Src family kinases mediate epidermal growth factor receptor signaling from lipid rafts in breast cancer cells

Activation of the epidermal growth factor receptor (EGFR) regulates cellular proliferation, survival, and migration of breast cancer cells. In particular, EGFR recruits signaling proteins to the cell membrane leading to their phosphorylation and activation. However, EGFR also localizes to other cellular structures, including endosomes, mitochondrion, and nuclei. Recently, we demonstrated that lipid raft localization of EGFR in triple-negative breast cancer cell lines promotes EGFR protein-dependent, EGFR kinase-independent activation of Akt. Here, we further define the mechanism by which lipid rafts regulate EGFR signaling to Akt. Specifically, we show that the non-receptor tyrosine kinase c-Src co-localizes and co-associates with EGFR and lipid rafts. Breast cancer cells resistant to treatment with EGFR inhibitors, were also resistant to treatment with Src family kinase (SFK) inhibitors; however, the combination of EGFR and SFK inhibitors synergistically decreases cell viability. We found that this decrease in cell viability observed with EGFR and SFK inhibitor co-treatment correlates with loss of Akt phosphorylation. In addition, we found that in breast cancer cell lines with EGFR and c-Src co-localized to lipid rafts, phospho-inositide 3 kinase (PI3K) was also associated with lipid rafts. Together, the data herein suggest that lipid rafts provide a platform for the interaction of EGFR, c-Src, and PI3K, leading to activation of cellular survival signaling in breast cancer cells.     

Characterization of epidermal growth factor receptor and action on human breast cancer cells in culture

Epidermal growth factor (EGF) may play a role in regulating growth of breast cancer cells in vivo. We have examined the action of EGF on breast cancer cells in vitro and characterized the EGF receptor as a model system for its action in vivo. All of the fourteen breast cancer cell lines which grow attached to culture dishes specifically bound EGF, including one purportedly normal breast line (HBL-100). The one cell line examined which grows as a suspension, DU-4475, did not express measurable levels of EGF binding. The number of EGF binding sites per cell for the different cell lines varied from 200 EGF binding sites/cell (for MDA-MB-436) to 700,000 EGF binding sites/cell (for MDA-MB-231), with most cell lines having approximately 10,000 EGF binding sites/cell. Scatchard analysis of EGF binding to four of the breast cell lines indicated a single class of high-affinity binding sites for MDA-MB-231 cells (Kd = 200 pM; n = 220 fmol of EGF bound/mg of cell protein); and for T-47D cells (Kd = 4 nM, n = 85 fmol of EGF bound/mg of cell protein) and curvilinear plots for MCF-7 cells and HBL-100 cells. The EGF binding to MDA-MB-231 cells was specific for EGF and was maximum after 2 hr at 37 degrees, followed by a progressive loss of cell-associated radio-activity, which was prevented by the action of the lysosomal inhibitory agent chloroquine. Specific covalent binding of 125I-EGF to MDA-MB-231 cells indicated that the EGF receptor had molecular weights of 165,000 and 140,000. MCF-7 cells and T-47D cells grown in serum-free medium supplemented with 10 nM EGF for 3 days had significantly increased protein, DNA, and cell number, whereas MDA-MB-231 and ZR-75-1 cells did not respond significantly to EGF. These results indicate that EGF receptors are consistently expressed by breast cells grown attached to a surface but that some cell lines expressing EGF receptors do not respond mitogenically to EGF. The biochemical characteristics of EGF receptors in MDA-MD-231 breast cells are similar to those observed for EGF receptors in other human tissues.     

