Phosphorylation of TNF-alpha converting enzyme by gastrin-releasing peptide induces amphiregulin release and EGF receptor activation

Molecular mechanisms of soluble cytokine receptor generation

Soluble cytokine receptors play key roles in regulating cytokine-mediated biological events by binding and modulating the activity of target ligands in either an antagonistic or agonistic fashion. This Minireview will provide an overview of the molecular mechanisms mediating the generation of soluble cytokine receptors, which include sheddase-mediated proteolytic cleavage of cell-surface receptors, generation of soluble receptors by alternative gene splicing, transcription and translation of cytokine-binding genes, and extracellular release of membrane-bound receptors within vesicles such as exosomes.

Three-dimensional extracellular matrix culture models of EGFR signalling and drug response

Three-dimensional extracellular matrix culture, on substrata such as Matrigel, restores many aspects of the differentiated state to non-malignant cells from a variety of tissues. We have adapted these techniques to study EGFR (epidermal growth factor receptor) signalling and drug response in breast cancer cell lines. EGFR-dependent breast cancer cell lines undergo a striking reversion of the malignant phenotype upon treatment with inhibitors targeting the receptor, or downstream signalling intermediates such as mitogen-activated protein kinase and PI3K (phosphoinositide 3-kinase). Using this approach, we have recently reported that EGFR signalling in breast cancer can be effectively inhibited by blocking the activity of a key protease, TACE [TNFalpha (tumour necrosis factor alpha)-converting enzyme], which regulates the bioavailability of EGFR ligands. These results suggest a new way to target EGFR signalling in tumours of the breast and other epithelial tissues and underline the value of three-dimensional extracellular matrix culture models for exploring cancer-relevant signalling processes ex vivo.

Tackling EGFR signaling with TACE antagonists: a rational target for metalloprotease inhibitors in cancer

TNF-alpha converting enzyme (TACE/ADAM17) is a transmembrane metalloprotease that plays a key role in the cleavage and mobilization of receptor ligands that are initially synthesized as membrane-tethered precursors. For many years, attention has focused on the role of TACE-dependent TNF-alpha cleavage in arthritis and, more recently, it has become apparent that TACE also plays an important role in regulating epidermal growth factor receptor activity in several tumor types. This review presents the background to these findings and a rationale for the continued development of TACE inhibitors for the treatment of epidermal growth factor receptor-dependent epithelial tumors.

Emerging roles of ADAM and ADAMTS metalloproteinases in cancer

A disintegrin and metalloproteinases (ADAMs) are a recently discovered family of proteins that share the metalloproteinase domain with matrix metalloproteinases (MMPs). Among this family, structural features distinguish the membrane-anchored ADAMs and the secreted ADAMs with thrombospondin motifs referred to as ADAMTSs. By acting on a large panel of membrane-associated and extracellular substrates, they control several cell functions such as adhesion, fusion, migration and proliferation. The current review addresses the contribution of these proteinases in the positive and negative regulation of cancer progression as mainly mediated by the regulation of growth factor activities and integrin functions.

Signaling pathways involved in cyclooxygenase-2 induction by hepatocyte growth factor in non small-cell lung cancer

Many studies have suggested a role for the hepatocyte growth factor (HGF)/c-Met pathway in tumorigenesis. Some actions of HGF are believed to be mediated by cyclooxygenase-2 (COX-2), resulting in the production of prostaglandin E2 (PGE(2)). We examined four c-Met-positive non-small-cell lung cancer (NSCLC) cell lines for effects of HGF on COX-2. HGF increased COX-2 protein expression 3-fold over basal levels. Induction of COX-2 occurred through both the extracellular signal-regulated kinase 1/2 and p38 pathways. HGF treatment caused activation of the activator protein-1, CCAAT/enhancer-binding protein, and cAMP response element-binding protein transcription factors, and COX-2 induction was blocked by actinomycin D. The half-life of COX-2 mRNA was also increased by HGF. HGF stimulation resulted in a 4-fold increase in PGE(2) secretion, and treatment of NSCLC cells with exogenous PGE(2) significantly increased cell proliferation. The addition of PGE(2) to NSCLC cells also led to rapid phosphorylation of c-Met in the absence of HGF, which was blocked by epidermal growth factor receptor (EGFR) inhibition. EGFR ligands were released in response to PGE(2). This suggests that secretion of PGE(2) induced by HGF/c-Met pathway activation can further activate the c-Met pathway via EGFR in a reinforcing loop that is independent of HGF. HGF and PGE(2) each significantly stimulated invasion in NSCLC cells. Cells transiently transfected with c-Met antisense plasmid showed a significant decrease in HGF- or PGE(2)-induced invasion. PGE(2)-induced invasion was EGFR-dependent, confirming a link between PGE(2), EGFR, and c-Met. Targeting of both the HGF/c-Met and PGE(2) pathways with a neutralizing antibody to HGF and celecoxib resulted in enhanced anti-invasion effects in response to HGF.

