Socs7, a target gene of microRNA-145, regulates interferon-β induction through STAT3 nuclear translocation in bladder cancer cells

S Noguchi,Y Akao,M Kumazaki,J Iwasaki,N Yamada,Y Yasui,S Naito

doi:10.1038/cddis.2013.11

Abstract

We recently reported that microRNA (miR)-145 is downregulated and induces apoptosis in human bladder cancer cells. Also, it is suggested that the ectopic expression of miR-145 induces apoptosis with the induction of TRAIL expression in several cancer cells. Here, we demonstrated a novel mechanism of apoptosis induction by miR-145 in bladder cancer cells. Exogenous miR-145 in T24 and NKB1 cells markedly increased the expression levels of interferon (IFN)-β, 2′–5′-oligoadenylate synthetase 1, which lies upstream of 2′–5′ oligoadenylates/RNase L system, and TRAIL, and induced apparent caspase-dependent apoptosis that was suppressed by cotreatment with a pan-caspase inhibitor; moreover, these expression levels were reduced by cotreatment with an miR-145 inhibitor. The apoptosis did not depend on Toll-like receptor 3 (TLR3) expression, because TLR3-silencing failed to inhibit IFN-β induction by miR-145. Then, we focused on the suppressor of cytokine signaling 7 (socs7), whose expression level was upregulated in bladder cancer cells compared with its level in normal human urothelial cells, as a putative target gene involved in IFN-β induction by miR-145. Expectedly, exogenous miR-145 decreased the expression level of SOCS7, and socs7-silencing enhanced IFN-β induction by transfection with a TLR3 ligand, polyinosinic acid-polycytidylic acid (PIC). The results of a luciferase reporter assay revealed that miR-145 targeted socs7. In addition, socs7-silencing significantly decreased the level of p-Akt and suppressed the growth of T24 cells. Furthermore, exogenous miR-145 or socs7-silencing promoted nuclear translocation of STAT3. In conclusion, the machinery of IFN-β induction through the regulation of SOCS7 by miR-145 was closely associated with the induction of apoptosis. Moreover, exogenous miR-145 promoted IFN-β induction by targeting socs7, which resulted in the nuclear translocation of STAT3. Additionally, our data indicate that SOCS7 functioned as an oncogene, the finding that revealed a novel mechanism of carcinogenesis in bladder cancer cells.

Highlights

MiR-145 is downregulated in human bladder cancer cells and human melanoma cells.[5–7] miR-145 functions as a tumor suppressor in various human cancers, and its target genes include c-myc,[8] fascin[1,9] yes,[10] oct[4], klf[4,11] and ilk.[7]
We successfully demonstrate a part of the mechanism of the induction of IFN-b and apoptosis by miR-145 in bladder cancer cells
It has been indicated that the biochemical mechanism of apoptosis induction by miR-145 involves the induction of TRAIL expression.[13]

Summary

Introduction

MiR-145 is downregulated in human bladder cancer cells and human melanoma cells.[5–7] miR-145 functions as a tumor suppressor in various human cancers, and its target genes include c-myc,[8] fascin[1,9] yes,[10] oct[4], klf[4,11] and ilk.[7]. Factor-related Apoptosis-Inducing Ligand (TRAIL)-induced apoptotic cell death.[13,14]. IFN-b is secreted from cells in response to a viral infection or the introduction of double-stranded RNA (dsRNA), including siRNA.[17,18]. One of the most important pathways for IFN induction by dsRNA is the Toll-like receptor 3 (TLR3)/TLR adapter molecule 1 (TRIF) pathway. Viral infection or the introduction of dsRNA induces activation of the 20–50 oligoadenylates (2–5A)/RNase L system, which is triggered by 20–50-oligoadenylate synthetase 1 (OAS1).[20]. Graduate School of Medical Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, Japan oct-4, octamer-binding transcription factor 4; PIC, polyinosinic acid-polycytidylic acid; RT-PCR, reverse transcription polymerase chain reaction; SAPK/JNK, activation of stress-activated protein kinase/jun amino-terminal kinase; siRNA, small interfering RNA; SOCS7, suppressor of cytokine signaling 7; STAT3, signal transducer and activator of transcription 3; TLR3, Toll-like receptor 3; TRAIL, tumor necrosis factor-related apoptosis-inducing ligand; TRIF, TLR adapter molecule 1; 2–52–5A, 20–50 oligoadenylates

Methods

Results

Conclusion