PHGDH and head and neck squamous cell carcinoma: In keratinocytes, p63 has a direct interaction with the promoter regions of many of the genes involved in serine de novo biosynthesis and OCM (PHGDH, PSAT1, PSPH and MTHFD2), which is also true in FaDu cells, a well-established HNSCC cell line model, where p63 shows the same binding to the promoter region of the abovementioned genes.