[Show abstract][Hide abstract] ABSTRACT: ErbB2 overexpression in breast tumors results in increased metastasis and angiogenesis and reduced survival. To study ErbB2 signaling mechanisms in metastasis and angiogenesis, we did a spontaneous metastasis assay using MDA-MB-435 human breast cancer cells stably transfected with constitutively active ErbB2 kinase (V659E), a kinase-dead mutant of ErbB2 (K753M), or vector control (neo). Mice injected with V659E had increased metastasis incidence and tumor microvessel density than mice injected with K753M or control. Increased angiogenesis in vivo from the V659E transfectants paralleled increased angiogenic potential in vitro. V659E produced increased vascular endothelial growth factor (VEGF) through increased VEGF protein synthesis. This was mediated through signaling events involving extracellular signal-regulated kinase, phosphatidylinositol 3-kinase/Akt, mammalian target of rapamycin (mTOR), and p70S6K. The V659E xenografts also had significantly increased phosphorylated Akt, phosphorylated p70S6K, and VEGF compared with controls. To validate the clinical relevance of these findings, we examined 155 human breast tumor samples. Human tumors that overexpressed ErbB2, which have been previously shown to have higher VEGF expression, showed significantly higher p70S6K phosphorylation as well. Increased VEGF expression also significantly correlated with higher levels of Akt and mTOR phosphorylation. Additionally, patients with tumors having increased p70S6K phosphorylation showed a trend for worse disease-free survival and increased metastasis. Our findings show that ErbB2 increases VEGF protein production by activating p70S6K in cell lines, xenografts, and in human cancers and suggest that these signaling molecules may serve as targets for antiangiogenic and antimetastatic therapies.
Cancer Research 03/2006; 66(4):2028-37. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Activation of Src kinase plays important roles in the development of many neoplasias. Most of the previous Src studies focused on the deregulation of Src kinase activity. The deregulated Src protein synthesis and stability in mediating malignant phenotypes of cancer cells, however, have been neglected. While investigating the signal transduction pathways contributing to ErbB2-mediated metastasis, we found that ErbB2-activated breast cancer cells that had higher metastatic potentials also had increased Src activity compared with ErbB2 low-expressing cells. The increased Src activity in ErbB2-activated cells paralleled higher Src protein levels, whereas Src RNA levels were not significantly altered. Our studies revealed two novel mechanisms that are involved in Src protein up-regulation and activation by ErbB2: (a) ErbB2 increased Src translation through activation of the Akt/mammalian target of rapamycin/4E-BP1 pathway and (b) ErbB2 increased Src stability most likely through the inhibition of the calpain protease. Furthermore, inhibition of Src activity by a Src-specific inhibitor, PP2, or a Src dominant-negative mutant dramatically reduced ErbB2-mediated cancer cell invasion in vitro and metastasis in an experimental metastasis animal model. Together, activation of ErbB2 and downstream signaling pathways can lead to increased Src protein synthesis and decreased Src protein degradation resulting in Src up-regulation and activation, which play critical roles in ErbB2-mediated breast cancer invasion and metastasis.
Cancer Research 04/2005; 65(5):1858-67. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Akt/mammalian target of rapamycin (mTOR)/4E-BP1 pathway is considered to be a central regulator of protein synthesis, involving the regulation of cell proliferation, differentiation, and survival. The inhibitors of mTOR as anticancer reagents are undergoing active evaluation in various malignancies including breast cancer. However, the activation status of the Akt/mTOR/4E-BP1 pathway and its potential roles in breast cancers remain unknown. Thus, we examined 165 invasive breast cancers with specific antibodies for the phosphorylation of Akt, mTOR, and 4E-BP1 by immunohistochemistry and compared them with normal breast epithelium, fibroadenoma, intraductal hyperplasia, and ductal carcinoma in situ. We discovered that the phosphorylation of Akt, mTOR, and 4E-BP1 increased progressively from normal breast epithelium to hyperplasia and abnormal hyperplasia to tumor invasion. Phosphorylated Akt, mTOR, and 4E-BP1 were positively associated with ErbB2 overexpression. Survival analysis showed that phosphorylation of each of these three markers was associated with poor disease-free survival independently. In vitro, we further confirmed the causal relationship between ErbB2 overexpression and mTOR activation, which was associated with enhanced invasive ability and sensitivity to a mTOR inhibitor, rapamycin. Our results, for the first time, demonstrate the following: (a) high levels of phosphorylation of Akt, mTOR, and 4E-BP1 in breast cancers, indicating activation of the Akt/mTOR/4E-BP1 pathway in breast cancer development and progression; (b) a link between ErbB2 and the Akt/mTOR/4E-BP1 pathway in breast cancers in vitro and in vivo, indicating the possible role of Akt/mTOR activation in ErbB2-mediated breast cancer progression; and (c) a potential role for this pathway in predicting the prognosis of patients with breast cancer, especially those treated with mTOR inhibitors.