TACE: a new target in epidermal growth factor receptor dependent tumors

Soluble proteins play vital roles in mediating intercellular communication. Many of these proteins are secreted as freely soluble molecules, but an important class of signaling proteins are first synthesized and presented at the cell surface as transmembrane precursor proteins. Unlike classically secreted proteins, many of these molecules are regulated at an additional level, requiring proteolytic cleavage for activity. This review focuses on a subset of these proteins, which are cleaved by tumor necrosis factor alpha-converting enzyme (TACE)/ADAM17, and on their role in cancer.

Angiotensin II signal transduction through the AT1 receptor: novel insights into mechanisms and pathophysiology

The intracellular signal transduction of AngII (angiotensin II) has been implicated in cardiovascular diseases, such as hypertension, atherosclerosis and restenosis after injury. AT(1) receptor (AngII type-1 receptor), a G-protein-coupled receptor, mediates most of the physiological and pathophysiological actions of AngII, and this receptor is predominantly expressed in cardiovascular cells, such as VSMCs (vascular smooth muscle cells). AngII activates various signalling molecules, including G-protein-derived second messengers, protein kinases and small G-proteins (Ras, Rho, Rac etc), through the AT(1) receptor leading to vascular remodelling. Growth factor receptors, such as EGFR (epidermal growth factor receptor), have been demonstrated to be 'trans'-activated by the AT(1) receptor in VSMCs to mediate growth and migration. Rho and its effector Rho-kinase/ROCK are also implicated in the pathological cellular actions of AngII in VSMCs. Less is known about the endothelial AngII signalling; however, recent studies suggest the endothelial AngII signalling positively, as well as negatively, regulates the NO (nitric oxide) signalling pathway and, thereby, modulates endothelial dysfunction. Moreover, selective AT(1)-receptor-interacting proteins have recently been identified that potentially regulate AngII signal transduction and their pathogenic functions in the target organs. In this review, we focus our discussion on the recent findings and concepts that suggest the existence of the above-mentioned novel signalling mechanisms whereby AngII mediates the formation of cardiovascular diseases.

Antitumor mechanisms of combined gastrin-releasing peptide receptor and epidermal growth factor receptor targeting in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is characterized by epidermal growth factor receptor (EGFR) overexpression, where EGFR levels correlate with survival. To date, EGFR targeting has shown limited antitumor effects in head and neck cancer when administrated as monotherapy. We previously identified a gastrin-releasing peptide/gastrin-releasing peptide receptor (GRP/GRPR) aurocrine regulatory pathway in HNSCC, where GRP stimulates Src-dependent cleavage of EGFR proligands with subsequent EGFR phosphorylation and mitogen-activated protein kinase (MAPK) activation. To determine whether GRPR targeting can enhance the antitumor efficacy of EGFR inhibition, we investigated the effects of a GRPR antagonist (PD176252) in conjunction with an EGFR tyrosine kinase inhibitor (erlotinib). Combined blockade of GRPR and EGFR pathways significantly inhibited HNSCC, but not immortalized mucosal epithelial cell, proliferation, invasion, and colony formation. In addition, the percentage of apoptotic cells increased upon combined inhibition. The enhanced antitumor efficacy was accompanied by increased expression of cleaved poly(ADP-ribose) polymerase (PARP) and decreased phospho-EGFR, phospho-MAPK, and proliferating cell nuclear antigen (PCNA). Using reverse-phase protein microarray (RPPA), we further detected decreased expression of phospho-c-Jun, phospho-p70S6K, and phospho-p38 with combined targeting. Cumulatively, these results suggest that GRPR targeting can enhance the antitumor effects of EGFR inhibitors in head and neck cancer.

