IL-9 Promotes Migratory Dissemination of Malignant T Cells by Activating the HIF-1α-Cofilin-1 Axis in Cutaneous T-cell Lymphoma.

Cutaneous T-cell lymphoma (CTCL) is a multistage disease characterized by rapid dissemination of malignant T lymphocytes from skin lesions to visceral organs and bone marrow. The cytokine IL-9 and its receptor (IL-9R) are aberrantly overexpressed in CTCL lesions and function to enhance tumor cell survival. In this study, we uncovered a critical new role for IL-9 as a potent inducer of migration of malignant T cells. Stimulation of IL-9R-expressing T-cell lymphoma cells with IL-9 induced a pseudohypoxic cellular state by elevating downstream levels of the promigratory and oxygen-sensing transcription factor hypoxia-inducible factor (HIF)-1α. High-throughput quantitative proteomic analyses of pseudohypoxic malignant T cells identified the actin-modulating protein cofilin-1 (CFL-1) as a promigratory CTCL-intrinsic target downstream of IL-9-HIF-1α signaling. Consistently, multicolor immunofluorescence staining revealed marked coexpression of CFL-1 with HIF-1α in both IL-9-treated human lymphoma cell lines and in patient CTCL skin biopsies compared with normal controls. Genetic knockdown of IL9R or HIF1A in human T-cell lymphoma lines by RNAi significantly reduced both HIF-1α and CFL-1 coexpression and reversed IL-9-induced migration. Finally, pharmacologic antagonism of HIF-1α activity using the FDA-designated orphan drug echinomycin significantly abrogated IL-9-triggered migration of both malignant T-cell lines and patient-derived T-cell lymphoma cells from CTCL biospecimens. IMPLICATIONS: Our results uncover a CTCL-intrinsic IL-9-HIF-1α-CFL-1 axis as a critical promoter of malignant T-cell migration. They further identify HIF-1α and CFL-1 as promising therapeutic targets to mitigate IL-9-induced CTCL dissemination.