Cathleen R. Carlin

We have derived and characterized single cell clones from a xenograft tumor of the teratocarcinoma cell line Tera-2. Isozyme and chromosomal analyses confirmed their common origin. When cultures of the clones were maintained at a high cell density, many cells exhibited a morphology and cell surface antigen phenotype typical of human embryonal carcinoma cells. These features included a high nucleo-cytoplasmic ratio, prominent nucleoli, and the expression of the globoseries glycolipid antigen SSEA-3. In addition, other cells, in many respects resembling these typical embryonal carcinoma cells, were distinguished by a marked tendency to accumulate cytoplasmic glycogen. Similar cells, together with more differentiated cells, were seen in low passage cultures of Tera-2 itself. When the clones were grown at a low cell density many cells assumed a larger, flatter shape, a few with multiple nucleoli. Also, the fucosylated lactosamine antigen SSEA-1 appeared on some cells, whereas expression of SSEA-3 and HLA-A,B,C tended to be reduced. Often the synthesis of fibronectin was increased. However, no obvious cytoplasmic differentiation was seen upon ultrastructural examination, and synthesis of human chorionic gonadotropin, alpha-fetoprotein, and laminin was not detected. In contrast to the limited spontaneous changes seen in culture, marked differentiation occurred in tumors obtained following injection of the cells into athymic (nu/nu) mice. In additional to embryonal carcinoma cells, these tumors contained a variety of somatic tissues that included glandular structures, possibly related to the primitive gut, and neural elements. These cell lines derived from Tera-2 constitute the first example of clonal human embryonal carcinoma cells, adapted to growth in vitro, that have retained the capacity for differentiation into diverse somatic tissues.

Cellular programs coupled to cycles of epithelial-mesenchymal transitions (EMTs) play critical roles during embryogenesis, as well as during tissue development, remodeling, and repair. Research over the last decade has established the importance of an ever-expanding list of master EMT transcription factors, whose activity is regulated by STAT3 and function to stimulate the rapid transition of cells between epithelial and mesenchymal phenotypes. Importantly, inappropriate reactivation of embryonic EMT programs in carcinoma cells underlies their metastasis to distant organ sites, as well as their acquisition of stem cell-like and chemoresistant phenotypes operant in eliciting disease recurrence. Thus, targeted inactivation of master EMT transcription factors may offer new inroads to alleviate metastatic disease. Here we review the molecular, cellular, and microenvironmental factors that contribute to the pathophysiological activities of STAT3 during its regulation of EMT programs in human carcinomas.

Aseptic loosening is thought to be due primarily to osteolysis induced by cytokines and prostaglandins that are produced in response to implant-derived wear particles. Because endotoxin has many of the same effects as have been reported for wear particles, we hypothesized that adherent endotoxin may be responsible for the biological responses induced by wear particles. We demonstrated the presence of significant levels of adherent endotoxin on commonly used preparations of titanium particles as well as on titanium and titanium-alloy implant surfaces. In contrast, supernatants obtained by centrifugation of particle suspensions contained approximately 1% as much endotoxin as did the particles. Therefore, it is erroneous to assume that particles do not contain endotoxin on the basis of data that it cannot be detected in their supernatants or filtrates. These results emphasize the importance of considering the potential role of adherent endotoxin when examining the in vitro effects of wear particles and the in vivo performance of orthopaedic implants. We also developed a protocol that removed more than 99.94% of the adherent endotoxin from the titanium particles without detectably affecting their size or shape. The removal of adherent endotoxin will allow comparison of the biological responses induced by particles with or without adherent endotoxin.

We previously established that overexpression of the EGF receptor (EGFR) is sufficient to induce tumor formation by otherwise nontransformed mammary epithelial cells, and that the initiation of epithelial-mesenchymal transition (EMT) is capable of increasing the invasion and metastasis of these cells. Using this breast cancer (BC) model, we find that in addition to EGF, adhesion to fibronectin (FN) activates signal transducer and activator of transcription 3 (STAT3) through EGFR-dependent and -independent mechanisms. Importantly, EMT facilitated a signaling switch from SRC-dependent EGFR:STAT3 signaling in pre-EMT cells to EGFR-independent FN:JAK2:STAT3 signaling in their post-EMT counterparts, thereby sensitizing these cells to JAK2 inhibition. Accordingly, human metastatic BC cells that failed to activate STAT3 downstream of EGFR did display robust STAT3 activity upon adhesion to FN. Furthermore, FN enhanced outgrowth in three-dimensional organotypic cultures via a mechanism that is dependent upon β1 integrin, Janus kinase 2 (JAK2), and STAT3 but not EGFR. Collectively, our data demonstrate that matrix-initiated signaling is sufficient to drive STAT3 activation, a reaction that is facilitated by EMT during BC metastatic progression.Background:Cells perceive their environment through soluble growth factors and in response to extracellular matrix.Results:STAT3 signaling can be activated by multiple pathways during breast cancer progression.Conclusion:Fibronectin:STAT3 signaling promotes three-dimensional outgrowth of breast cancer cells.Significance:This study demonstrates a novel mechanism by which STAT3 becomes activated by the extracellular matrix independent of the canonical EGF receptor signaling network. We previously established that overexpression of the EGF receptor (EGFR) is sufficient to induce tumor formation by otherwise nontransformed mammary epithelial cells, and that the initiation of epithelial-mesenchymal transition (EMT) is capable of increasing the invasion and metastasis of these cells. Using this breast cancer (BC) model, we find that in addition to EGF, adhesion to fibronectin (FN) activates signal transducer and activator of transcription 3 (STAT3) through EGFR-dependent and -independent mechanisms. Importantly, EMT facilitated a signaling switch from SRC-dependent EGFR:STAT3 signaling in pre-EMT cells to EGFR-independent FN:JAK2:STAT3 signaling in their post-EMT counterparts, thereby sensitizing these cells to JAK2 inhibition. Accordingly, human metastatic BC cells that failed to activate STAT3 downstream of EGFR did display robust STAT3 activity upon adhesion to FN. Furthermore, FN enhanced outgrowth in three-dimensional organotypic cultures via a mechanism that is dependent upon β1 integrin, Janus kinase 2 (JAK2), and STAT3 but not EGFR. Collectively, our data demonstrate that matrix-initiated signaling is sufficient to drive STAT3 activation, a reaction that is facilitated by EMT during BC metastatic progression. Cells perceive their environment through soluble growth factors and in response to extracellular matrix. STAT3 signaling can be activated by multiple pathways during breast cancer progression. Fibronectin:STAT3 signaling promotes three-dimensional outgrowth of breast cancer cells.