Tumor cells of non-hematopoietic and hematopoietic origins express activation-induced C-type lectin, the ligand for killer cell lectin-like receptor F1

Abstract

Killer cell lectin-like receptor F1 (KLRF1) is an activating C-type lectin-like receptor expressed on human NK cells and subsets of T cells. In this study, we show that activation-induced C-type lectin (AICL) is a unique KLRF1 ligand expressed on tumor cell lines of hematopoietic and non-hematopoietic origins. We screened a panel of human tumor cell lines using the KLRF1 reporter cells and found that several tumor lines expressed KLRF1 ligands. We characterized a putative KLRF1 ligand expressed on the U937 cell line. The molecular mass for the deglycosylated ligand was 28 kDa under non-reducing condition and 17 kDa under reducing condition, suggesting that the KLRF1 ligand is a homodimer. By expression cloning from a U937 cDNA library, we identified AICL as a KLRF1 ligand. We generated mAbs against AICL to identify the KLRF1 ligands on non-hematopoietic tumor lines. The anti-AICL mAbs stained the tumor lines that express the KLRF1 ligands and importantly the interaction of KLRF1 with the KLRF1 ligand on non-hematopoietic tumors was completely blocked by the two anti-AICL mAbs. Moreover, NK cell degranulation triggered by AICL-expressing targets was partially inhibited by the anti-AICL mAb. Finally, we demonstrate that AICL is expressed in human primary liver cancers. These results suggest that AICL is expressed on tumor cells of non-hematopoietic origins and raise the possibility that AICL may contribute to NK cell surveillance of tumor cells.

Genetically coupled receptor–ligand pair NKp80-AICL enables autonomous control of human NK cell responses

“…LLT1 is expressed by the NK cell line YT and several B cell lines, but no expression by nonhematopoietic cell lines has been reported. 25,26,34 Similarly, we found human NK cell lines and some other hematopoietic cell lines to express AICL, but in contrast to a previous report, 23 no AICL expression by the epithelial cell line HeLa or other nonhematopoietic cell lines. However, reports on expression of LLT1 and AICL by glioblastoma and liver cancer, respectively, indicate that tumor cells may aberrantly express these CLEC2 proteins.…”

“…However, reports on expression of LLT1 and AICL by glioblastoma and liver cancer, respectively, indicate that tumor cells may aberrantly express these CLEC2 proteins. 23,35 We find that NK cell activation by monokines results in an upregulation of AICL and downregulation of NKp80 at the cell surface that is paralleled by changes in levels of the corresponding transcripts. Because changes in NKp80 transcript levels were moderate, additional regulatory mechanisms may contribute to the observed changes in cell surface expression.…”

“…19 A more recent report describes AICL also on a few nonhematopoietic cell lines. 23 The present study was initiated by the incidental observation of substantial AICL expression by human NK cell lines. Subsequently, we assessed AICL expression by human NK cells and found them to contain intracellular stores of AICL that surface upon activation.…”

Generation and Preclinical Characterization of an NKp80-Fc Fusion Protein for Redirected Cytolysis of Natural Killer (NK) Cells against Leukemia

“…AICL is expressed preferentially on the surface of myeloid cells, especially on malignant leukemia cells, but not on nonmyeloid hematopoietic cells or nonhematopoietic cells (8). AICL expression increases the susceptibility of myeloid cells to NK cell-mediated cytolysis (7).…”

“…The only known ligand for NKp80 to date is expressed by hematopoietic cells, especially by malignant myeloid cells in acute myeloid leukemia and chronic myeloid leukemia, and by non-hematopoietic cells, including carcinoma and melanoma cells (8). Researchers have already demonstrated that expression of AICL, which engages NKp80, increases the susceptibility of myeloid cells to NK cell-mediated cytolysis.…”