Integrin-mediated activation of latent transforming growth factor β

Members of the integrin family recognize a variety of spatially-restricted extracellular ligands. Classically, ligation of integrins activates cytoplasmic signals in the integrin-expressing cell and contributes to cell adhesion, migration, proliferation and survival. At least two members of this family, αvβ6 and αvβ8 perform an additional function, activation of latent complexes of transforming growth factor β. In effect, this process allows integrins on one cell to activate signals on adjacent (in the case of αvβ6) or nearby cells (in the case of αvβ8). Integrin-mediated TGFβ activation has been shown to play important roles in modulating tissue fibrosis, acute lung injury and pulmonary emphysema. Given the important roles that TGFβ plays in modulating epithelial cell growth, epithelial-to-mesenchymal transformation and tumor invasion and metastasis, integrin-mediated TGFβ activation is likely to play important roles in tumor growth ad metastasis.     

Stromal interaction essential for vascular endothelial growth factor A-induced tumour growth via transforming growth factor-β signalling

Background:

High vascular endothelial growth factor (VEGFA) levels at the time of diagnosis confer a worse prognosis to multiple malignancies. Our aim was to investigate the role of VEGFA in promoting tumour growth through interaction with its environment.

Methods:

HL-60 cells were transduced with VEGFA165 or control vector using retroviral constructs. Control cells (n=7) or VEGFA165 cells (n=7) were subcutaneously injected into NOD/SCID mice. Immunohistochemistry of markers for angiogenesis (CD31) and cell proliferation (Ki67) and gene expression profiling of tumours were performed. Paracrine effects were investigated by mouse-specific cytokine arrays.

Results:

In vivo we observed a twofold increase in tumour weight when VEGFA165 was overexpressed (P=0.001), combined with increased angiogenesis (P=0.002) and enhanced tumour cell proliferation (P=0.001). Gene expression profiling revealed human genes involved in TGF-β signalling differentially expressed between both tumour groups, that is, TGFBR2 and SMAD5 were lower expressed whereas the inhibitory SMAD7 was higher expressed with VEGFA165. An increased expression of mouse-derived cytokines IFNG and interleukin 7 was found in VEGFA165 tumours, both described to induce SMAD7 expression.

Conclusion:

These results suggest a role for VEGFA-driven tumour growth by TGF-β signalling inhibition via paracrine mechanisms in vivo, and underscore the importance of stromal interaction in the VEGFA-induced phenotype.     

Are basic fibroblast growth factor and vascular endothelial growth factor prognostic indicators in pediatric patients with malignant solid tumors?

Angiogenesis plays an important role in the growth, progression, and metastasis of solid tumors. Among angiogenic factors, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) appear to be useful markers in adults with cancer. The aim of this pilot study was to determine the levels of VEGF in serum and bFGF in serum and urine of children with solid tumor at diagnosis (as measured by ELISA), and to investigate whether these parameters provide prognostic information. Forty consecutive patients with different types of cancer were prospectively included in this study. Median values of all studied angiogenic factors were higher in patients than in controls (n = 40), and the differences were statistically significant for bFGF in serum and urine: 10 versus 3 pg/ml (P = 0.0004) and 6406 versus 0 pg/g of creatinine (P < 0.0001), respectively. Among patients, median serum values of bFGF and VEGF were higher in children with metastatic disease (n = 14) than in those with localized disease (n = 26). The difference was statistically significant for serum bFGF: 17.5 versus 6 pg/ml (P = 0.02). Serum angiogenic factor levels correlated with outcome. The estimated event-free survival at 3 years was 79% for patients with normal bFGF values (n = 13) versus 42% (n = 26; P = 0.02) for those with high levels, and 71% in case of normal VEGF values (n = 20) versus 38% (n = 19; P = 0.04) for those with high levels. No benefit of normal urinary bFGF values was observed. Our results provide a rationale for exploring the clinical interest of bFGF and VEGF measurements in body fluids of a larger group of children with cancer.     

