Molecular Medicine in Practice Exon 11 Skipping of E-Cadherin RNA Downregulates Its Expression in Head and Neck Cancer Cells

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 1⁄4 9), prostate (30%, n 1⁄4 9) and head and neck (75%, n 1⁄4 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 twoto sixfold lower than the head andneck tumor cell lines.Mechanistic studies reveal that SFRS2 (SC35), a splicing factor, as one of the regulators that increases missplicing and downregulates Ecadherin expression. Furthermore, this splicing factorwas found tobeoverexpressed in5 of 7headandneck cell lines and primary head and neck tumors. Also, methylation of E-cadherin gene acts as a regulator of this aberrant splicingprocess. In 2 headandneck cell lines,wild-type transcript expression increased 16to 25-folds, whereas the percentage of exon 11-skipped transcripts in both the cell lines decreased fiveto 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. Mol Cancer Ther; 10(9); 1751–9. 2011 AACR.