Inhibitory Effect Of LRRC4 On Invasion Of Human Gliomas Through The SDF-1α/CXCR4-Mediated ERK1/2 And AKT Signaling Pathways

【Background of LRRC4 and SDF-1α/CXCR4 axis】Glioblastomas are the most common and lethal human primary brain tumors, and are characterized by high invasiveness. Leucine-rich repeats containing 4 (LRRC4) is a potential glioma suppressive gene. The conspicuous absence of LRRC4 in high-grade gliomas directly contributes to increasing tumor grade. The reexpression of LRRC4 can significantly suppress glioblastomas U251 cells tumorigenesis in vivo and cell proliferation and invasion in vitro. LRRC4 controls glioblastoma cells proliferation by ERK/AKT/NF-κB signaling pathway. Stromal cell-derived factor SDF-1 (recently renamed CXCL12) and its CXC chemokine receptor 4 (CXCR4) are involved in normal and malignant glial cell proliferation and migration. SDF-1αexerts its activity by interacting with the CXCR4 receptor, a member of the G protein-coupled receptor superfamily. Recent data showed that CXCR4 and SDF-1 mRNAs are co-localized in glioblastomas and that their expression increase with the tumor grade and is associated with regions of necrosis and angiogenesis.【LRRC4 inhibits invasion of U251 cells through SDF-1α/CXCR4 axis】The absence of LRRC4 in high-grade gliomas and the over-expression of CXCR4 contribute to increasing tumor grade. In the present study, we demonstrate that CXCR4 is expressed in human glioblastoma U251 cell line, and that SDF-1αinduces proliferation, adhesion ability chemotaxis, mobility and invasion in CXCR4~+ glioblastoma U251 cells. The reintroduction of LRRC4 in U251 cells inhibits the expression of CXCR4 and SDF-1α/CXCR4 axis-induced proliferative, adhesive, chemotactic and invasive effects. LRRC4 can greatly enhance GJIC of U251 cells.【LRRC4 down-regulates the SDF- 1α/CXCR4-mediated ERK1/2 and Akt signaling pathways and inhibit MMP-2 activity】LRRC4 exerts its inhibitory role in U251 cells by down-regulating the SDF- 1α/CXCR4-mediated phosphorylation activation of ERK1/2 and Akt. We also provide evidence for proMMP-2 activation involvement in the SDF-1α/ CXCR4 axis-mediated signaling pathway. LRRC4 significantly inhibits proMMP-2 activation by SDF-1α/CXCR4 axis-mediated ERK1/2 and Akt signaling pathway. We did not find impact of LRRC4 on MMP-9 activity.【LRRC4 induces U251 cells to differentiate into astrocyte-like cells】U251 cells transfected with LRRC4 become smaller and round in shape and their axon grow longer as compared with U251 cells. LRRC4 significantly increases the expression of GFAP, which is regarded as a specific mark for gliomas and is related to the differentiation of gliomas. Hence, LRRC4 can induce U251 cells to differentiate into astrocyte-like cells.Collectively, these results suggest a possible important "cross-talk" between LRRC4 and SDF-1α/CXCR4 axis-mediated intracellular pathways that can link signals of cell chemotaxis and invasion in glioblastoma, and LRRC4 induce the differentiation of gliomas, which may represent a new target for development of new therapeutic strategies in glioma.