Gastrin-releasing peptide activates Akt through the epidermal growth factor receptor pathway and abrogates the effect of gefitinib

Gastrin-releasing peptide (GRP) is a mitogen for lung epithelial cells and initiates signaling through a G-protein-coupled receptor, gastrin-releasing peptide receptor (GRPR). Because GRPR transactivates the epidermal growth factor receptor (EGFR), we investigated induction by GRP of Akt, an EGFR-activated signaling pathway, and examined effects of GRP on viability of non-small cell lung carcinoma (NSCLC) cells exposed to the EGFR tyrosine kinase inhibitor gefitinib. GRP induced Akt activation primarily through c-Src-mediated transactivation of EGFR. Transfection of dominant-negative c-Src abolished GRP-induced EGFR and Akt activation. GRP induced release of amphiregulin, and pre-incubation with human amphiregulin neutralizing antibody eliminated GRP-induced Akt phosphorylation. Pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 completely blocked GRP-initiated Akt phosphorylation. These results suggest that GRP stimulates Akt activation primarily via c-Src activation, followed by extracellular release of the EGFR ligand amphiregulin, leading to the activation of EGFR and PI3K. Pretreatment of NSCLC cells with GRP resulted in an increase in the IC(50) of gefitinib of up to 9-fold; this protective effect was mimicked by the pretreatment of cells with amphiregulin and reversed by Akt or PI3K inhibition. GRP appears to rescue NSCLC cells exposed to gefitinib through release of amphiregulin and activation of the Akt pathway, suggesting GRPR and/or EGFR autocrine pathways in NSCLC cells may modulate therapeutic response to EGFR inhibitors.

Cross-talk between G Protein–Coupled Receptor and Epidermal Growth Factor Receptor Signaling Pathways Contributes to Growth and Invasion of Head and Neck Squamous Cell Carcinoma

G protein-coupled receptors (GPCR) and the epidermal growth factor receptor (EGFR) are often both overexpressed and contribute to the growth of cancers by activating autocrine pathways. GPCR ligands have been reported to trigger EGFR signaling via receptor cross-talk in cancer cells. Here, we show that GPCR ligands prostaglandin E2 (PGE2) and bradykinin (BK) activate EGFR signaling. Inhibition of EGFR using several strategies, including small-molecule inhibitors and an EGFR-specific antibody, resulted in partial attenuation of signaling downstream of EGFR. PGE2 and BK triggered EGFR signaling by increasing selective autocrine release of transforming growth factor-alpha (TGF-alpha). Inhibition of tumor necrosis factor-alpha-converting enzyme abrogated BK- or PGE2-mediated activation of EGFR signaling. Both PGE2 and BK stimulated head and neck squamous cell carcinoma (HNSCC) invasion via EGFR. Treatment of HNSCC cells with the BK antagonist CU201 resulted in growth inhibition. The combination of CU201 with the EGFR small-molecule inhibitor erlotinib resulted in additive inhibitory effects on HNSCC cell growth in vitro. Inhibition of the PGE2 synthesis pathway with sulindac induced HNSCC cytotoxicity at high doses (EC(50), 620 micromol/L). However, combined inhibition of both EGFR with the tyrosine kinase inhibitor erlotinib and GPCR with sulindac at low doses of 6 and 310 micromol/L, respectively, resulted in synergistic killing of HNSCC tumor cells. Combined blockade of both EGFR and GPCRs may be a rational strategy to treat cancers, including HNSCC that shows cross-talk between GPCR and EGFR signaling pathways.

Insulin-like growth factor-1 receptor and ligand targeting in head and neck squamous cell carcinoma

IGF-1 receptor (IGF-1R) signaling is associated with increased tumorigenesis of epithelial cancers. In light of recent epidemiological studies correlating high circulating levels of IGF-1 with increased risk of second primary tumors (SPTs) of the head and neck, we examined IGF system and epidermal growth factor receptor (EGFR) expression in human head and neck squamous cell carcinoma (HNSCC) matched pairs and a cross-section of HNSCC cell lines. Employing the latter, we demonstrated that IGF-1 stimulated S-phase transition in a PI 3-K/Akt and Erk-dependent manner in 5 of 8 cell lines, with Erk activation being dependent upon EGFR kinase activity. IGF-1 stimulated thymidine incorporation was inhibited by treatment with IGFBP-3, the IGF-1R tyrosine kinase inhibitor NVP-AEW541, or the EGFR tyrosine kinase inhibitor AG1478. Combining IGFBP-3 with NVP-AEW541 or AG1478 abrogated IGF-1 responses at 10-fold lower doses than either compound alone. These results demonstrate the potential for co-targeting the IGF system and EGFR in HNSCC.