Oncostatin M promotes STAT3 activation,VEGF production,and invasion in osteosarcoma cell lines

Background  

We have previously demonstrated that both canine and human OSA cell lines, as well as 8 fresh canine OSA tumor samples, exhibit constitutive phosphorylation of STAT3, and that this correlates with enhanced expression of matrix metalloproteinase-2 (MMP2). While multiple signal transduction pathways can result in phosphorylation of STAT3, stimulation of the cytokine receptor gp130 through either IL-6 or Oncostatin M (OSM) is the most common mechanism through which STAT3 is activated. The purpose of this study was to evaluate the role of IL-6 and OSM stimulation on both canine and human OSA cell lines to begin to determine the role of these cytokines in the biology of OSA.     

Insulin receptor substrate is a mediator of phosphoinositide 3-kinase activation in quiescent pancreatic cancer cells

Phosphoinositide 3-kinase (PI3K) is activated in pancreatic cancer cells and plays a central role in their proliferation, survival, and drug resistance. Although the mechanism is unclear, PI3K activation in these cells could be due to physical interaction between its regulatory subunit (p85) and specific tyrosine kinases or their mediators. Consistent with this possibility, PI3K was precipitated with anti-phosphotyrosine antibodies and Akt phosphorylation was blocked by the tyrosine kinase inhibitors SU6656 and PD158780 in quiescent pancreatic cancer cells. Pull-down assays with a fusion protein (GST-p85NC-SH2), and coimmunoprecipitation studies, indicated that the insulin receptor substrate (IRS), and not the epidermal growth factor and insulin-like growth factor receptors or the Src tyrosine kinase, was physically associated with PI3K in these cells. Our data also indicated that SU6656 and PD158780 inhibited Akt activation in pancreatic cancer cells by interfering with the ability of IRS-1 to recruit PI3K. Furthermore, IRS-1 was phosphorylated on a p85-binding site (Y(612)), and IRS-specific small interfering RNA potently inhibited activation of PI3K and Akt in transfected cells. Taken together, these observations indicate that IRS is a mediator of PI3K activation in quiescent pancreatic cancer cells.     

VEGF as a key mediator of angiogenesis in cancer

Vascular endothelial growth factor (VEGF) is a homodimeric glycoprotein with a molecular weight of approximately 45 kDa. It is the key mediator of angiogenesis (the formation of new blood vessels), and binds two VEGF receptors (VEGF receptor-1 and VEGF receptor-2), which are expressed on vascular endothelial cells. In healthy humans, VEGF promotes angiogenesis in embryonic development and is important in wound healing in adults. VEGF is the key mediator of angiogenesis in cancer, in which it is up-regulated by oncogene expression, a variety of growth factors and also hypoxia. Angiogenesis is essential for cancer development and growth: before a tumor can grow beyond 1-2 mm, it requires blood vessels for nutrients and oxygen. The production of VEGF and other growth factors by the tumor results in the 'angiogenic switch', where new vasculature is formed in and around the tumor, allowing it to grow exponentially. Tumor vasculature formed under the influence of VEGF is structurally and functionally abnormal. Blood vessels are irregularly shaped, tortuous, have dead ends and are not organized into venules, arterioles and capillaries. They are also leaky and hemorrhagic, which leads to high interstitial pressure. These characteristics mean that tumor blood flow is suboptimal, resulting in hypoxia and further VEGF production. This central role of VEGF in the production of tumor vasculature makes it a rational target for anticancer therapy.     

STAT 3 activation in head and neck squamous cell carcinomas is controlled by the EGFR

Proliferation of squamous cell carcinoma of the head and neck (SCCHN) depends on epidermal growth factor receptor (EGFR) expression. As STAT 3 activation as well contributes to the cell growth in SCCHN, the interaction of STAT 3 and the EGFR is of great interest when considering treatment options through inhibition of STAT 3. We, therefore, evaluated the influence of blocking or activating the EGFR in human SCCHN cell lines and in vivo tumors on STAT 3 activation. We compared the effects on STAT 3 activation with the regulation of MAP Kinase under these conditions. We found that STAT 3 can be strongly inhibited via EGFR blocking in vitro as well as in vivo. However, the influence of EGFR regulation on the MAP Kinase pathway seemed to be very slight. These findings provide evidence that STAT 3 signal activity in head and neck carcinomas, which is partially responsible for proliferative activity, can be controlled via the EGFR.     

Thromboxane A2 is a mediator of cyclooxygenase-2-dependent endothelial migration and angiogenesis.

Cyclooxygenase-2 (COX-2) inhibitors reduce angiogenic responses to a variety of stimuli, suggesting that products of COX-2 may mediate critical steps. Here, we show that thromboxane A2 (TXA2) is one of several eicosanoid products generated by activated human microvascular endothelial cells. Selective COX-2 antagonists inhibit TXA2 production, endothelial migration, and fibroblast growth factor-induced corneal angiogenesis. Endothelial migration and corneal angiogenesis are similarly inhibited by a TXA2 receptor antagonist, SQ29548. A TXA2 agonist, U46619, reconstitutes both migration and angiogenesis responses under COX-2-inhibited conditions. These findings identify TXA2 as a COX-2 product that functions as a critical intermediary of angiogenesis.     