HER-2 amplification, steroid receptors and epidermal growth factor receptor in primary breast cancer

Amplification of HER-2 oncogene was analysed in DNAs obtained from 291 primary human mammary carcinomas. 52/291 (18%) were found to contain amplified HER-2 oncogene. Moderate amplification (2- to 5-fold) was noted in 36/291 (12%). Thirteen tumors (4.5%) had a copy number of 5 to 10. A 10- to 20-fold and greater than 20-fold amplification was observed in 2 and 1 patient, respectively. Sample sizes allowed the determination of estrogen receptor (ER) and progesterone receptor (PgR) levels in 253/291 primary breast cancers. HER-2 gene amplification was noted in 14% of ER+ patients and in 28% of ER- patients, respectively (P = 0.02). Similarly a significantly greater number of PgR- primary mammary carcinoma exhibited an amplification of the HER-2 gene compared to PgR+ cases (22% vs. 16%, P = 0.01). Although statistically not significant, tumors with HER-2 gene amplification were found to have lower levels of ER and PgR. No association of HER-2 amplification with the androgen receptor and EGF receptor was observed. Present data combine to suggest that tumor progression is more stringently controlled by the oncogene upon loss of hormone dependency. Differences found in HER-2 amplification between steroid receptor positive and negative tumors could be helpful to define a specific subset of women to whom adjuvant therapy should be directed.     

Transactivation of epidermal growth factor receptor through platelet-activating factor/receptor in ovarian cancer cells

Background

We previously identified platelet-activating factor receptor (PAFR) as being overexpressed in ovarian cancer and found that its ligand PAF evoked EGFR phosphorylation using the phospho-antibody microarray. Epidermal growth factor receptor (EGFR) are also overexpressed in ovarian cancer and contribute to the growth of ovarian cancer cells. Here, we investigated the mechanisms of crosstalk between PAFR and EGFR signaling in ovarian cancer cells to further determine whether the interaction between PAFR and EGFR synergistic contribute to the progression of ovarian cancer.

Methods

Expression and localization of PAFR in several ovarian cancer cell lines were assessed by Western blot, realtime-PCR and immunofluorescence. The ovarian cancer cells were stimulated with PAF or PAF and in some experiments also pharmacological inhibitors. Phosphorylation of proteins in signaling pathways were measured by Western blot. HB-EGF concentrations of the supernatant from stimulated ovarian cancer cells were measured by enzyme-linked immunosorbent assay.

Results

Our data show that PAF increases EGFR phosphorylation through PAFR in a time- and dose- dependent manner in SKOV-3 ovarian cancer cells. This transactivation is dependent on phospholipase C-β and intracellular calcium signaling. This pathway is also Src tyrosine kinase- and metalloproteinase- dependent. PAF triggers EGFR activation through the increased heparin-binding EGF-like growth factor (HB-EGF) release in metalloprotease-dependent manner. Several studies involving EGFR transactivation through G-protein coupled receptor (GPCR) have demonstrated EGFR-dependent increase in ERK1/2 phosphorylation. Yet in SKOV-3 cells, PAF treatment also increases ERK1/2 phosphorylation in a EGFR-independent manner.

Conclusions

The results suggest that in SKOV-3 ovarian cancer cells, PAF transactivates EGFR and downstream ERK pathways, thus diversifying the GPCR-mediated signal. The crosstalk between PAFR and EGFR suggests a potentially important signaling linkage between inflammatory and growth factor signaling in ovarian cancer cells.     

Role of epidermal growth factor receptor in breast cancer

Decades of research in molecular oncology have brought about promising new therapies which are designed to target specific molecules which promote tumor growth and survival. The epidermal growth factor receptor (EGFR) is one of the first identified important targets of these novel antitumor agents. Approximately half of cases of triple-negative breast cancer (TNBC) and inflammatory breast cancer (IBC) overexpress EGFR. Thus, EGFR inhibitors for treatment of breast cancer have been evaluated in several studies. However, results so far have been disappointing. One of the reasons for these unexpected results is the lack of biomarkers for predicting which patients are most likely to respond to EGFR inhibitors. Recent studies have shown that EGFR and its downstream pathway regulate epithelial-mesenchymal transition, migration, and tumor invasion and that high EGFR expression is an independent predictor of poor prognosis in IBC. Further, recent studies have shown that targeting EGFR enhances the chemosensitivity of TNBC cells by rewiring apoptotic signaling networks in TNBC. These studies indicate that EGFR-targeted therapy might have a promising role in TNBC and IBC. Further studies of the role of EGFR in TNBC and IBC are needed to better understand the best way to use EGFR-targeted therapy??e.g., as a chemosensitizer or to prevent metastases??to treat these aggressive diseases.     

