pSlug^S158 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^S158 (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^S158 identifying mitotic figures, we performed immunohistochemistry (IHC) for pSlug^S158 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^S158 protein increased specifically at M phase and decreased at the G1/S phases in vitro. In almost all tested tissues, nuclear stain of pSlug^S158 was identified in the cell with mitotic figures. There was no significant difference in mitotic counts between HE- and pSlug^S158-stained sections. In conclusion, pSlug^S158 may be a novel and practical immunohistochemical marker for detecting mitotic figures in human tissues.