Background
D-type cyclins (i.e., Cyclin D1, D2, and D3) are regulators of the Cyclin-dependent kinases 4 and 6 (Cdk4 and Cdk6) and mediate the growth factor-induced progression through the G1 phase in the cell cycle [
1]. CDKs promote cell cycle transitions in mammalian cells by phosphorylating key substrates cyclins [
2]. Therefore, abnormal expression of cyclins was reported to be involved in many cancers progression. Cyclin D3 was widely expressed in many tumor cells. Cyclin D3 gene is amplified in bladder carcinoma in situ [
3]. Genomic changes disrupting the expression of Cyclin D3 are associated with aberrant growth of several human B-lymphoid malignancies [
4]. Targeting Cyclin D3 by miR-138 could induce cell cycle arrest in hepatocellular carcinoma [
5]. Furthermore, Cyclin D3 is selectively required for proliferative expansion of germinal center B cells [
6].
Breast cancer is the most common malignancy among women and represents an important public health issue [
7]. Previous studies showed that Cyclin D1 and D3 are overexpressed in human breast cancer cell lines and primary invasive breast cancers and Cyclin D3 frequently exceeded the expression of Cyclin D1 in ErbB2-positive cases [
1]. E1AF promotes breast cancer cell cycle progression via upregulation of Cyclin D3 transcription [
8]. Rapamycin causes a G1 arrest in HER-2-overexpressing breast cancer cells that is associated with a differential destabilization and subsequent down-regulation of Cyclin D3 protein level [
9]. All these studies showed that Cyclin D3 might play an important role in breast cancer.
In the present study, the relationship between Cyclin D3 and BC patients’ prognosis was uncovered. Breast cancer tissue array was employed to examine Cyclin D3 expression in breast cancer patients and its relationship with the patients’ prognosis. We also detected the proteins which interacted with Cyclin D3 to further elucidate the mechanism in Cyclin D3 mediated pathway in breast cancer.
Discussion
D-type cyclins (D1, D2, and D3) bind cyclin dependent kinases 4 and 6 (CDK4/6), and the activity of cyclin D/CDK complexes promotes entry into cell cycle [
10,
11]. Aberrant cell cycle regulation is a common thread to all forms of cancers [
12]. Deregulated expression of all D-type cyclins is frequently observed in hematopoietic malignancies [
13] [
14,
15].
Compared to cyclin D1 and cyclin D2, little was known about Cyclin D3’s function. Previous researches demonstrated that Cyclin D3 interacted with p58PITSLRE, a member of the PITSLRE protein kinase family and evidently enhanced its kinase activity [
16]. Also, Cyclin D3 interacts with both retinoic acid receptor (RAR) and cellular retinoic acid-binding protein II to form a ternary complex and up-regulate retinoic acid-mediated transcription [
17]. Cycin D3 could interact with vitamin D receptor and regulates its transcription activity [
18]. Previous data have suggested that Notch signaling directly regulates Cyclin D3 expression and blocking Cyclin D3 expression by γ-secretase inhibition of Notch signaling prevents cell cycle progression in human T-ALL cell lines in vitro [
19]. And abnormal Cyclin D3 was also found in other cancers, such as leukemia [
20], HCC [
21], gliomas [
22], bladder carcinoma [
23], prostate cancer [
24] and osteosaroma [
25]. These data suggested that D-type cyclins and/or their downstream interacting partners could be attractive therapeutic targets in the cancer.
We demonstrated here that Cyclin D3 was up-regulated in breast cancer. Cyclin D3 expression was positively correlated with ER, PR and negatively correlated with HER2 and tumor differention status (p < 0.05). DFS was significantly worse in breast cancer patients with high Cyclin D3 expression (p = 0.01).
When the correlation between DFS and each clinical-pathological variables were examined in univariate analysis, Cyclin D3 status (HR 5.545; 95 % CI 1.705–18.032; p = 0.004) were associated with higher risk of recurrence and remained statistically significant during multivariate analysis. It suggested that Cyclin D3 could be an independent factor for predicting the prognosis of BC patients.
Further investigation revealed that Cyclin D3 prompted the migration and invasion of breast cancer cells. MS analysis suggested Cyclin D3 interacted with actin and it was further validated by CO-IP assay and GST-Pull down assay.
As we known, cell migration requires dynamic remodeling of the actomyosin network [
26]. It is reported that decreased beta-actin expression in normal corneal stroma clearly disrupts the cytoskeletal structure and functions, including keratocyte motility and wound healing [
27]. A 130-kDa protein 4.1B was found to regulate cell adhesion, spreading, and migration of mouse embryo fibroblasts by influencing actin cytoskeleton organization [
28]. Furthermore, RAGE-binding S100A8/A9 promoted the migration and invasion of human breast cancer cells through actin polymerization [
29]. Actin was possibly involved in the cell dynamic remodeling and movement. Previous studies showed that cGMP-dependent protein kinase I beta regulated breast cancer cell migration and invasion via interaction with the actin/myosin-associated protein caldesmon [
30]. Besides, actins are localized both in cytoplasm and in nucleus. The nuclear actins combine with actin binding protein and polymeraseIIto form the transcriptional machinery and regulate multiple gene transcription [
31]. Base on our results, Cyclin D3 and actin were mainly co-localized in the cellular nucleus. Nuclear actin was reported to be involved in the gene transcription regulation, so we speculated that Cyclin D3 promoted the progression and invasion of breast cancer by interacting with actin to regulate some metastasis related genes or oncogene transcription. However it needs further investigation.
In this study, we provided the evidence that Cyclin D3 predicted disease-free survival in breast cancer and could serve as an independent prognostic biomarker in breast cancer.
