ATF6 Identification Sensitizes B-Cell Precursor Acute Lymphoblastic Leukemia Cells to Doxorubicin

Activating transcription factor 6 (ATF6) is a part of the unfolded protein response (UPR) system, which plays an important role in regulating endoplasmic reticulum stress. The overexpression of ATF6 has been reported in various malignancies; however, its expression and functional significance in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) are poorly understood.

Bone marrow samples from 69 pediatric patients with ALL (48 newly diagnosed, 21 relapsed) and peripheral blood/bone marrow samples from 29 nonleukemic healthy children (controls) were collected. To investigate the effect of ATF6 inhibition on the viability of BCP-ALL derived cell lines, NALM-6 and SUP-B15 cells were treated with the ATF6 inhibitor Ceapin-A7 both alone and in combination with doxorubicin. Apoptosis was quantitatively assessed using flow cytometry. The expression levels of ATF6, BCL-2 family members, and ATF6 target genes were determined by qRT-PCR, and the protein levels of ATF6, caspase-3, PARP, cell cycle regulators by Western blot analysis.

Our results revealed that the ATF6 expression was higher in pediatric patients with relapsed ALL than in newly diagnosed patients. Furthermore, inhibition of ATF6 with Ceapin-A7 enhanced doxorubicin-induced apoptosis in the BCP-ALL cell lines NALM-6 and SUP-B15. Upon inhibition of ATF6, both BCP-ALL cell lines were arrested at the G1 phase of the cell cycle. Combined treatment altered the expression of apoptosis-related and cell cycle regulatory genes and proteins, and ATF6 target genes were upregulated by Ceapin-A7 alone but attenuated in the combined treatment group.

ATF6 inhibition combined with doxorubicin represents a promising therapeutic strategy for enhancing apoptosis in BCP-ALL cells.