Glucosamine inhibits IGF-1R at the post-translational level. (A) Semiquantitative RT-PCR analysis of IGF-1R and COX-2 mRNA levels in A549 cells. (B) A549 cells were treated with the indicated doses of glucosamine and the proteasome inhibitor MG132 for 1 day. (C) A549 cells were pretreated with the indicated concentrations of glucosamine for 16 hours and then with cycloheximide for 2 hours. (D) A549 cells were treated with the indicated concentrations of glucosamine or tunicamycin for 6 hours. (E) A549 cells were treated with 1 mM glucosamine or 0.5 μg/ml tunicamycin for 12 hours in the absence or presence of 25 μM MG132. (F) Western blot analysis of the expression of various ER stress- and unfolded protein response-related genes was performed using cell lysates from harvested A549 cells.