ИСТИНА

Prostate cancer is the most common malignant disease in aging males, it ranks as the highest cancer related death cause in industrially developed countries. Asymptomatic tumor development leads to its diagnosis at the late stage. The only approved diagnostic marker PSA gives lots of false-positive as well as false-negative results. In our research we compared 2D electrophoretic maps of serum proteins among three groups: healthy and untreated patients with benign prostate hyperplasia and cancer. Serum samples were depleted of major serum proteins by preincubation with lectins (concanavalin A and ricin) bound to sepharose. Depletion of major blood proteins is one of the most promising approaches to access low abundant biomarkers using proteomics. We have found significant content differences among distinct alpha1-antitrypsin isoforms bound to lectins. The protein is a major serine-protease inhibitor and it’s main target is neutrophil elastase, that protects the body from damage while innate immune response. It consists of eight isoforms, which have different isoelectric points due to different type of glycosylation as well as truncated N-terminus (M7, M8). We found that M8 glycosylation type switches to more branched N-glycans during cancer development, thus decreasing its binding capacity to conconavalin A. We also observed the decrease (M8) or even loss (M1) of isoform binding to ricin because of its degalactosylation. We also shown, that alpha1-antitrypsin serum concentration is significantly elevated in the prostate cancer group compared to healthy controls. The group of benign prostate hyperplasia exhibits middle values of protein level in serum, but doesn’t differ significantly from both of the other groups. We supposed that protein expression by cancer cells may contribute to its elevated concentration in serum during cancer development. Using real-time PCR we revealed that prostate tumor cell lines of different invasive potential (LNCaP, Du145 and PC3) express SERPINA1 gene, which encodes alpha1-antitrypsin. The most relative expression was observed in Du145 cell line, which originates from brain metastasis. it was previously shown, that alpha1-antitrypsin can inhibit caspase-3 activity, that can be one of apoptotic resistance mechanisms of prostate cancer cells. Furthermore, it was also shown, that some cancer cell lines may secrete the protein with tri-branched glycans, and this modified protein inhibits natural killer cells activity more effectively than bi-branch glycosylated protein. We suppose that high protein expression helps the metastasizing cell to avoid inner immune defenses of the tumor host, and alpha1-antitrypsin may be a potential diagnostic biomarker and a therapeutic target.