Luteolin inhibits insulin-like growth factor 1 receptor signaling in prostate cancer cells

Insulin-like growth factor 1 receptor (IGF-1R) activation is required for prostate cell proliferation. Prostate cancer is one of the most commonly diagnosed malignant tumors in Western countries. Overexpression of IGF-1R in prostate cancer is associated with tumor growth. These suggest that IGF-1R inhibitory agents may be of preventive and/or therapeutic value. With evidence accumulating for a chemopreventive role of flavonoids, the effects of luteolin, a bioactive flavonoid, on IGF-1R signaling in prostate cancer cells were examined. Luteolin inhibited insulin-like growth factor 1 (IGF-1) induced activation of IGF-1R and AKT in prostate cancer PC-3 and DU145 cells. Inhibition of AKT by luteolin resulted in decreased phosphorylation of its downstream targets, including p70S6K1, GSK-3beta and FKHR/FKHRL1. Luteolin also inhibited the IGF-1-induced activation of EGFR and MAPK/ERK signaling. Luteolin inhibited expression of cyclin D1 and increased expression of p21. As a result, luteolin suppressed proliferation and induced apoptosis of prostate cancer cells. Knockdown of IGF-1R by siRNA led to inhibition of proliferation of prostate cancer cells. Results of in vivo tumor growth assay indicated that luteolin inhibited PC-3 tumor growth. Immunoblotting of the extracts of tumor tissues showed that luteolin inhibited IGF-1R/AKT signaling. Our results provide a new insight into the mechanisms that luteolin is against cancer cells.     

Receptors for epidermal growth factor and steroid hormones in human breast cancer

Epidermal growth factor (EGF) seems to play an important role in regulating the proliferation of human breast cancer. Fifty-five primary breast tumors and 7 lymph node metastases were simultaneously assayed for the presence of EGF receptors (EGFR), estrogen receptors (ER), and progesterone receptors (PR). Overall, 42% (23/55) of the tumors were EGFR positive. EGFR were more frequently present in ER- and PR-negative than in ER- and PR-positive tumors. In particular, a negative correlation between EGFR and PR (chi 2 = 6.8; p greater than 0.01) was observed. All metastatic tumors were EGFR negative, and in all cases but 1 the levels of EGFR were higher in metastatic than in primary tumors. Our results suggest the presence of a subclass of breast tumors, the growth of which is primarily regulated by EGF or EGF-like substances rather than by steroid hormones. In this group, not amenable to endocrine therapy, EGF receptors should represent a target for therapeutic intervention.     

表皮生长因子受体通路在乳腺癌耐药机制中的研究及应用

表皮生长因子受体在多种肿瘤中存在过度表达.在三苯氧胺耐药(TAM-R)的乳腺癌细胞中表皮生长因子受体(EGFR)的过度表达预示着肿瘤预后不良.研究乳腺癌TAM-R的机制及寻找克服耐药的方案十分重要.已有大量临床前研究显示EGFR信号通路的激活导致乳腺癌细胞产生TAM-R,临床上已有应用EGFR抑制剂于TAM-R乳腺癌的报道,但并非所有患者都能从中获益.EGFR抑制剂的原发或继发耐药是临床上遇到的新难题.     