Melanoma cell-derived factor stimulation of fibroblast glycosaminoglycan synthesis—The role of platelet-derived growth factor

The hyaluronan-rich matrix surrounding many tumours may facilitate tumour growth, invasion and angiogenesis, with the majority of this hyaluronan apparently being synthesised by normal fibroblasts, stimulated to do so by tumour cell-derived factors. Melanoma cell-conditioned medium (CM) stimulates up to a 6-fold increase in fibroblast glycosaminoglycan (GAG) synthesis, with the active factors being present in tumour CM ultrafiltration fractions >30 kDa and <1 kDa. These fractions are poorly active individually, but when recombined, the activity is substantially greater than the additive effect. The objective of this study was to identify the factors present in the ultrafiltration fraction >30 kDa that produce a greater than additive effect with the fraction <1 kDa in stimulating the incorporation of ³H glucosamine into fibroblast GAGs. A number of factors including basic fibroblast growth factor (bFGF), interleukin (IL)-1β, pleiotrophin, platelet-derived growth factor (PDGF), transforming growth factor-β (TGF-β), tumour necrosis factor-α (TNF-α) and vascular endothelial growth factor (VEGF) failed to stimulate any significant increase in GAG synthesis, but when added to the <1 kDa tumour CM fraction, both PDGF and to a lesser extent, bFGF, exhibited potent stimulating activities. Neutralising antibodies to PDGF and bFGF added to the melanoma CM decreased the fibroblast GAG-stimulating activity by 29% and 40%, respectively, in C8161 melanoma CM and by 47% and 45%, respectively, in Hs294T melanoma CM. The activities of PDGF-AA and PDGF-BB isoforms were indistinguishable, suggesting the PDGF-α receptor plays a role in the GAG-stimulatory response. Western analysis following treatment with PDGF, bFGF or melanoma CM revealed banding patterns for PDGF and melanoma CM that were similar. Immunoprecipitation of the PDGF-α receptor revealed it to be phosphorylated in fibroblasts treated with PDGF and melanoma CM, but not with control fibroblast CM. These studies suggest that PDGF plays an important role in the GAG-stimulating activity of the melanoma CM, but requires the presence of an as yet unidentified novel low molecular weight factor for full activity.     

Expression of basic fibroblast growth factor, transforming growth factor β1 and their 3 receptors in osteosarcoma and its relationship to angiogenesis

Objective: To investigate the expression of angiogenic factors, basic fibroblast, growth factor (bFGF) and transforming growth factor (TGF)-β₁ in osteosarcoma, its association with neovascularization and prognosis. Methods: The expression of bFGF, β₁ and their receptors, as well as intratumoral microvessel count (MVD) were studied in 80 osteosarcomas by immunohistochemical staining and morphometry. The relationship between the angiogenic factors expression and prognosis was evaluated by a multivariate analysis using Cox proportion hazard model. Results: Among 80 cases of osteosarcoma, 46 cases were positive for TGF/TGF-β (57.5%), and 31 cases for β₁, (RI)(38.8%) respectively. The MVD and bFGF, TGFβ_{1 1} were important indicators to predict the prognosis of patients with osteosarcoma by the Cox proportion hazard model analysis. Conclusion: The angiogenic factors bFGF and TGF-β₁ are involved in the angiogenesis of osteosarcoma, and the angiogenesis influences the prognosis. Also they may be useful in the evaluation of the prognosis of patients with osteosarcoma. This work was supported by a grant from the Youth Scientific Research Foundation of the 9th Five-year Plan of the PLA.     

