Autocrine and paracrine growth regulation of human breast cancer

Summary We consider the hypothesis that estrogen control of hormone dependent breast cancer is mediated by autocrine and paracrine growth factors secreted by the breast cancer cells themselves. Though we show direct, unmediated effects of estrogen on specific cell functions, we also provide evidence that human breast cancer cells secrete a collection of growth factors (IGF-I, TGF, TGF, a PDGF-like competency factor, and at least one new epithelial colony stimulating factor). Some of these are estrogen-regulated in hormone dependent cells, and are constitutively increased in cells which acquire independence either spontaneously or byras transfection. Collectively, the secreted growth factors are capable of promoting tumor formation by MCF-7 cells in nude mice, though not to the same extent as estrogens. There would seem to be potential for clinical intervention in the autocrine and paracrine control of breast cancer cells, including some cells which are no longer dependent on estrogens.     

Autocrine and paracrine growth inhibitors of breast cancer cells

Breast epithelial cells produce both mitogens and growth inhibitors which are involved in the control of mammary gland development through autocrine and paracrine pathways. While the mechanisms of action of several growth factors have been well established and related strategies proposed for breast cancer therapy, little is known concerning growth inhibitors. In this review, we present an overview of current information about major autocrine and paracrine growth inhibitors of breast epithelial cells, and we discuss their potential functions in the control of breast cancer development.     

Autocrine and paracrine growth regulation of breast cancer: Clinical implications

Summary Research using experimental models of human breast cancer has broadened our understanding of the possible biochemical pathways regulating breast cancer growth. Breast cancer cells express receptors for and respond to a variety of steroid and polypeptide hormones and growth factors. Specific oncogenes are also expressed in breast cancer cells, and levels of expression may relate to tumor growth and aggressiveness. Recent studies have shown that breast cancer cells can even synthesize and secrete various growth factors that could stimulate tumor growth through autocrine and/or paracrine mechanisms. Secretion of some of these growth factors is regulated by estrogen, providing a possible mechanism for estrogen induced growth. Knowledge of these growth regulatory pathways has potentially important clinical implications. Blockade of these pathways offers new possible treatment strategies, much as antiestrogens have been used to inhibit tumor growth. Quantification of the expression of certain oncogenes, growth factor receptors, or the growth factors themselves, may provide prognostic information for the individual patient. Finally, it is plausible that measurement of these tumor products in body fluids might provide tumor markers that are useful in the diagnosis and treatment of breast cancer.     

Autocrine/paracrine erythropoietin signalling promotes JAK/STAT-dependent proliferation of human cervical cancer cells

Erythropoietin (Epo) regulates erythropoiesis by binding to its receptor (EpoR) and promoting cell proliferation, differentiation and inhibition of apoptosis. Epo is widely used to treat cervical cancer-related anaemia. However, there are data suggesting that administration of Epo is associated with an increment in recurrence rate, and decreased disease-free and overall survival. In the present study, we investigated the expression of Epo and EpoR on cervical cancer cell lines. We observed that both EpoR and extracellular Epo are constitutively expressed in cervical cancer cells. Inhibition of either Epo or EpoR expression with siRNA attenuated cell proliferation, whereas addition of exogenous Epo led to a significant increase in cell growth, both in vitro and in vivo. Epo-induced proliferation was associated with the activation of JAK2, JAK3, STAT3 and STAT5 but not JAK1 and STAT1. Our results are consistent with the existence of a functional, endogenous Epo/EpoR system in cervical cancer with the capacity to activate the transduction of signals resulting in an increased proliferation potential.     

Autocrine/paracrine erythropoietin regulates migration and invasion potential and the stemness of human breast cancer cells

Recent studies suggest that erythropoietin (EPO) has pleiotropic effects in several cell types in addition to hematopoietic cells; however, the role of EPO-mediated cell signaling in nonhematopoietic cells, including in cancer cells, remains controversial. Here, we report our findings of autocrine/paracrine production of EPO by breast cancer cells and its functional significance. We detected a significant level of autocrine/paracrine EPO in the conditioned medium from the culture of SKBR3 breast cancer cells, particularly when the cells were cultured in hypoxia. Through knockdown of EPO and EPO receptor expression and experimental elevation of EPO receptor expression in SKBR3 breast cancer cells, we demonstrated novel roles of autocrine/paracrine EPO-mediated cell signaling in regulating migration and invasion potential and stemness-like properties of breast cancer cells.     

