Abstract P1-09-03: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Kotsopoulos J, Zaman T, Lubinski J, Sun P, Salmena L, Narod SA. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-09-03.

Abstract P5-09-01: Plasma osteoprotegerin and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers

This abstract was withdrawn by the authors.

Prognostic value of INPP4B protein immunohistochemistry in ovarian cancer

PURPOSE OF INVESTIGATION

Ovarian cancer is associated with poor prognosis and altered protein expression patterns may be useful for identifying patients likely to have poor disease outcomes. The impact of altered INPP4B protein expression on prognosis is unclear. The aim of this study was to evaluate the implication of INPP4B expression changes in a large series of ovarian cancer tissue samples.

MATERIALS AND METHODS

Tissue microarrays were constructed from 599 epithelial ovarian tumors and stained with antibodies for INPP4B, p53, and PTEN. Proportional hazard models were used to estimate survival hazard ratios (HRs) associated with altered protein expression.

RESULTS

Seventy-nine percent of the ovarian cancers demonstrated loss of INPP4B, whereas 53% showed aberrant p53 expression (i.e., complete loss of p53 or over-expression of p53) and 8% showed loss of PTEN. INPP4B was frequently lost in serous and endometrioid cancer subtypes, aberrant p53 expression was most common among serous subtype, and loss of PTEN was most common among endometrioid tumors (p for all three proteins across histologic subtypes ≤ 0.0001). INPP4B loss or aberrant p53 expression were both associated with increased mortality (HR = 1.84; 95% CI 1.27 - 2.68 and HR = 3.10; 95% CI 2.33 - 4.11, respectively); however, in multivariate models, only the relationship with p53 achieved statistical significance (HR = 1.20; 95% CI 0.82 - 1.76 for INPP4B and HR = 1.73; 95% CI 1.28 - 2.34 for p53). Conclusion: The INPP4B protein is frequently lost in serous and endometrioid subtypes of ovarian cancer. A possible prognostic role of INPP4B for endometrioid ovarian tumors requires further evaluation.

CD95 apoptosis resistance in certain cells can be overcome by noncanonical activation of caspase-8

CD95 apoptosis resistance of tumor cells is often acquired through mutations in the death domain (DD) of one of the CD95 alleles. Furthermore, Type I cancer cells are resistant to induction of apoptosis by soluble CD95 ligand (CD95L), which does not induce efficient formation of the death-inducing signaling complex (DISC). Here, we report that tumor cells expressing a CD95 allele that lacks a functional DD, splenocytes from heterozygous lpr(cg) mice, which express one mutated CD95 allele, and Type I tumor cells stimulated with soluble CD95L can all die through CD95 when protein synthesis or nuclear factor kappa B is inhibited. This noncanonical form of CD95-mediated apoptosis is dependent on the enzymatic activity of procaspase-8 but does not involve fully processed active caspase-8 subunits. Our data suggest that it is possible to overcome the CD95 apoptosis resistance of many tumor cells that do not efficiently form a DISC through noncanonical activation of the caspase-8 proenzyme.

Role of proteasomal degradation in the cell cycle-dependent regulation of DNA topoisomerase IIalpha expression

1DNA topoisomerase II (topo II) is a nuclear enzyme that modifies DNA topology and also serves as a target to mediate the cytotoxicity of several antineoplastic agents. Several reports have demonstrated that a reduction of topo II is associated with reduced sensitivity to these agents. Topo II exists as two isoforms in mammalian cells: topo IIalpha and topo IIbeta. In MCF-7 cells, the half-life (mean +/- SEM) values of topo IIalpha and topo IIbeta in situ were 6.6 +/- 0.3 and 17.6 +/- 2.3 hr, respectively, as determined by [(35)S]methionine/cysteine pulse-chase analysis. Degradation of topo IIalpha in situ was abrogated by the presence of proteasome inhibitors, and the relative activities were carbobenzoxy-leucyl-leucyl-leucinal (MG132) > carbobenzoxy-leucyl-leucyl-norvalinal (MG115) > ALLN congruent with lactacystin. ATP-dependent degradation of topo IIalpha, but not topo IIbeta, was observed in extracts of asynchronously dividing HeLa and MCF-7 cells. Furthermore, degradation of topo IIalpha was abrogated by the proteasome inhibitors MG132 and MG115, but not by lactacystin, in extracts of asynchronously dividing MCF-7 cells. Finally, degradation of topo IIalpha, but not topo IIbeta, was observed to occur in a cell cycle-dependent fashion, in extracts of synchronized HeLa cells, with maximal loss of the alpha isoform occurring 2 hr after release from mitotic arrest. This degradation of topo IIalpha appeared to be facilitated by an ATP-dependent activity. Furthermore, high molecular weight bands (>200 kDa), which may represent polyubiquitinated-topo IIalpha conjugates, were also detected in extracts of synchronized HeLa cells. This study provides evidence for a role of the ubiquitin-proteasome pathway in the cell cycle-dependent regulation of topo IIalpha expression.

p53 gene status and chemosensitivity of childhood acute lymphoblastic leukemia cells to adriamycin

The role of p53 as a determinant of sensitivity of ten childhood acute lymphoblastic leukemia (ALL) cell lines to Adriamycin (ADR) was investigated. ADR-sensitive cell lines were found to have wild-type (wt) p53, whereas resistant cell lines contained point mutations in the gene. The basal level of wt p53 protein in sensitive cells was lower than that of mutant p53 in resistant cells, however, after ADR treatment a 6- to 20-fold dose-dependent increase in wt p53 was observed, whereas mutant p53 increased only twofold. The percentage of apoptotic cells in ADR-sensitive lines with wt p53 ranged from 43 to 93% following ADR treatment, whereas that in resistant lines with mutant p53 was only 8-13%. The ratio of constitutive levels of Bax/Bcl-2 was significantly higher in cells containing wt p53 than in cells with mutant p53. These results suggest that p53 gene status and the ability of p53 to induce apoptosis may be determinants of sensitivity to ADR in childhood ALL cells.