Protein expression in prostate cancer

Abstract

The molecular pathology of prostate cancer (PCa) is complex and the pathways and the acquired molecular defects responsible for PCa initiation, development and progression are still largely unknown. Tumors of the prostate have an unpredictable behavior and in clinically detected cancers it is presently not possible to assess tumor aggressiveness. PSA is currently the only clinically used biomarker for detection of PCa, but its specificity is low and there is a need for additional tissue and serum biomarkers for early PCa detection and for prediction of prognosis.

In this thesis two-dimensional gel electrophoresis (2-DE) was used to study the protein expression in benign and malignant prostate tissue. 2-DE is a powerful method that can visualize the protein phenotype of a cell and downstream effects of specific gene regulations that cannot be detected on a genetic level. Proteins are separated according to their size and charge and 2-DE has therefore the potential to separate post-translational modifications (PTMs), including truncated protein variants.

In PCa, tumor heterogeneity and the small size of the tumors make it difficult to sample representative cells for 2-DE analysis. We have developed and evaluated a modified non-enzymatic sample preparation (NESP) scraping technique to extract cells from fresh prostate tissue.

The human prostate is composed of three anatomical zones: the peripheral (PZ), central (CZ) and transition (TZ) zone. The functional roles of the zones remain largely unknown. A majority of clinically diagnosed cancers arise in the PZ. We found 18 protein spots in 2-DE gels with significantly different expression levels between the three anatomical zones. The identified proteins suggest functional differences between the zones, and also support the hypothesis that CZ may be of different embryonic origin than PZ and TZ.

We analyzed the protein expression profile of PCa in order to identify proteins with decreased or increased expression in malignant cells, possibly contributing to the understanding of carcinogenesis in the prostate. We detected 63 polypeptides with differential expression in benign prostatic tissue and PCa. By correlating the protein expression with the differentiation markers Gleason grade and DNA ploidy we could distinguish 39 polypeptides which expression levels associated with tumor dedifferentiation. Some of the findings may have the potential to become diagnostic or prognostic biomarkers for PCa. We also showed that multivariate analysis may be applied to discriminate potentially high malignant samples within a group of samples with unpredictable outcome.