Oct-4B isoform is differentially expressed in breast cancer cells: hypermethylation of regulatory elements of Oct-4A suggests an alternative promoter and transcriptional start site for Oct-4B transcription.

The human Oct-4 gene has three isoforms, Oct-4A, Oct-4B and Oct-4B1, which are thought to be derived from alternative splicing. It remains controversial whether the Oct-4 gene is expressed in cancer cells. Expression of Oct-4A is regulated by two elements, the PE (proximal enhancer) and DE (distal enhancer), but the expression and regulation of Oct-4B are not well known. Here, we firstly report that Oct-4B is expressed at low levels in MCF-7 cells, while the Oct-4A gene is inactivated. By analysing the function of different promoter constructs and the DNA methylation status of three regulatory regions, we demonstrate that the Oct-4A gene in MCF-7 cells is repressed by epigenetic control rather than transcriptional control. In addition, we speculate that the transcription of Oct-4B in MCF-7 cells is differentially regulated by additional regulatory elements. This work will enhance the understanding of Oct-4 gene in differential regulation.