Figure 2.

ITGα6 confers resistance to PI3K inhibitors. (A) Immunohistochemical staining of integrin α6 (ITGα6) in castrate-resistant LuCaP (castrate) PDX tumors relative to uncastrated parental tumors. (B) ITGα6 and ITGβ1 mRNA expression, from microarray data, in castration-resistant LuCaP PDX tumors relative to uncastrated parental tumors. (C) PC3 cells or two different LuCaP PDX tumors were implanted subcutaneously (SC) or intratibially (Bone) and grown for 4 weeks. Tumors from each group were fixed and immunostained for ITGα6 and (D) positive staining was quantified. (E) LNCaP or C4-2 cells adherent to laminin were cultured in hypoxia for 24 h and levels of HIF-1α, ITGα6, ITGβ1, and Tubulin (Tub) protein assessed by immunoblotting. (F) LNCaP and C4-2 cells adherent to laminin were stimulated with 10 nM R1881 for 24 h prior to and in the presence of increasing concentrations of PX866, and cell viability measured by trypan blue exclusion 48 h later. (G) C4-2 cells were plated on laminin with or without ITGα6-blocking antibody (Iα6 Ab), then treated with or without 10 nM R1881 for 24 hours prior to and during 48 h treatment with 400 nM PX866 or DMSO (control). Cell death was assessed by trypan blue exclusion. *P < 0.05; n = 3; error bars indicate SEM.