Autocrine TNFalpha signaling renders human cancer cells susceptible to Smac-mimetic-induced apoptosis

A small-molecule mimetic of Smac/Diablo that specifically counters the apoptosis-inhibiting activity of IAP proteins has been shown to enhance apoptosis induced by cell surface death receptors as well as chemotherapeutic drugs. Survey of a panel of 50 human non-small-cell lung cancer cell lines has revealed, surprisingly, that roughly one-quarter of these lines are sensitive to the treatment of Smac mimetic alone, suggesting that an apoptotic signal has been turned on in these cells and is held in check by IAP proteins. This signal has now been identified as the autocrine-secreted cytokine tumor necrosis factor alpha (TNFalpha). In response to autocrine TNFalpha signaling, the Smac mimetic promotes formation of a RIPK1-dependent caspase-8-activating complex, leading to apoptosis.     

Autocrine and paracrine motility factors and their involvement in invasiveness in a human oral carcinoma cell line.

Invasive potentials of malignant cancer cells are regulated by cell motility factors. To examine the regulation of motility and invasiveness in oral squamous carcinoma, we investigated autocrine- and/or paracrine-acting cell motility factors, using a newly established human cell line (IF cells) from oral squamous cell carcinoma, which has highly invasive and metastatic characteristics. Conditioned medium derived from IF cells stimulated cell scattering and migration of GB-d1 gallbladder carcinoma cells, indicating that IF cells secreted cell motility factors. Using antibodies, IF-derived cell motility factors proved to be transforming growth factor (TGF)-alpha and TGF-beta1. Antibodies against TGF-alpha and TGF-beta1 inhibited autonomous migration of the IF cells. On the other hand, in vitro invasion of IF cells was strongly enhanced by hepatocyte growth factor (HGF) but only slightly by TGF-alpha and TGF-beta1. The conditioned medium from fibroblasts enhanced in vitro invasion of IF cells, an event abrogated by anti-HGF antibody, but not by antibodies against TGF-alpha and TGF-beta1. Importantly, IF cells secreted a factor inducing HGF production in fibroblasts and the factor was identified as interleukin-1, which means that a mutual interaction exists between tumour cells and fibroblasts, as mediated by the HGF/HGF-inducer loop. These results indicate that IF cells utilize TGF-alpha and TGF-beta1 as autocrine-acting motility factors and HGF as a paracrine-acting motility factor, and that invasiveness of IF cells is particularly stimulated by HGF derived from stromal fibroblasts. Utilization of multiple cell motility/invasion factors that act in distinct pathways may confer highly invasive and metastatic potentials in IF oral squamous carcinoma cells.     

Autocrine erythropoietin signaling inhibits hypoxia-induced apoptosis in human breast carcinoma cells

Disordered perfusion and the resulting hypoxia are important features conferring tumor heterogeneity, which may contribute to relapse. Hypoxic tumor cells have been associated with resistance both to radiation and to cytotoxic drugs. Hypoxia may also serve as a selection pressure in tumors by promoting apoptosis of some cells and expanding variants with decreased apoptotic potential, and thus play a role in the development of a more aggressive phenotype. Erythropoietin (Epo), induced by hypoxia, controls erythropoiesis and plays a role in protection of neurons from hypoxic damage. We have recently demonstrated hypoxia-stimulated expression of Epo and Epo receptor (EpoR) in human breast and cervix cancers, suggesting a role for autocrine Epo signaling in the hypoxic adaptations of carcinomas. In the current study we provide evidence that increased autocrine Epo signaling induced by moderate levels of hypoxia inhibits hypoxia-induced apoptosis and promotes survival in MCF-7 human breast cancer cells. The anti-apoptotic effect of Epo correlates with upregulation of bcl-2 and bcl-XL, suggesting a mechanism similar to those described in hematopoietic cells. The resulting decreased apoptotic potential of hypoxic tumor cells may contribute to increased aggressiveness and therapy resistance of breast cancers.     

