Down-regulation of proteasomal subunit MB1 is an independent predictor of improved survival in ovarian cancer

ObjectiveTo investigate the expression and to determine the prognostic impact of components of the antigen processing and presentation pathway (APPP) in ovarian cancer.MethodsExpression of MB1, LMP7, TAP1, TAP2, ERp57, ERAP1, β2-microglobulin and the α-chains, HLA-B/C and HLA-A, of the MHC class I molecules was evaluated on tissue microarrays containing primary tumor samples from 232 FIGO stages I–IV ovarian cancer patients. Expression levels were correlated to clinicopathological data and disease specific (DSS) survival.ResultsPatients with expression of all components of the MHC class I complex, i.e. HLA-A+–β2-m+ and HLA-B/C+–β2-m+ patients, more often had expression of LMP7, a component of the immunoproteasome than patients with other phenotypes (p < 0.001). These patients were also more prone to loss of MB1, part of the constitutive multicatalytic proteasome (p < 0.05). Nuclear MB1 expression was an independent predictor of worse DSS (HR 1.94, 95% CI 1.16–3.26, p = 0.012). The HLA-B/C+–β2-m+ phenotype was an independent predictor of a better prognosis (HR 0.63, 95% CI 0.40–0.99, p = 0.047). Median DSS was longer for patients with normal nuclear expression of LMP7 (57.4 vs. 31.0 months, p = 0.029).ConclusionsThe prognostic influence of the proteasomal subunit MB1 and the MHC class I complex in ovarian cancer provides a rationale for targeting these specific APPP components in ovarian cancer.