Oncostatin M (OSM) is an interleukin-6 (IL-6) type cytokine originally described by its capacity to inhibit melanoma proliferation in vitro. Here, the mechanisms involved in resistance to growth inhibition by OSM were analysed for the first time on a large panel of metastatic melanoma cell lines. OSM resistance did not strictly correlate with IL-6, interferon-c or tumor necrosis factora resistance. Rather, it correlated with a specific loss of the OSM receptor-b (OSMRb) subunit, in conjunction with a lower level of histone acetylation in the OSMRb promoter region. Treatment of various OSM-resistant melanoma cells with the histone deacetylase inhibitor Trichostatin A increased activity and histone acetylation of the OSMRb promoter as well as expression of OSMRb mRNA and protein, allowing OSM to activate the signal transducer and activator of transcription 3 (STAT3) and to inhibit proliferation. Other defects associated with OSM resistance were identified at the level of OSMRb transcription or protein expression, as well as downstream of or parallel to STAT3 activation. Altogether, our results suggest a role for OSM in the prevention of melanoma progression and that metastatic melanoma cells could escape this growth control by the epigenetic silencing of OSMRb.
Immunotherapy by adoptive transfer of autologous tumour-infiltrating lymphocytes (TIL) shows promising clinical results for stage III (lymph nodes metastasis) melanoma patients, but some of them remain unresponsive. Here we analysed retrospectively the impact of resistance of melanoma cells to anti-proliferative cytokines on the clinical outcome of 24 TIL-treated metastatic melanoma patients. Patient relapse-free survival correlated significantly with Oncostatin M (OSM) and/or IL-6 sensitivity of melanoma cells, but not with interferon (IFN) gamma or tumour necrosis factor (TNF) alpha sensitivity. However, OSM/IL-6 sensitivity did not correlate with other known prognostic factors. Moreover, OSM and IL-6 were produced by TIL just before their injection to patients. In immunodeficient mice, OSM reduced human melanoma xenograft tumour growth, this effect being directly through inhibition of tumour cell proliferation rather than induction of apoptosis or necrosis. Thus, OSM/IL-6 resistance of melanoma cells appears to be a new escape mechanism to TIL treatment that could be added to the existing prognostic factors for early stage melanoma patients. This mechanism of action could be also relevant in other immunotherapy protocols, and could lead to better prognosis and anti-cancer treatments.
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