Transforming growth factor-beta1 activates interleukin-6 expression in prostate cancer cells through the synergistic collaboration of the Smad2, p38-NF-kappaB, JNK, and Ras signaling pathways.
Transforming growth factor (TGF)-beta1 acts as a potent growth inhibitor of prostate epithelial cells, and aberrant function of its receptor type I and II correlates with tumor aggressiveness. However, intracellular and serum TGF-beta1 levels are elevated in prostate cancer patients and further increased in patients with metastatic carcinoma, suggesting the oncogenic switch of TGF-beta1 role in prostate tumorigenesis. Recently, we reported the mitogenic conversion of TGF-beta1 effect by oncogenic Ha-Ras in prostate cancer cells. Here, we show that TGF-beta1 activates interleukin (IL)-6, which has been implicated in the malignant progression of prostate cancers, via multiple signaling pathways including Smad2, nuclear factor-kappaB (NF-kappaB), JNK, and Ras. TGF-beta1-induced IL-6 gene expression was strongly inhibited by DN-Smad2 but not by DN-Smad3 while it was further activated by wild-type Smad2 transfection. IL-6 activation by TGF-beta1 was accompanied by nuclear translocation of NF-kappaB, which was blocked by the p38 inhibitors SB202190 and SB203580 or by IkappaBalphaDeltaN transfection, indicating the crucial role for the p38-NF-kappaB signaling in TGF-beta1 induction of IL-6. TGF-beta1 activated c-Jun phosphorylation, and IL-6 induction by TGF-beta1 was severely impeded by DN-c-Jun and DN-JNK or AP-1 inhibitor curcumin, showing that the JNK-c-Jun-AP-1 signaling plays a pivotal role in TGF-beta1 stimulation of IL-6. It was also found that the Ras-Raf-MEK1 cascade is activated by TGF-beta1 and participates in the TGF-beta1 induction of IL-6 in an AP-1-dependent manner. Cotransfection assays demonstrated that TGF-beta1 stimulation of IL-6 results from the synergistic collaboration of the Smad2, p38-NF-kappaB, JNK-c-Jun-AP-1, or Ras-Raf-MEK1 cascades. In addition, a time course IL-6 decay revealed that mRNA stability of IL-6 is modestly increased by TGF-beta1, indicating that TGF-beta1 also regulates IL-6 at the post-transcriptional level. Intriguingly, IL-6 inactivation restored the sensitivity to TGF-beta1-mediated growth arrest and apoptosis, suggesting that elevated IL-6 in advanced prostate tumors might act as a resistance factor against TGF-beta1. Collectively, our data demonstrate that IL-6 expression is stimulated by tumor-producing TGF-beta1 in human prostate cancer cells through multiple signaling pathways including Smad2, p38, JNK, and Ras, and enhanced expression of IL-6 could contribute to the oncogenic switch of TGF-beta1 role for prostate tumorigenesis, in part by counteracting its growth suppression function.
Park
Jae-Il
JI
Department of Pathology, College of Medicine, Kyung Hee University, Seoul, 130-701, Republic of Korea.
Lee
Min-Goo
MG
Cho
Kyucheol
K
Park
Bum-Joon
BJ
Chae
Kwon-Seok
KS
Byun
Do-Sun
DS
Ryu
Byung-Kyu
BK
Park
Yong-Keun
YK
Chi
Sung-Gil
SG
D017209:Apoptosis; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics*; D048031:JNK Mitogen-Activated Protein Kinases; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D016328:NF-kappa B / Q000502:physiology*; D011471:Prostatic Neoplasms / Q000209:etiology*; D012333:RNA, Messenger / Q000032:analysis; D051899:Smad2 Protein; D015534:Trans-Activators / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases
D004268:DNA-Binding Proteins; D015850:Interleukin-6; D016328:NF-kappa B; D012333:RNA, Messenger; C497782:SMAD2 protein, human; D051899:Smad2 Protein; C508960:TGFB1 protein, human; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases