FIGURE 3:

β8 integrin suppresses Rac1 and Cdc42 activation in GBM cells. (A) Schematic model for regulation of Rho GTPase and Pak1 activation by extracellular cues. (B) Lysates from LN229 cells expressing scrambled siRNAs or siRNAs targeting β8 integrin were immunoblotted for β8 integrin or actin. (C) Integrin-dependent levels of phosphorylated-Pak1 or GTP-bound Rac1, Cdc42, and RhoA were analyzed in LN229 cell lysates. Phosphorylated Pak1 levels are increased after integrin silencing. Similarly, elevated levels of GTP-bound Rac1 and Cdc42, but not RhoA, were detected in cells expressing diminished levels of β8 integrin. (D, E) Intracranial tumors generated from LN229 cells expressing scrambled shRNAs (D) or β8 shRNAs (E) were analyzed by double immunofluorescence using anti–phospho-Pak1 (red) and anti-GFP (green) antibodies. At least three different sections from four different tumors were analyzed per cell type, with representative images shown. Note the elevated levels of phosphorylated Pak1 in tumor cells expressing β8 shRNAs. Scale bars, 100 μm.