Significance of epidermal growth factor receptor expression in breast cancer

Colorectal cancer is one of the most common cancers worldwide. The anticancer effect of Wolfberry (Lycium barbarum) polysaccharide (LBP) on colon cancer cells is largely unknown. To investigate the growth effect of LBP on human colon cancer cell and its possible mechanisms, human colon cancer SW480 and Caco-2 cells were treated with 100–1,000 mg/l LBP for 1–8 days. Cell growth was measured by MTT assay and crystal violet assay. Distribution of the cell cycle was analyzed by flow cytometry. Western blotting was used to indicate changes in the level of cyclins and cyclin-dependent kinases (CDKs). LBP treatment inhibited both colon cancer cell lines in a dose-dependent manner. At concentrations from 400 to 1,000 mg/l, LBP significantly inhibited the growth of SW480 cells (400 mg/l, P < 0.01; 800 and 1,000 mg/l, P < 0.001); while at concentrations from 200 to 1,000 mg/l, LBP significantly inhibited the growth of Caco-2 cells (200 mg/l, P < 0.05; 400–1,000 mg/l, P < 0.001). Crystal violet assay showed that LBP had a long-term anti-proliferative effect. More importantly, cells were arrested at the G0/G1 phase. The changes in cell-cycle-associated protein, cyclins, and CDKs were consistent with the changes in cell-cycle distribution. This is one of the first studies to focus on LBP-induced interruption of the cell cycle in human colon carcinoma cells. The results suggest that LBP is a candidate anticancer agent.     

Immunohistochemical expression of epidermal growth factor receptor in breast cancer

Background  

Molecular-targeting drugs able to treat breast cancer expressing epidermal growth factor receptor (EGFR) would be clinically valuable. The aim of the current study was to determine the further significance of immunohistochemical expression of EGFR in breast cancer.     

Significance of epidermal growth factor receptor expression in breast cancer

Recent interest of many investigators is focused on epidermal growth factor receptor (EGFR) family, because of their potential role in the pathogenesis and progression of breast cancer. Paraffin tumor sections were collected retrospectively from 181 breast cancer patients diagnosed between 2002 and 2003. Immunohistochemical staining with ErbB-1, ErbB-2, ErbB-3, and ErbB-4 monoclonal antibodies was performed. The ErbB expression was correlated with the other clinicopathological variables. Overexpression of ErbB-1, ErbB-2, ErbB-3, and ErbB-4 was observed in 20.6, 18.2, 14.3, and 5.7% cases, respectively. Overexpression of ErbB-1 and ErbB-2 was associated with poor prognostic features and decreased 5-year disease-free survival. The patients with co-overexpression of ErbB-1 and ErbB-2 had a shorter DFS, although this difference was not statistically significant. ErbB-1 overexpression may indicate a subset of patients with a poor disease prognosis. Assays for ErbB-1 and ErbB-2 may be more useful than a single assay in predicting prognosis of a breast cancer patient.     

Significance of epidermal growth factor receptor expression in breast cancer

Recent interest of many investigators is focused on epidermal growth factor receptor (EGFR) family, because of their potential role in the pathogenesis and progression of breast cancer. Paraffin tumor sections were collected retrospectively from 181 breast cancer patients diagnosed between 2002 and 2003. Immunohistochemical staining with ErbB-1, ErbB-2, ErbB-3, and ErbB-4 monoclonal antibodies was performed. The ErbB expression was correlated with the other clinicopathological variables. Overexpression of ErbB-1, ErbB-2, ErbB-3, and ErbB-4 was observed in 20.6, 18.2, 14.3, and 5.7% cases, respectively. Overexpression of ErbB-1 and ErbB-2 was associated with poor prognostic features and decreased 5-year disease-free survival. The patients with co-overexpression of ErbB-1 and ErbB-2 had a shorter DFS, although this difference was not statistically significant. ErbB-1 overexpression may indicate a subset of patients with a poor disease prognosis. Assays for ErbB-1 and ErbB-2 may be more useful than a single assay in predicting prognosis of a breast cancer patient.