Clinical Cancer Research 11/2004; 10(20):6779-88. · 7.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ErbB2-targeting antibody, trastuzumab (Herceptin), has remarkable therapeutic efficacy in certain patients with ErbB2-overexpressing tumors. The overall trastuzumab response rate, however, is limited and what determines trastuzumab response is poorly understood. Here we report that PTEN activation contributes to trastuzumab's antitumor activity. Trastuzumab treatment quickly increased PTEN membrane localization and phosphatase activity by reducing PTEN tyrosine phosphorylation via Src inhibition. Reducing PTEN in breast cancer cells by antisense oligonucleotides conferred trastuzumab resistance in vitro and in vivo. Patients with PTEN-deficient breast cancers had significantly poorer responses to trastuzumab-based therapy than those with normal PTEN. Thus, PTEN deficiency is a powerful predictor for trastuzumab resistance. Additionally, PI3K inhibitors rescued PTEN loss-induced trastuzumab resistance, suggesting that PI3K-targeting therapies could overcome this resistance.
Cancer Cell 09/2004; 6(2):117-27. · 24.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Clinical investigations have shown that in patients with breast carcinoma, tumors that overexpress the erb-B2 gene are less responsive to certain chemotherapy regimens compared with tumors that express low levels of ErbB2, suggesting that ErbB2 overexpression may be used as a marker for poor response to chemotherapy in patients with breast carcinoma. The combination of cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) is one of the most widely used chemotherapy regimens in patients with breast carcinoma. Patients who have ErbB2-overexpressing breast carcinomas have poorer responses to CMF compared with patients who have breast carcinomas with low ErbB2 expression. ErbB2-overexpressing breast tumor cells are resistant to taxol-induced apoptotic cell death. The underlying molecular mechanism is that ErbB2 inhibits p34(Cdc2) activation, which is required for taxol-induced apoptosis, by up-regulating p21(Cip1) and by hyperphosphorylating p34(Cdc2) on tyrosine-15. However, the relation between ErbB2, p21(Cip1), and p34(Cdc2) in patients with breast carcinoma remains elusive. The contribution of these molecular alterations to ErbB2-mediated CMF resistance has not been examined.
Formalin-fixed, paraffin-embedded, 5 microm thick tissue sections from 107 patients with invasive breast carcinoma were immunostained using specific antibodies against ErbB2, p21(Cip1), and phosphorylated tyrosine (Tyr)-15 of p34(Cdc2). Ninety-four of 107 patients were treated with the CMF regimen. In situ hybridization of p21(Cip1)mRNA also was performed in 20 of the sections described above. ErbB2 expression levels, p21(Cip1) expression levels, and phosphorylation status on Tyr15 of p34(Cdc2) were analyzed for correlations with clinicopathologic parameters for the 107 patients and for correlations with disease-free survival (DFS) in the 94 patients who were treated with the CMF regimen.
Among 94 patients with breast carcinoma who were treated with CMF, it was found that ErbB2 overexpression was associated significantly with poor DFS (P < 0.01). Patients who had higher p21(Cip1) expression had worse DFS compared with patients who had low p21(Cip1) expression (P = 0.02). However, no significant correlation was found between p34(Cdc2)-Tyr15 phosphorylation and DFS (P > 0.05). It is noteworthy that p21(Cip1) expression and p34(Cdc2)-Tyr15 phosphorylation were correlated significantly and positively with ErbB2 expression (P < 0.01).
The current study suggests that p21(Cip1) expression, but not p34(Cdc2)-Tyr15 phosphorylation, may play a role in ErbB2-mediated CMF resistance, which may contribute to the poor survival of patients with ErbB2-overexpressing breast carcinomas who were treated on the CMF regimen. In addition, ErbB2 overexpression was correlated with p21(Cip1) up-regulation and with increased p34(Cdc2)-Tyr15 phosphorylation in breast tumors.
