Constitutive expression of SOCS3 confers resistance to IFN-alpha in chronic myelogenous leukemia cells.

Because suppressor of cytokine signaling (SOCS) proteins are negative regulators of cytokine-induced signaling, it has been hypothesized that aberrant SOCS expression confers resistance against cytokine therapy. This study reports on the constitutive expression of SOCS3 in most chronic myelogenous leukemia (CML) cell lines, which are resistant to treatment with interferon alpha (IFN-alpha). In contrast, the KT-1/A3 cell line, in which constitutive expression of SOCS3 is barely detectable, is sensitive to IFN-alpha treatment. Forced expression of SOCS3 in the KT-1/A3 cell line confers resistance to IFN-alpha treatment. Furthermore, most of the blast cells from patients in CML blast crisis, which are usually resistant to IFN-alpha therapy, showed constitutive expression of SOCS3. These findings indicate that constitutive SOCS3 expression affects the IFN-alpha sensitivity of CML cell lines and blast cells from patients with CML blast crisis.