1. ¹Institute of Biophysics, Academy of Sciences of the Czech Republic v.v.i., Kralovopolska 135, 612 65 Brno, Czech Republic
2. ²Department of Experimental Oncology, Masaryk Memorial Cancer Institute, Zluty kopec 7, 656 53 Brno, Czech Republic
3. ³Faculty of Medicine and Science, Institute of Biostatistics and Analyses, Masaryk University, Kamenice 126/3, 625 00 Brno, Czech Republic

Correspondence: Dr V Boudny, E-mail: boudny@mou.cz

Received 17 November 2006; Revised 22 May 2007; Accepted 22 May 2007; Published online 19 June 2007.

Abstract

The resistance to interferons (IFNs) limits their anticancer therapeutic efficacy. Here we studied the evolution of an IFN-resistant state in vitro using melanoma cell lines. We found that the cells became less sensitive to antiproliferative effect of IFN- after prolonged cultivation enabling us to isolate sensitive and resistant subclones of the parental line. We investigated transcription of signal transducer and activator of transcription (STAT) 1–6 and suppressor of cytokine signalling (SOCS) 1–3 genes, and phosphorylation of STAT 1 protein. The resistant subline (termed WM 1158R) differed from the sensitive subline (WM 1158S) by a constitutive expression of SOCS 3, lack or weak SOCS 1–3 activation following IFN-, and short duration of cytokine activatory signal. Similar correlations were observed in additional melanoma lines differing in IFN sensitivities. At the protein level, IFN- induced strong and prolonged STAT 1 activation at serine 727 (S727) in WM 1158R while in WM 1158S cells phosphorylation of this amino acid was much less pronounced. On the other hand, phosphorylation of tyrosine 701 (Y701) was stimulated regardless of the sensitivity phenotype. In conclusion, constitutive expression of SOCS 3 is correlated with attenuation of its induction following IFN treatment. These results suggest that progression of melanoma cells from IFN sensitivity to IFN insensitivity associates with changes in SOCS expression.