ErbB-2-induced mammary tumor growth: the role of cyclin D1 and p27Kip1

Silencing geranylgeranyltransferase I inhibits the migration and invasion of salivary adenoid cystic carcinoma through RhoA/ROCK1/MLC signaling and suppresses proliferation through cell cycle regulation

Geranylgeranyltransferase type I (GGTase-I) significantly affects Rho proteins, such that the malignant progression of several cancers may be induced. Nevertheless, the effect and underlying mechanism of GGTase-I in the malignant progression of salivary adenoid cystic carcinoma (SACC) remain unclear. This study primarily aimed to investigate the role and mechanism of GGTase-I in mediating the malignant progression of SACC. The level of GGTase-I gene in cells was stably knocked down by short hairpin RNA-EGFP-lentivirus. The effects of GGTase-I silencing on the migration, invasion, and spread of cells were examined, the messenger RNA levels of GGTase-I and RhoA genes of SACC cells after GGTase-I knockdown were determined, and the protein levels of RhoA and RhoA membrane of SACC cells were analyzed. Moreover, the potential underlying mechanism of silencing GGTase-I on the above-mentioned aspects in SACC cells was assessed by examining the protein expression of ROCK1, MLC, p-MLC, E-cadherin, Vimentin, MMP2, and MMP9. Furthermore, the underlying mechanism of SACC cells proliferation was investigated through the analysis of the expression of cyclinD1, MYC, E2F1, and p21CIP1/WAF1 . Besides, the change of RhoA level in SACC tissues compared with normal paracancer tissues was demonstrated through quantitative reverse-transcription polymerase chain reaction and western blot experiments. Next, the effect after GGTase-I silencing was assessed through the subcutaneous tumorigenicity assay. As indicated by the result of this study, the silencing of GGTase-I significantly reduced the malignant progression of tumors in vivo while decreasing the migration, invasion, and proliferation of SACC cells and RhoA membrane, Vimentin, ROCK1, p-MLC, MMP2, MMP9, MYC, E2F1, and CyclinD1 expression. However, the protein expression of E-cadherin and p21CIP1/WAF1 was notably upregulated. Subsequently, no significant transform of RhoA and MLC proteins was identified. Furthermore, RhoA expression in SACC tissues was significantly higher than that in paracancerous tissues. As revealed by the results of this study, GGTase-I shows a correlation with the proliferation of SACC through the regulation of cell cycle and may take on vital significance in the migration and invasion of SACC by regulating RhoA/ROCK1/MLC signaling pathway. GGTase-I is expected to serve as a novel exploration site of SACC.

HMGA1 participates in MHCC97H cell proliferation and invasion through the ILK/Akt/GSK3β signaling pathway

Hepatocellular carcinoma (HCC) is one of the major causes of cancer‑related mortality, and the prognosis of HCC patients is unsatisfactory. It is known that the occurrence and development of HCC involves numerous genes, as well as various steps and stages in the pathological process. High mobility group AT‑hook 1 (HMGA1) and integrin‑linked kinase (ILK) may be overexpressed in HCC and may serve important roles in the development of cancer; however, the relationship between HMGA1 and ILK in HCC has not been examined. The present study demonstrated that inhibition of HMGA1 expression significantly decreased the levels of expression of ILK and the downstream elements phosphorylated (p)‑Akt, p‑glycogen synthase kinase 3β (GSK3β), matrix metalloproteinase (MMP)2, MMP9, CyclinD1 and c‑Myc. Transfection with an ILK expression vector was able to recover the decreased expression of these downstream genes, and affected cell proliferation and apoptosis. In addition, results from Transwell and wound‑healing experiments indicated that HMGA1 participates cell invasion and migration through the ILK/Akt/GSK3β pathway. The present study aimed to improve our understanding about the regulatory pathway involved in HCC and provides the basis for exploring HMGA1 inhibition as a therapy for patients with HCC and a new treatment strategy to prevent the development of HCC.

