Down-regulation of Suppressor of Cytokine Signaling-3 Causes Prostate Cancer Cell Death through Activation of the Extrinsic and Intrinsic Apoptosis Pathways

Abstract

Suppressor of cytokine signaling-3 (SOCS-3) acts as a negative feedback regulator of the Janus-activated kinase/ signal transducers and activators of transcription factors signaling pathway and plays an important role in the development and progression of various cancers. To better understand the role of SOCS-3 in prostate cancer, SOCS-3 expression was down-regulated in DU-145, LNCaP-IL-6+, and PC3 cells by consecutive SOCS-3 small interfering RNA transfections. SOCS-3 mRNA and protein expression as measured by quantitative reverse transcription-PCR and Western blot, respectively, were decreased by f70% to 80% compared with controls. We observed a significant decrease in cell proliferation and viability in all SOCS-3-positive cell lines but not in the parental LNCaP cell line, which is SOCS-3 negative. In this study, we show that down-regulation of SOCS-3 leads to an increased cell death in prostate cancer cell lines. We found a considerable increase in the activation of the proapoptotic caspase-3/caspase-7, caspase-8, and caspase-9. A significant up-regulation of cleaved poly(ADPribose) polymerase and inhibition of Bcl-2 expression was observed in all SOCS-3-positive cell lines. Overexpression of Bcl-2 could rescue cells with decreased SOCS-3 levels from going into apoptosis. Tissue microarray data prove that SOCS-3 is highly expressed in castration-refractory tumor samples. In conclusion, we show that SOCS-3 is an important protein in the survival machinery in prostate cancer and is overexpressed in castration-resistant tumors. SOCS-3 knockdown results in an increase of cell death via activation of the extrinsic and intrinsic apoptosis pathways.

SOCS3 Modulates the Response to Enzalutamide and Is Regulated by Androgen Receptor Signaling and CpG Methylation in Prostate Cancer Cells

“…SOCS3 has been previously studied in androgen receptor-negative cell lines in which siRNAmediated knockdown of SOCS3 led to massive cell death (20). Androgen receptor-negative prostate cancer cell lines harbor an autocrine IL6 loop and secrete large amounts of IL6 into the supernatant (42).…”

“…SOCS3 is able to inhibit STAT3 activation by various mechanisms (12). Previous publications could show that SOCS3 is an essential survival factor in androgen receptor-negative prostate cancer cell lines with an autocrine IL6 loop and that its RNAi-mediated knockdown led to cell death (20). In contrast to this, several publications could demonstrate that SOCS3 is frequently inactivated by promoter hypermethylation in different types of cancer, including prostate cancer (21)(22)(23).…”

PIM Kinase Inhibitors Downregulate STAT3Tyr705 Phosphorylation

“…Some of these results have been duplicated in prostate cancer cell lines, as downregulation of SOCS-1 by siRNA increases the proliferation of DU-145 cells. However, SOCS-3 may have an opposite function in DU-145 cells, as downregulation of SOCS-3 in DU-145 cells decreases cell proliferation (44,45). A role for PIM-3 in the regulation of SOCS proteins has not Tyr705 expression analysis are presented as in Fig.…”

Inhibition of the Acetyltransferases p300 and CBP Reveals a Targetable Function for p300 in the Survival and Invasion Pathways of Prostate Cancer Cell Lines

“…Western blot was done as described before (22). For p300 and CBP, 3% to 8% Tris/acetate gels and for p65, p50, and Bcl-xL, 4% to 12% Bis/Tris gels were used.…”

“…Cells were incubated for the last 16 hours with 37 kBq/ well 3 H-thymidine, and DNA was measured as described before (22).…”