Stanislav Zelivianski

Cyclin-Dependent Kinase 4–Mediated Phosphorylation Inhibits Smad3 Activity in Cyclin D–Overexpressing Breast Cancer Cells

Smad3, a component of the transforming growth factor β signaling cascade, contributes to G1 arrest in breast cancer cells. Cyclin D1/cyclin-dependent kinase 4 (CDK4) promotes G1-S–phase transition, and CDK phosphorylation of Smad3 has been associated with inhibition of Smad3 activity. We hypothesized that overexpression of cyclin D1 exerts tumorigenic effects in breast cancer cells through CDK4-mediated phosphorylation and inhibition of Smad3 and release of G1 arrest. Real-time quantitative reverse transcription-PCR and immunoblotting were used to evaluate expression of study proteins in cyclin D1–overexpressing breast cancer cells. Smad3 transcriptional activity and cell cycle control were examined in cells transfected with wild-type (WT) Smad3 or Smad3 with single or multiple CDK phosphorylation site mutations (M) in the presence or absence of the CDK4 inhibitor or cotransfection with cdk4 small interfering RNA (siRNA). Transfection of the Smad3 5M construct resulted in decreased c-myc and higher p15INK4B expression. Compared with WT Smad3, overexpression of the Smad3 T8, T178, 4M, or 5M mutant constructs resulted in higher Smad3 transcriptional activity. Compared with cells transfected with WT Smad3, Smad3 transcriptional activity was higher in cells overexpressing Smad3 mutant constructs and treated with the CDK4 inhibitor or transfected with cdk4 siRNA. Cells transfected with Smad3 T8 or T178 and treated with the CDK4 inhibitor showed an increase in the G1 cell population. Inhibition of CDK-mediated Smad3 phosphorylation released cyclin D1–regulated blockade of Smad3 transcriptional activity and recovered cell cycle arrest in breast cancer cells. Targeted inhibition of CDK4 activity may have a role in the treatment of cyclin D–overexpressing breast cancers. Mol Cancer Res; 8(10); 1375–87. ©2010 AACR.

Impact of cyclin E overexpression on Smad3 activity in breast cancer cell lines.

Smad3, a component of the TGFβ signaling pathway, contributes to G1 arrest in breast cancer cells. Overexpression of the cell cycle mitogen, cyclin E, is associated with poor prognosis in breast cancer, and cyclin E/CDK2 mediated phosphorylation of Smad3 has been linked with inhibition of Smad3 activity. We hypothesized that the biological aggressiveness of cyclin E overexpressing breast cancer cells would be associated with CDK2 phosphorylation and inhibition of the tumor suppressant action of Smad3. Expression constructs containing empty vector, wild type (WT) Smad3, or Smad3 with CDK phosphorylation site mutations were co-transfected with a Smad3-responsive reporter construct into parental, vector control (A1), or cyclin E overexpressing (EL1) MCF7 cells. Smad3 function was evaluated by luciferase reporter assay and mRNA analysis. The impact of a Cdk2 inhibitor and cdk2 siRNA on Smad3 activity was also assessed. Cells expressing Smad3 containing mutations of the CDK phosphorylation sites had higher p15 and p21 and lower c-myc mRNA levels, as well as higher Smad3-responsive reporter activity, compared with controls or cells expressing WT Smad3. Transfection of cdk2 siRNA resulted in a significant increase in Smad3-responsive reporter activity compared with control siRNA; reporter activity was also increased after the treatment with a Cdk2 inhibitor. Thus, cyclin E-mediated inhibition of Smad3 is regulated by CDK2 phosphorylation of the Smad3 protein in MCF7 cells. Inhibition of CDK2 may lead to restoration of Smad3 tumor suppressor activity in breast cancer cells, and may represent a potential treatment approach for cyclin E overexpressing breast cancers.

Effect of infertility treatment and pregnancy-related hormones on breast cell proliferation in vitro

BACKGROUND Breast cancer development involves a series of mutations in a heterogeneous group of proto-oncogenes/tumor suppressor genes that alter mammary cells to create a microenvironment permissive to tumorigenesis. Exposure to hormones during infertility treatment may have a mutagenic effect on normal mammary epithelial cells, high-risk breast lesions and early-stage breast cancers. Our goal was to understand the association between infertility treatment and normal and cancerous breast cell proliferation. METHODS MCF-10A normal mammary cells and the breast cancer cell lines MCF-7 [estrogen receptor (ER)-positive, well differentiated] and HCC 1937 (ER-negative, aggressive, BRCA1 mutation) were treated with the weak ER activator clomiphene citrate and hormones that are increased during infertility treatment. Direct effects of treatment on cell proliferation and colony growth were determined. RESULTS While clomiphene citrate had no effect on MCF-10A cells or MCF-7 breast cancer cells, it decreased proliferation of HCC 1937 versus untreated cells (P= 0.003). Estrogen had no effect on either MCF-10A or HCC 1937 cells but, as expected, increased cell proliferation (20-100 nM; P≤0.002) and colony growth (10-30 nM; P< 0.0001) of MCF-7 cells versus control. Conversely, progesterone decreased both proliferation (P= 0.001) and colony growth (P= 0.01) of MCF-10A cells, inhibited colony size of MCF-7 cells (P= 0.01) and decreased proliferation of HCC 1937 cells (P= 0.008) versus control. hCG (100 mIU/ml) decreased both proliferation (P ≤ 0.01) and colony growth (P ≤ 0.002) of all three cell lines. CONCLUSIONS Although these data are preclinical, they support possible indirect estrogenic effects of infertility regimens on ER-positive breast cancer cells and validate the potential protective effect of pregnancy-related exposure to hCG.

