Western blot was performed using Anti-RSK1 Polyclonal Antibody (Product # PA5-17168) and a 80 kDa band corresponding to Ribosomal protein S6 kinase alpha-1 was observed. Whole cell extracts (30 µg lysate) of HEK-293 (Lane 1), HeLa (Lane 2), HEL 92.1.7 (Lane 3) and BJ (Lane 4) were electrophoresed using NuPAGE™ 4-12% Bis-Tris Protein Gel (Product # NP0322BOX). Resolved proteins were then transferred onto a Nitrocellulose membrane (Product # IB23001) by iBlot® 2 Dry Blotting System (Product # IB21001). The blot was probed with the primary antibody (1:1000) and detected by chemiluminescence with Goat anti-Rabbit IgG (Heavy Chain) Superclonal™ Recombinant Secondary Antibody, HRP (Product # A27036, 1:4000) using the iBright FL 1000 (Product # A32752). Chemiluminescent detection was performed using Novex® ECL Chemiluminescent Substrate Reagent Kit (Product # WP20005). As expected, BJ expressed lower levels of RSK1 compared to HEL 92.1.7.