Thiophilic interaction chromatography of prostate-specific antigen

Cysteine inhibits the fibrillisation and cytotoxicity of amyloid-β 40 and 42: implications for the contribution of the thiophilic interaction

Inhibitors of amyloid fibril formation have been at the centre of intense research efforts for the prevention of amyloidosis. Here, we hypothesise that a specific non-covalent interaction, the thiophilic interaction between the side chain of an aromatic residue in a polypeptide and a sulphur atom of the compound, effectively inhibits amyloid fibril formation. Fluorescence spectroscopy and transmission electron microscopy revealed that sulphur compounds, particularly Cys, inhibit the fibrillisation of amyloid-β 1-40 (Aβ40) and 1-42 (Aβ42). Interestingly, aggregates of Aβ40 and Aβ42 induced by Cys were less cytotoxic than those induced by catechin, which is the most typical inhibitor of amyloid fibril formation. Because the essential amino acid, Cys, is an abundant molecule in the blood and cytosol, our data provide a new basis for the prevention of amyloid-related diseases and the elucidation of the mechanism of these diseases.

Enzymatic activity of free-prostate-specific antigen (f-PSA) is not required for some of its physiological activities

BACKGROUND

Prostate specific antigen (PSA) is a well known biomarker for early diagnosis and management of prostate cancer. Furthermore, PSA has been documented to have anti-angiogenic and anti-tumorigenic activities in both in vitro and in vivo studies. However, little is known about the molecular mechanism(s) involved in regulation of these processes, in particular the role of the serine-protease enzymatic activity of PSA.

METHODS

Enzymatic activity of PSA isolated directly from seminal plasma was inhibited specifically (>95%) by incubation with zinc2+ . Human umbilical vein endothelial cells (HUVEC) were utilized to compare/contrast the physiological effects of enzymatically active versus inactive PSA.

RESULTS

Equimolar concentrations of enzymatically active PSA and PSA enzymatically inactivated by incubation with Zn2+ had similar physiological effects on HUVEC, including inhibiting the gene expression of pro-angiogenic growth factors, like VEGF and bFGF, and up-regulation of expression of the anti-angiogenic growth factor IFN-γ; suppression of mRNA expression for markers of blood vessel development, like FAK, FLT, KDR, TWIST-1; P-38; inhibition of endothelial tube formation in the in vitro Matrigel Tube Formation Assay; and inhibition of endothelial cell invasion and migration properties.

DISCUSSION

Our data provides compelling evidence that the transcriptional regulatory and the anti-angiogenic activities of human PSA are independent of the innate enzymatic activity.

Purification of the 90 kDa heat shock protein (hsp90) and simultaneous purification of hsp70/hsc70, hsp90 and hsp96 from mammalian tissues and cells using thiophilic interaction chromatography

Heat shock proteins (HSPs) hsp70/hsc70, hsp90 and hsp96 were separated from mammalian cells and tissues on a gel obtained by the reaction of beta-mercaptoethanol with divinyl sulfone-activated Sepharose CL-6B (thiophilic gel or T-gel). Hsp90 revealed a much higher affinity towards the T-gel than the other HSPs. One-step thiophilic interaction chromatography of proteins resulted in a more than 80% purity and 85% yield of hsp90. Based on this observation, a simple and efficient method for the purification of hsp90 and a procedure for the simultaneous purification of several HSPs (hsp70/hsc70, hsp90 and hsp96) using thiophilic interaction chromatography was developed. All the HSPs were recovered with a high yield and purity (90-99%). The results indicated that the thiophilic gel is a highly efficient affinity matrix for the purification of hsp90 and can be used in the protocols of purification of different HSPs from cells and tissues of various animal species.

Thiophilic-interaction chromatography of enzymatically active tissue prostate-specific antigen (T-PSA) and its modulation by zinc ions

Prostate-specific antigen (PSA) is a serine protease secreted both by normal prostate glandular epithelial cells and prostate cancer cells. We explored "thiophilic-interaction chromatography" (TIC) to isolate tissue prostate-specific antigen (T-PSA) from fresh human prostate cancer tissue harvested by radical prostatectomy for the purpose to characterize T-PSA for its enzymatic activity and sensitivity to zinc ions. We have shown, for the first time, that T-PSA has strong affinity for the thiophilic gel (T-gel). The average recovery of T-PSA from T-gel is over 87%. The presence of PSA in the column eluate was confirmed by ELISA and SDS/PAGE. Western blot developed with monoclonal antibody to PSA revealed that T-PSA was predominantly in the "free" form having a molecular weight of 33 kDa. Furthermore, T-PSA was found to be enzymatically active. T-PSA was found to be less enzymatically active as compared to seminal plasma PSA. The inhibition of enzymatic activity of both f-PSA and T-PSA over a wide range of concentrations of Zn(2+) ions (10nM to 50 microM) was comparable. In contrast, the enzymatic activity of chymotrypsin, another serine-protease, was affected differently. At higher concentrations of Zn(2+) (10 microM and higher) the enzymatic activity of chymotrypsin was inhibited, whereas, at lower concentrations of Zn(2+) (5 microM and lower), the enzymatic activity was enhanced.

