Expression patterns of cathepsins B, H, K, L and S in the human endometrium.

Cathepsins B, H, K, L and S belong to the family of lysosomal cysteine proteinases and participate in a variety of proteolytic processes, including degradation of the extracellular matrix (ECM). In the present study, we used Northern hybridization to demonstrate the presence of mRNAs for cathepsins B, H, K, L and S in human endometrium during both the proliferative and secretory phases of menstrual cycle. The mRNA levels for cathepsins H and K were significantly lower in secretory phase endometrium in comparison with proliferative phase endometrium. Immunohistochemical localization of the different cathepsins revealed widespread distribution of all cathepsins in both stroma and epithelial cells. The immunoreactivity for cathepsins B, H and K exhibited changes related to endometrial location and/or to the phase of the cycle. The strongest immunoreactivity for cathepsins B, H, L and S was observed in the surface epithelium of the endometrium. The staining for cathepsins was predominantly intracellular, but immunoreactivity was also detected on the surface of small lymphoid cells in the stroma. The findings of the present study suggest that cysteine cathepsins are needed for normal development and function of human endometrium during both the proliferative and secretory phases.