Stefin B deficiency reduces tumor growth via sensitization of tumor cells to oxidative stress in a breast cancer model

Abstract

Lysosomal cysteine cathepsins contribute to proteolytic events promoting tumor growth and metastasis. Their enzymatic activity, however, is tightly regulated by endogenous inhibitors. To investigate the role of cathepsin inhibitor stefin B (Stfb) in mammary cancer, Stfb null mice were crossed with transgenic polyoma virus middle T oncogene (PyMT) breast cancer mice. We show that ablation of Stfb resulted in reduced size of mammary tumors but did not affect their rate of metastasis. Importantly, decrease in tumor growth was correlated with an increased incidence of dead cell islands detected in tumors of Stfb-deficient mice. Ex vivo analysis of primary PyMT tumor cells revealed no significant effects of ablation of Stfb expression on proliferation, angiogenesis, migration and spontaneous cell death as compared with control cells. However, upon treatment with the lysosomotropic agent Leu-Leu-OMe, cancer cells lacking Stfb exhibited a significantly higher sensitivity to apoptosis. Moreover, Stfb-ablated tumor cells were significantly more prone to cell death under increased oxidative stress. These results indicate an in vivo role for Stfb in protecting cancer cells by promoting their resistance to oxidative stress and to apoptosis induced through the lysosomal pathway.

Proteolysis mediated by cysteine cathepsins and legumain—recent advances and cell biological challenges

“…However, what happens if these control mechanisms are not in place, such as is observed in certain tumor cells which exhibit reduced or completely abolished expression of cytoplasmic cysteine protease inhibitors (Alvarez-Diaz et al 2009;Butinar et al 2014). In these cases, the proteolytic enzymes become enzymatically active in a cellular compartment in which they are otherwise supposed to remain inactive under healthy conditions.…”

A Role for Stefin B (Cystatin B) in Inflammation and Endotoxemia

“…Interestingly, Lehtinen et al (60) showed that stefin B protects cerebellar granule neurons from the oxidative stress, and the stefin B deficiency resulted in the increased apoptosis in the cerebellum. In addition, Butinar et al (61) reported that stefin B-deficient tumor cells were significantly more sensitive to cell death upon the increased oxidative stress. Furthermore, Shimada et al (51) showed that staurosporin (STS), a pro-apoptotic protein kinase inhibitor, was sufficient to act as a second signal for the NLRP3 inflammasome activation.…”

Cystatins as regulators of cancer

“…The role of stefin B has been examined in breast cancer with Stfb null mice (Butinar et al, 2014). In transgenic PyMT mice that were stefin B knockout no effect on proliferation, angiogenesis, migration, and spontaneous cell death was noted.…”