[Effects of geranylgeranyltransferaseⅠsilencing on the proliferation of tongue squamous cancer cells]

Objective This study aims to investigate the effect of geranylgeranyltransferaseⅠ (GGTase-Ⅰ) on the proliferation and growth of tongue squamous cancer cells. Methods Three small interfering RNAs (siRNAs) were designed on the basis of the GGTase-Ⅰ sequence in GeneBank. These siRNAs were then transfected into tongue squamous cancer cells Cal-27. The mRNA and protein expression of GGTase-Ⅰ and RhoA were examined by real-time quantitative polymerase chain reaction and Western blotting, respectively. The expression of Cyclin D1 and p21 were examined by Western blotting. The proliferation and growth ability were analyzed by cell counting kit-8 assay and flow cytometry. Results The mRNA and protein expression of GGTase-Ⅰ in Cal-27 was reduced significantly after the GGTase-Ⅰ siRNAs were transfected (P<0.05). No significant difference in RhoA mRNA and protein expression was detected (P>0.05). Cyclin D1 expression decreased, whereas p21 expression increased significantly. The cell cycle was altered, and the growth-proliferative activity was inhibited (P<0.05). Conclusion GGTase-Ⅰ siRNA can inhibit the expression of GGTase-Ⅰ and the proliferative activity of tongue squamous cancer cells. GGTase-Ⅰ may be a potential target for gene therapy in tongue squamous cell cancer.

Brk/Protein tyrosine kinase 6 phosphorylates p27KIP1, regulating the activity of cyclin D-cyclin-dependent kinase 4

Cyclin D and cyclin-dependent kinase 4 (cdk4) are overexpressed in a variety of tumors, but their levels are not accurate indicators of oncogenic activity because an accessory factor such as p27(Kip1) is required to assemble this unstable dimer. Additionally, tyrosine (Y) phosphorylation of p27 (pY88) is required to activate cdk4, acting as an "on/off switch." We identified two SH3 recruitment domains within p27 that modulate pY88, thereby modulating cdk4 activity. Via an SH3-PXXP interaction screen, we identified Brk (breast tumor-related kinase) as a high-affinity p27 kinase. Modulation of Brk in breast cancer cells modulates pY88 and increases resistance to the cdk4 inhibitor PD 0332991. An alternatively spliced form of Brk (Alt Brk) which contains its SH3 domain blocks pY88 and acts as an endogenous cdk4 inhibitor, identifying a potentially targetable regulatory region within p27. Brk is overexpressed in 60% of breast carcinomas, suggesting that this facilitates cell cycle progression by modulating cdk4 through p27 Y phosphorylation. p27 has been considered a tumor suppressor, but our data strengthen the idea that it should also be considered an oncoprotein, responsible for cyclin D-cdk4 activity.

The effect of miR-338-3p on HBx deletion-mutant (HBx-d382) mediated liver-cell proliferation through CyclinD1 regulation

OBJECTIVE

Hepatitis B Virus (HBV) DNA integration and HBV X (HBx) deletion mutation occurs in HBV-positive liver cancer patients, and C-terminal deletion in HBx gene mutants are highly associated with hepatocarcinogenesis. Our previous study found that the HBx-d382 deletion mutant (deleted at nt 382-400) can down-regulate miR-338-3p expression in HBx-expressing cells. The aim of the present study is to examine the role of miR-338-3p in the HBx-d382-mediated liver-cell proliferation.

METHODS

We established HBx-expressing LO2 cells by Lipofectamine 2000 transfection. A miR-338-3p mimics or inhibitor was transfected into LO2/HBx-d382 and LO2/HBx cells using miR-NC as a control miRNA. In silico analysis of potential miR-338-3p targets revealed that miR-338-3p could target the cell cycle regulatory protein CyclinD1. To confirm that CyclinD1 is negatively regulated by miR-338-3p, we constructed luciferase reporters with wild-type and mutated CyclinD1-3'UTR target sites for miR-338-3p binding. We examined the CyclinD1 expression by real-time PCR and western blot, and proliferation activity by flow cytometric cell cycle analysis, Edu incorporation, and soft agar colony.

