HGF and central nervous system cancer: Xu et al. first reported that CD44 is a co-stimulator of the MET signaling pathway in glioma cells and attenuated CD44 expression was found to diminish the HGF-induced phosphorylation of Erk1/2 kinase but not that of AKT kinase, suggesting that CD44 preferentially modulates proliferation but not survival signaling pathways activated by HGF growth factors [62].