Conclusive Evidence for OCT4 Transcription in Human Cancer Cell Lines: Possible Role of a Small OCT4-Positive Cancer Cell Population

The role of octamer-binding transcription factor 4 (OCT4) in human cancer is still debated. Although many studies have been published on human OCT4, determining which of the findings are accurate or which are false-positives is currently challenging. We thus developed the most reliable method to date for highly specific and comprehensive detection of genuine OCT4-transcript variants without false-positive results. Our results provided clear evidence that the transcripts of OCT4A, OCT4B, OCT4B1, and other novel splicing variants are indeed present in many cancer cell lines, but are rarely detected in normal tissue-derived differentiated cells. Using the tagged genomic transgene, we then verified endogenous OCT4A translation in cancer cell subpopulations. Moreover, analysis of possible other protein isoforms by enforced expression of OCT4B variants showed that the B164 isoform, designated human OCT4C, is preferentially produced in a cap-dependent manner. We confirmed that the OCT4C isoform, similar to OCT4A, can transform non-tumorigenic fibroblasts in vitro. Finally, ablation of OCT4-positive cells using promoter-driven diphtheria toxin A in high malignant cancer cells caused a significant decrease in migration and Matrigel invasion. These findings strongly suggest a significant contribution of OCT4 to the phenotype of human cancer cells.