Introduction: Kallikreins (KLKs) are a subgroup of serine proteases expressed in various tissues including endocrine hormone-generating and/or target organs. Besides their role in physiology, they have been associated with diverse cancer. Due to their altered regulation in endocrine-related malignancies, KLKs promise high diagnostic potential, and KLK3 is already used as a biomarker for prostate cancer. KLK7 functions in the degradation of corneodesmosomal proteins, thereby enabling desquamation of corneocytes and contributing to the skin’s homeostasis. KLK7 is also proposed to facilitate metastasis by excessive degradation of extracellular matrix components and is therefore under investigation as a novel biomarker for skin cancer.
Methods: Antibodies against KLK2, KLK3, and KLK7 were used in immunofluorescence and/or immunoblotting experiments to investigate (1) the influence of thyroid stimulating hormone (TSH) on KLKs expression and localization in thyroid epithelial cells in situ, and (2) the localization of KLK7 in human skin sections and HaCaT keratinocytes versus the related A5-RT3 cancerous cell line.
Results: KLK2 and KLK3 were found to co-localize with cysteine cathepsin B in endo-lysosomes of FRTL-5 cells and redistributed from the peri-nuclear region to the cell periphery upon TSH stimulation. In keratinocytes, the nuclear localization of KLK7 in HaCaT cells was less pronounced in A5-RT3 cells, and mimicked localization of cysteine cathepsin V. Additionally, immunoblotting revealed a band corresponding to the size of active KLK7 in A5-RT3 whole cell lysates, which was absent from HaCaT keratinocytes.
Conclusion: The redistribution of KLK2 and KLK3 upon TSH stimulation hints to novel functions of these enzymes in the thyroid gland. Active KLK7 within the nuclei of A5RT-3 cells would, together with the change in localization in cancerous vs. normal cells, strengthen the hypothesis of a specific role of KLK7 upon tumorigenesis.