Western blot analysis was performed on whole cell extracts (30 µg lysate) of HeLa (1), H-1975 (2), HCT 116 (3), HT-29 (4), A-431 (5), A549 (6), MDA-MB-231 (7), U-87 MG (8) and MCF7 (9). The blot was probed with Anti-MEK1 Rabbit Polyclonal Antibody (Product # PA1-29035, 1 µg/mL) and detected by chemiluminescence using Goat anti-Rabbit IgG (Heavy Chain) Superclonal™ Secondary Antibody, HRP conjugate (Product # A27036, 0.25 µg/mL, 1:4000 dilution). A 45 kDa band corresponding to MEK1 was detected across all cell lines tested. Known quantity of protein samples were electrophoresed using Novex® NuPAGE® 4-12 % Bis-Tris gel (Product # NP0321BOX), XCell SureLock™ Electrophoresis System (Product # EI0002) and Novex® Sharp Pre-Stained Protein Standard (Product # LC5800). Resolved proteins were then transferred onto a nitrocellulose membrane with iBlot® 2 Dry Blotting System (Product # IB21001). The membrane was probed with the relevant primary and secondary Antibody following blocking with 5 % skimmed milk. Chemiluminescent detection was performed using Pierce™ ECL Western Blotting Substrate (Product # 32106).