B, OTUB1 overexpression does not affect serum-induced MAPK activation in mutant KRAS A549 lung adenocarcinoma cells. A,B, Serum-starved lung cells expressing Flag-OTUB1 or an empty vector (V) were stimulated with 10% serum for the indicated time periods. Whole cell lysates were analyzed by immunoblotting using antibodies against pERK1/2, ERK1/2, Flag and vinculin. 