Vitamin D3 and its active form calcitriol suppress erythroleukemia through upregulation of CHAC1 and downregulation of NOTCH1.

Abstract

Vitamin D3 (VD3) and its active form calcitriol (Ca) exhibit anti-neoplastic activity against several types of cancer, although the underlying mechanism is not fully understood. Herein, we tested the effects of VD3 and Ca on erythro-leukemogenesis and investigated the underlying mechanism. VD3 and Ca treatment strongly inhibited cancer progression in a mouse model of erythroleukemia induced by the Friend virus. In tissue culture, VD3 and Ca inhibited proliferation of leukemic cell lines. Growth inhibition was associated with induction of G1 phase cell cycle arrest and apoptosis. Transcription of the VD3 receptor, VDR, is strongly induced by Ca, but not VDR. However, leukemia growth suppression by both VD3 and Ca is shown to be independent of VDR. In leukemic cells, both VD3 and Ca induced genes associated with metabolic pathways. Both VD3 and Ca induce the cytosolic glutathione degradase CHAC1 through activation of the ER stress response pathway ATF3/ATF4/CHOP genes. Higher expression of CHAC1 also suppressed the oncogene NOTCH1. Accordingly, knockdown of CHAC1 antagonized the inhibitory effect of VD3 and Ca on leukemic growth leading to higher NOTCH1 expression. Conversely, overexpression of CHAC1 suppressed leukemia cell growth and inhibited the expression of NOTCH1. Additionally, glutathione antagonized leukemia cell suppression induced by VD3 and Ca, demonstrating that this vitamin inhibits the proliferation of leukemic cells via CHAC1. Taken together, our results demonstrated that VD3 and Ca can prolong the survival of leukemia mice and inhibit the proliferation of erythroleukemia cell HEL through CHAC1 or CHAC1-mediated NOTCH1 inhibition.