KSHV activation of VEGF secretion and invasion for endothelial cells is mediated through viral upregulation of emmprin-induced signal transduction

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma (KS)-one of the most common tumors arising in the setting of immune suppression. Hallmarks of KS lesions include KSHV-infected cells of endothelial lineage and neoangiogenesis. Promigratory factors secreted in the tumor microenvironment by KSHV-infected cells promote endothelial cell (EC) migration and angiogenesis but existing therapies targeting these pathways are not widely utilized. This underscores the need for additional characterization of KSHV-host interactions relevant to EC pathogenesis to identify new therapeutic targets. We recently demonstrated that de novo infection by KSHV promotes EC invasion through upregulation of extracellular matrix metalloproteinase inducer (emmprin)-a multifunctional glycoprotein previously shown to induce tumor cell invasion and regional angiogenesis through upregulation of signal transduction and promotion of tumor-stroma interactions. This study was undertaken to determine whether EC invasion for KSHV-infected cells is induced through activation of specific signal transduction pathways and proangiogenic factors by emmprin. We found that KSHV activation of emmprin induces PI3K/Akt- and mitogen-activated protein kinase (MAPK)-dependent secretion of vascular endothelial growth factor (VEGF). Functionally, EC invasion following de novo infection is induced by emmprin-dependent PI3K/Akt and MAPK activation of VEGF. These findings support the potential utility of targeting emmprin for reducing VEGF secretion and EC migration in the KS microenvironment.     

STAT3 activation is required for Asp(816) mutant c-Kit induced tumorigenicity

Activating mutations of c-kit at codon 816 (Asp(816)) have been identified in variety of malignancies, including acute myeloid leukemia (AML), mastocytosis and germ cell tumors. The mutant c-Kit receptor confers cytokine independence and induces tumorigenicity. However, the molecular mechanisms, particularly the changes in the signal transduction pathways, responsible for these biological effects induced by mutant c-Kit are largely undefined. Using the human embryonic kidney cell line, 293, we show in the current report that constitutive activation of STAT3 and STAT1 is associated with D816H mutant c-Kit. Transfection of dominant negative STAT3, but not STAT1 inhibits mutant c-Kit mediated anchorage-independent growth in vitro and tumor formation in vivo. Expression of constitutively activated STAT3 restores the mutant c-Kit receptor's transforming ability in 293 cells. These results demonstrate that activation of STAT3 by Asp(816) mutant c-Kit is required for the anchorage-independent growth and tumorigenicity induced by Asp(816) mutant c-Kit.     

STAT3和VEGF在肺鳞癌组织中的表达及其临床意义

目的:探讨肺鳞癌组织中信号转导子和转录激活子3(STAT3)和血管内皮生长因子(VEGF)的表达及其与临床病理特征的关系。方法:采用免疫组织化学方法检测肺正常组织(30例)、肺鳞癌组织(60例)中STAT3和VEGF的表达,分析其与肺鳞癌临床病理特征的关系。结果:STAT3在肺正常组织和肺鳞状细胞癌中的阳性表达率分别为33.3％和56.7％,而VEGF的阳性表达率分别为23.3％和80％。STAT3和VEGF在肺鳞状细胞癌中的阳性表达率均明显高于肺正常黏膜(P<0.05)。肺鳞状细胞癌中STAT3、VEGF的表达与肿瘤浸润深度、淋巴结转移、临床分期之间明显相关(P<0.05),但是两者与患者的性别、年龄及肿瘤的病理分级无明显相关(P>0.05)。结论:STAT3和VEGF的表达增加,提示两者与肺鳞状细胞癌的发生发展有关,并且有助于判断肿瘤的侵袭和淋巴结转移。     

AFP、VEGF及STAT3在胃癌组织中的表达及意义

[目的]探讨AFP、VEGF及STAT3的表达与胃癌临床病理特征之间的关系，以及3个指标之间的相关关系。[方法]采用SP免疫组化方法检测AFP、VEGF及STAT3在胃癌组织中的表达。[结果]胃癌组织中AFP、VEGF、STAT3阳性率分别为16．0％、74．0％、34．7％，癌组织中AFP的表达分别与患者性别、年龄、肿瘤部位及大小、Borrmann分型、分化程度无显著相关性（p〈0．05），与浸润深度、临床分期、淋巴结转移、肝转移相关。VEGF的表达分别与浸润深度、临床分期、淋巴结转移相关。STAT3的表达分别与分化程度、临床分期相关。VEGF阳性率在AFP阳性胃癌组织中显著高于普通型胃癌。胃癌组织中VEGF与STAT3表达呈正相关。[结论]AFP阳性胃癌是一种恶性程度更高、浸润性更强、预后更差的特殊胃癌。VEGF的高表达可能是导致AFP阳性胃癌患者预后不良的原因之一。STAT3与VEGF之间的相关性支持VEGF基因直接由STAT3蛋白调节的论点。