells than in DOXsensitive RPMI8226/S cells. Similarly, compared with K562 cells, there is an increased PI3K/AKT/mTOR signaling and enhanced autophagic activity in imatinibresistant human chronic myelogenous leukemia K562R cells (38).…”

The autophagy inhibitor spautin-1, either alone or combined with doxorubicin, decreases cell survival and colony formation in canine appendicular osteosarcoma cells

“…Spautin-1, an autophagy inhibitor that increases beclin-1 degradation, typically results in decreased beclin-1 expression using western blot [ 45 , 46 , 66 – 68 , 71 , 75 ]. Although we observed this pattern in our cell lines derived from 2° osteosarcoma, which were the cells most sensitive to spautin-1 in our study, no effect on beclin-1 was observed in the non-cancer and 1° osteosarcoma cell lines (lanes 1 vs 2 vs 3; Fig 3 ).…”

The interplay between exosomes and autophagy – partners in crime

“…Association of the PI3K complex with Run domain Beclin-1-interacting and cysteine-rich domain-containing protein (Rubicon), an effector of RAB7, has been shown to suppress autophagy and endocytosis (Sun et al, 2010), and to also be required for LC3-associated phagocytosis (Martinez et al, 2015). The destabilization of the PI3K complex that occurs upon suppressing Beclin1, either via siRNA-mediated knockdown or Spautin-1 treatment, reduces both exosome release and autophagy flux in chronic myeloid leukemia (CML) cells (Liu et al, 2016). Given its role in endocytosis and autophagy, the impact of various components of the PI3K complex in exosome biogenesis is worthy of further investigation.…”