Tumor cell extravasation is a key step during cancer metastasis, yet the precise mechanisms that regulate this dynamic process are unclear. We utilized a high-resolution time-lapse intravital imaging approach to visualize the dynamics of cancer cell extravasation in vivo. During intravascular migration, cancer cells form protrusive structures identified as invadopodia by their enrichment of MT1-MMP, cortactin, Tks4, and importantly Tks5, which localizes exclusively to invadopodia. Cancer cells extend invadopodia through the endothelium into the extravascular stroma prior to their extravasation at endothelial junctions. Genetic or pharmacological inhibition of invadopodia initiation (cortactin), maturation (Tks5), or function (Tks4) resulted in an abrogation of cancer cell extravasation and metastatic colony formation in an experimental mouse lung metastasis model. This provides direct evidence of a functional role for invadopodia during cancer cell extravasation and distant metastasis and reveals an opportunity for therapeutic intervention in this clinically important process.

Maspin (mammary serine protease inhibitor or SerpinB5) acts as a tumor suppressor when overexpressed in aggressive cancer cell lines. However, its role in human cancer is controversial. Maspin expression has been associated with a poor prognosis in some studies, whereas in others, with favorable outcome. The clinical data suggest, however, that nuclearlocalized maspin is associated with improved survival. We hypothesized that the tumor suppressor activity of maspin may require nuclear localization, and that the discordance between clinical and experimental reports is a consequence of the variable subcellular distribution of maspin. Furthermore, we surmized that nuclear maspin could function as a tumor suppressor through the regulation of genes involved in tumor growth and invasion. Maspin or maspin fused to a nuclear export signal were expressed in metastatic human breast and epidermoid carcinoma cell lines. We found that pan-cellular localized maspin inhibited in vivo tumor growth and metastasis when assessed in xenograft chicken embryo and murine mammary fat pad injection models. However, when maspin was excluded from the nucleus via a nuclear exclusion signal, it no longer functioned as a metastasis suppressor. Using chromatin immunoprecipitation, we show that nuclear maspin was enriched at the promoter of colony-stimulating factor-1 (CSF-1) and associated with diminished levels of CSF-1 mRNA. Our findings demonstrate that the nuclear localization of maspin is required for its tumor and metastasis suppressor functions in vivo, and suggest that its mechanism of action involves, in part, direct association of maspin with target genes. KEYWORDS: breast cancer; chromatin immunoprecipitation; maspin; metastasis; nuclear localization Maspin (mammary serine protease inhibitor or SerpinB5), a member of the serpin family of serine protease inhibitors, was identified in 1994 as a tumor and metastasis suppressor. 1Overexpression of maspin inhibits cell motility and invasion in vitro, and decreases tumor formation, metastasis and angiogenesis in vivo.2 Initially, secreted maspin was thought to inhibit migration and increase cell adhesion via interaction with b1-integrin and other extracellular matrix components. 2 However, the molecular mechanism of such activity has yet to be convincingly demonstrated, and remains the subject of debate. Indeed, the very existence of extracellular maspin has recently been questioned. 3 Maspin has also been detected in the nucleus. 2 Maspin expression has been characterized in different cancers, particularly in breast cancer. Several studies showed that maspin mRNA is reduced in primary tumors and undetectable in metastases. 4,5 Conversely, others have shown that increased maspin is associated with poor prognosis. 6,7 These conflicting observations might be explained by distinct subcellular localization of maspin in cancer cells. Indeed, recent studies indicate that nuclear maspin associates with well-differentiated phenotype and improved survival, whereas cytoplasmic maspin is associated...

The diagnostic value of a new tumor marker, c-erbB-2, was studied in the sera of 50 controls, 112 patients with benign diseases and 534 patients with malignancies. Using 15 U/ml as the cutoff, no healthy subjects, patients with benign diseases (excluding liver cirrhosis) or patients with no evidence of disease (45 patients) had serum levels higher than this limit. Abnormal c-erbB-2 levels were found in 38.5% (10 of 26) of the patients with liver cirrhosis and in 26.7% (8 of 30) of those patients with primary liver cancer. No differences were found between the c-erbB-2 serum concentrations in liver cirrhosis or primary liver cancer, suggesting the possible catabolism of this antigen in the liver. Abnormal levels of this antigen were found in 20% (56 of 278) of the patients with breast carcinoma (lo-coregional 7%, metastases 41.5%), in 21 % (6 of 28) of ovarian carcinomas (stage I-II 0%, stage III-IV 42.8%), in 21% (3 of 14) of the colorectal tumors (locoregional 0%, metastases 30%), and in 13.3% (11 of 83) of the patients with lung cancer (locoregional 11.5%, metastases 16%). C-erbB-2 sensitivity in other patients with advanced disease was: 25% (9 of 36) in prostatic cancer; 22% (2 of 9) in gastric cancer, and 11% (1 of 9) in vesical tumors. When patients with liver metastases were excluded, abnormal c-erbB-2 serum levels were only found in breast, lung, prostatic and ovarian carcinomas. C-erbB-2 sensitivity in patients with lung cancer was related to tumor histology with significantly higher values in non-small cell lung cancer (mainly adenocarcinomas) than in patients with small cell lung cancer (p < 0.013). C-erbB-2 concentrations in patients with breast cancer were significantly higher in patients with recurrence (mainly bone and liver metastases) and in patients with progesterone receptor-negative ( < 15 fmol/mg) tumors (p < 0.01). In conclusion, c-erbB-2 is not a specific tumor marker and abnormal serum levels may be found in patients with liver pathologies. Its sensitivity suggests its possible application as a tumor marker in breast, ovarian, lung (mainly adenocarcinomas) and prostatic tumors.

