DeltaNp63 silencing, DNA methylation shifts and epithelial mesenchymal transition resulted from TAp63 genome editing in squamous cell carcinoma [microarray]

TP63 (p63) is strongly expressed in lower-grade carcinomas of head-and-neck, skin, breast, urothelium, etc. to maintain the well-differentiated phenotype. TP63 has two transcription start sites at exon 1 and exon 3’ to produce TAp63 and DeltaNp63 isoforms, respectively. The major protein, DeltaNp63alpha, epigenetically activates genes essential for epidermal/craniofacial differentiation, including DeltaNp63 itself. To examine whether weakly expressed TAp63 has a specific role, we disrupted exon 1 by CRISPR-Cas9 homology directed repair in a head and neck squamous cell carcinoma (SCC) line. Surprisingly, TAp63 knockout cells, either by monoallelic GFP cassette insertion paired with a frameshift deletion allele or by biallelic GFP cassette insertion, caused DeltaNp63 silencing. Loss of keratinocyte-specific gene expression, switching of intermediate filaments from KRT(s) to VIM, and suppression of cell-cell and cell-matrix adhesion components indicated core events of epithelial mesenchymal transition. Most of the positively and negatively impacted genes including DeltaNp63 displayed local DNA methylation changes. Furthermore, DeltaNp63 expression was partially rescued by transfection of TAp63alpha followed by incubation with DNA methyltransferase inhibitor Zebularine. TAp63, as a minor part of TP63 gene, may possibly be involved in the auto-activation mechanism of DeltaNp63 by which keratinocyte-specific epigenome is maintained in SCC. Comparison of genome-wide gene expression between parental (control) FaDu squamous cell carcinoma line and two TAp63 knockout cell lines derived from FaDu