Fig. 2.

Expression pattern of membrane receptors and intracellular transport markers in lung cancer cell lines. a Expression of EGFR detected by immunoblotting was high in A549, H226, and H1437; moderate in H838 and H2087; and low in H23 and H2009 cells. EGFR was not detected in H125 cells. Molecular weight of EGFR in H838, H2087 (about 175 kDa), and H1437 (about 185 kDa) was higher than that in A549, H23, H226, and H2009 (about 170 kDa) cells. Interestingly, only H1437 cells expressed both HGF and c-Met. Expression of SAE2, on the other hand, was detected as a 100-kDa protein in lung cancer cells. Expression of β-actin was a monitoring standard. SAE2 expression was high in A549, H23, H226, and H2087; moderate in H125; and low in H838 and H1437 cells. SAE2 was not detected in H2009 cells. b Addition of EGF increased expression level and the phosphorylated forms (pEGFR) of EGFR in H2009 cells, which did not express c-Met. However, no evident molecular weight upshifting of EGFR was detected. Addition of EGF increased SAE2 protein expression as well. c Addition of HGF increased molecular weight upshifting of EGFR from 170 to 185 kDa in A549 cells. d Following treatment of H1437 cells with calf intestinal phosphatase (CIP), protein levels and molecular weights of 185 kDa EGFR reduced, suggesting that phosphorylation was critical for EGFR stability. e Using siRNA to knockdown EGFR (EGFR^KD) expression for 48 h reduced protein levels of SAE2. f Silencing of EGFR gene expression for 48 h (EGFR^KD-48hr) reduced SAE2 expression. g However, expression of c-Met and pc-Met was increased in EGFR^KD-48hr cells. Such short-term effect dwindled when EGFR gene silencing was continued to 96 h; and at this time, protein level of c-Met and ATAD3A reduced markedly