Although once primarily recognized for its roles in hemostasis and thrombosis, the platelet has been increasingly recognized as a multipurpose cell. Indeed, circulating platelets have the ability to influence a wide range of seemingly unrelated pathophysiologic events. Here, we highlight some of the notable observations that link platelets to inflammation, reinforcing the platelet’s origin from a lower vertebrate cell type with both hemostatic and immunologic roles. In addition, we consider the relevance of platelets in cancer biology by focusing on the hallmarks of cancer and the ways platelets can influence multistep development of tumors. Beyond its traditional role in hemostasis and thrombosis, the platelet’s involvement in the interplay between hemostasis, thrombosis, inflammation, and cancer is likely complex, yet extremely important in each disease process. The existence of animal models of platelet dysfunction and currently used antiplatelet therapies provide a framework for understanding mechanistic insights into a wide range of pathophysiologic events. Thus, the basic scientist studying platelet function can think beyond the traditional hemostasis and thrombosis paradigms, while the practicing hematologist must appreciate platelet relevance in a wide range of disease processes.

Persistent gastritis induced by Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the distal stomach, yet only a fraction of colonized persons ever develop gastric cancer. The H. pylori cytotoxin-associated gene ( cag ) pathogenicity island encodes a type IV secretion system that delivers the bacterial effector CagA into host cells after bacterial attachment, and cag ⁺ strains augment gastric cancer risk. A host effector that is aberrantly activated in gastric cancer precursor lesions is β-catenin, and activation of β-catenin leads to targeted transcriptional up-regulation of genes implicated in carcinogenesis. We report that in vivo adaptation endowed an H. pylori strain with the ability to rapidly and reproducibly induce gastric dysplasia and adenocarcinoma in a rodent model of gastritis. Compared with its parental noncarcinogenic isolate, the oncogenic H. pylori strain selectively activates β-catenin in model gastric epithelia, which is dependent on translocation of CagA into host epithelial cells. β-Catenin nuclear accumulation is increased in gastric epithelium harvested from gerbils infected with the H. pylori carcinogenic strain as well as from persons carrying cag ⁺ vs. cag ^- strains or uninfected persons. These results indicate that H. pylori -induced dysregulation of β-catenin-dependent pathways may explain in part the augmentation in the risk of gastric cancer conferred by this pathogen.

Helicobacter pylori is the strongest known risk factor for gastric adenocarcinoma, and strains that possess the cag secretion system, which translocates the bacterial effector CagA into host cells, augment cancer risk. H. pylori strains that express the vacuolating cytotoxin or the outer membrane protein OipA are similarly associated with severe pathologic outcomes. We previously reported that an in vivo adapted H. pylori strain, 7.13, induces gastric adenocarcinoma in rodent models of gastritis. In the current study, we used carcinogenic strain 7.13 as a prototype to define the role of virulence constituents in H. pylori–mediated carcinogenesis. Mongolian gerbils were infected with wild-type strain 7.13 or cagA⁻, vacA⁻, or oipA⁻ mutants for 12 to 52 weeks. All infected gerbils developed gastritis; however, inflammation was significantly attenuated in animals infected with the cagA⁻ but not the vacA⁻ or oipA⁻ strains. Gastric dysplasia and cancer developed in >50% of gerbils infected with either the wild-type or vacA⁻ strain but in none of the animals infected with the cagA⁻ strain. Inactivation of oipA decreased β-catenin nuclear localization in vitro and reduced the incidence of cancer in gerbils. OipA expression was detected significantly more frequently among H. pylori strains isolated from human subjects with gastric cancer precursor lesions versus persons with gastritis alone. These results indicate that loss of CagA prevents the development of cancer in this model. Inactivation of oipA attenuates β-catenin nuclear translocation and also decreases the incidence of carcinoma. In addition to defining factors that mediate H. pylori–induced cancer, these results provide insight into mechanisms that may regulate the development of other malignancies arising within the context of inflammatory states. [Cancer Res 2008;68(2):379–87]

