[Molecular mechanism of LRIG1 cDNA-induced apoptosis in human glioma cell line H4].

Background & Objective: Leucine-rich repeats and immunoglobulin-like domains 1(LRIG1)is a kind of transmembrane glycoprotein,which is induced by epidermal growth factor (EGF),and develops inhibitory negative feedback by specific binding with epidermal growth factor receptor (EGFR). This research was to explore the molecular mechanism of LRIG1 inhibiting EGFR signal pathway.
Methods: Plasmid p3XFLAG-CMV9-LRIG1 was transfected into neuroglioma cell line H4. Changes of LRIG1 and EGFR expression at mRNA and protein levels were measured by RT-PCR and Western blot, respectively. Changes of cell proliferation and apoptosis were analyzed by MTT and flow cytometry methods.
Results: LRIG1 mRNA level in p3XFLAG-CMV9-LRIG1 transfected H4 cells (1.997+/-0.114) was significantly higher than that in control H4 cells (0.500+/-0.031),and p3XFLAG-CMV9 transfected group (0.357+/-0.035) (P< 0.001). LRIG1 protein level in p3XFLAG-CMV9-LRIG1 transfected H4 cells (1.790+/-0.119) was significantly higher than that in control H4 cells (0.717+/-0.038, P< 0.001), and p3XFLAG-CMV9 transfected H4 cells (0.930+/-0.076, P=0.001). EGFR mRNA level in p3XFLAG-CMV9-LRIG1 transfected H4 cells (0.463+/-0.033) was significantly lower than that in control H4 cells (1.157+/-0.067, P< 0.001), and p3XFLAG-CMV9 transfected H4 cells (0.933+/-0.058, P=0.002). EGFR protein level in p3XFLAG-CMV9-LRIG1 transfected H4 cells (0.703+/-0.067) was significantly lower than that in control H4 cells (1.280+/-0.078, P=0.003),and p3XFLAG-CMV9 transfected H4 cells (1.163+/-0.068,P=0.009). Apoptosis rate in LRIG1-transfected H4 cells (18.89%)was lower than that in control H4 cells (3.11%), and vector-transfected H4 cells (5.42%, P< 0.001).
Conclusion: LRIG1 participates in construction of negative feedback loop of EGFR, which may inhibits growth of glioma cells.