Interplay between thyroid cancer cells and macrophages: effects on IL-32 mediated cell death and thyroid cancer cell migration

Purpose Interleukin 32 (IL-32) is a pro-inflammatory cytokine of which different isoforms have been identified. Recently, IL-32 has been shown to act as a potent inducer of cell migration in several types of cancer. Although previous research showed that IL-32 is expressed in differentiated thyroid cancer (TC) cells, the role of IL-32 in TC cell migration has not been investigated. Furthermore, tumour-associated macrophages (TAMs) may play a facilitating role in cancer cell migration. The aim of this study was to explore whether the interaction between TC cells and TAMs results in increased expression of IL-32 in TC cells and to investigate whether this affects TC cell migration. Methods TPC-1 cells were co-culture with TC-induced or naive macrophages. Next, transcriptome analysis on TPC-1 cells was performed and supernatants were used for stimulation of TPC-1 cells. IL-32 beta and IL-32 gamma were exogenously overexpressed in TPC-1 cells using transient transfection, after which an in vitro gap closure assay was performed to assess cell migration, and the expression of migratory factors was assessed using RT-qPCR. Results We found that TC-induced macrophages induced IL-32 expression in TC cells and that TAM-derived TNF alpha was the main inducer of IL-32 beta expression in TC cells. Overexpression of IL-32 beta and IL-32 gamma did not affect TC cell migration, but increased cell death. Finally, we found that IL-32 beta overexpression led to increased mRNA expression of the pro-survival cytokine IL-8, while the expression of other migratory factors was not affected. Conclusions From our data, we conclude that TAM-derived TNF alpha induces IL-32 beta in TC cells. Although IL-32 beta does not affect TC cell migration, alternative splicing of IL-32 towards the IL-32 beta isoform may be beneficial for TC cell survival through induction of the pro-survival cytokine IL-8.