STAT3 knockdown by siRNA induces apoptosis in human cutaneous T-cell lymphoma line Hut78 via downregulation of Bcl-xL.

Cutaneous T-cell lymphomas (CTCLs) are non-Hodgkin's lymphomas resulting from clonal expansion and localization of malignant T-lymphocytes to the skin. CTCL cells have defective apoptosis. Signal transducers and activators of transcription (STAT) are a family of transcription factors known to play important roles in the development and progression of several human cancers by promoting cell proliferation and protecting against apoptosis. In this study, we investigated the specific role of STAT3, a major component of the STAT family, in growth and survival of human CTCL cell line Hut78. Western immunoblot analysis showed elevated expression of STAT3 and phospho-STAT3(Y705) in human CTCL cells as compared to freshly isolated peripheral blood lymphocytes (PBLs). Specific knockdown of STAT3 expression in Hut78 cells by RNA interference induced morphological and biochemical changes indicating apoptotic cell death. Moreover, STAT3 inhibition downregulated the expression of Bcl2 family of anti-apoptotic gene Bcl-xL. These observations suggest that STAT3 is required for the survival of CTCL cells and strongly indicate that targeting STAT3 using siRNA techniques may serve a novel therapeutic strategy for the treatment of CTCL.