Antiangiogenic and proteolytic activities of prostate-specific antigen

Prostate-specific antigen (PSA) is a very useful biomarker for prostate cancer. The PSA concentration in circulation increases due to leakage of PSA from cancerous tissue. Normally PSA, a serine protease with chymotrypsin-like enzymatic activity, is secreted into seminal fluid by the epithelial cells of the prostate. The major physiological function of PSA in seminal fluid is to digest semenogelins, which leads to liquefaction of the seminal clot. Several other functions have also been suggested for PSA, some of which are associated with cancer. PSA exerts antiangiogenic activity, but PSA may also promote tumor growth and metastatic dissemination. The aim of the research presented in this thesis was to characterize the antiangiogenic and proteolytic activities of PSA. One of the main goals was to elucidate whether the enzymatic activity of PSA is a requirement for its antiangiogenic activity. The antiangiogenic activity of PSA was studied using an in vitro angiogenesis model based on tube formation of human umbilical vein endothelial cells (HUVEC). In this model only enzymatically active PSA was able to inhibit angiogenesis. Peptides that stimulate the proteolytic activity of PSA enhanced the antiangiogenic activity, while small molecule compounds that inhibit PSA abolished this activity. DNA microarray study showed that PSA-induced changes in the gene expression of HUVECs were small during tube formation, and it was not clear whether these changes were primary or secondary to the antiangiogenic activity of PSA. The results of this thesis suggest that the antiangiogenic activity of PSA is mediated by a proteolytic product generated by PSA. The proteolytic activity of PSA was studied using several peptide and protein substrates. Semenogelins are the major physiological substrates of PSA and they were shown to be degraded much more rapidly than any other protein substrate studied. Nidogen-1, a component of the basement membrane, was identified as a novel substrate for PSA by mass spectrometry. However, the cleavage of nidogen-1 did not explain the antiangiogenic activity of PSA, since either its fragments or full-length form did not affect HUVEC tube formation. Contrary to a previous report, we showed that the antiangiogenic activity of PSA was not mediated by angiostatin-like fragments generated by the cleavage of plasminogen. The results of this thesis established that the proteolytic activity is necessary for the antiangiogenic activity of PSA and that the antiangiogenic activity can be enhanced by PSA-stimulating peptides and abolished by PSA-inhibitors. The comparison of the efficiency of PSA to cleave different protein substrates and the identification of nidogen-1 as one of these substrates provided new information about the biological role of PSA. The typically slow growth of most prostate cancers may be caused by the antiangiogenic activity of PSA, as there are high concentrations of active PSA present in prostatic tissue. Therefore, peptides that stimulate the antiangiogenic activity of PSA and reduce tumor angiogenesis could be used to control prostate cancer growth.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2014

Author dc:creator

• Mattsson, Johanna

• biolääketiede

Statement dc:rights

• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
• This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
• Publikationen är skyddad av upphovsrätten. Den får läsas och skrivas ut för personligt bruk. Användning i kommersiellt syfte är förbjuden.

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/136464

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F136464