Cancer 10/2003; 98(6):1123-30. · 5.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The recombinant humanized anti-ErbB2/HER2 monoclonal antibody Herceptin (Trastuzumab) has been shown to significantly enhance the tumoricidaleffects of antitumor drugs such as paclitaxel (Taxol) in patients with ErbB2-overexpressing breast cancers. Here, we investigated the molecular mechanisms by which Herceptin enhances the antitumor effects of Taxol. Because activation of p34(Cdc2) is required for Taxol-induced apoptosis and because overexpression of ErbB2 blocks Taxol-induced apoptosis by inhibiting p34(Cdc2) activation, we studied the effect of Herceptin treatment on p34(Cdc2) kinase activation and apoptosis in Taxol-treated human breast carcinoma cell lines MDA-MB-435, SKBr3, MDA-MB-453, and 435.eB, which is an ErbB2 transfectant of MDA-MB-435. Herceptin treatment down-regulated ErbB2, reduced the inhibitory phosphorylation of Cdc2 on Tyr-15, and down-regulated the expression of p21(Cip1), a Cdc2 inhibitor. Herceptin plus Taxol treatment led to higher levels of p34(Cdc2) kinase activity and apoptosis in ErbB2-overexpressing breast cancer cells, which is likely attributable to inhibition of Cdc2-Tyr-15 phosphorylation and p21(Cip1) expression. Because significant dephosphorylation of Cdc2-Tyr-15 and down-regulation of p21(Cip1) occur at least 24 h after Herceptin treatment, we investigated whether 24 h Herceptin pretreatment will render ErbB2-overexpressing breast cancer cells more sensitive to Taxol-induced apoptosis compared with the simultaneous treatment of Herceptin plus Taxol. Indeed, Herceptin pretreatment increased Taxol-induced apoptosis and cytotoxicity in vitro and more effectively inhibited the growth of tumor xenografts with enhanced in vivo apoptosis. Thus, Herceptin treatment of ErbB2-overexpressing cells can inhibit ErbB2-mediated Cdc2-Tyr-15 phosphorylation and p21(Cip1) up-regulation, which allows effective p34(Cdc2) activation and induction of apoptosis upon Taxol treatment. Herceptin pretreatment renders ErbB2-overexpressing breast cancers more susceptible to Taxol-induced cell death, which may have important clinical therapeutic implications.
Cancer Research 11/2002; 62(20):5703-10. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The angiogenic factor vascular endothelial growth factor (VEGF)-A plays an important role in breast cancer progression. However, the involvement of VEGF-C and VEGF-D, two newer members of the VEGF family, in breast carcinoma and their relationship with clinicopathologic parameters have not been clearly demonstrated.
In this study, the expression levels of VEGF-A, VEGF-C, and VEGF-D protein in 107 breast carcinoma cases and 22 nonmalignant breast tissue samples were examined by immunohistochemistry and quantitated by image analysis.
Higher expression of VEGF-C and VEGF-D was found in breast carcinomas than in nonmalignant breast tissue samples. Moreover, expression of VEGF-A, VEGF-C, and VEGF-D was significantly and positively correlated with ErbB2 expression. High levels of VEGF-A expression were associated with shorter disease-free survival (DFS). Patients with tumors expressing high levels of VEGF-C or VEGF-D showed a notable trend for worse DFS, however, it was not statistically significant. The combination of VEGF-A and VEGF-C status predicted survival better than either marker alone.
Our study suggests that expression of the angiogenic and lymphangiogenic factors (i.e., VEGFs) might be regulated at least in part by ErbB2. In addition, the combination of VEGF-A and VEGF-C status may better predict prognosis of patients with breast carcinoma than VEGF-A alone.
Cancer 07/2002; 94(11):2855-61. · 5.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Matrix metalloproteinase-9 (MMP-9) plays important roles in tumor invasion and angiogenesis. Secretion of MMP-9 has been reported in various cancer types including lung cancer, colon cancer, and breast cancer. In our investigation of MMP-9 regulation by growth factors, MMP-9 was activated by heregulin-beta1 as shown by zymography in both SKBr3 and MCF-7 breast cancer cell lines. Increase in MMP-9 activity was due to increased MMP-9 protein and mRNA levels, which mainly results from transcriptional upregulation of MMP-9 by heregulin-beta1. Heregulin-beta1 activates multiple signaling pathways in breast cancer cells, including Erk, p38 kinase, PKC, and PI3-K pathways. We examined the pathways involved in heregulin-beta1-mediated MMP-9 activation using chemical inhibitors that specifically inhibit each of these heregulin-beta1-activated pathways. The PKC inhibitor RO318220 and p38 kinase inhibitor SB203580 completely blocked heregulin-beta1-mediated activation of MMP-9. MEK-1 inhibitor PD098059 partially blocked MMP-9 activation, whereas PI3-K inhibitor wortmannin had no effect on heregulin-beta1-mediated MMP-9 activation. Therefore, at least three signaling pathways are involved in the activation of MMP-9 by heregulin-beta1. Since MMP-9 is tightly associated with invasion/metastasis and angiogenesis, our studies suggest that blocking heregulin-beta1-mediated activation of MMP-9 by inhibiting the related signaling pathways may provide new strategies for inhibition of cancer metastasis and angiogenesis.