Trop-2 is up-regulated in invasive prostate cancer and displaces FAK from focal contacts.

In this study, we show that the transmembrane glycoprotein Trop-2 is up-regulated in human prostate cancer (PCa) with extracapsular extension (stages pT3/pT4) as compared to organ-confined (stage pT2) PCa. Consistent with this evidence, Trop-2 expression is found to be increased in metastatic prostate tumors of Transgenic Adenocarcinoma of Mouse Prostate mice and to strongly correlate with α5ß1 integrin levels. Using PCa cells, we show that Trop-2 specifically associates with the α5 integrin subunit, as binding to α3 is not observed, and that Trop-2 displaces focal adhesion kinase from focal contacts. In support of the role of Trop-2 as a promoter of PCa metastatic phenotype, we observe high expression of this molecule in exosomes purified from Trop-2-positive PCa cells. These vesicles are then found to promote migration of Trop-2-negative PCa cells on fibronectin, an α5ß1 integrin/focal adhesion kinase substrate, thus suggesting that the biological function of Trop-2 may be propagated to recipient cells. In summary, our findings show that Trop-2 promotes an α5ß1 integrin-dependent pro-metastatic signaling pathway in PCa cells and that the altered expression of Trop-2 may be utilized for early identification of capsule-invading PCa.

Growth inhibition by microRNAs that target the insulin receptor substrate-1.

We have examined several microRNAs (miRs) indicated by the databases as targeting the signaling pathway of the type-1 insulin-like growth factor receptor (IGF-IR). Most of the miRs tested had multiple targets, as expected, leading to cell death. However, miR145 seemed to affect its tumor suppressor activity largely by downregulating the docking protein of the IGF-IR, the insulin receptor substrate-1 (IRS-1). These results suggest that, despite the many targets provided by the databases, in some cases a single target can be predominant in determining the end results.

Stromelysin-1 activation correlates with invasiveness in squamous cell carcinoma.

The expression of selected metalloproteinases and tissue inhibitors of metalloproteinases (TIMP) was examined in three squamous cell carcinoma (SCC) cell lines (FaDu, SiHa, A431) and a keratinocyte cell line (HaCaT) to determine which metalloproteinases function in SCC invasiveness. A Matrigel invasion assay was used to assess invasiveness of the cell lines. Only the FaDu cell line showed invasiveness in this assay, and invasion of Matrigel by FaDu cells was inhibited by treatment with the metalloproteinase inhibitor, batimastat. No correlation was found between mRNA expression for matrilysin, stromelysins 1-3, TIMP-1, or TIMP-3 and secretion of these proteins, indicating that the extracellular activity of these molecules is regulated post-transcriptionally. The SCC cell lines differed from the HaCaT line in that matrilysin and TIMP-1 proteins were detected in conditioned medium from all SCC cell lines, but not in medium from HaCaT cells. Only the invasive cell line, FaDu, released active stromelysin-1 into the culture medium. These results indicate that while matrilysin contributes to the invasive phenotype, activation of stromelysin-1 is a key regulatory step for invasiveness in SCC cells.