RESULTS

HBx-d382 exhibited enhanced proliferation and CyclinD1 expression in LO2 cells. miR-338-3p expression inhibited cell proliferation in LO2/HBx-d382 cells (and LO2/HBx cells), and also negatively regulated CyclinD1 protein expression. Of the two putative miR-338-3p binding sites in the CyclinD1-3'UTR region, the effect of miR-338-3p on the second binding site (nt 2397-2403) was required for the inhibition.

CONCLUSION

miR-338-3p can directly regulate CyclinD1 expression through binding to the CyclinD1-3'UTR region, mainly at nt 2397-2403. Down-regulation of miR-338-3p expression is required for liver cell proliferation in both LO2/HBx and LO2/HBx-d382 mutant cells, although the effect is more pronounced in LO2/HBx-d382 cells. Our study elucidated a novel mechanism, from a new miRNA-regulation perspective, underlying the propensity of HBx deletion mutants to induce hepatocarcinogenesis at a faster rate than HBx.

miR-338-3p is down-regulated by hepatitis B virus X and inhibits cell proliferation by targeting the 3'-UTR region of CyclinD1

Hepatitis B virus X protein (HBx) is recognized as an oncogene in hepatocellular carcinoma (HCC). HBx regulates microRNA expression, including down-regulating miR-338-3p in LO2 cells. Here, we investigated miR-338-3p function in HBx-mediated hepatocarcinogenesis. In 23 HBV-infected HCC clinical patient tumor and adjacent non-tumor control tissues, 17 and 19 tumors expressed HBx mRNA and protein, respectively. When considered as a group, HBV-infected HCC tumors had lower miR-338-3p expression than controls; however, miR-338-3p was only significantly down-regulated in HBx-positive tumors, indicating that HBx inversely correlated with miR-338-3p. Functional characterization of miR-338-3p indicated that miR-338-3p mimics inhibited cell proliferation by inducing cell cycle arrest at the G1/S phase as assessed by EdU and cell cycle assays in HBx-expressing LO2 cells. CyclinD1, containing two putative miR-338-3p targets, was confirmed as a direct target using 3′-UTR luciferase reporter assays from cells transfected with mutated binding sites. Mutating the 2397–2403 nt binding site conferred the greatest resistance to miR-338-3p suppression of CyclinD1, indicating that miR-338-3p suppresses CyclinD1 at this site. Overall, this study demonstrates that miR-338-3p inhibits proliferation by regulating CyclinD1, and HBx down-regulates miR-338-3p in HCC. This newly identified miR-338-3p/CyclinD1 interaction provides novel insights into HBx-mediated hepatocarcinogenesis and may facilitate therapeutic development against HCC.

A crosstalk imbalance between p27(Kip1) and its interacting molecules enhances breast carcinogenesis

p27(Kip1) (p27) is an inhibitor of cyclin/cyclin-dependent kinase complexes, the nuclear loss of which indicates poor prognoses in various solid tumors. In breast cancer cells, the p27 expression level usually decreases during tumor development and progression. In addition, p27 cytoplasmic mislocalization has been reported, but the exact molecular mechanisms remain unclear. Studies have indicated that its phosphorylation status is the key regulator and that several signal transduction pathways are involved in the regulation of both the expression and distribution of p27. To further understand the signals involved, the differences in the profiles of interacting proteins between tumor and normal cells should be elucidated. It is well known that p27 has various interacting partners, such as cyclin, cyclin-depend kinases, CRM1, Jab1, SKP2, and Spy1. Assays used to profile these proteins show differing intracellular p27 expression and localization depending on the cell-cycle phase. We hypothesize that the imbalance of crosstalk between p27 and the other molecules involved in the same signaling pathways plays an indispensable role in breast cancer carcinogenesis.

