Interleukin-6 inhibits cell proliferation in a rat model of hepatocellular carcinoma.
BACKGROUND
Interleukin-6 (IL-6) plays a critical role in normal hepatic growth and liver regeneration. The aims of the present study are to determine the expression of components of IL-6 signaling in an in vivo model of hepatocellular carcinoma (HCC) and address the role of IL-6 signaling in the progression of HCC.


METHODS
An in vivo rat HCC model was established and IL-6 receptor (IL-6R) and downstream signaling pathway expression and activity were determined in HCC and normal liver specimens. Tumorigenic HCC cells from resected HCC samples and normal hepatocytes were then isolated and cultured in the presence and absence of recombinant human IL-6 (rhIL-6).


RESULTS
HCC specimens demonstrated decreased IL-6Ralpha/gp130 expression as compared with the normal liver. In contrast, HCC samples had significantly increased IL-6 messenger RNA expression and signal transducers and activators of transcription (STAT)3 activity. Using in vitro cell cultures, we demonstrated that IL-6 stimulated STAT3 and extracellular regulated kinase (ERK) activity in both HCC cells and isolated hepatocytes. However, while STAT3 activation profiles were similar, IL-6 stimulated ERK activity in a biphasic manner in HCC cells and a monophasic, sustained ERK activation in hepatocytes. In HCC cells, a significant induction of cyclin-dependent kinase (CDK) inhibitors, p21(waf1/cip1) and p27(Kip1) occurred, an effect that was not observed in normal hepatocytes. Finally, we established that IL-6 acted to inhibit serum-stimulated DNA synthesis and cell mitogenesis in HCC cells in vitro.


CONCLUSIONS
These data demonstrate altered expression of components of IL-6 signaling in HCC in vivo. IL-6 treatment of HCC cells inhibits serum-stimulated mitogenesis, possibly via differences in activation profiles of intracellular signaling pathways and their effect on CDK inhibitor expression/activity.
Moran
Diarmuid M
DM
Department of Biology, University of North Carolina at Charlotte, 9201 University City Boulevard, Charlotte, NC 28223, USA.
Mayes
Nicholas
N
Koniaris
Leonidas G
LG
Cahill
Paul A
PA
McKillop
Iain H
IH
D000818:Animals; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D022781:Hepatocytes / Q000166:cytology*; D015850:Interleukin-6 / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008969:Molecular Sequence Data; D011336:Probability; D012334:RNA, Neoplasm / Q000032:analysis; D011897:Random Allocation; D051381:Rats; D011912:Rats, Inbred ACI; D019947:Receptors, Interleukin-6 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*
D004268:DNA-Binding Proteins; D015850:Interleukin-6; D012334:RNA, Neoplasm; D019947:Receptors, Interleukin-6; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; D015534:Trans-Activators; D048052:Mitogen-Activated Protein Kinase 3