Activation of epidermal growth factor receptor tyrosine phosphorylation by tumor necrosis factor correlates with loss of cytotoxic activity

TNF-alpha increases tyrosine phosphorylation of vascular endothelial cadherin and opens the paracellular pathway through fyn activation in human lung endothelia

Tumor necrosis factor (TNF)-alpha is a key mediator of sepsis-associated multiorgan failure, including the acute respiratory distress syndrome. We examined the role of protein tyrosine phosphorylation in TNF-alpha-induced pulmonary vascular permeability. Postconfluent human lung microvascular and pulmonary artery endothelial cell (EC) monolayers exposed to human recombinant TNF-alpha displayed a dose- and time-dependent increase in transendothelial [(14)C]albumin flux in the absence of EC injury. TNF-alpha also increased tyrosine phosphorylation of EC proteins, and several substrates were identified as the zonula adherens proteins vascular endothelial (VE)-cadherin, and beta-catenin, gamma-catenin, and p120 catenin (p120(ctn)). Prior protein tyrosine kinase (PTK) inhibition protected against the TNF-alpha effect. TNF-alpha activated multiple PTKs, including src family PTKs. Prior PTK inhibition with the src-selective agents PP1 and PP2 each protected against approximately 60% of the TNF-alpha-induced increment in [(14)C]albumin flux. PP2 also blocked TNF-alpha-induced tyrosine phosphorylation of VE-cadherin, gamma-catenin, and p120(ctn). To identify which src family kinase(s) was required for TNF-alpha-induced vascular permeability, small interfering RNA (siRNA) targeting each of the three src family PTKs expressed in human EC, c-src, fyn, and yes, were introduced into the barrier function assay. Only fyn siRNA protected against the TNF-alpha effect, whereas the c-src and yes siRNAs did not. These combined data suggest that TNF-alpha regulates the pulmonary vascular endothelial paracellular pathway, in part, through fyn activation.

Lack of EGF receptor contributes to drug sensitivity of human germline cells

Germline mutations have been associated with generation of various types of tumour. In this study, we investigated genetic alteration of germline tumours that affect the drug sensitivity of cells. Although all germline tumour cells we tested were hypersensitive to DNA-damaging drugs, no significant alteration was observed in their DNA repair activity or the expression of DNA repair proteins. In contrast, germline tumours expressed very low level of epidermal growth factor receptor (EGFR) compared to drug-resistant ovarian cancer cells. An immunohistochemical analysis indicated that most of the primary germline tumours we tested expressed very low level of EGFR. In accordance with this, overexpression of EGFR in germline tumour cells showed an increase in drug resistance, suggesting that a lack of EGFR, at least in part, contributes to the drug sensitivity of germline tumours.

Induced Autocrine Signaling through the Epidermal Growth Factor Receptor Contributes to the Response of Mammary Epithelial Cells to Tumor Necrosis Factor α

In contrast to the well known cytotoxic effects of tumor necrosis factor (TNF) alpha in many mammary cancer cells, we have found that TNF stimulates the proliferation and motility of human mammary epithelial cells (HMECs). Since the response of HMECs to TNF is similar to effects mediated by epidermal growth factor receptor (EGFR) activation, we explored the potential role of cross-talk through the EGFR signaling pathways in mediating cellular responses to TNF. Using a microarray enzyme-linked immunoassay, we found that exposure to TNF stimulated the dose-dependent shedding of the EGFR ligand transforming growth factor alpha (TGFalpha). Both proliferation and motility of HMECs induced by TNF was prevented either by inhibiting membrane protein shedding with a metalloprotease inhibitor, by blocking epidermal growth factor receptor (EGFR) kinase activity, or by limiting ligand-receptor interactions with an antagonistic anti-EGFR antibody. EGFR activity was also necessary for TNF-induced release of matrix metalloprotease-9, thought to be an essential regulator of mammary cell migration. The cellular response to TNF was associated with a biphasic temporal pattern of extracellular signal-regulated kinase (ERK) phosphorylation, which was EGFR-dependent and modulated by inhibition of metalloprotease-mediated shedding. Significantly, the late phase of ERK phosphorylation, detectable within 4 h after exposure, was blocked by the metalloprotease inhibitor batimastat, indicating that autocrine signaling through ligand shedding was responsible for this secondary wave of ERK activity. Our results indicate a novel and important role for metalloprotease activation and EGFR transmodulation in mediating the cellular response to TNF.

