The wild-type FOS cDNA clone was purchased from Origene (#SC116873, OriGene Technologies Inc., Rockville, MD, USA). To construct FOS mutant to prevent phosphorylation, FOS clone containing alanine replacements on Thr-232, Thr-325, Thr-331, and Ser-374 was generated by the QuikChange Lightning Site-Directed Mutagenesis Kit (#210518, Stratagene, La Jolla, CA). The primer sequences used for mutagenesis are listed in Supplementary Table 2. The FOS wild-type and FOS mutant plasmids were transfected into KAT18 cells using Lipofectamine 3000 (Invitrogen) according to the manufactory’s protocol.