Progression from a primary tumor to distant metastases requires extensive interactions between tumor cells and their microenvironment. The primary tumor is not only the source of metastatic cells but also can also modulate host responses to these cells, leading to an enhancement or inhibition of metastasis. Tumor-mediated stimulation of bone marrow can result in pre-metastatic niche formation and increased metastasis. However, a primary tumor can also inhibit metastasis through concomitant tumor resistance-inhibition of metastatic growth by existing tumor mass. Here, we report that the presence of a B16F10 primary tumor significantly restricted numbers and sizes of experimental lung metastases through reduction of circulating platelets and reduced formation of metastatic tumor cell-associated thrombi. Tumor-bearing mice displayed splenomegaly, correlated with primary tumor size and platelet count. Reduction in platelet numbers in tumor-bearing animals was responsible for metastatic inhibition, as restoration of platelet numbers using isolated platelets re-established both tumor cell-associated thrombus formation and experimental metastasis. Consumption of platelets due to a B16F10 primary tumor is a form of concomitant tumor resistance and demonstrates the systemic impact of a growing tumor. Understanding the interplay between primary tumors and metastases is essential, as clarification of concomitant tumor resistance mechanisms may allow inhibition of metastatic growth following tumor resection. Key messages Mice with a primary B16F10 tumor had reduced metastasis vs. mice without a primary tumor. Tumor-bearing mice had splenomegaly and fewer platelets and tumor-associated thrombi. Restoring platelets restored tumor-associated thrombi and increased metastasis. This work shows the impact that a primary tumor can have on systemic metastasis. Understanding these interactions may lead to improved ways to inhibit metastasis.

TBX3 is a member of the highly conserved family of T-box transcription factors involved in embryogenesis, organogenesis and tumor progression. While the functional role of TBX3 in tumorigenesis has been widely studied, less is known about the specific functions of the different isoforms (TBX3iso1 and TBX3iso2) which differ in their DNA-binding domain. We therefore sought to investigate the functional consequence of this highly conserved splice event as it relates to TBX3-induced tumorigenesis. By utilizing a nude mouse xenograft model, we have identified differential tumorigenic potential between TBX3 isoforms, with TBX3iso1 overexpression more commonly associated with invasive carcinoma and high tumor vascularity. Transcriptional analysis of signaling pathways altered by TBX3iso1 and TBX3iso2 overexpression revealed significant differences in angiogenesis-related genes. Importantly, osteopontin (OPN), a cancer-associated secreted phosphoprotein, was significantly up-regulated with TBX3iso1 (but not TBX3iso2) overexpression. This pattern was observed across three non/weakly-tumorigenic breast cancer cell lines (21PT, 21NT, and MCF7). Up-regulation of OPN in TBX3iso1 overexpressing cells was associated with induction of hyaluronan synthase 2 (HAS2) expression and increased retention of hyaluronan in pericellular matrices. These transcriptional changes were accompanied by the ability to induce endothelial cell vascular channel formation by conditioned media in vitro, which could be inhibited through addition of an OPN neutralizing antibody. Within the TCGA breast cancer cohort, we identified an 8.1-fold higher TBX3iso1 to TBX3iso2 transcript ratio in tumors relative to control, and this ratio was positively associated with high-tumor grade and an aggressive molecular subtype. Collectively, the described changes involving TBX3iso1-dependent promotion of angiogenesis may thus serve as an adaptive mechanism within breast cancer cells, potentially explaining differences in tumor formation rates between TBX3 isoforms in vivo. This study is the first of its kind to report significant functional differences between the two TBX3 isoforms, both in vitro and in vivo.