title: Exon 11 skipping of E-cadherin RNA downregulates its expression in head and neck cancer cells.
abstract: E-cadherin is an important tumor suppressor gene whose expression is lost when cells acquire a metastatic phenotype. We analyzed the role of E-cadherin missplicing as a mechanism of its downregulation by analyzing a misspliced E-cadherin transcript that lacks exon 11 of this gene. This results in a frameshift and a premature termination codon that targets this transcript for degradation. Tumor tissues, including breast (20%, n = 9), prostate (30%, n = 9) and head and neck (75%, n = 8) cancer, express the exon 11-skipped transcripts (vs. nonmalignant controls) and its levels inversely correlate with E-cadherin expression. This is a novel mechanism of E-cadherin downregulation by missplicing in tumor cells, which is observed in highly prevalent human tumors. In the head and neck cancer model, nontumorigenic keratinocytes express exon 11-skipped splice product two- to sixfold lower than the head and neck tumor cell lines. Mechanistic studies reveal that SFRS2 (SC35), a splicing factor, as one of the regulators that increases missplicing and downregulates E-cadherin expression. Furthermore, this splicing factor was found to be overexpressed in 5 of 7 head and neck cell lines and primary head and neck tumors. Also, methylation of E-cadherin gene acts as a regulator of this aberrant splicing process. In 2 head and neck cell lines, wild-type transcript expression increased 16- to 25-folds, whereas the percentage of exon 11-skipped transcripts in both the cell lines decreased five- to 30-folds when cells were treated with a hypomethylating agent, azacytidine. Our findings reveal that promoter methylation and an upregulated splicing factor (SFRS2) are involved in the E-cadherin missplicing in tumors.
authors.affiliation: Division of Hematology Oncology, UCLA West Los Angeles VA Medical Center, 11301 Wilshire Blvd, Bldg 304, Rm E1-115, Los Angeles, CA 90073, USA. sasharma@mednet.ucla.edu
authors.forename: Sanjai
authors.initials: S
authors.lastname: Sharma
authors.forename: Wei
authors.initials: W
authors.lastname: Liao
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Zhou
authors.forename: David T W
authors.initials: DT
authors.lastname: Wong
authors.forename: Alan
authors.initials: A
authors.lastname: Lichtenstein
mesh_terms: D017398:Alternative Splicing; D015820:Cadherins / Q000235:genetics*; D045744:Cell Line, Tumor; D019175:DNA Methylation; D005091:Exons; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D023061:Gene Order; D005822:Genetic Vectors / Q000235:genetics; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D020871:RNA Stability; D012261:Ribonucleoproteins / Q000378:metabolism; D000068103:Serine-Arginine Splicing Factors; D014158:Transcription, Genetic
chemical_list: D015820:Cadherins; D009687:Nuclear Proteins; D012261:Ribonucleoproteins; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors