AP-2alpha induces epigenetic silencing of tumor suppressive genes and microsatellite instability in head and neck squamous cell carcinoma.
BACKGROUND
Activator protein 2 alpha (AP-2alpha) is involved in a variety of physiological processes. Increased AP-2alpha expression correlates with progression in various squamous cell carcinomas, and a recent publication found AP-2alpha to be overexpressed in approximately 70% of Head and Neck Squamous Cell Carcinoma (HNSCC) patient samples. It was found to repress transcription of the tumor suppressor gene C/CAAT Enhancer Binding Protein alpha (C/EBPalpha), and its binding site correlated with upstream methylation of the C/EBPalpha promoter. Therefore, we investigated the potential for AP-2alpha to target methylation to additional genes that would be relevant to HNSCC pathogenesis.


RESULTS
Stable downregulation of AP-2alpha stable by shRNA in HNSCC cell lines correlated with decreased methylation of its target genes' regulatory regions. Furthermore, methylation of MLH1 in HNSCC with and without AP-2alpha downregulation revealed a correlation with microsatellite instability (MSI). ChIP analysis was used to confirm binding of AP-2alpha and HDAC1/2 to the targets. The effects of HDAC inhibition was assessed using Trichostatin A in a HNSCC cell line, which revealed that AP-2alpha targets methylation through HDAC recruitment.


CONCLUSIONS
These findings are significant because they suggest AP-2alpha plays a role not only in epigenetic silencing, but also in genomic instability. This intensifies the potential level of regulation AP-2alpha has through transcriptional regulation. Furthermore, these findings have the potential to revolutionize the field of HNSCC therapy, and more generally the field of epigenetic therapy, by targeting a single gene that is involved in the malignant transformation via disrupting DNA repair and cell cycle control.
Bennett
Kristi L
KL
Genomic Medicine Institute, Lerner Research Institute and Taussig Cancer Institute, Cleveland Clinic, Cleveland, Ohio, United States of America.
Romigh
Todd
T
Eng
Charis
C
D002294:Carcinoma, Squamous Cell / Q000235:genetics*; D045744:Cell Line, Tumor; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006258:Head and Neck Neoplasms / Q000235:genetics*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D053842:Microsatellite Instability; D018895:Microsatellite Repeats; D008954:Models, Biological; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D050656:Transcription Factor AP-2 / Q000378:metabolism / Q000502:physiology*
D006877:Hydroxamic Acids; D011500:Protein Synthesis Inhibitors; D050656:Transcription Factor AP-2; C012589:trichostatin A; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human