Contributions of the tumor microenvironment (TME) to progression in thyroid cancer are largely unexplored and may illuminate a basis for understanding rarer aggressive cases of this disease. In this study, we investigated the relationship between the TME and thyroid cancer progression in a mouse model where thyroid-specific expression of oncogenic BRAF and loss of Pten (Braf^V600E/Pten^−/−/TPO-Cre) leads to papillary thyroid cancers (PTC) that rapidly progress to poorly differentiated thyroid cancer (PDTC). We found that fibroblasts were recruited to the TME of Braf^V600E/Pten^−/−/TPO-Cre thyroid tumors. Conditioned media from cell lines established from these tumors, but not tumors driven by mutant H-ras, induced fibroblast migration and proliferation in vitro. Notably, the extracellular matrix of Braf^V600E/Pten^−/−/TPO-Cre tumors was enriched with stromal-derived fibrillar collagen, compared with wild-type or Hras-driven tumors. Further, type I collagen enhanced the motility of Braf^V600E/Pten^−/−/TPO-Cre tumor cells in vitro. In clinical specimens, we found COL1A1 and LOX to be upregulated in PTC and expressed at highest levels in PDTC and anaplastic thyroid cancer. Additionally, increased expression levels of COL1A1 and LOX were associated with decreased survival in thyroid cancer patients. Overall, our results identified fibroblast recruitment and remodeling of the extracellular matrix as pivotal features of the TME in promoting thyroid cancer progression, illuminating candidate therapeutic targets and biomarkers in advanced forms of this malignancy. Cancer Res; 76(7); 1804–13. ©2016 AACR.

Persistent infection with Helicobacter pylori confers an increased risk for the development of gastric cancer. However, the exact mechanisms whereby this bacterium causes carcinogenesis have not been completely elucidated. Recent evidence indicates that aberrant activation of the signal transducers and activators of transcription 3 (STAT3) signaling pathway may play a role in gastric carcinogenesis. Therefore, we hypothesized that H. pylori infection modulates STAT3 signaling, favoring gastric cancer development. In epithelial cells infected with H. pylori, STAT3 was activated, as assessed by immunoblotting for phosphorylated STAT3, immunofluorescence of translocated STAT3, fluorescence recovery after photobleaching, and luciferase activation in transfected cells. Activation was dependent on translocation but not phosphorylation of cytotoxin-associated gene A (CagA) in host cells. Activation seemed to be receptor-mediated because preincubation of cells with the interleukin-6 (IL-6) receptor superantagonist sant7 or inhibition of gp130 by a monoclonal antibody prevented H. pylori–mediated STAT3 activation. However, activation was not related to autocrine activation by IL-6 or IL-11. CagA+ wild-type H. pylori, but not the noncarcinogenic cagA− mutant, activated STAT3 in gastric epithelial cells in vivo in the gerbil model of H. pylori–mediated gastric carcinogenesis. Collectively, these results indicate that H. pylori CagA activates the STAT3 signaling pathway in vitro and in vivo, providing a potential mechanism by which chronic H. pylori infection promotes the development of gastric cancer. [Cancer Res 2009;69(2):632–9]

We developed mice with germline endogenous expression of oncogenic Hras to study effects on development and mechanisms of tumor initiation. They had high perinatal mortality, abnormal cranial dimensions, defective dental ameloblasts, and nasal septal deviation, consistent with some of the features of human Costello syndrome. These mice developed papillomas and angiosarcomas, which were associated with Hras ^G12V allelic imbalance and augmented Hras signaling. Endogenous expression of Hras ^G12V was also associated with a higher mutation rate in vivo. Tumor initiation by Hras ^G12V likely requires augmentation of signal output, which in papillomas and angiosarcomas is achieved via increased Hras -gene copy number, which may be favored by a higher mutation frequency in cells expressing the oncoprotein.