Malignant melanoma associates with deficient IFN-induced STAT 1 phosphorylation.
STAT 1, a member of signal transducers and transcription activators of STAT family proteins, has been implicated as important mediator of IFN signaling. Functional activation of STAT 1 requires tyrosine and serine phosphorylation. Defects in its expression or activation in response to IFNs were observed in numerous pathological conditions including cancer. To further explore cancer-associated impaired STAT 1 response to IFNs, the inducibility of serine (S 727) and tyrosine (Y 701) phosphorylation by IFN-alpha/-gamma was assessed in 21 melanoma cell lines and in 35 primary cultures derived from melanoma patients. STAT 1 levels and inducibility of its activated phospho-forms were detected by Western analysis using specific polyclonal and monoclonal antibodies. All cell lines as well as patient melanoma samples expressed STAT 1 with variable signal intensity. Significant impaired IFN-induced STAT 1 S 727 phosphorylation was observed in both model systems with average of 77% of non-responders recorded in patient melanoma cells and 76% in melanoma cell lines. Failure of PY 701 induction occurred in patient samples (63% after IFN-alpha and 34% after IFN-gamma induction) and to a lesser degree in cell lines (i.e. response absence to IFN-alpha in 5 and to IFN-gamma in 2 melanoma lines). Our study demonstrates STAT 1 functional abnormalities in melanoma cells. On the basis of detailed analyses of patient melanoma cells with respect to the inducibility of STAT 1 phosphorylation by IFNs, four categories of patients could be distinguished: a) activation on both S 727 and Y 701, b) not inducible response, c) activation on Y 701 but not on S 727, d) heterogeneous response. Clinical study is now in progress to establish the significance of in vitro STAT 1 activation for predicting the response to IFN-based therapy and to explore biological consequences in cases responding in vitro to IFN-induced STAT 1 activation on only one of the critical amino acid residues.
Kovarik
Jan
J
Masaryk Memorial Cancer Institute, 656 53 Brno, Czech Republic. kovarik@mou.cz
Boudny
V
V
Kocak
I
I
Lauerova
L
L
Fait
V
V
Vagundova
M
M
D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000378:metabolism*; D006801:Humans; D016898:Interferon-alpha / Q000378:metabolism*; D007371:Interferon-gamma / Q000378:metabolism*; D008545:Melanoma / Q000378:metabolism*; D010766:Phosphorylation; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000172:deficiency / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D007371:Interferon-gamma