Abstract
Estrogen signaling is one of the known mechanisms to affect breast cancer cell proliferation, apoptosis, and survival, which promotes tumorigenesis by regulating the production of numerous downstream effector proteins. Serine protease PRSS23 is a newly identified protein since the human genome project. Interestingly, in breast cancers, PRSS32 was coexpressed with estrogen receptor α (ERα), which was one of the prominent biomarkers and therapeutic target for breast cancer therapy. Meanwhile, recent studies implied that PRSS23 might be been associated with tumor progression in various types of cancers. In the present study, the first specific aim was to characterize properties of PRSS23 in silico. Analysis of published breast cancer microarray datasets revealed that the gene expression correlation between ERα and PRSS23 was highly significant among all ERα-associated proteases in breast cancer. Based on the deduced amino acid sequence, the analytical results implied that PRSS23 might be a basic and hydrophilic serine protease with a leading hydrophobic motif. As a result of the model of three-dimensional structural simulation which showed PRSS23 was structurally analogous to mannose-binding protein-associated serine protease 2, His135, and Asp246, and Ser316 might comprise the component residues of the hypothetical catalytic triad of PRSS23. The preliminary information would pave the way for studies in the future. Subcellular localization may imply the function of a protein. Thus, after gene cloning and anti-PRSS23 production, the second specific aim of this study was to identify the subcellular localization of PRSS23 in MCF-7 breast cancer cells. Firstly, the results of the immunocytochemical study showed endogenous PRSS23 was located at cell nucleus. Furthermore, the nuclear localization sequence of PRSS23 was identified in the study of eGFP-PRSS23 mutagenesis. Therefore, the results indicated PRSS23 was located in the cell nucleus in MCF-7 cells. Accordingly, it was conceivable to hypothesize that PRSS23 might participate in cell proliferation, differentiation, and even gene expression. To investigate whether PRSS23 expression was regulated by ERα in breast cancer cells, the third specific aim was to clarify the correlation between and functional implication of ERα and PRSS23 in breast cancer. PRSS23 expression was then assessed in 56 primary breast cancers biopsies and eight cancer cell lines. The results consistently confirmed the coexpression of PRSS23 and ERα with clinicopathological significance. In vitro assays in MCF-7 cells demonstrated that PRSS23 expression was induced by 17β-estradiol-activated ERα through an interaction with an upstream promoter region. On the other hand, PRSS23 knockdown may suppress estrogen-driven cell proliferation of MCF-7 cells. These findings implied that PRSS23 might be a critical component of estrogen-mediated cell proliferation of ERα-positive breast cancer cells. In conclusion, the present study highlights the potential for PRSS23 to be a novel therapeutic target in breast cancer research.