The mitogenic potential of heparin-binding epidermal growth factor in the human endometrium is mediated by the epidermal growth factor receptor and is modulated by tumor necrosis factor-alpha

Heparin-binding epidermal growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, is implicated in a variety of biological processes, including reproduction. Previous studies describe increased levels of HB-EGF in the human endometrium during the midsecretory stage of the menstrual cycle, suggesting a function for HB-EGF in implantation of the human blastocyst. Here we have investigated the expression and function of the soluble and transmembrane forms of HB-EGF in the human endometrium. We show that the expression of the transmembrane form of HB-EGF in the human endometrium is modulated according to the stage of the menstrual cycle. We present data demonstrating that both the soluble and transmembrane forms of HB-EGF induce DNA synthesis in human endometrial stromal cells. Furthermore, TNFalpha has a cooperative effect on HB-EGF, EGF, TGFalpha, and betacellulin-induced DNA synthesis in stromal cells, suggesting roles for the EGF family and TNFalpha in regeneration and maturation of human endometrium. Induction of DNA synthesis by HB-EGF and its modulation by TNFalpha in endometrial stromal cells are mediated by the EGF receptor and not the HB-EGF receptor ErbB4. Our data suggest key functions for HB-EGF, TNFalpha, and the EGF receptor in endometrial maturation, via autocrine/paracrine and juxtacrine pathways, in preparation for embryo implantation.

Further evidence for the involvement of epidermal growth factor in the signaling pathway of vitamin B12 (cobalamin) in the rat central nervous system

In order to get further evidence for a mandatory involvement of epidermal growth factor (EGF) in the neutrophic action of vitamin B12 (cobalamin (Cbl)) in the central nervous system (CNS) of the rat, we observed the effects of repeated intracerebroventricular (ICV) microinjections of EGF in rats made Cbl-deficient through total gastrectomy. Morphometric analysis demonstrated a significant reduction in both intramyelinic and interstitial edema in the white matter of the spinal cord (SC) of totally gastrectomized (TGX) rats after treatment. Intramyelinic and interstitial edema are characteristic of Cbl-deficient central neuropathy in the rat. Similar lesions were also present in SC white matter of rats treated with repeated ICV microinjections of specific anti-EGF antibodies without any modification in their Cbl status. These results, together with those of a previous study showing the cessation of EGF synthesis in the CNS of TGX rats, demonstrate that: a) EGF is necessarily involved in the signaling pathway of Cbl in the rat CNS; and b) the lack of a neurotrophic growth factor EGF, and not the mere withdrawal of Cbl, causes or at least contributes to neurodegenerative Cbl-deficient central neuropathy.

Tumor necrosis factor receptor and Fas signaling mechanisms

Four members of the tumor necrosis factor (TNF) ligand family, TNF-alpha, LT-alpha, LT-beta, and LIGHT, interact with four receptors of the TNF/nerve growth factor family, the p55 TNF receptor (CD120a), the p75 TNF receptor (CD120b), the lymphotoxin beta receptor (LT beta R), and herpes virus entry mediator (HVEM) to control a wide range of innate and adaptive immune response functions. Of these, the most thoroughly studied are cell death induction and regulation of the inflammatory process. Fas/Apo1 (CD95), a receptor of the TNF receptor family activated by a distinct ligand, induces death in cells through mechanisms shared with CD120a. The last four years have seen a proliferation in knowledge of the proteins participating in the signaling by the TNF system and CD95. The downstream signaling molecules identified so far--caspases, phospholipases, the three known mitogen activated protein (MAP) kinase pathways, and the NF-kappa B activation cascade--mediate the effects of other inducers as well. However, the molecules that initiate these signaling events, including the death domain- and TNF receptor associated factor (TRAF) domain-containing adapter proteins and the signaling enzymes associated with them, are largely unique to the TNF/nerve growth factor receptor family.