Prostate-specific antigen modulates the expression of genes involved in prostate tumor growth

Prostate-specific antigen (PSA) is a serine protease that is widely used as a surrogate marker in the early diagnosis and management of prostate cancer. The physiological relevance of tissue PSA levels and their role in prostate tumor growth and metastasis are not known. Free-PSA (f-PSA) was purified to homogeneity from human seminal plasma by column chromatography, eliminating hk2 and all known PSA complexes and retaining its protease activity. Confluent monolayers of prostate cancer cell lines, PC-3M and LNCaP, were treated with f-PSA in a series of in vitro experiments to determine the changes in expression of various genes that are known to regulate tumor growth and metastasis. Gene array, quantitative polymerase chain reaction (QPCR), and enzyme-linked immunosorbent assay (ELISA) results show significant changes in the expression of various cancer-related genes in PC-3M and LNCaP cells treated with f-PSA. In a gene array analysis of PC-3M cells treated with 10 muM f-PSA, 136 genes were upregulated and 137 genes were downregulated. In LNCaP cells treated with an identical concentration of f-PSA, a total of 793 genes was regulated. QPCR analysis reveals that the genes for urokinase-type plasminogen activator (uPA), VEGF, and Pim-1 oncogene, known to promote tumor growth, were significantly downregulated, whereas IFN-gamma, known to be a tumor-suppressor gene, was significantly upregulated in f-PSA-treated PC-3M cells. The effect of f-PSA on VEGF and IFN-gamma gene expression and on protein release in PC-3M cells was distinctly dose-dependent. In vivo studies showed a significant reduction (P = .03) in tumor load when f-PSA was administered in the tumor vicinity of PC-3M tumor-bearing BALB/c nude mice. Our data support the hypothesis that f-PSA plays a significant role in prostate tumor growth by regulating various proangiogenic and antiangiogenic growth factors.

Thiophilic interaction chromatography facilitates detection of various molecular complexes of prostate-specific antigen in biological fluids

BACKGROUND

It is known that total PSA values are often greater than the sum total of free-PSA (f-PSA) and PSA-ACT complex. It is primarily because other PSA complexes are present in the patient serum and currently cannot be quantified. Our studies were aimed in developing methodology that will permit recovery of all molecular forms of PSA from various biological fluids.

METHODS

Thiophilic interaction (3S,T-gel) chromatography procedure was used to isolate various PSA molecular forms present in biological fluids. f-PSA and PSA complexes were shown to have strong affinity for T-gel. PSA forms eluted from the column were analyzed by SDS-PAGE/Western blot and were identified by immunostaining with antibody-specific to PSA and to various protease inhibitors. The identity of PSA complexes was also confirmed by Enzyme-linked Immunosorbent-assay (ELISA).

RESULTS

One step affinity chromatography procedure (3S,T-gel) was used to isolate different molecular forms of PSA in seminal plasma, patient sera, and in prostate cancer cell culture medium. Seminal plasma was shown to contain f-PSA, PSA-ACT, PSA-A2M, and PSA-PCI. Sera from prostate cancer patients at different stages of the disease contained f-PSA, PSA-ACT, and PSA-A2M. Besides these PSA forms, some patients at late stage of the disease (T3 and T4) also contained two additional PSA-complexes that have not been identified as of yet. Conditioned medium from LNCaP cells was shown to contain f-PSA, PSA-ACT, and PSA-A2M complexes.

CONCLUSIONS

Thiophilic gel has strong affinity for all known molecular forms of PSA present in any biological material. Visualization of PSA molecular forms in Western-blot analysis was feasible only after patient serum was processed through T-gel. Our procedure can be used to screen hybridoma and antibodies specific to the individual PSA complex. The PSA molecular forms isolated from patient serum after T-gel procedure may provide useful internal calibrators, and thus may significantly enhance the reliability of PSA measurements.