Epigenetic Alteration of Polo-like Kinase 4 Plk4 in Methylation in Colorectal Cancer and Hepatocellular Carcinoma Cell Lines

Polo and Polo-like kinases Plks comprise a serinethreonine kinase family, which is highly conserved from yeasts to humans. This family is also known to be deeply involved in many events during cell division. Plk4 is a member of this family and is suggested to play a role in M phase progression, and Plk4 expression is reported to be frequently reduced in human hepatocellular carcinoma and in head and neck squamous cell carcinomas. In addition, the Plk4 gene has a CpG island in promoter area in front of exon 1 This evidence suggests that the down-regulation of Plk4 positively a#ects carcinogenesis. Therefore, it is important to identify the mechanism of Plk4 down-regulation. However, Plk4 expression and epigenetic status have not been thoroughly investigated, even in cell lines. We thus investigated whether the Plk4 gene is associated with epigenetic alteration, particularly DNA methylation, in hepatocellular and colorectal cancers. Our study clearly showed that Plk4 gene expression levels were su$ciently high by reverse transcription-polymerase chain reaction analysis in hepatocellular and colorectal carcinoma cell lines. No di#erences in Plk4 gene expression levels were seen with or without 5-aza-2’-deoxycytidin treatment. Moreover, no DNA methylation in the exon 1 promoter area of the Plk4 gene was seen in any of the cell lines analyzed.