Leucine-rich repeat C4 (LRRC4) has been shown to inhibit
glioma cell proliferation, however, little is known about the mechanism(s) underlying the action of LRRC4. Here, we show that two glioblstoma U251 cell clones stably expressing LRRC4 were established. LRRC4 expression significantly inhibited the expression of some
cytokines and their receptors determined by microarray and Western blot assays, and dramatically reduced
cytokine-induced
AP-1,
NF-kB, and CyclinD1 activation in
glioma cells. Furthermore, LRRC4 expression in
glioma cells significantly downregulated spontaneous and
cytokine-induced expression of K-RAS and phosphorylation of c-Raf, ERK, AKT, NF-kBp65,
p70S6K, and PKC, suggesting that LRRC4 inhibited
receptor tyrosine kinase (RTK) signaling pathways. Moreover, treatment with bFGF, IGF1, or IGF2 stimulated LRRC4(-/-), but not the LRRC4(+),
glioma cell proliferation, indicating that LRRC4 mitigated
cytokine-stimulated proliferation in
glioma cells. In addition, treatment of LRRC4(-/-)
glioma cells with
EGF, IGF2, or PDGF promoted long distance mobilization, but induced little migration in LRRC4(+)
glioma cells, suggesting that LRRC4 retarded
cytokine-promoted
glioma cell migration in vitro. Finally, human vessel endothelial cells (ECV304) treated with
VEGF grew, aligned and formed hollow tube-like structures in vitro. In contrast, LRRC4(+) ECV304 treated with
VEGF failed to form vessel-tube structures. Collectively, LRRC4 expression inhibited the expression of some
growth factors,
cytokines and their receptors, and the capacity of
glioma cells responding to
cytokine stimulation, leading to inhibition of
glioma cell proliferation. Conceivably, induction of LRRC4 expression may provide new intervention for human
glioma in the clinic.