Hunk is required for HER2/neu-induced mammary tumorigenesis

Understanding the molecular pathways that contribute to the aggressive behavior of human cancers is a critical research priority. The SNF1/AMPK-related protein kinase Hunk is overexpressed in aggressive subsets of human breast, ovarian, and colon cancers. Analysis of Hunk(–/–) mice revealed that this kinase is required for metastasis of c-myc–induced mammary tumors but not c-myc–induced primary tumor formation. Similar to c-myc, amplification of the proto-oncogene HER2/neu occurs in 10%–30% of breast cancers and is associated with aggressive tumor behavior. By crossing Hunk(–/–) mice with transgenic mouse models for HER2/neu-induced mammary tumorigenesis, we report that Hunk is required for primary tumor formation induced by HER2/neu. Knockdown and reconstitution experiments in mouse and human breast cancer cell lines demonstrated that Hunk is required for maintenance of the tumorigenic phenotype in HER2/neu-transformed cells. This requirement is kinase dependent and resulted from the ability of Hunk to suppress apoptosis in association with downregulation of the tumor suppressor p27(kip1). Additionally, we find that Hunk is rapidly upregulated following HER2/neu activation in vivo and in vitro. These findings provide what we believe is the first evidence for a role for Hunk in primary tumorigenesis and cell survival and identify this kinase as an essential effector of the HER2/neu oncogenic pathway.

Synergistic proapoptotic effects of the two tyrosine kinase inhibitors pazopanib and lapatinib on multiple carcinoma cell lines

Pazopanib and lapatinib are two tyrosine kinase inhibitors that have been designed to inhibit the VEGF tyrosine kinase receptors 1, 2 and 3 (pazopanib), and the HER1 and HER2 receptors in a dual manner (lapatinib). Pazopanib has also been reported to mediate inhibitory effect on a selected panel of additional tyrosine kinases such as PDGFR and c-kit. Here, we report that pazopanib and lapatinib act synergistically to induce apoptosis of A549 non-small-cell lung cancer cells. Systematic assessment of the kinome revealed that both pazopanib and lapatinib inhibited dozens of different tyrosine kinases and that their combination could suppress the activity of some tyrosine kinases (such as c-Met) that were not or only partially affected by either of the two agents alone. We also found that pazopanib and lapatinib induced selective changes in the transcriptome of A549 cells, some of which were specific for the combination of both agents. Analysis of a panel of unrelated human carcinoma cell lines revealed a signature of 52 genes whose up- or downregulation reflected the combined action of pazopanib and lapatinib. Indeed, pazopanib and lapatinib exerted synergistic cytotoxic effects on several distinct non-small-cell lung cancer cells as well as on unrelated carcinomas. Altogether, these results support the contention that combinations of tyrosine kinase inhibitors should be evaluated for synergistic antitumor effects. Such combinations may lead to a 'collapse' of pro-survival signal transduction pathways that leads to apoptotic cell death.

Prolyl isomerase Pin1 is highly expressed in Her2-positive breast cancer and regulates erbB2 protein stability

Overexpression of HER-2/Neu occurs in about 25–30% of breast cancer patients and is indicative of poor prognosis. While Her2/Neu overexpression is primarily a result of erbB2 amplification, it has recently been recognized that erbB2 levels are also regulated on the protein level. However, factors that regulate Her2/Neu protein stability are less well understood. The prolyl isomerase Pin1 catalyzes the isomerization of specific pSer/Thr-Pro motifs that have been phosphorylated in response to mitogenic signaling. We have previously reported that Pin1-catalyzed post-phosphorylational modification of signal transduction modulates the oncogenic pathways downstream from c-neu. The goal of this study was to examine the expression of prolyl isomerase Pin1 in human Her2+ breast cancer, and to study if Pin1 affects the expression of Her2/Neu itself.

Rapamycin inhibits multiple stages of c-Neu/ErbB2 induced tumor progression in a transgenic mouse model of HER2-positive breast cancer

Amplification of the HER2 (ErbB2, c-Neu) proto-oncogene in breast cancer is associated with poor prognosis and high relapse rates. HER2/ErbB2, in conjunction with ErbB3, signals through the Akt/phosphatidylinositol 3-kinase pathway and leads to the activation of mammalian target of rapamycin (mTOR), a critical mRNA translation regulator that controls cell growth. Gene expression analysis of mammary tumors collected from mouse mammary tumor virus-c-Neu transgenic mice revealed that mRNA levels of several mTOR pathway members were either up-regulated (p85/phosphatidylinositol 3-kinase and p70S6 kinase) or down-regulated (eIF-4E-BP1) in a manner expected to enhance signaling through this pathway. Treatment of these mice with the mTOR inhibitor rapamycin caused growth arrest and regression of primary tumors with no evidence of weight loss or generalized toxicity. The treatment effects were due to decreased proliferation, associated with reduced cyclin D1 expression, and increased cell death in primary tumors. Whereas many of the dead epithelial cells had the histopathologic characteristics of ischemic necrosis, rapamycin treatment was not associated with changes in microvascular density or apoptosis. Rapamycin also inhibited cellular proliferation in lung metastases. In summary, data from this preclinical model of ErbB2/Neu-induced breast cancer show that inhibition of the mTOR pathway with rapamycin blocks multiple stages of ErbB2/Neu-induced tumorigenic progression.