The role of transforming growth factor Β in glioma progression

This review examines the apparently paradoxical conversion of transforming growth factor 's (TGF) regulatory role as a growth inhibitor among normal glial cells to that of a progression factor among glioblastomas (GM). In vitro, TGF functions as an autocrine growth inhibitor of near-diploid gliomas of any grade. In contrast, hyperdiploid glioblastoma multiforme (HD-GM) cultures proliferate in response to TGF, which is mediated by induction of platelet-derived growth factor B chain (PDGF-BB). The dominant hypothesis of TGF's pathogenetic association with malignant transformation has been predicated upon acquisition of resistance to its growth inhibitory effects. However, the lack of obvious correlation with TGF receptor (TR) expression (or loss) between the HD-GM and the TGF-inhibited GM cultures suggests the existence of intrinsically opposed regulatory mechanisms influenced by TGF. The mechanism of conversion might be explained either by the loss of a putative tumor suppressor gene (TSG) which mediates TGF's inhibition of growth or by enhancement of an active oncogenic pathway among the HD-GM. The frequency of mutations within glioma-associated TSG, such as TP53 and RB, suggests that defects in TGF's inhibitory signaling pathway may have analogous effects in the progression to HD-GM, and TGF's conversion to a mitogen. Alternative sites of inactivation which might explain the loss of TGF's inhibitory effect include inactivating mutation/loss of the TR type II, alterations in post-receptor signal transmission or the cyclin/cyclin dependent kinase system which regulates the phosphorylation of pRB. Loss or inactivation of a glial TSG with a consequent failure of inhibition appears to allow TGF's other constitutive effects, such as induction of c-sis, to become functionally dominant. Mechanistically, TGF's conversion from autocrine inhibitor to mitogen promotes 'clonal dominance' by conferring a Darwinian advantage to the hyperdiploid subpopulations through qualitative and quantitative differences in its modulation of PDGF-A and c-sis, with concomitant paracrine inhibition of competing, near-diploid elements. Abbreviations: transforming growth factor (TGF) and receptor (TR); retinoblastoma gene (RB) and protein (pRB); platelet-derived growth factor (PDGF) and receptor (PDGFR); epidermal growth factor (EGF) and receptor (EGFR); fibroblast growth factor (FGF); malignant glioma (MG), astrocytoma (AST), anaplastic astrocytoma (AAST), glioblastoma (GM); hyperdiploid glioblastoma (HD-GM); glioblastoma multiforme (GM); normal rat kidney (NRK); tumor suppressor gene (TSG); loss of heterozygosity (LOH); TP53 wild type (TP53wt); TP53 mutant (TP53m)     

Basic fibroblast growth factor and vascular endothelial growth factor serum levels in breast cancer patients and healthy women: useful as diagnostic tools?

Introduction  

The aim of the present study was to analyze the relationship between the expression of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in breast cancer cells and the corresponding serum levels in individual patients. The study also evaluated the potential of serum levels of the two growth factors as diagnostic markers in a case–control study.     

Insulin-like growth factor receptor inhibitors: baby or the bathwater?

The success of targeted therapies for cancer is undisputed; strong preclinical evidence has resulted in the approval of several new agents for cancer treatment. The type I insulin-like growth factor receptor (IGF1R) appeared to be one of these promising new targets. Substantial population and preclinical data have all pointed toward this pathway as an important regulator of tumor cell biology. Although early results from clinical trials that targeted the IGF1R showed some evidence of response, larger randomized phase III trials have not shown clear clinical benefit of targeting this pathway in combination with conventional strategies. These disappointing results have resulted in the discontinuation of several anti-IGF1R programs. However, the conduct of these trials has brought to the forefront several important factors that need to be considered in the conduct of future clinical trials. The need to develop biomarkers, a clearer understanding of insulin receptor function, and defining rational combination regimens all require further consideration. In this commentary, the current state of IGF1R inhibitors in cancer therapy is reviewed.     

Mutant epidermal growth factor receptor contributes to head and neck cancer growth and resistance to EGFR targeting

Epidermal growth factor receptor (EGFR) is overexpressed in head and neck squamous-cell carcinoma (HNSCC) and its expression levels correlate with decreased patient survival. Nonetheless, therapies aiming at blocking EGFR has shown limited efficacy in a proportion of patients with HNSCC in clinical trials. Sok et al. in a recent paper (Clin Cancer Res, 2006, 12:5064-5073 ) attempted to ascertain whether it is due to mutation of EGFR. As the most common form of mutation of EGFR seen in several other types of cancer is a truncation mutation, EGFR     

Sensitivities to various epidermal growth factor receptor‐tyrosine kinase inhibitors of uncommon epidermal growth factor receptor mutations L861Q and S768I: What is the optimal epidermal growth factor receptor‐tyrosine kinase inhibitor?

