CDKN1A and melanoma: We identified by mass spectrometry phosphorylation of Ser78 in endogenous CDKN1A upon UVB irradiation in mouse melanoma cells (Figure S5D), Phosphorylation on Ser78 was significantly decreased in LKB1 depleted cells (30% vs. 1% of peptide phosphorylated respectively; p<0.0001) (Figure S5E).