Autocrine factors that sustain glioma invasion and paracrine biology in the brain microenvironment

Invasion is a defining hallmark of glioblastoma multiforme, just as metastasis characterizes other high-grade tumors. Glial tumors invariably recur due to the regrowth of invasive cells, which are unaffected by standard treatment modalities. Drivers of glioma invasion include autocrine signals propagated by secreted factors that signal through receptors on the tumor. These secreted factors are able to diffuse through the peritumoral stroma, thereby influencing parenchymal cells that surround the tumor mass. Here we describe various autocrine motility factors that are expressed by invasive glioma cells and explore the effects that they may have on normal cells present in the path of invasion. Conversely, normal brain parenchymal cells secrete ligands that can stimulate receptors on invasive glioma cells and potentially facilitate glioma invasion or create a permissive microenvironment for malignant progression. Parallel observations have been made for solid tumors of epithelial origin, in which parenchymal and stromal cells either support or suppress tumor invasion. Most autocrine and paracrine interactions involved in glioma invasion constitute known signaling systems in stages of central nervous system development that involve the migration of precursor cells that populate the developing brain. Key paracrine interactions between glioma cells and the brain microenvironment can influence glioma pathobiology and therefore contribute to its poor prognosis. Current therapies for glioma that could have an impact on paracrine communication between tumors and normal cells are discussed. We suggest that cells in the normal brain parenchyma be considered as potential targets for adjuvant therapies to control glioma growth because such cells are less likely to develop resistance than glioma cells.     

mTOR signaling in human cancer

Inhibitors of mTOR, the mammalian target of rapamycin, have been extensively studied in clinical trials for cancer treatment. Results have been promising, mostly in certain lymphomas, but in solid tumours the results have been generally less encouraging. However, recent results, particularly in renal cell carcinoma, have provided renewed interest in the role of mTOR inhibitors in solid tumours. A rational, and potentially more successful, development of these agents (i.e., RAD001, temsirolimus and AP23573) likely relies in a deeper knowledge of mTOR signalling in cancer, both at the preclinical and clinical levels. These would allow a better selection of patients more likely to respond to the use of biologically active doses of the agents and the development of mechanistically based combinations with other agents. The goal of this review is to provide an update on the complex signalling of mTOR in cancer and on the biological effects of mTOR inhibitors in cancer cells. Supported by an unrestricted educational grant from Pfizer.     

Fibulin-3 promotes glioma growth and resistance through a novel paracrine regulation of Notch signaling

Malignant gliomas are highly invasive and chemoresistant brain tumors with extremely poor prognosis. Targeting of the soluble factors that trigger invasion and resistance, therefore, could have a significant impact against the infiltrative glioma cells that are a major source of recurrence. Fibulin-3 is a matrix protein that is absent in normal brain but upregulated in gliomas and promotes tumor invasion by unknown mechanisms. Here, we show that fibulin-3 is a novel soluble activator of Notch signaling that antagonizes DLL3, an autocrine inhibitor or Notch, and promotes tumor cell survival and invasion in a Notch-dependent manner. Using a strategy for inducible knockdown, we found that controlled downregulation of fibulin-3 reduced Notch signaling and led to increased apoptosis, reduced self-renewal of glioblastoma-initiating cells, and impaired growth and dispersion of intracranial tumors. In addition, fibulin-3 expression correlated with expression levels of Notch-dependent genes and was a marker of Notch activation in patient-derived glioma samples. These findings underscore a major role for the tumor extracellular matrix in regulating glioma invasion and resistance to apoptosis via activation of the key Notch pathway. More importantly, this work describes a noncanonical, soluble activator of Notch in a cancer model and shows how Notch signaling can be reduced by targeting tumor-specific accessible molecules in the tumor microenvironment.     