Differential expression and translocation of protein tyrosine phosphatase 1B-related proteins in ME-180 tumor cells expressing apoptotic sensitivity and resistance to tumor necrosis factor: potential interaction with epidermal growth factor receptor

Tumor necrosis factor (TNF)-induced apoptosis can be inhibited by overexpression of specific tyrosine kinases or activation of tyrosine kinase cascades, suggesting potential antagonism between apoptotic and tyrosine kinase signaling processes. In this report, the effects of TNF on EGF receptor tyrosine phosphorylation in ME-180 cell variants selected for apoptotic sensitivity (Sen) or resistance (Res) to TNF, previously shown to differentially express EGFr, were examined. Prior to the onset of apoptosis, TNF caused a significant reduction in the level of EGFr tyrosine phosphorylation in Sen cells but mediated only limited suppression of EGFr tyrosine phosphorylation in apoptotically resistant Res cells. In vitro incubation of cellular membranes with TNF derived from Sen cells stimulated a resident protein tyrosine phosphatase (PTP) activity which was able to dephosphorylate EGFr or tyrosine phosphopeptides mimicking an EGFr autophosphorylation site. In membrane preparations, PTPIB complexed with tyrosine phosphorylated EGFr and this association was disrupted by TNF through an apparent stimulation of PTP activity and turnover of phosphotyrosine. Intrinsic enzymatic activity of PTP1B was 2-3-fold higher in Sen versus Res cell lysates and a family of PTP1B-related proteins with altered C-termini was found to be highly expressed in Sen cells but absent or expressed at reduced levels in Res cells. Cytoplasmic extracts of Sen cells contained PTP1B-like proteins and TNF incubation resulted in the time dependent accumulation of PTP1B-like proteins in Sen cells but did not effect these proteins in Res cells. Together, these results suggest that specific changes in expression and subcellular distribution of phosphotyrosine modulatory proteins may play a role in conveying intrinsic apoptotic sensitivity to TNF in some tumor cell types.

Tumor necrosis factor-induced apoptosis stimulates p53 accumulation and p21WAF1 proteolysis in ME-180 cells

Tumor necrosis factor (TNF)-mediated apoptotic signaling has been characterized by activation of specific protease or protein kinase cascades that regulate the onset of apoptosis. TNF has also been shown to induce oxidative or genotoxic stress in some cell types, and apoptotic potential may be determined by the cellular response to this stress. To determine the role of genotoxic stress in TNF-mediated apoptosis, we examined cellular accumulation of p53 in TNF-treated ME-180 cells selected for apoptotic sensitivity (ME-180S) or resistance (ME-180R) to TNF. Although TNF was able to activate receptor-mediated signaling in either cell line, p53 accumulation was measurable only in apoptotically sensitive ME-180S cells. TNF-induced changes in p53 levels were detected 1 h after treatment, and peak levels were measurable 4-8 h after TNF exposure. TNF was unable to induce p21WAF1 in either cell line but affected the stability of this protein in apoptotically responsive ME-180S cells. Evidence of p21WAF1 proteolysis was detected by monitoring the appearance of a 16-kDa immunoblottable p21WAF1 fragment, which became detectable 4 h after TNF addition and increased in content before the onset of DNA fragmentation (16-24 h). The kinetics of p21WAF1 proteolysis closely paralleled those of poly(ADP-ribose) polymerase, suggesting cleavage of p21WAF1 by activation of an apoptotic protease. Pretreatment of ME-180S cells with the apoptotic protease inhibitor YVAD blocked TNF-induced apoptosis and prevented both poly(ADP-ribose) polymerase and p21WAF1 degradation but did not affect p53 induction. These results provide evidence for the early onset of genotoxic stress in cells committed to TNF-mediated apoptosis and for divergence in propagation of this signal in non-responsive cells. In addition, TNF-induced p21WAF1 proteolysis may be mediated by an apoptotic protease and may contribute to the apoptotic process by disrupting p53 signaling, altering cell cycle inhibition, and limiting cellular recovery from genotoxic stress.