A novel interaction between HER2/neu and cyclin E in breast cancer

Abstract

HER2/neu (HER2) and cyclin E are important prognostic indicators in breast cancer. Since both are involved in cell cycle regulation we investigated whether there was a direct interaction between the two. HER2 and cyclin E expression levels were determined in 395 breast cancer patients. Patients with HER2-overexpression and high levels of cyclin E had decreased 5-year disease-specific survival compared with low levels of cyclin E (14% versus 89%, P < .0001) In vitro studies were performed in which HER2-mediated activity in HER2-overexpressing breast cancer cell lines was downregulated by transfection with HER2 siRNA or treatment with trastuzumab. Cyclin E expression levels were determined, and functional effects investigated using kinase assays, MTT assays to assess cell viability as a marker of proliferation, and FACS analysis to determine cell cycle profiles. Decreased HER2-mediated signaling resulted in decreased expression of cyclin E, particularly the low molecular weight (LMW) isoforms. Decreased HER2 and LMW cyclin E expression had functional effects, including decreased cyclin E-associated kinase activity and decreased proliferation, due to increased apoptosis and an increased accumulation of cells in the G1 phase. In vivo studies performed in a HER2-overexpressing breast cancer xenograft model confirmed the effects of trastuzumab on cyclin E expression. Given the relationship between HER2 and cyclin E, in vitro clonogenic assays were performed to assess combination therapy targeting both proteins. Isobologram analysis showed a synergistic interaction between the two agents (trastuzumab targeting HER2 and roscovitine targeting cyclin E). Taken together, these studies demonstrate that HER2-mediated signaling effects LMW cyclin E expression, which in turn effects cell cycle regulation. LMW cyclin E has prognostic and predictive roles in HER2-overexpressing breast cancer, warranting further study of its potential as a therapeutic target.

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

“…HE-12 antibody, which is commonly used to detect cyclin E by Western blot analysis, revealed that, although EL was expressed in all cell lines, LMW-E was expressed only in three of the tumor cell lines (SKBR3, AU565, and MDA-MB-436) as previously reported. 54,55 The only other antibody that showed similar pattern of full-length and LMW-E expression was the C-19 antibody (Figure 1). We next interrogated which one of the eight antibodies could differentially detect full-length (nuclear) and LMW-E (cytoplasmic) by immunostaining.…”

Glucosamine, a naturally occurring amino monosaccharide, inhibits A549 and H446 cell proliferation by blocking G1/S transition

“…In particular, shortening of the G1 phase promotes S phase entry in the cell cycle (12). Cyclin E and Skp2 are key factors controlling G1/S phase transition, and the overexpression of cyclin E and Skp2 induces cell proliferation (13). In the present study, we initially investigated the association of cyclin E and Skp2 levels with cell proliferation in the A549 and H446 lung cancer cell lines.…”

“…Cyclin E expression and, consequently, cyclin E/CDK2 activity is closely associated with the G1/S checkpoint (12). Various studies have indicated that cyclin E is overexpressed in several tumor cells, such as breast cancer cells, and it has been reported to be a prognostic biomarker (13,14). p27…”

Novel Therapeutic Strategies and Combinations for HER2-Overexpressing Breast Cancer

“…4). Cyclin E expression has been shown to be regulated by HER2 expression status, in that HER2 knockdown resulted in reduced cyclin E level and reduced cyclin E-associated kinase activity (Mittendorf, 2010). In addition, HER2-overexpressing breast cancers that also show increased cyclin E expression have lower 5 year disease-free survival versus those that have lower cyclin E levels (Mittendorf, 2010).…”

“…Cyclin E expression has been shown to be regulated by HER2 expression status, in that HER2 knockdown resulted in reduced cyclin E level and reduced cyclin E-associated kinase activity (Mittendorf, 2010). In addition, HER2-overexpressing breast cancers that also show increased cyclin E expression have lower 5 year disease-free survival versus those that have lower cyclin E levels (Mittendorf, 2010). Recently, cyclin E overexpression 12 in HER2-overexpressing breast cancer cells that have acquired trastuzumab resistance was shown to be due to amplification of the cyclin E gene (Scaltriti, 2011).…”