Most patients with non‐small cell lung cancer (NSCLC) harboring common epidermal growth factor receptor (EGFR) mutations, such as deletions in exon 19 or the L858R mutation in exon 21, respond dramatically to EGFR tyrosine kinase inhibitors (EGFR‐TKI), and their sensitivities to various EGFR‐TKI have been well characterized. Our previous article showed the in vitro sensitivities of EGFR exon 18 mutations to EGFR‐TKI, but little information regarding the sensitivities of other uncommon EGFR mutations is available. First, stable transfectant Ba/F3 cell lines harboring EGFR L858R (Ba/F3‐L858R), L861Q (Ba/F3‐L861Q) or S768I (Ba/F3‐S768I) mutations were created and their drug sensitivities to various EGFR‐TKI were examined. Both the Ba/F3‐L861Q and Ba/F3‐S768I cell lines were less sensitive to erlotinib, compared with the Ba/F3‐L858R cell line, but their sensitivities to afatinib were similar to that of the Ba/F3‐L858R cell line. The Ba/F3‐L861Q cell line was similarly sensitive and the Ba/F3‐S768I cell line was less sensitive to osimertinib, compared with the Ba/F3‐L858R cell line. The results of western blot analyses were consistent with these sensitivities. Next, similar experiments were also performed using the KYSE270 (L861Q) and KYSE 450 (S768I) cell lines, and their results were compatible with those of the transfectant Ba/F3 cell lines. Our findings suggest that NSCLC harboring the EGFR L861Q mutation might be sensitive to afatinib or osimertinib and that NSCLC harboring the EGFR S768I mutation might be sensitive to afatinib. Overall, afatinib might be the optimal EGFR‐TKI against these uncommon EGFR mutations.     

Why the epidermal growth factor receptor? The rationale for cancer therapy

There is a need for new, selective anticancer agents that differentiate between malignant and nonmalignant cells. The benefits of such agents would include a higher therapeutic index and lower toxicity than conventional therapies. Although expressed in nonmalignant cells, the epidermal growth factor receptor (EGFR) is highly expressed in a variety of tumors, and its expression correlates with poor response to treatment, disease progression, and poor survival. Evidence for a role for the EGFR in the inhibition and pathogenesis of various cancers has led to the rational design and development of agents that selectively target this receptor. Activation of the EGFR signaling pathway in cancer cells has been linked with increased cell proliferation, angiogenesis, and metastasis, and decreased apoptosis. Preclinical data show that anti-EGFR therapies can inhibit these effects in vitro and in vivo. In addition, preclinical data confirm that many such agents have the potential to increase the effectiveness of current cytotoxic agents. Following accelerated drug development programs, phase III trials are now under way for a number of EGFR-targeted therapies, including the monoclonal antibody IMC-C225 and the EGFR-tyrosine kinase inhibitors ZD1839 (Iressa) and OSI-774. Thus, the rationale for EGFR-targeted approaches to cancer treatment is apparent and now well established, and there is increasing evidence that they may represent a significant contribution to cancer therapy.     

