Certain
tumor cell responses to the
growth factor-inducible early response gene product CCN1/Cyr61 overlap with those induced by the
hepatocyte growth factor (HGF)/c-Met signaling pathway. In this study, we investigate if Cyr61 is a downstream effector of HGF/c-Met pathway activation in human
glioma cells. A semiquantitative immunohistochemical analysis of 112 human
glioma and normal brain specimens showed that levels of
tumor-associated
Cyr61 protein correlate with
tumor grade (P < 0.001) and with c-Met
protein expression (r(2) = 0.4791, P < 0.0001). Purified HGF rapidly upregulated Cyr61
mRNA (peak at 30 minutes) and
protein expression (peak at 2 hours) in HGF(-)/c-Met(+) human
glioma cell lines via a transcription- and translation-dependent mechanism. Conversely, HGF/c-Met pathway inhibitors reduced Cyr61 expression in HGF(+)/c-Met(+) human
glioma cell lines in vitro and in HGF(+)/c-Met(+)
glioma xenografts. Targeting Cyr61 expression with
small interfering RNA (
siRNA) inhibited HGF-induced cell migration (P < 0.01) and cell growth (P < 0.001) in vitro. The effect of Cyr61 on HGF-induced Akt pathway activation was also examined. Cyr61
siRNA had no effect on the early phase of HGF-induced Akt phosphorylation (Ser(473)) 30 minutes after stimulation with HGF. Cyr61
siRNA inhibited a second phase of Akt phosphorylation measured 12 hours after cell stimulation with HGF and also inhibited HGF-induced phosphorylation of the Akt target
glycogen synthase kinase 3alpha. We treated preestablished subcutaneous
glioma xenografts with Cyr61
siRNA or control
siRNA by direct intratumoral delivery. Cyr61
siRNA inhibited Cyr61 expression and
glioma xenograft growth by up to 40% in a dose-dependent manner (P < 0.05). These results identify a Cyr61-dependent pathway by which c-Met activation mediates cell growth, cell migration, and long-lasting signaling events in
glioma cell lines and possibly astroglial
malignancies.