MAPK1 and lung cancer: To validate the ERK/MEK pathway as a novel signaling pathway that modulates TRF1 foci formation, we selected 5 structurally different MEK inhibitors and three structurally different ERK inhibitors (see Materials and Methods) and tested these compounds at 1 μM during 24 h in the CHA‐9.3 mouse lung cancer cell line followed by TRF1 immunofluorescence analysis.