Hyperthermia promotes degradation of the acute promyelocytic leukemia driver oncoprotein ZBTB16/RARα.

The acute promyelocytic leukemia (APL) driver ZBTB16/RARα is generated by the t(11;17) (q23;q21) chromosomal translocation, which is resistant to combined treatment of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) or conventional chemotherapy, resulting in extremely low survival rates. In the current study, we investigated the effects of hyperthermia on the oncogenic fusion ZBTB16/RARα protein to explore a potential therapeutic approach for this variant APL. We showed that Z/R fusion protein expressed in HeLa cells was resistant to ATO, ATRA, and conventional chemotherapeutic agents. However, mild hyperthermia (42 °C) rapidly destabilized the ZBTB16/RARα fusion protein expressed in HeLa, 293T, and OCI-AML3 cells, followed by robust ubiquitination and proteasomal degradation. In contrast, hyperthermia did not affect the normal (i.e., unfused) ZBTB16 and RARα proteins, suggesting a specific thermal sensitivity of the ZBTB16/RARα fusion protein. Importantly, we found that the destabilization of ZBTB16/RARα was the initial step for oncogenic fusion protein degradation by hyperthermia, which could be blocked by deletion of nuclear receptor corepressor (NCoR) binding sites or knockdown of NCoRs. Furthermore, SIAH2 was identified as the E3 ligase participating in hyperthermia-induced ubiquitination of ZBTB16/RARα. In short, these results demonstrate that hyperthermia could effectively destabilize and subsequently degrade the ZBTB16/RARα fusion protein in an NCoR-dependent manner, suggesting a thermal-based therapeutic strategy that may improve the outcome in refractory ZBTB16/RARα-driven APL patients in the clinic.

Effects of Saposhnikovia divaricata extract combined with arsenic trioxide on the proliferation and apoptosis in K562 cells / 国际中医中药杂志

ObjectiveTo investigate the effects of Saposhnikovia divaricata extract combined with arsenic trioxide (ATO) on the proliferation and apoptosis in chronic myelogenous leukemia K562 cells. MethodsSaposhnikovia divaricata extract was prepared.Cultured K562 cells were treated with different concentration of Saposhnikovia divaricataextract or/and ATO for 48h. Cell proliferation was determined using the MTT assay. Apoptosis and cell cycle were detected using flow cytometry.ResultsThe MTT assay showed that Saposhnikovia divaricata extract of 750,1 000,1 250,1 500 μg/ml had a significantly proliferation inhibitory effect compared with control group, the inhibitory rates were 23.29% ± 3.31%, 48.30% ± 2.50%, 79.62% ± 3.41% and 88.94% ± 0.06%, respectively (allP<0.05); Saposhnikovia divaricata extract of 500 μg/ml combined with ATO of 1.0, 0.5 μg/ml significantly increased inhibitor rates compared with ATO of 1.0, 0.5 μg/ml (64.99% ± 5.18%vs. 44.48% ± 3.31%,38.59% ± 3.88%vs.26.30% ± 5.03%; allP<0.05). FCM showed that Saposhnikovia divaricata extract of 500 μg/ml combined with ATO of 2.0, 1.0, 0.5 μg/ml significantly increased apoptotic rate compared with ATO group of 2.0, 1.0, 0.5 μg/ml (33.97% ± 0.59%vs.20.97% ± 2.17%, 13.53% ± 0.47%vs.9.77%±0.64%、6.63%±&0.40%vs.4.00%±0.46%; allP<0.05 ). Cell cycle results showed that Saposhnikovia divaricata extract of 500μg/ml combined with ATO of 2.0,1.0, 0.5μg/ml significantly increased the rate of S phase compared with ATO group of 2.0, 1.0, 0.5 μg/ml (60.25 ± 2.59%vs.55.61 ± 1.28%, 60.89 ± 1.53%vs.37.96 ± 1.02%, 47.76 ± 0.87%vs.39.90 ± 0.92%; allP<0.05).ConclusionsSaposhnikovia divaricataextract could obviously inhibit the proliferation of K562 cells and enhance the apoptotic effect of ATO. ATO could induce a G2/M phase arrest, while Saposhnikovia divaricata extract combined with ATO could induce a S phase arrest in K562 cells.