pSlug immunohistochemistry is a novel promising mitotic marker for FFPE samples: a pilot study

Slug is a transcription factor belonging to the slug/snail superfamily. The protein is involved in embryonic development and epithelial-mesenchymal transition of tumors. Slug is also under temporal regulation during cell cycle. Here, we examined relationship between pSlug (site-specific phosphorylation) and the cell cycle, and checked whether its phosphorylation level reflects mitotic activity in tissue specimens. Cell cycle analysis was performed after cell synchronization. To evaluate pSlug identifying mitotic figures, we performed immunohistochemistry (IHC) for pSlug in various formalin-fixed paraffin-embedded tissues; in addition, mitotic counts were compared with those in sections stained with hematoxylin and eosin (HE) and IHC for PHH3, a mitotic marker. We found that the level of pSlug protein increased specifically at M phase and decreased at the G1/S phases in vitro. In almost all tested tissues, nuclear stain of pSlug was identified in the cell with mitotic figures. There was no significant difference in mitotic counts between HE- and pSlug-stained sections. In conclusion, pSlug may be a novel and practical immunohistochemical marker for detecting mitotic figures in human tissues.