PHF1Is Involved In Gene Transcriptional Repression And Promotes Tumorigenesis And Metastasis Of Breast Cancer

PHF1(PHD finger protein1), which consists of567amino acids, is a protein encoded by the PHF1gene on human chromatin6p21.3. It was named after the distinctive PHD (plant homodomain) zinc finger domain. It has been found that PHF1is homologous with PCL in drosophila melanogaster. There are three homologues of PCL in mammal, which are PHF1, MTF2and PHF19. Containing one TUDOR domain and two tandem PHD zinc finger domains is their common feature. Although PHF1has no enzyme activity, these distinctive recognition domains make it a very important reader in epigenetic regulation. It has been reported that PHF1interacts with PRC2complex and influences trimethylation of histone H3K27and HOX gene silencing. Moreover, PHF1can recognize trimethylation of histone H3K36and trimethylation of histone H3tK27, which suggests that PHF1might play an important role in different kinds of histone codes recognition.Our research found that PHF1interacts with NuRD complex, SIN3A complex, CRL4B complex, p160family and PRMT5/MEP50complex, and it transcriptional represses the expression of FBXW7. Furthermore, PHF1promotes growth, invasion and metastasis of breast cancer cells. Our study found new ways how PHF1participates in transcriptional regulation and verified the function of PHF1in tumorigenesis and development which provide a new target for clinical diagnosis and therapy of tumors, especially breast cancer.In order to find more proteins associated with PHF1in vivo, we analyzed the associated proteins by affinity purification and mass spectrometryassay. In these proteins we found, AIB1, EZH2, SUZ12, MTA1, PRMT5, HDAC2, MEP50and EED are concerned with epigenetic regulation. Co-immunoprecipitation experiments were performed to verify that PHF1interacts with NuRD complex, SIN3A complex, CRL4B complex, p160family and PRMT5/MEP50complex.To further indicate the role of PHF1in transcriptional regulation, ChIP-on-chip assays were performed to analyze target genes which PHF1regulates. The results revealed that the703genes found in ChIP-on-chip assay play a part in many vital cell signal pathways such as Ras, MAPK, PI3K-Akt, Jak-STAT, cytokine and cancer pathways. We next found that PHF1occupies on the promotors of CBX4, CTNNA1, E-cadherin, ERa,FBXW7, GATA5, ING3, POU1F1, SMAD7and SIAH2. Among the target genes, FBXW7was selected to be further investigated. Except for occupied on the promoter of FBXW7, PHF1transcriptional represses the expression of FBXW7.To determine the influnce on tumorigenesis and development of PHF1and its biological significance, we used growth curve assays, colony formation assays and transwell assays to find out the role of PHF1in tumorigenesis and development. The results showed that, PHF1promotes growth, EMT progress, invasion and metastasis of breast cancer cells.To sum up, we found that PHF1interacts with many transcriptional regulation complexes and affect many vital cell signal pathways by repressing gene expression. It also transcriptional represses the expression of FBXW7and promotes growth and metastasis of breast cancer cells. These findings will help us understanding and further investigating the mechanism in epigenetic regulation of PHF1and its role in cancers.