Sensitizing HER2-overexpressing cancer cells to luteolin-induced apoptosis through suppressing p21(WAF1/CIP1) expression with rapamycin

HER2 overexpression, which confers resistance to various therapeutic regimens, correlates with a poor clinical prognosis. In this study, we showed that luteolin, a naturally occurring flavonoid, is a potent stimulator of HER2 degradation. Luteolin effectively inhibited cell proliferation and induced apoptosis in HER2-overexpressing cancer cells. Furthermore, we found that low doses of luteolin up-regulated p21 expression and high doses of luteolin down-regulated its expression. Examination of the Akt/mammalian target of rapamycin (mTOR) signaling revealed that this signaling was only transiently inhibited by low doses of luteolin, which suggested that the inability to cause sustained Akt/mTOR inhibition may contribute to p21 induction and provide a survival advantage to HER2-overexpressing cancer cells. To test this hypothesis, we showed that the combined use of luteolin and mTOR inhibitor rapamycin prevented low doses of luteolin from inducing p21 expression, and HER2-overexpressing cancer cells would be sensitized toward luteolin-induced apoptosis. In addition, p21 small interfering RNA also increased the luteolin-induced cell death. In nude mice with xenografted SKOV3.ip1-induced tumors, luteolin significantly inhibited HER2 expression and tumor growth in a dose-dependent manner, and rapamycin further enhanced the effect of luteolin with a concomitant p21 inhibition. These results reveal an intriguing finding that suppressing p21 expression might have therapeutic implications and further suggest that combination of mTOR inhibitors may be a promising strategy to help increase the efficacy of preventive or therapeutic compounds against HER2-overexpressing tumors.

Extra copies of chromosomes 16 and X in invasive breast carcinomas are related to aggressive phenotype and poor prognosis

BACKGROUND

Breast cancer is a genetically complex disease, which involves the accumulation of various structural and numerical chromosomal aberrations.

AIM

To assess the numerical status of chromosomes 16 and X by interphase cytogenetics, in 114 women with primary invasive breast carcinomas, in relation to clinicopathological parameters, patients' overall survival and indices of cell growth (c-erbB-2, topoisomerase IIalpha (topoIIalpha)) and cell survival (caspase-3, bcl-2).

EXPERIMENTAL DESIGN

Chromogenic in situ hybridisation with pericentromeric probes was performed for molecular analysis, while oestrogen and progesterone receptors, cerbB-2, topoIIalpha, caspase-3 and bcl-2 expression was immunohistochemically detected (ABC/HRP). The results were statistically assessed by univariate and multivariate analyses.

RESULTS

Polysomy of chromosomes 16 and X was detected as the predominant aberration (73.7% and 57.9%, respectively). Gain of chromosome 16 copies was associated with high nuclear grade (p = 0.009), increased tumour size (p = 0.041), advanced stage (p = 0.002), the expression of topoIIalpha (p = 0.005) and worse overall survival by multivariate analysis (p = 0.032). Chromosome X polysomy was increased in ductal carcinomas of high histological grade (p = 0.008), in high nuclear grade tumours (p = 0.001), and was associated with the expression of topoIIalpha (p = 0.005), loss of caspase-3 (p = 0.036) and impaired prognosis of ductal carcinomas (p = 0.041).

CONCLUSIONS

Polysomy of chromosomes 16 and X was reported as the predominant alteration in phenotypically aggressive breast tumours, characterised by poor differentiation, increased growth potential and impaired prognosis, whereas gain of chromosome X in particular is probably implicated in cell survival.

