Induction of neurite outgrowth by interleukin-6 is accompanied by activation of Stat3 signaling pathway in a variant PC12 cell (E2) line.
PC12-E2 cells, a stable variant subcloned from native cell populations, produce neurites in a rapid, transcription-independent manner upon exposure to nerve growth factor (NGF) or basic fibroblast growth factor (bFGF). They also give a similar morphological response to interleukin-6 (IL-6), which is, however, transcription-dependent and with a slower onset, a phenomenon basically not observed in native PC12 cells. The response profile of PC12-E2 cells to NGF and bFGF is similar to that observed for native PC12 cells pre-exposed (primed) to NGF, and such cells also respond to IL-6 in a fashion indistinguishable from PC12-E2 cells. Mechanistically, NGF and bFGF induce a sustained phosphorylation and activation of ERK1 and ERK2 in both cells, while IL-6 produces only a transient and weak tyrosine phosphorylation. However, it does stimulate a prolonged and biphasic tyrosine phosphorylation and nuclear translocation of Stat3 (signal transducers and activators of transcription 3; at least 24 h) and, to a lesser extent, Stat1. Gel shift and supershift analyses confirm that IL-6 predominantly activates Stat3 (and some Stat1) and stimulates sis-inducible element binding activity. Other members of the same cytokine subfamily, including ciliary neurotrophic factor and leukemia inhibitory factor, also cause a transient initial phase of tyrosine phosphorylation and activation of Stat1 and Stat3 (up to 1 h) but fail to stimulate a second phase of response and do not produce significant neurites. These results suggest that sustained signaling of either STAT or ERK pathways in PC12-E2 cells leads to induction of neuronal differentiation. However, only the latter is effective in native PC12 cells as the activation of Stat3 and Stat1 in native PC12 cells by IL-6 fails to induce neuronal differentiation. Thus, the response of PC12-E2 cells to IL-6 suggests the constitutive expression of a required factor(s) for differentiation, that is induced in native PC12 cells by NGF or bFGF (possibly by ERK activation), but not by IL-6 via Janus kinase/STAT activation. This factor(s), which has a sufficient half-life to allow primed cells to remain responsive to IL-6 for several days, is necessary but not sufficient for differentiation (as measured by neurite proliferation) to occur.
Wu
Y Y
YY
Department of Biological Chemistry, College of Medicine, University of California, Irvine, California 92717-1700, USA.
Bradshaw
R A
RA
D000209:Acute-Phase Proteins / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005346:Fibroblast Growth Factors / Q000378:metabolism; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology*; D007700:Kinetics; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000378:metabolism; D016501:Neurites / Q000187:drug effects* / Q000378:metabolism; D016716:PC12 Cells; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D000209:Acute-Phase Proteins; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D009414:Nerve Growth Factors; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494081:Stat1 protein, rat; C494088:Stat3 protein, rat; D015534:Trans-Activators; D014443:Tyrosine; D005346:Fibroblast Growth Factors; D004247:DNA; D011494:Protein Kinases