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Heat shock protein 27 (Hsp27), a member of the heat shock protein (Hsp) family, is critical in the regulation of cancer development, progression and chemotherapy resistance. However, the role of Hsp27 in the pathogenesis of pediatric acute leukemia (AL) remains unknown. In this study, we evaluated the expression levels of Hsp27 in bone marrow samples from 94 children with newly diagnosed acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML) and 5 leukemia cell lines. Additionally, we transfected a target-specific siRNA duplex against Hsp27 into leukemia cells, and examined the chemosensitivity and cell apoptosis in the response to antitumor drugs. Hsp27 was abundantly expressed in newly diagnosed AML-M4/M5 bone marrow mononuclear cells (BMMCs) and THP-1, OCI/AML-3 leukemia cell lines. Furthermore, its expression was positively correlated with the clinical status in pediatric M4/M5 subtypes. Knockdown of Hsp27 expression increased the chemosensitivity of leukemia cells and the anticancer drug-induced apoptosis. These results support the theory that Hsp27 plays a contributory role in the pathogenesis of pediatric AML-M4/M5. Therefore, Hsp27 may be exploited as a new target for enhancing the efficacy of chemotherapeutic drugs against leukemia.

Chemoresistance has become a major obstacle to the successful treatment of leukemia. Autophagy, a regulated process of degradation and recycling of cellular constituents, has recently caught increasing attention for its roles in conferring resistance to various commonly used anticancer therapies. Here we showed that the member of the S100 calcium-binding protein family, S100A8, is a critical regulator of chemoresistance in the autophagy process. It positively correlated with the clinical status in childhood acute myeloblastic leukemia (AML) and it was released from leukemia cells after chemotherapy-induced cytotoxicity. Knockdown of S100A8 expression increased the sensitivity of leukemia cells to chemotherapy and apoptosis. Moreover, suppressing S100A8 expression decreased autophagy as evaluated by the increased expression of the autophagic marker microtubule-associated protein light chain 3 (LC3)-II, degradation of SQSTM1/Sequestosome 1 (p62) and formation of autophagosomes. Furthermore, stimuli that enhanced reactive oxygen species (ROS) promoted cytosolic translocation of S100A8 and thereby enhanced autophagy. S100A8 directly interacted with the autophagy protein Beclin1 displacing Bcl-2. These results suggest that S100A8 is a critical pro-autophagic protein that enhances cell survival and regulates chemoresistance in leukemia cells likely through disassociating the Beclin1-Bcl-2 complex.