Increased expression of cathepsins L and B and decreased activity of their inhibitors in metastatic, ras‐transformed NIH 3T3 cells

Abstract

We previously found that the T24 Ha-ras oncogene induces metastatic ability in NIH 3T3 cells and that this change depends on expression of the ras oncogene. As part of our studies on mechanisms by which ras may induce metastasis, we investigated expression and activity of two cysteine proteinases, cathepsin L (major excreted protein) and cathepsin B, as well as cysteine proteinase inhibitor activity, in ras-transformed NIH 3T3 cells. In a series of cel lines that expressed differing amounts of ras, we found a good correlation between levels of ras expression and cathepsin L expression (r = 0.80). There was also a good correlation between secreted procathepsin L protein levels and experimental metastatic ability (r = 0.88). We found a similar but less strong association between cathepsin B levels and metastatic ability in these cells (r = 0.76 and r = 0.72 for 2.2-kb and 4.1-kb transcripts, respectively). Functional cathepsin L plus B activity (both secreted and cell-associated) was found to be higher in ras-transformed cells and was dependent on cell confluency in culture. Coupled with increased expression and activity of cysteine proteinases, ras-transformed NIH 3T3 cells showed reduced cysteine proteinase inhibitor activity. We conclude that the balance between expression of cysteine proteinases and their inhibitors may be coregulated by ras expression. Our results suggest that ras-induced increases in production of degradative enzymes such as cathepsins L and B, along with decreased activities of their inhibitors, may contribute to the increased malignant properties of ras-transformed NIH 3T3 cells.

The oncolytic effect in vivo of reovirus on tumour cells that have survived reovirus cell killing in vitro

“…Since high levels of protease activity are known to exist in the microenvironment of many tumours, particularly at the tumour -stroma interface, and increased protease production occurs in a variety of transformed cells (Rubin, 2003), tumours present an ideal environment for reovirus replication. Furthermore, cells transformed with oncogenic Ras have increased expression of proteases (Chambers et al, 1992), and we have shown that reovirus selectively infects cells with an activated Ras pathway Strong et al, 1998). Collectively, our data suggest that the proteolytic environment in tumours probably facilitates reovirus uncoating, and this could account for its enhanced oncolytic capability in vivo.…”

Addition of Exogenous Protease Facilitates Reovirus Infection in Many Restrictive Cells

“…The mechanism by which Ras activation increases reovirus growth has been suggested to involve inactivation of the interferoninduced eIF2␣ kinase PKR (64). Interestingly, it has been demonstrated that Ras activation can result in increased expression of various proteases, including cathepsin L (17,18,44). Since reovirus infection can be mediated by cathepsin L, higher levels of this protease could make Ras-activated cells more permissive to infection.…”

Cathepsin B, a Cysteine Protease Implicated in Metastatic Progression, is also Expressed During Regression of the Rat Prostate and Mammary Glands

“…The level of cathepsin B expression is elevated in human breast and ovarian cancers (Woynarowska et al, 1989;Gabrijelcic et al, 1992;Lah et al, 1992), and in several metastatic cell lines, including ras-transformed NIH 3T3 cells and Lewis lung carcinoma cells, in which the level of expression has been correlated with the increased malignancy (Brodt et al, 1992;Chambers et al, 1992). In many malignant cell lines, the enzyme is localized to the plasma membrane and is clearly secreted in most instances (Sloane et al, 1986).…”