IL-9 promotes migratory dissemination of malignant T-cells by activating the HIF-1α-Cofilin-1 axis in cutaneous T-cell lymphoma.

Abstract

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. Here, 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 pro-migratory and oxygen-sensing transcription factor, hypoxia inducible factor (HIF)-1α. High-throughput quantitative proteomics analyses of pseudohypoxic malignant T-cells identified the actin-modulating protein, Cofilin-1, as a pro-migratory CTCL-intrinsic target downstream of IL-9-HIF-1α signaling. Consistently, multicolor immunofluorescence staining revealed marked co-expression of Cofilin-1 with HIF-1α in both IL-9-treated human lymphoma cell lines and in patient CTCL skin biopsies compared to normal controls. Genetic knockdown of IL-9R or HIF-1α in human T-cell lymphoma lines by RNA interference significantly reduced both HIF-1α and Cofilin-1 co-expression and reversed IL-9-induced migration. Finally, pharmacological antagonism of HIF-1α activity using the FDA-designated orphan drug, echinomycin, significantly abrogated IL-9-triggered migration of both malignant T-cell lines as well as patient-derived T-cell lymphoma cells from CTCL biospecimens. Implications: Our results uncover a CTCL-intrinsic IL-9-HIF-1α-Cofilin-1 axis as a critical promoter of malignant T-cell migration. They further identify HIF-1α and Cofilin-1 as promising therapeutic targets to mitigate IL-9-induced CTCL dissemination.