     

Survivin expression is regulated by coexpression of human epidermal growth factor receptor 2 and epidermal growth factor receptor via phosphatidylinositol 3-kinase/AKT signaling pathway in breast cancer cells

Survivin, a member of the inhibitor of apoptosis protein family, is widely expressed in a variety of human cancer tissues. Survivin inhibits activation of caspases, and its overexpression can lead to resistance to apoptotic stimuli. In this study, survivin protein expression was assessed by immunohistochemical staining of 195 invasive breast cancer specimens. Overall, 79.5% of the tumors were positive for survivin. The expression of epidermal growth factor receptor (EGFR) family, human epidermal growth factor receptor 2 (HER2) and EGFR, was also examined in 53 cases, and consequently, it was indicated that survivin positivity might be correlated with the coexpression of HER2 and EGFR. To clarify the regulatory mechanism of survivin expression in breast cancer cells, the effect of HER2 and/or EGFR expression on the survivin levels was examined. It was revealed that the survivin protein level was up-regulated by the coexpression of HER2 and EGFR, leading to the increased resistance against etoposide-induced apoptosis in breast cancer cells. Conversely, survivin levels and apoptosis resistance were decreased when cells were treated with HER2-specific inhibitor, Herceptin. Although Herceptin could down-regulate both phosphatidylinositol 3-kinase (PI3K)/AKT signal and mitogen-activated protein/extracellular signal-related kinase (ERK) kinase 1 (MEK1)/ERK signal in HER2-positive breast cancer cells, PI3K-specific inhibitor but not MEK1-specific inhibitor could decrease the survivin levels. The present study clarified the regulatory mechanism of HER2 in the expression of survivin protein in breast cancer cells.     

Cytokine regulation by epidermal growth factor receptor inhibitors and epidermal growth factor receptor inhibitor associated skin toxicity in cancer patients

AimEpidermal growth factor receptor inhibitor (EGFRI) induced skin toxicity has a prognostic value suggesting skin toxicity can be a useful surrogate marker for successful epidermal growth factor receptor (EGFR) inhibition, improved response and survival. But the pathophysiology of EGFRI induced skin toxicity remains elusive. However the involvement of immunological mechanisms has been speculated. This study investigates the possible underlying mechanism of EGFR inhibition associated cytokine production in keratinocytes as well as in patients after treatment with epidermal growth factor receptor inhibitors (EGFRIs).MethodsNormal human epidermal keratinocytes (NHEK) were incubated for 2 and 24 h with different concentrations of EGFRI (erlotinib) for Western blot analysis and cytokine expression analysis, respectively. Inhibition of EGFR, extracellular-signal-regulated kinase 1/2 (Erk 1/2) and c-Jun was examined by Western blot analysis. Cytokine concentrations were measured by enzyme-linked immunosorbent assay (ELISA) in the NHEK cell supernatant and also in the serum of 186 cancer patients who are followed up for EGFRI induced skin rash.ResultsA significant inhibitory effect of EGFRI was seen on EGFR (Y845), Erk 1/2 and c-Jun in a dose dependent manner. Further downstream, increased CC-chemokine ligand 2 (CCL2), CC-chemokine ligand 5 (CCL5) and decreased interleukin-8 (IL-8) or CXCL8 expression was observed in keratinocytes. In EGFRI treated patients, low levels of serum CXCL8 corresponding to stronger EGFR inhibition were associated with a higher grade of skin toxicity (p = 0.0016) and a prolonged overall survival (p = 0.018).ConclusionsThe results obtained in this study indicate that EGFRI can regulate cytokines by modulating EGFR signalling pathway in keratinocytes. Moreover, serum levels of CXCL8 in EGFRI treated patients may be important for individual EGFRI induced skin toxicity and patient’s survival.     

