Cyclin E low-molecular-weight isoform as a predictor of breast cancer in Japanese women

Cytoplasmic Cyclin E Predicts Recurrence in Patients with Breast Cancer

Purpose: Low molecular weight cyclin E (LMW-E) detected by Western blot analysis predicts for reduced breast cancer survival; however, it is impractical for clinical use. LMW-E lacks a nuclear localization signal that leads to accumulation in the cytoplasm that can be detected by IHC. We tested the hypothesis that cytoplasmic staining of cyclin E can be used as a predictor of poor outcome in different subtypes of breast cancer using patient cohorts with distinct clinical and pathologic features.Experimental Design: We evaluated the subcellular localization of cyclin E in breast cancer specimens from 2,494 patients from 4 different cohorts: 303 from a prospective study and 2,191 from retrospective cohorts [NCI, MD Anderson Cancer Center (MDA), and the United Kingdom (UK)]. Median follow-up times were 8.0, 10.1, 13.5, and 5.7 years, respectively.Results: Subcellular localization of cyclin E on IHC was associated with full-length (nuclear) and low molecular weight isoforms (cytoplasmic) of cyclin E on Western blot analysis. In multivariable analysis, cytoplasmic cyclin E staining was associated with the greatest risk of recurrence compared with other prognostic factors across all subtypes in three (NCI, MDA, and UK) of the cohorts. In the MDA cohort, cytoplasmic cyclin E staining outperformed Ki67 and all other variables as prognostic factors.Conclusions: Cytoplasmic cyclin E identifies patients with the highest likelihood of recurrence consistently across different patient cohorts and subtypes. These patients may benefit from alternative therapies targeting the oncogenic isoforms of cyclin E. Clin Cancer Res; 23(12); 2991-3002. ©2016 AACR.

Cytoplasmic Cyclin E and Phospho-Cyclin-Dependent Kinase 2 Are Biomarkers of Aggressive Breast Cancer

Cyclin E and its co-activator, phospho-cyclin-dependent kinase 2 (p-CDK2), regulate G1 to S phase transition and their deregulation induces oncogenesis. Immunohistochemical assessments of these proteins in cancer have been reported but were based only on their nuclear expression. However, the oncogenic forms of cyclin E (low molecular weight cyclin E or LMW-E) in complex with CDK2 are preferentially mislocalized to the cytoplasm. Here, we used separate nuclear and cytoplasmic scoring systems for both cyclin E and p-CDK2 expression to demonstrate altered cellular accumulation of these proteins using immunohistochemical analysis. We examined the specificity of different cyclin E antibodies and evaluated their concordance between immunohistochemical and Western blot analyses in a panel of 14 breast cell lines. Nuclear versus cytoplasmic staining of cyclin E readily differentiated full-length from LMW-E, respectively. We also evaluated the expression of cyclin E and p-CDK2 in 1676 breast carcinoma patients by immunohistochemistry. Cytoplasmic cyclin E correlated strongly with cytoplasmic p-CDK2 (P < 0.0001), high tumor grade, negative estrogen/progesterone receptor status, and human epidermal growth factor receptor 2 positivity (all P < 0.0001). In multivariable analysis, cytoplasmic cyclin E plus phosphorylated CDK2 (as one variable) predicted breast cancer recurrence-free and overall survival. These results suggest that cytoplasmic cyclin E and p-CDK2 can be readily detected with immunohistochemistry and used as clinical biomarkers for aggressive breast cancer.

Cyclin E Associates with the Lipogenic Enzyme ATP-Citrate Lyase to Enable Malignant Growth of Breast Cancer Cells

Cyclin E is altered in nearly a third of invasive breast cancers where it is a powerful independent predictor of survival in women with stage I-III disease. Full-length cyclin E is posttranslationally cleaved into low molecular weight (LMW-E) isoforms, which are tumor-specific and accumulate in the cytoplasm because they lack a nuclear localization sequence. We hypothesized that aberrant localization of cytosolic LMW-E isoforms alters target binding and activation ultimately contributing to LMW-E-induced tumorigenicity. To address this hypothesis, we used a retrovirus-based protein complementation assay to find LMW-E binding proteins in breast cancer, identifying ATP-citrate lyase (ACLY), an enzyme in the de novo lipogenesis pathway, as a novel LMW-E-interacting protein in the cytoplasm. LMW-E upregulated ACLY enzymatic activity, subsequently increasing lipid droplet formation, thereby providing cells with essential building blocks to support growth. ACLY was also required for LMW-E-mediated transformation, migration, and invasion of breast cancer cells in vitro along with tumor growth in vivo In clinical specimens of breast cancer, the absence of LMW-E and low expression of adipophilin (PLIN2), a marker of lipid droplet formation, associated with favorable prognosis, whereas overexpression of both proteins correlated with a markedly worse prognosis. Taken together, our findings establish a novel relationship between LMW-E isoforms of cyclin E and aberrant lipid metabolism pathways in breast cancer tumorigenesis, warranting further investigation in additional malignancies exhibiting their expression. Cancer Res; 76(8); 2406-18. ©2016 AACR.

Cyclin E amplification, over-expression, and relapse-free survival in HER-2-positive primary breast cancer

Cyclin E is a well-characterized cell cycle regulator and an amplified oncogene in breast cancer. Over-expression of cyclin E has generally been associated with poor survival. Recent studies have shown an interaction between HER-2 (ERBB2) and cyclin E, but the exact mechanism is unknown. Interestingly, cyclin E over-expression has been associated with trastuzumab resistance. We studied cyclin E over-expression, CCNE1 amplification, and relapse-free survival in HER-2-positive primary breast cancers treated with and without trastuzumab therapy. Formalin-fixed paraffin-embedded tissue samples from 202 HER-2-positive breast carcinomas were studied. Expression levels of cyclin E and proliferation marker Ki-67 were determined using immunohistochemistry. Chromogenic in situ hybridization (CISH) with a gene-specific bacterial artificial chromosome (BAC) probe was used to analyze presence of CCNE1 amplification. Majority of HER-2-positive breast carcinomas exhibited nuclear staining for cyclin E protein. Cyclin E was highly expressed (≥50 % cells) in 37 % of cases. Incidence of CCNE1 amplification (≥6 gene copies/cell or clusters) was 8 %. Cyclin E amplification and over-expression were strongly associated with each other, grade, hormone receptors, and Ki-67. Neither high cyclin E expression nor CCNE1 amplification was associated with relapse-free survival (RFS) irrespective of short-term (9-week regimen) adjuvant trastuzumab therapy. These results confirm cyclin E and HER-2 gene co-amplification in a fraction of HER-2-positive breast cancers. Cyclin E is frequently over-expressed but appears to have limited value as a prognostic or predictive factor in HER-2-positive breast cancer regardless of trastuzumab therapy.