Impact of infertility regimens on breast cancer cells: follicle-stimulating hormone and luteinizing hormone lack a direct effect on breast cell proliferation in vitro.

OBJECTIVE To examine the impact of hormones used for controlled ovarian hyperstimulation (COH) on normal and malignant breast cell growth and proliferation. DESIGN In vitro study of cultured normal and malignant breast cell lines. SETTING Academic medical center. PATIENT(S) None. INTERVENTION(S) Normal and malignant breast cell lines cultured in two- and three-dimensional (2D and 3D) systems and treated with follicle-stimulating hormone (FSH), luteinizing hormone (LH), or FSH with LH or human chorionic gonadotropin (hCG). MAIN OUTCOME MEASURE(S) Effects of treatment on cell proliferation in 2D culture using the MTS assay and on colony growth in 3D culture. RESULT(S) Compared with untreated cells, normal MCF-10A cells showed a decrease in proliferation and colony size when exposed to a combination of FSH and hCG. The HCC 1937 cells treated with FSH and LH also showed a decrease in colony growth but no change in proliferation. None of the treatments had an effect on the proliferation or colony size of the MCF-7 cells. CONCLUSION(S) Follicle-stimulating hormone, LH, and hCG do not appear to cause an increase in cell proliferation or colony growth in either normal or malignant mammary epithelial cell lines. The potential risk for mammary cell transformation associated with these agents may be related to indirect endocrine effects on breast cell physiology.

CDK4 inhibition and doxorubicin mediate breast cancer cell apoptosis through Smad3 and survivin

Cyclin D1/CDK4 activity is upregulated in up to 50% of breast cancers and CDK4-mediated phosphorylation negatively regulates the TGFβ superfamily member Smad3. We sought to determine if CDK4 inhibition and doxorubicin chemotherapy could impact Smad3-mediated cell/colony growth and apoptosis in breast cancer cells. Parental and cyclin D1-overexpressing MCF7 cells were treated with CDK4 inhibitor, doxorubicin, or combination therapy and cell proliferation, apoptosis, colony formation, and expression of apoptotic proteins were evaluated using an MTS assay, TUNEL staining, 3D Matrigel assay, and apoptosis array/immunoblotting. Study cells were also transduced with WT Smad3 or a Smad3 construct resistant to CDK4 phosphorylation (5M) and colony formation and expression of apoptotic proteins were assessed. Treatment with CDK4 inhibitor/doxorubicin combination therapy, or transduction with 5M Smad3, resulted in a similar decrease in colony formation. Treating cyclin D overexpressing breast cancer cells with combination therapy also resulted in the greatest increase in apoptosis, resulted in decreased expression of anti-apoptotic proteins survivin and XIAP, and impacted subcellular localization of pro-apoptotic Smac/DIABLO. Additionally, transduction of 5M Smad3 and doxorubicin treatment resulted in the greatest change in apoptotic protein expression. Collectively, this work showed the impact of CDK4 inhibitor-mediated, Smad3-regulated tumor suppression, which was augmented in doxorubicin-treated cyclin D-overexpressing study cells.

CDK4 Phosphorylation Regulates Smad3 Activity in Cyclin D1 Overexpressing Breast Cancer Cells.