Inhibitory effect of soluble platelet-derived growth factor receptor β on intraosseous growth of breast cancer cells in nude mice

Bone metastasis is a frequent complication of advanced breast cancer. On the basis of functional and molecular evidence, signaling mediated by the binding of platelet-derived growth factor (PDGF)-BB and -DD to PDGF receptor β (PDGFRβ) is critical for the survival and growth of metastatic breast cancer cells within the bone microenvironment. In this study, we propose a new approach to blocking PDGFRβ signaling using soluble PDGFRβ (sPDGFRβ) as a decoy receptor for PDGF-BB and -DD secreted from tumor cells and bone marrow stromal cells. A bone-seeking TNBCT/Bo cell line was established by in vivo selection from TNBCT human breast cancer cells, which are negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 protein expression. The TNBCT/Bo cells were transfected with a mammalian expression vector encoding the extracellular domain of PDGFRβ. A stable transfectant (TNBCT/Bo-sPDGFRβ) grew at a similar rate to that of control cells under normal culture conditions, although growth stimulation of human fibroblasts with PDGF-BB was neutralized by the culture medium from TNBCT/Bo-sPDGFRβ cells. Intratibial injection of TNBCT/Bo-sPDGFRβ cells into athymic nude mice resulted in a significant decrease in tumor incidence compared with control mice (P < 0.01). This attenuated growth correlated with decreased cancer cell proliferation, angiogenesis, and recruitment of stromal cells, and with an increase in the number of apoptotic cells. These findings suggest that sPDGFRβ is useful for the treatment of breast cancer bone metastasis.     

Insulin receptor substrate-1 involvement in epidermal growth factor receptor and insulin-like growth factor receptor signalling: implication for Gefitinib (‘Iressa’) response and resistance

Classically the insulin receptor substrate-1 (IRS-1) is an essential component of insulin-like growth factor type 1 receptor (IGF-IR) signalling, providing an interface between the receptor and key downstream signalling cascades. Here, however, we show that in tamoxifen-resistant MCF-7 (Tam-R) breast cancer cells, that are highly dependent on epidermal growth factor receptor (EGFR) for growth, IRS-1 can interact with EGFR and be preferentially phosphorylated on tyrosine (Y) 896, a Grb2 binding site. Indeed, phosphorylation of this site is greatly enhanced by exposure of these cells, and other EGFR-positive cell lines, to EGF. Importantly, while IGF-II promotes phosphorylation of IRS-1 on Y612, a PI3-K recruitment site, it has limited effect on Y896 phosphorylation in Tam-R cells. Furthermore, EGF and IGF-II co-treatment, reduces the ability of IGF-II to phosphorylate Y612, whilst maintaining Y896 phosphorylation, suggesting that the EGFR is the dominant recruiter of IRS-1 in this cell line. Significantly, challenge of Tam-R cells with the EGFR-selective tyrosine kinase inhibitor gefitinib, for 7 days, reduces IRS-1/EGFR association and IRS-1 Y896 phosphorylation, while promoting IRS-1/IGF-IR association and IRS-1 Y612 phosphorylation. Furthermore, gefitinib significantly enhances IGF-II-mediated phosphorylation of IRS-1 Y612 and AKT in Tam-R cells. Importantly, induction of this pathway by gefitinib can be abrogated by inhibition/downregulation of the IGF-IR. Our data would therefore suggest a novel association exists between the EGFR and IRS-1 in several EGFR-positive cancer cell lines. This association acts to promote phosphorylation of IRS-1 at Y896 and drive MAPK signalling whilst preventing recruitment of IRS-1 by the IGF-IR and inhibiting signalling via this receptor. Treatment with gefitinib alters the dynamics of this system, promoting IGF-IR signalling, the dominant gefitinib-resistant growth regulatory pathway in Tam-R cells, thus, potentially limiting its efficacy.     

LRIG inhibitors of growth factor signalling – double-edged swords in human cancer?

The leucine-rich repeats and immunoglobulin-like domains (LRIG) proteins are newly discovered negative regulators of growth factor signalling and proposed tumour suppressors. They antagonise signalling by interacting with growth factor receptors and by enhancing their ubiquitylation and degradation. Data on the expression of LRIG in human cancer have recently begun to accumulate; however, not all data appear consistent with the notion that the LRIG proteins always function as tumour suppressors. In the present review, we argue that the LRIG proteins could be double-edged swords, promoting or suppressing human cancer depending on cellular context.