Increasing TIMP3 expression by hypomethylating agents diminishes soluble MICA, MICB and ULBP2 shedding in acute myeloid leukemia, facilitating NK cell-mediated immune recognition

Abstract

Acute myeloid leukemia (AML) is a disease with great morphological and genetic heterogeneity, which complicates its prognosis and treatment. The hypomethylating agents azacitidine (Vidaza®, AZA) and decitabine (Dacogen®, DAC) have been approved for the treatment of AML patients, but their mechanisms of action are poorly understood. Natural killer (NK) cells play an important role in the recognition of AML blasts through the interaction of the activating NKG2D receptor with its ligands (NKG2DL: MICA/B and ULBPs1-3). However, soluble NKG2DL (sNKG2DL) can be released from the cell surface, impairing immune recognition. Here, we examined whether hypomethylating agents modulate the release of sNKG2DL from AML cells. Results demonstrated that AZA- and DAC-treated AML cells reduce the release of sNKG2DL, preventing downregulation of NKG2D receptor on the cell surface and promoting immune recognition mediated by NKG2D-NKG2DL engagement. We show that the shedding of MICA, MICB and ULBP2 is inhibited by the increased expression of TIMP3, an ADAM17 inhibitor, after DAC treatment. The TIMP3 gene is highly methylated in AML cells lines and in AML patients (25.5%), in which it is significantly associated with an adverse cytogenetic prognosis of the disease. Overall, TIMP3 could be a target of the demethylating treatments in AML patients, leading to a decrease in MICA, MICB and ULBP2 shedding and the enhancement of the lytic activity of NK cells through the immune recognition mediated by the NKG2D receptor.

NKG2D Ligands–Critical Targets for Cancer Immune Escape and Therapy

“…Metalloproteases, most prominently ADAM10, ADAM17 ( 40 , 41 ), and MMP14 ( 42 ) are frequently expressed in the tumor microenvironment but also on platelets ( 43 ), cleave and thereby remove MICA, MICB, or ULBP proteins from the tumor cell surface ( 44 – 48 ). The process of shedding is influenced by proteins that inhibit metalloprotease activity like TIMP3 ( 49 ), or that enable or facilitate the proteolytic cleavage, like the disulfide-isomerase ERp5 ( 50 ). Accordingly, high ERp5 and ADAM10 expression were shown to yield a high load of soluble NKG2D ligands in supernatants of primary cancer cell cultures ( 51 ).…”

“…But not every new target requires a new drug development: some clinically applied drugs appear to reduce shedding of ligands as a pleasant “side effect,” as shown for hypomethylating agents ( 49 ) or tyrosine kinase inhibitors ( 82 ).…”

Cell-mediated immune resistance in cancer

“…Tumor cells also have the propensity to evade detection by NK cells by modulating the expressions of the MHC class I-like NKG2D ligands, which bind to the activating NKG2D receptors on NK cells to trigger tumor cell lysis [54] . Post-translational regulation of these ligands occurs via intracellular retention [55] , internalization and proteasomal degradation [56] , and cleavage and shedding [57] , each leading to inhibition of NKG2D-mediated cell targeting by NK cells.…”

Immune Escape after Hematopoietic Stem Cell Transplantation (HSCT): From Mechanisms to Novel Therapies

“…Leukemic cells may reduce the expression of NK ligands through an aberrant hyper-methylation of genes encoding ligands for the activating receptor NKG2D (NKG2DL), namely MICA, ULBP1, ULBP2, and ULBP3 genes [56], and may also release a soluble form of NKG2DLs (sNKG2DL) which induces the down-regulation of NKG2D receptor [57]. Both of these mechanisms of immune disruption can be removed by HMA, which is thought to block MICA, MICB and ULBP2 shedding by increasing the expression of TIMP3 and may also reduce the release of sNKG2DLs [58]. In addition, AML cells which present ligands for NK activating receptors, namely CD112 and CD155, can decrease the expression of some other NK cell activating receptors, namely DNAM-1, NKp30, and NKp46, by physically interacting with NK cells [59,60].…”