Introduction: Overexpression of cyclin D1 is associated with poor prognosis in breast cancer. Cyclin D1 regulates the noncanonical phosphorylation of Smad3, a member of the TGFΒ signaling cascade, through CDK4 and inhibits Smad3 activity in normal mouse fibroblasts and epithelial cells. We hypothesize that overexpression of cyclin D1 exerts tumorigenic effects in breast cancer cells through a CDK4 mediated inhibition of Smad3 cell cycle control.Methods: To examine the impact of cyclin D1 overexpression on Smad3 function, constructs containing empty vector (V), WT Smad3 (WT), and Smad3 with single or multiple CDK phosphorylation site mutations were cotransfected with a Smad3 reporter into cyclin D1 overexpressing MCF-7 and T47D cells. Smad3 containing mutant CDK sites is resistant to inhibitory CyclinD1/CDK4 phosphorylation. Study cells were also transfected with V, WT or mutant Smad3 and treated with a CDK4 inhibitor. Smad3 function was examined by luciferase reporter assays and cell cycle analysis. Levels of mRNA for cell cycle regulators cyclin dependent kinase inhibitor (cdki) p15 and c-myc were measured by qRT-PCR.Results: As expected, higher amounts of c-myc mRNA and lower amounts of cdki p15 mRNA were observed in parental, vector control and cyclin D1 overexpressing cells. While subsequent transfection with WT Smad3 resulted in a decrease in c-myc and an increase in p15 mRNA levels, the greatest decrease in c-myc and increase in p15 mRNA was found after transfection with CDK mutated Smad3, most prominently in the cyclin D1 overexpressing cells. Transfection of all individual Smad3 CDK phosphorylation site mutations resulted in an increase in Smad3 reporter activity as compared to transfection with WT Smad3. Transfection of Smad3 constructs with 4 and 5 CDK sites mutated resulted in highest overall Smad3 reporter activity, compared to WT Smad3, in the study cells. A dose dependent increase in Smad3 reporter activity was shown when MCF-7 and T47D cells were transfected with WT Smad3 and treated with increasing concentrations of a specific CDK4 inhibitor. Comparatively higher Smad3 reporter activity was found when the study cells were transfected with individual Smad3 mutant constructs and treated with the CDK4 inhibitor. Interestingly, transfection with the Smad3 construct with all CDK sites mutated and treatment with the CDK4 inhibitor resulted in inhibition of Smad3 reporter activity in the study cells. Lastly, cell cycle analysis revealed that MCF-7 and T47D cells treated with the CDK4 inhibitor showed an increase in the G1 cell cycle population.Conclusions: Mutation of CDK phosphorylation sites in the Smad3 construct or direct inhibition of CDK4 appear to facilitate release of cyclin D1/CDK4 mediated inhibition of Smad3 in breast cancer cells. To this end, restoration of Smad3 activity resulted in increasing p15 and decreasing c-myc mRNA levels in the study cells. However, mutation of all Smad3 CDK phosphorylation sites and treatment with the CDK4 inhibitor resulted in a decrease in Smad3 reporter activity, indicating that some CDK activity is necessary for Smad3 function. By helping to restore cell cycle control, inhibition of CDK4 activity may have a role in the treatment of primary and metastatic breast cancers overexpressing cyclin D. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2152.

Cyclin overexpression inhibits Smad 3 tumor suppression in breast cancer cells.

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #5033 Introduction: The transcription factor Smad 3, a member of the TGFβ signaling cascade, contributes to G1 cell cycle arrest in breast cancer cell lines. Overexpression of the cell cycle regulatory protein cyclin E, and its low molecular weight (LMW) counterparts, has been associated with poor prognosis in breast cancer. Cyclin E has been shown to mediate phosphorylation within or near the linker region of Smad 3 by cyclin dependent kinase 2 (CDK 2), and to inhibit Smad 3 activity in normal mouse fibroblasts and epithelial cells. We hypothesize that overexpression of cyclin E may exert tumorigenic effects in breast cancer cell lines through the functional inhibition of Smad 3 mediated by CDK 2 phosphorylation. Methods: Endogenous levels of Smad 3 and phosphorylated Smad 3 in parental, vector only control, full length (FL), and two LMW forms of cyclin E overexpressing MCF-7 breast cancer cell lines were determined by western blotting. To elucidate the impact of cyclin E overexpression on Smad 3 function, constructs containing an empty vector, WT Smad 3, Smad 3 with a CDK phosphorylation site mutation within the linker region (Thr178), and outside the linker region (Thr8) were co-transfected with a Smad 3 reporter into the panel of MCF-7 cells. CDK2 or scrambled control siRNA was also transfected into the study panel of cells. Smad 3 function was then evaluated by luciferase reporter assays. Results: MCF-7 cells overexpressing FL or LMW cyclin E had a higher level of P- SMAD 3 as compared to the parental and vector only control cells. Total SMAD 3 levels were similar in all cells examined. Transfection of WT Smad 3 elicited an increase in reporter activity in parental and vector control cells, while both FL and LMW forms of cyclin E overexpressing cells were resistant to WT Smad 3 reporter induction. In parental and vector control MCF-7 cells, expression of the Smad 3 Thr178 mutation resulted in a three-fold induction in Smad 3 reporter activity as compared to the WT Smad 3 response. In FL and LMW cyclin E overexpressing cells, induction by the Thr178 mutation was more pronounced, as seen by a 5-fold and 8-fold induction of reporter activity in FL and LMW cyclin E cells, respectively. Transient transfection of the Thr8 mutation failed to evoke a reporter response in any of the panel of MCF-7 cells. MCF-7, FL, and LMW cyclin E cells demonstrated the greatest fold induction of Smad 3 reporter activity when transfected with CDK 2 siRNA. Conclusions: Overexpression of cyclin E may circumvent the growth inhibitory effects of Smad 3 signal transduction through the modulation of Smad 3 function. Specifically, this work indicates that cyclin E mediates Smad 3 inhibition in a CDK 2 dependent fashion in breast cancer cells. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5033.