The Y-Box binding protein, YB-1, belongs to a group in the DNA and RNA binding protein family. YB-1 is known to be expressed in a number of different cancers and reported to protect cells against DNA-damaging agents such as ultraviolet light. The purpose of this study was to determine if YB-1 levels are altered in photodynamic therapy (PDT)-treated nasopharyngeal cancer (NPC) cells. In this report, we show for the first time that YB-1 is expressed at both the mRNA and protein levels in well-differentiated NPC in vivo. YB-1 mRNA expression in tumor tissues from a murine well-differentiated HK1/NPC model showed no significant difference in mRNA levels following hypericin-PDT. Localization of the YB-1 protein by immuno-histochemistry revealed the presence of cytoplasmic YB-1 in the more mature and better differentiated cells of the untreated group, as well as cells that survived PDT treatment. Expression of the YB-1 protein may possibly influence the cellular stress response to hypericin-PDT and protect the cells from phototoxicity.

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