Panoply™ Human CTSC Knockdown Stable Cell Line

Lung metastasis is a leading cause of breast cancer-related death. A neutrophil-associated inflammatory microenvironment facilitates metastatic colonization of tumor cells in the lungs. Here, researchers demonstrate that the tumor-secreted protease cathepsin C (CTSC) promotes lung metastasis of breast cancer by regulating neutrophil recruitment and the formation of neutrophil extracellular traps (NETs). CTSC enzymatically activates neutrophil membrane-binding protein 3 (PR3), promoting the processing of interleukin-1β (IL-1β) and activation of nuclear factor κB, thereby upregulating IL-6 and CCL3 to recruit neutrophils. Furthermore, the CTSC-PR3-IL-1β axis induces neutrophils to produce reactive oxygen species and form NETs, ​​which degrade platelet-reactive protein-1, thus supporting the metastatic growth of cancer cells in the lungs. CTSC expression and secretion are closely associated with NET formation and lung metastasis in human breast tumors. Importantly, in a mouse model, targeting CTSC with the compound AZD7986 effectively inhibited lung metastasis of breast cancer. In summary, these findings reveal how tumor cells regulate neutrophils in the metastatic microenvironment and support cancer treatments targeting CTSCs.

Researchers found that neutrophils cultured in SCP28 and 4TO7 conditioned medium (CM) overexpressing CTSC, rather than in control CM, formed extensive NET structures similar to those induced by phorbol-12-myristate-13-acetate (PMA). Immunofluorescence staining revealed expression of citrullinated histone H3 (a marker of chromatin decondensation and extrusion), as well as granulocyte myeloperoxidase and neutrophil elastase (NE) (Figure 1A). Conversely, CM-stimulated NETosis was significantly reduced in CTSC-knockdown LM2 and 4T1 cells (Figure 1A). Furthermore, treatment of neutrophils with recombinant CTSC protein promoted NETosis, while Sivelestat blocked this process. Importantly, overexpression of CTSC in SCP28 cells enhanced NETosis around lung cancer cells and in the blood after intravenous injection of cancer cells or their conditioned medium, while the opposite effect was produced in CTSC-knockdown LM2 cells (Figure 1B). In immunocompetent mice, the regulatory role of CTSCs on NETosis in the early metastatic microenvironment was further confirmed using 4TO7 cells.

Figure 1. Tumoral CTSC induces neutrophils to form pro-metastatic NETs. (Xiao Y, et al., 2021)