Tumors Initiated by Constitutive Cdk2 Activation Exhibit Transforming Growth Factor β Resistance and Acquire Paracrine Mitogenic Stimulation during Progression

Cyclin D1/cyclin-dependent kinase 2 (Cdk2) complexes are present at high frequency in human breast cancer cell lines, but the significance of this observation is unknown. This report shows that expression of a cyclin D1-Cdk2 fusion protein under the control of the mouse mammary tumor virus (MMTV) promoter results in mammary gland hyperplasia and fibrosis, and mammary tumors. Cell lines isolated from MMTV-cyclin D1-Cdk2 (MMTV-D1K2) tumors exhibit Rb and p130 hyperphosphorylation and up-regulation of the protein products of E2F-dependent genes. These results suggest that cyclin D1/Cdk2 complexes may mediate some of the transforming effects that result from cyclin D1 overexpression in human breast cancers. MMTV-D1K2 cancer cells express the hepatocyte growth factor (HGF) receptor, c-Met. MMTV-D1K2 cancer cells also secrete transforming growth factor beta (TGFbeta), but are relatively resistant to TGFbeta antiproliferative effects. Fibroblasts derived from MMTV-D1K2 tumors secrete factors that stimulate the proliferation of MMTV-D1K2 cancer cells, stimulate c-Met tyrosine phosphorylation, and stimulate the phosphorylation of the downstream signaling intermediates p70(s6k) and Akt on activating sites. Together, these results suggest that deregulation of the Cdk/Rb/E2F axis reprograms mammary epithelial cells to initiate a paracrine loop with tumor-associated fibroblasts involving TGFbeta and HGF, resulting in desmoplasia. The MMTV-D1K2 mice should provide a useful model system for the development of therapeutic approaches to block the stromal desmoplastic reaction that likely plays an important role in the progression of multiple types of human tumors.

Rapamycin Disrupts Cyclin/Cyclin-Dependent Kinase/p21/Proliferating Cell Nuclear Antigen Complexes and Cyclin D1 Reverses Rapamycin Action by Stabilizing These Complexes

Rapamycin and its derivatives are promising anticancer agents, but the exact mechanisms by which these drugs induce cell cycle arrest and inhibit tumor growth are unknown. A biochemical analysis of human mammary tumor cell lines indicated that rapamycin-induced antiproliferative effects correlated with down-regulation of cellular p21 levels and the levels of p21 in cyclin-dependent kinase (Cdk) 2 and 4 complexes. Cyclin D1 overexpression reversed rapamycin action and this reversal correlated with increased levels of cellular p21, higher levels of p21 associated with Cdk2, and stabilization of cyclin D1/Cdk2/p21/proliferating cell nuclear antigen (PCNA) complexes. Experiments using a novel cyclin D1-Cdk2 fusion protein or a kinase-dead mutant of the fusion protein indicated that reversal of rapamycin action required not only the formation of complexes with p21 and PCNA but also complex-associated kinase activity. Similar results were observed in vivo. The rapamycin derivative RAD001 (everolimus) inhibited the growth of mouse mammary tumors, which correlated with the disruption of cyclin D1/Cdk2 complexes. The potential implications of these results with respect to the use of rapamycin derivatives in breast cancer therapy are discussed.

Gene expression profiling: cell cycle deregulation and aneuploidy do not cause breast cancer formation in WAP-SVT/t transgenic animals

Microarray studies revealed that as a first hit the SV40 T/t antigen causes deregulation of 462 genes in mammary gland cells (ME cells) of WAP-SVT/t transgenic animals. The majority of deregulated genes are cell proliferation specific and Rb-E2F dependent, causing ME cell proliferation and gland hyperplasia but not breast cancer formation. In the breast tumor cells a further 207 genes are differentially expressed, most of them belonging to the cell communication category. In tissue culture breast tumor cells frequently switch off WAP-SVT/t transgene expression and regain the morphology and growth characteristics of normal ME cells, although the tumor-revertant cells are aneuploid and only 114 genes regain the expression level of normal ME cells. The profile of retransformants shows that only 38 deregulated genes are tumor-specific, and that none of them is considered to be a typical breast cancer gene.

