Mesenchymal cells regulate the response of acute lymphoblastic leukemia cells to asparaginase
Shotaro Iwamoto, Keichiro Mihara, James R. Downing, Ching-Hon Pui, Dario Campana
Shotaro Iwamoto, Keichiro Mihara, James R. Downing, Ching-Hon Pui, Dario Campana
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Research Article Oncology

Mesenchymal cells regulate the response of acute lymphoblastic leukemia cells to asparaginase

Abstract

Because of their low asparagine synthetase (ASNS) expression and asparagine biosynthesis, acute lymphoblastic leukemia (ALL) cells are exquisitely sensitive to asparagine depletion. Consequently, asparaginase is a major component of ALL therapy, but the mechanisms regulating the susceptibility of leukemic cells to this agent are unclear. In 288 children with ALL, cellular ASNS expression was more likely to be high in T-lineage ALL and low in B-lineage ALL with TEL-AML1 or hyperdiploidy. However, ASNS expression levels in bone marrow–derived mesenchymal cells (MSCs), which form the microenvironment where leukemic cells grow, were on average 20 times higher than those in ALL cells. MSCs protected ALL cells from asparaginase cytotoxicity in coculture experiments. This protective effect correlated with levels of ASNS expression: downregulation by RNA interference decreased the capacity of MSCs to protect ALL cells from asparaginase, whereas enforced ASNS expression conferred enhanced protection. Asparagine secretion by MSCs was directly related to their ASNS expression levels, suggesting a mechanism — increased concentrations of asparagine in the leukemic cell microenvironment — for the protective effects we observed. These results provide what we believe to be a new basis for understanding asparaginase resistance in ALL and indicate that MSC niches in the bone marrow can form a safe haven for leukemic cells.

Authors

Shotaro Iwamoto, Keichiro Mihara, James R. Downing, Ching-Hon Pui, Dario Campana

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Figure 6

The protective effects of MSCs against asparaginase cytotoxicity are mediated by asparagine biosynthesis.

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The protective effects of MSCs against asparaginase cytotoxicity are med...
(A) RS4;11 ALL cells were cultured for 48 hours in the presence of asparaginase (0.001 IU/ml). The effect of adding increasing concentrations of asparagine to the tissue culture medium are shown. Values are mean and SD of 4 measurements. (B) Concentration of asparagine in asparagine-free, FCS-free tissue culture medium (MEM) was measured after 24 hours of culture with MSCs expressing different levels of ASNS. Compared are MSCs with downregulated ASNS by siRNA and MSCs transduced with a scrambled sequence as well as MSCs with upregulated ASNS by retroviral transduction and MSCs transduced with an empty vector. Levels of control amino acids serine, glycine, and valine are also shown. (C) RS4;11 cells were cultured either in the absence of MSCs (Plastic), in direct contact with MSCs, in Transwell inserts suspended over MSCs (no MSC contact), in MSC-conditioned medium (collected after 48 hours of culture; MSC Sup) or with a mixture of MSC-derived cytokines (IL-1α, IL-1β, IL-3, IL-6, IL-7, IL-11, stem cell factor, and Fms-like tyrosine kinase 3 ligand; Cyto). Cytotoxicity was measured after 48 hours of exposure to 0.001 IU/ml asparaginase. Values are mean and SD of 4 measurements.