Autocrine and/or paracrine growth of aggressive ATLL cells caused by HGF and c-Met

Adult T-cell leukemia/lymphoma (ATLL) is a neoplasia characterized by the massive invasion of various organs by tumor cells. Previously, we found that expression of the gene for c-Met, a receptor tyrosine kinase for hepatocyte growth factor (HGF), was specific to the acute type among 41 patients with ATLL by microarray. First in the present study, we analyzed the survival of the patients in relation to expression of c-Met and HGF in ATLL cells. Expression of the former but not the latter was associated with poor prognosis. Then, we analyzed the growth of ATLL cells caused by HGF and c-Met. c-Met was expressed in 0/7 chronic ATLLs, 12/14 acute ATLLs, 1/1 IL-2-independent ATLL cell line and 1/7 IL-2-dependent ATLL cell lines as assessed by flow cytometry. HGF induced the proliferation of primary cells from most acute cases examined as well as the c-Met-positive KK1 cell line in contrast to c-Met-negative cells. HGF induced autophosphorylation of c-Met in c-Met-positive cells from an acute case and KK1 cells. The plasma level of HGF was elevated in acute as compared to chronic cases. The levels of HGF and/or IL-6 which induces the production of HGF by stromal cells, were elevated in the supernatant of short-term cultured cells from certain patients with acute or chronic disease. Finally, infiltrated ATLL cells and adjacent stromal cells in liver were shown to be positive for c-Met/HGF and HGF, respectively, in acute cases. Autocrine and/or paracrine growth caused by HGF and c-Met was suggested in aggressive ATLL cells secreting HGF and/or IL-6, respectively.     

EphB/EphrinB receptors and Wnt signaling in colorectal cancer

Eph receptors and their ephrin ligands mediate cell repulsion during embryonic development. In the intestinal epithelium, EphB receptors are Wnt signaling target genes that control cell compartmentalization along the crypt axis. Recent findings have shown that this family of receptors are key players during colorectal cancer progression. Here, we review the current knowledge of the EphB/ephrinB system in the intestinal epithelium and we discuss their tumor suppressor role in the context of the multistep progression of colorectal cancer.     

ERBB receptors in cancer: signaling from the inside

ERBB receptor tyrosine kinases are activated by ligand-induced dimerization followed by activation and transphosphorylation of their intracellular kinase domains. A recent study by Bill and colleagues demonstrates that receptor transphosphorylation can be regulated from inside the cell by members of the cytohesin protein family. These data highlight a novel mechanism of amplification of ERBB receptor signaling output that may contribute to embryogenesis and cancer progression.     

Notch信号在人类乳腺癌中的作用

目的观察Notch1和JAG1在乳腺癌中的表达及其与乳腺癌相关因素的关系,探讨Notch信号在人类乳腺癌中的作用。方法应用逆转录聚合酶链反应(RT-PCR)检测62例乳腺癌组织及22例癌旁正常乳腺组织中Notch1和JAG1的表达,对乳腺癌组织与癌旁正常乳腺组织进行表达率和表达强度标准化系数的统计学比较,并在不同的腋窝淋巴结转移情况间、不同的临床分期间进行Notch1表达强度标准化系数的统计学比较。结果乳腺癌组织Notch1的表达率和标准化系数分别为98.0%和0.91,均明显高于癌旁正常乳腺组织,乳腺癌组织中JAG1的表达率为15.0%,癌旁组织中无JAG1表达;伴腋窝淋巴结转移的病例Notch1标准化系数高于无腋窝淋巴结转移的病例;乳腺癌Ⅰ期病例Notch1标准化系数(0.66)低于Ⅱ期(1.20),Ⅱ期高于Ⅲ期(0.62),Ⅰ期与Ⅲ期差异无统计学意义。结论人类乳腺癌中存在Notch1和JAG1的异常高表达,提示Notch1的异常表达与活化人能与人类乳腺癌的形成有关,Notch1在人类乳腺癌不同发展阶段的作用可能不同。