Oleic acid, the main monounsaturated fatty acid of olive oil, suppresses Her-2/neu (erbB-2) expression and synergistically enhances the growth inhibitory effects of trastuzumab (Herceptin) in breast cancer cells with Her-2/neu oncogene amplification

BACKGROUND

The relationship between the intake of olive oil, the richest dietary source of the monounsaturated fatty acid oleic acid (OA; 18:1n-9), and breast cancer risk and progression has become a controversial issue. Moreover, it has been suggested that the protective effects of olive oil against breast cancer may be due to some other components of the oil rather than to a direct effect of OA.

METHODS

Using flow cytometry, western blotting, immunofluorescence microscopy, metabolic status (MTT), soft-agar colony formation, enzymatic in situ labeling of apoptosis-induced DNA double-strand breaks (TUNEL assay analyses), and caspase-3-dependent poly-ADP ribose polymerase (PARP) cleavage assays, we characterized the effects of exogenous supplementation with OA on the expression of Her-2/neu oncogene, which plays an active role in breast cancer etiology and progression. In addition, we investigated the effects of OA on the efficacy of trastuzumab (Herceptin), a humanized monoclonal antibody binding with high affinity to the ectodomain of the Her-2/neu-coded p185(Her-2/neu) oncoprotein. To study these issues we used BT-474 and SKBr-3 breast cancer cells, which naturally exhibit amplification of the Her-2/neu oncogene.

RESULTS

Flow cytometric analyses demonstrated a dramatic (up to 46%) reduction of cell surface-associated p185(Her-2/neu) following treatment of the Her-2/neu-overexpressors BT-474 and SK-Br3 with OA. Indeed, this effect was comparable to that found following exposure to optimal concentrations of trastuzumab (up to 48% reduction with 20 microg/ml trastuzumab). Remarkably, the concurrent exposure to OA and suboptimal concentrations of trastuzumab (5 microg/ml) synergistically down-regulated Her-2/neu expression, as determined by flow cytometry (up to 70% reduction), immunoblotting, and immunofluorescence microscopy studies. The nature of the cytotoxic interaction between OA and trastuzumab revealed a strong synergism, as assessed by MTT-based cell viability and anchorage-independent soft-agar colony formation assays. Moreover, OA co-exposure synergistically enhanced trastuzumab efficacy towards Her-2/neu overexpressors by promoting DNA fragmentation associated with apoptotic cell death, as confirmed by TUNEL and caspase-3-dependent PARP cleavage. In addition, treatment with OA and trastuzumab dramatically increased both the expression and the nuclear accumulation of p27(Kip1), a cyclin-dependent kinase inhibitor playing a key role in the onset and progression of Her-2/neu-related breast cancer. Finally, OA co-exposure significantly enhanced the ability of trastuzumab to inhibit signaling pathways downstream of Her-2/neu, including phosphoproteins such as AKT and MAPK.

CONCLUSIONS

These findings demonstrate that OA, the main monounsaturated fatty acid of olive oil, suppresses Her-2/neu overexpression, which, in turn, interacts synergistically with anti-Her-2/neu immunotherapy by promoting apoptotic cell death of breast cancer cells with Her-2/neu oncogene amplification. This previously unrecognized property of OA offers a novel molecular mechanism by which individual fatty acids may regulate the malignant behavior of breast cancer cells and therefore be helpful in the design of future epidemiological studies and, eventually, dietary counseling.

Deregulated Cyclin D1 Expression Is Associated with Decreased Efficacy of the Selective Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor Gefitinib in Head and Neck Squamous Cell Carcinoma Cell Lines

PURPOSE

Despite promising initial results, recent Phase III trials of the selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor gefitinib ("Iressa"; AstraZeneca, Wilmington, Delaware) in advanced head and neck squamous cell carcinoma (HNSCC) have been equivocal. Cyclin D1, an EGFR target gene, is frequently overexpressed in HNSCC, has been implicated in its pathogenesis, and is strongly associated with poor prognosis in this disease. Therefore, we examined the relationship between deregulated cyclin D1 expression and sensitivity to gefitinib to determine whether this frequently occurring oncogenic change affected the cellular response to gefitinib.