酒精对乳腺癌细胞表皮生长因子受体-钙激活中性蛋白酶通路及细胞迁移的影响

背景与目的：酒精(ethyl alcohol,EtOH)可促进乳腺癌的恶性演进,但其信号机制尚未完全明了。本研究通过观察EtOH对乳腺癌细胞钙激活中性蛋白酶(calcium-activated neutral protease,CANP)-周期蛋白E/局部黏着斑激酶(focal adhesion kinase,FAK)信号通路和细胞迁移的影响,以及表皮生长因子受体(epidermal growth factor receptor,EGFR)在其中的介导作用,探讨EtOH促进乳腺癌细胞迁移的信号机制。方法：以人乳腺肿瘤细胞系MCF-7为模型细胞(MCF-10A乳腺上皮细胞为对照);采用蛋白[质]印迹法(Western blot)分析周期蛋白E和FAK蛋白剪切反应;通过伤口愈合实验观察细胞迁移效应;采用EGFR抑制剂(EGFR inhibitor, EGFR-I)或CANP抑制剂Calpeptin抑制EGFR或CANP活性,观察抑制剂对EtOH诱导CANP1大亚基、周期蛋白E/FAK蛋白剪切及细胞迁移的影响。结果：以EtOH(0.3%)处理模型细胞可观察到周期蛋白E和FAK出现明显蛋白剪切且该效应呈剂量和时间依赖性,还观察到EtOH刺激细胞迁移活动(+47.30%,P<0.05),但EtOH对MCF-10A细胞迁移无明显影响;以Calpeptin(10μmol/L)预处理模型细胞,可见EtOH(0.3%)或EGF(10 ng/mL)诱导的周期蛋白E/FAK蛋白剪切效应受到明显抑制;EGFR-I(3μmol/L)可显著抑制EtOH诱导的CANP1大亚基和周期蛋白E/FAK蛋白剪切及细胞迁移效应(-53.00%,P<0.01)。结论：EtOH可通过EGFR激活乳腺癌细胞CANP信号活动并促进细胞迁移,EGFR-CANP通路参与介导EtOH与EGF之间的串话,提示EGFR-CANP信号通路中的关键分子可为防止乳腺癌转移的潜在药物靶点。     

Effects of Src inhibitors on cell growth and epidermal growth factor receptor and MET signaling in gefitinib-resistant non-small cell lung cancer cells with acquired MET amplification

The efficacy of epidermal growth factor receptor (EGFR)–tyrosine kinase inhibitors such as gefitinib and erlotinib in non-small cell lung cancer (NSCLC) is often limited by the emergence of drug resistance conferred either by a secondary T790M mutation of EGFR or by acquired amplification of the MET gene. We now show that the extent of activation of the tyrosine kinase Src is markedly increased in gefitinib-resistant NSCLC (HCC827 GR) cells with MET amplification compared with that in the gefitinib-sensitive parental (HCC827) cells. In contrast, the extent of Src activation did not differ between gefitinib-resistant NSCLC (PC9/ZD) cells harboring the T790M mutation of EGFR and the corresponding gefitinib-sensitive parental (PC9) cells. This activation of Src in HCC827 GR cells was largely abolished by the MET-TKI PHA-665752 but was only partially inhibited by gefitinib, suggesting that Src activation is more dependent on MET signaling than on EGFR signaling in gefitinib-resistant NSCLC cells with MET amplification. Src inhibitors blocked Akt and Erk signaling pathways, resulting in both suppression of cell growth and induction of apoptosis, in HCC827 GR cells as effectively as did the combination of gefitinib and PHA-665752. Furthermore, Src inhibitor dasatinib inhibited tumor growth in HCC827 GR xenografts to a significantly greater extent than did treatment with gefitinib alone. These results provide a rationale for clinical targeting of Src in gefitinib-resistant NSCLC with MET amplification. ( Cancer Sci 2009)     

Prognostic value of epidermal growth factor receptor in node-positive breast cancer

Summary The prognostic significance of EGFR (epidermal growth factor receptor) was studied in a cohort of 68 node-positive patients with breast cancer, who entered a controlled protocol of adjuvant therapy between February 1980 and June 1984. EGFR radioligand binding assay was carried out on frozen stored samples. Twenty five (37%) of 68 primary sites and 9 (41%) of 19 lymph node metastases assayed were EGFR-positive with a cut off value of 5 fmol/mg membrane protein; there is no statistical difference between the two distributions. EGFR was significantly correlated to ER and histological grade. EGFR-positive tumors and high levels of EGFR were mainly found in the ER-negative group of tumors (p = 0.008) and in histological grade III (p = 0.007). Fifty five patients could be followed for 40 to 92 months. EGFR was an independent prognostic factor for survival after 40 months (p = 0.05). EGFR⁺/ER^– patients had the lowest survival probability, but statistical significance was not reached (p = 0.06). The EGFR phenotype appeared as a prognostic parameter in node-positive patients, individualizing subgroups of patients with different early outcome, with potential therapeutic implication especially in the group of ER-negative patients. These results emphasize the need for a standardized assay methodology and for further clinical studies, particularly in protocols where adjuvant hormonal therapy is prescribed on the basis of steroid hormone receptor status, in order to assess the respective prognostic worth of EGFR and ER (or PR).     