Methods
Patients’ samples
A total of 243 primary breast cancer samples of stage I to III invasive ductal carcinoma cases and ANCT were collected randomly at the Department of Breast Surgery in Fudan University Shanghai Cancer Center (FDUSCC, Shanghai, P. R. China). Each case was given a unique identifier and linked to a database containing clinical-pathological data. ANCT means the normal breast tissue and it was diagnosed by the pathologists through H.E. staining. The tumors were assessed according to the WHO classification by two academic pathologists. In addition, the pathological data including (ER, PR), HER2, P53 and Ki67 status/expression were assessed and diagnosed by the pathologists based on the ASCO breast cancer guideline. Patient information and tumor pathology are summarized. This study was approved by the Ethical Committee of Fudan University Shanghai Cancer Center for Clinical Research (Reference number: 050432-4-1212B). The written informed consents were obtained from all the patients.
Immunohistochemical (IHC) staining
A total of 243 FFPE blocks of breast cancer tissues and ANCT were collected for tissue microarrays. Two breast cancer tissue cores and two ANCT cores from the same patient’s FFPE blocks were arranged on recipient paraffin block (with a 1-mm core per specimen). Paraffin sections (3-μm thick) were deparaffinized in xylene and rehydrated in a graded alcohol series, boiled with 10 mmol/L of citrate buffer (pH 6) for 15 min and pre-incubated in blocking solution (10 % normal goat sera) for 1 h at room temperature. The steps were performed using the Envision two-step method. The Envision and DAB Color Kit was purchased from Gene Tech Company Limited (Shanghai, China). A mouse anti-human monoclonal antibody against Cyclin D3 was used at a 1:100 dilution. PBS (phosphate buffered saline) was used as a negative control. The tissue microarray slides were concurrently evaluated by two of the authors. For Cyclin D3 protein in this study, a moderate/strong nucleus staining was defined as positive staining, and a weak or negative staining was defined as negative staining.
Cell culture and regents
Nine breast cell lines were obtained from cell bank of our lab. MCF-7, BCAP 37 and BT474 cells were grown using 1640 medium. MDA-MB231, MDA-MB231BO MDA-MB231HM cells were cultured using F15. MDA-MB436 and MDA-MB468 cells were cultured with DMEM medium. MCF10A were cultured with F12/DMEM 1:1 medium. All medium are with 10 % FBS, 100 ug/ml penicillin and 100 ug/ml streptomycin. The cells were cultured at 37 °C and 5 % CO2.
RNA extraction and quantitative RT-PCR
Total RNA was extracted using TRIzol reagent (Invitrogen). After converting total RNA to cDNA in a reverse transcription (RT) reaction, qPCR were used to quantify the mRNA expression levels. To detect Cyclin D3 expression, we used the SYBR-Green method. GAPDH was used as an internal control. 2−∆Ct values were used to determine their relative expression.
Transwell assay
Cell invasion was assayed using BD BioCoat Growth Factor Reduced (GFR) Matrigel Invasion Chambers (BD, CA). Transfected MDA-MB231 cells (0.5 ml; 5 × 104 cells/ml) were added to the inside of the inserts and incubated for 3 h. After incubation, non-invading cells were removed from the upper surface of the membrane using cotton-tipped swabs. The cells on the lower surface of the membrane were stained with Crystal violet and counted in the central field of triplicate membranes.
Immunoprecipitation and western blotting
MCF-7 and MDA-MB231cells were transfected with 4 μg of HA-actin. Approximately 48 h after transfection, cells were washed with ice-cold phosphate- buffered saline and solubilized with 1 ml of coimmunoprecipitation buffer (50 mM Tris–HCl (pH 7.5), 150 mM NaCl, 0.1 % Nonidet P-40, 5 mM EDTA, 5 mM EGTA, 15 mM MgCl2, 60 mM-glycerophosphate, 0.1 mM sodium orthovanadate, 0.1 mM NaF, 0.1 mM benzamide, 10 μg/ml aprotinin, 10 μg/ml leupeptin, 1 mM PMSF). Detergent-insoluble materials were removed by centrifugation. Cell lysates were incubated with 2 μg of relevant antibody at 4 °C for 2 h. Pre-equilibrated protein G-agarose beads were added and collected by centrifugation after incubation overnight and then gently washed three times with the lysis buffer. The bound proteins were eluted and analyzed using Western blots. An antibody to GAPDH was used to ensure equivalent loading.
GST pull-down assay
GST-actin was purified from bacterial lysates using glutathione-agarose beads (Amersham Biosciences). His-Cyclin D1, His-Cyclin D proteins were purified from Escherichia coli using high performance nickel-Sepharose (GE Healthcare). 20 μl of His-tagged proteins were incubated with 5 μl (about 10 μg) of GST-tagged fusion protein or control protein (GST) in 300 μl of lysis buffer and rotated for 3–5 h at 4 °C. Pre-equilibrated glutathione-sepharose 4B beads were added and collected by centrifugation after incubation overnight and then gently washed three times with the lysis buffer. The beads were resuspended in SDS-PAGE sample buffer, boiled for 5 min, electrophoresed on a 10 % SDSpolyacrylamide gel, and analyzed by Western blot.
Statistical analysis
Analyses were performed using SPSS software. Kaplan–Meier survival analysis was also performed using SPSS. Differences with p values <0.05 are considered significant. Univariate analysis was used in multivariate analysis on the basis of Cox proportional hazards model. Two-sided p values were calculated and a probability level of 0.05 was chosen for statistical significance.
Authors’ contributions
JW and YC conceived and designed the study. YC and SH performed the experiments. ML and XS analyzed the data. NH and LG contributed reagents, materials, and analysis tools. YC wrote the paper. All authors read and approved the final manuscript.