EXPERIMENTAL DESIGN

A panel of six EGFR-overexpressing HNSCC cell lines was used to correlate CCND1 gene copy number, cyclin D1 expression, and response to gefitinib. The effect of constitutive overexpression of cyclin D1 was assessed by establishing stably transfected clonal SCC-9 cell lines.

RESULTS

Three of six cell lines displayed cyclin D1 amplification and/or overexpression, and these cell lines were resistant to gefitinib. SCC 9 clones overexpressing cyclin D1 continued to proliferate and maintained their S-phase fraction when treated with gefitinib, whereas empty vector control clones and the parental SCC 9 cells were profoundly inhibited and displayed marked reductions in S-phase. The resistance of cyclin D1-overexpressing clones and cyclin D1-amplified cell lines was associated with maintenance of cyclin D1 expression after gefitinib treatment.

CONCLUSIONS

These data suggest that deregulated cyclin D1 overexpression may be associated with resistance of HNSCC to EGFR inhibitors. Therefore, the role of cyclin D1 as a marker of therapeutic response and its utility as a prognostic marker in HNSCC warrant additional analysis.

Role of the CDK inhibitor p27 (Kip1) in mammary development and carcinogenesis: insights from knockout mice

The cyclin-dependent kinase inhibitor p27 (Kip1) is an important cell cycle regulatory gene in breast cancer, and decreased p27 expression is associated with poor prognosis. Some investigations of its role in mammary development have demonstrated reduced cyclin D1 expression and consequent lack of lobuloalveolar development, but others have found increased cyclin E-Cdk2 activity and increased proliferation balanced by increased apoptosis. It is unclear at present why these apparently divergent results have been obtained. Mice with reduced p27 gene dosage alone do not develop mammary carcinomas but do display substantially shorter tumor latency upon overexpression of erbB2, consistent with a role for p27 as a mammary tumor suppressor gene. In this review we summarize these and other data addressing the role of p27 in normal mammary epithelium and experimental models of mammary carcinogenesis.

Growth factor regulation of cell cycle progression in mammary epithelial cells

Growth factors are among the critical positive and negative regulators of cell proliferation for normal mammary/breast epithelial cells and for breast cancer cells. The mechanisms by which specific growth factors regulate the cell cycle in mammary/breast epithelial cells is beginning to be understood for several growth factor families, including the epidermal growth factor, insulin-like growth factor, and transforming growth factor-beta families. A critical issue for understanding how growth factors regulate the cell cycle in vivo is how individual factors interact with other growth factors or hormones to enhance or inhibit specific molecular targets in the cell cycle machinery. This review addresses what is currently known about how growth factors regulate the cell cycle in mammary/breast epithelial cells both individually and in coordination with other growth regulators.

The prognostic impact of hormone receptors and c-erbB-2 in pregnancy-associated breast cancer and their correlation with BRCA1 and cell cycle modulators

A population-based series of 122 patients with pregnancy-associated breast carcinomas was histologically revised and the relationship between hormone receptors, c-erbB-2, BRCA1, p27, cyclin E, and cyclin D1 was studied. The 5-year overall survival was 41%; 70% had tumor size >20 mm; 72% had metastasized to regional lymph nodes; 95% were histologic grade II or III; 66% and 75% were negative for estrogen and progesterone receptor, respectively; and c-erbB-2 expression was high (44%). BRCA1 expression was reduced in 33% of the cases. The expression of p27, cyclin D1, and cyclin E was low, 11%, 9%, and 16%, respectively. Cyclin D1 was positively associated with the hormone receptors (p< or =0.01). In multivariate analysis, lymph node status, progesterone receptor, and c-erbB-2 were significant prognostic factors. In subdividing the group according to lymph node status, c-erbB-2 and progesterone receptor retained a prognostic significance in the node positive group only. In conclusion, pregnancy-associated breast carcinomas are aggressive tumors, with low expression of hormone receptors, BRCA1, p27, and cyclin E and D1, and high expression of c-erbB-2.