Racial disparity of epidermal growth factor receptor expression in prostate cancer.

PURPOSE: The epidermal growth factor receptor (EGFR) plays a critical role in prostate cancer (PC) signal transduction and is the target of a novel class of anticancer agents. Despite recent reports of interethnic variation in response to EGFR inhibitors, limited information exists regarding differences in expression of EGFR in PC patients. This has therapeutic relevance because a better understanding of the molecular basis underlying the ethnic variability will help in the design of individualized treatment regimens using EGFR inhibitors. PATIENTS AND METHODS: We investigated EGFR expression in a well-characterized cohort of PC patients to determine the association between EGFR expression and race. Tumor tissues from 202 radical prostatectomies performed between 1990 and 2000 at the Veterans Administration Medical Center (New York, NY) were studied (142 African Americans, 60 whites; median age, 67 years; stage T2, n = 130; stage > or = T3, n = 72; Gleason score < 7, n = 110; Gleason score > or = 7, n = 92). Membrane-specific EGFR expression was evaluated immunohistochemically. RESULTS: EGFR overexpression, defined as complete membrane staining in more than 10% of tumor cells, was observed in 75 of 202 patients (37%). There was a significant association between EGFR overexpression and African American race (P = .0006), higher pretreatment prostate-specific antigen (PSA; P = .02), and stage (P = .02), but not Gleason score (P = .33). The association between African American race and EGFR overexpression remained significant in a multivariate model after controlling for grade, stage, and pretreatment PSA simultaneously (P = .003). CONCLUSION: Our data demonstrate that race contributes significantly to variability of EGFR expression in prostate cancer. Racial background may have an impact on the design of clinical trials to test the efficacy of anti-EGFR agents.     

Luteinizing hormone-releasing hormone agonist limits DU-145 prostate cancer growth by attenuating epidermal growth factor receptor signaling.

PURPOSE: Advanced prostate cancer is treated initially by central suppression of androgen production by luteinizing hormone-releasing hormone (LHRH) agonists. Intriguingly, even hormone-independent cancers often show some, if only slight, growth retardation when these agonists are delivered in pharmacological doses. Previous studies have shown in cell lines and animal xenograft models that activation of peripheral LHRH receptors on prostate carcinoma cells lead to growth suppression. In parallel, there is a decrease of epidermal growth factor receptors (EGFRs) and activity. Because autocrine EGFR stimulation exists in most, if not all, prostate carcinomas and is required for cell proliferation, we asked whether LHRH signaling cross-attenuated EGFR to limit tumor growth. One possible mechanism was suggested by LHRH receptors triggering phospholipase-C (PLC) to activate protein kinase C (PKC) because PKC activation limits EGFR tyrosine kinase activity by phosphorylating EGFR at threonine 654. EXPERIMENTAL DESIGN: To determine the role of this cross-attenuation mechanism, we mutated the threonine 654 amino acid to an alanine (A654) to abrogate this inhibition. DU-145 cells stably expressing wild-type and A654 EGFR were grown as xenografts in the s.c. space of athymic mice. RESULTS: DU-145 cells, overexpressing wild-type EGFR, formed tumors in athymic mice that were inhibitable by goserelin acetate (Zoladex). Tumors expressing the A654 EGFR were resistant to this growth inhibition. These results paralleled in vitro studies in which goserelin acetate blocked proliferation of the WT DU-145 but not A654 DU-145 cells. CONCLUSIONS: These data support the model of LHRH agonists preventing EGFR-mediated tumor growth through a PKC pathway. This suggests new targets of modulatory intervention to limit the growth of androgen-independent prostate carcinomas.