Background
Intracellularly, the ubiquitin-proteasome system participates in crucial functions such as cell cycling, differentiation, proliferation, gene transcription, and apoptosis. However, in malignancies including ovarian cancer increased extracellular concentrations of circulating 20S proteasomes (c-proteasomes) have been detected in blood. We tested the hypothesis that the c-proteasome plasma concentration is a biomarker associated with the clinical course of ovarian cancer patients.
Conclusions
Circulating proteasome concentrations correlate with residual tumor mass and might be a prognostic variable in ovarian cancer following primary therapy.
Methods
20S-proteasome venous plasma concentration was measured by ELISA in patients presenting with ovarian cancer before (n=120) and after (n=68) primary treatment, and in healthy volunteers (n=55). The median follow-up time was 19 months. To assess the relation of proteasome expression with c-proteasome concentration, tumor specimens from 27 patients were immunohistochemically stained for 20S proteasome using an antibody directed against the core subunits of the catalytic domain of the 20S proteasome.
Results
Median c-proteasome concentration was higher (p<0.0001) in untreated ovarian cancer patients (457.5 ng/ml, range: 200-12540 ng/ml) than in healthy controls 290 ng/ml, range: 140-425 ng/ml). Following completion of primary treatment, the median c-proteasome concentration increased (p=0.003) relative to baseline (595 ng/ml, range: 200-20000 ng/ml) and concentrations positively correlated (p=0.031) with residual disease left at primary surgery. Patients with post-treatment c-proteasome concentrations exceeding the cohort's median showed a diminished survival (p=0.045). We found no correlation between c-proteasome concentration and strength of proteasomal staining in tumor specimens. Conclusions: Circulating proteasome concentrations correlate with residual tumor mass and might be a prognostic variable in ovarian cancer following primary therapy.