Panoply™ Human CSF1R Over-expressing Stable Cell Line

Colony-stimulating factor 1 receptor (CSF1R) is a classic tyrosine kinase receptor and has been identified as a proto-oncogene in various cancers. The CSF1/CSF1R axis is crucial for the survival and differentiation of M2 phenotype tumor-associated macrophages (M2 TAMs). Here, researchers found that CSF1R expression is silenced in colorectal cancer (CRC), while re-expressed CSF1R in CRC cells can be cleaved by caspase enzymes and inhibit tumor growth in vitro and in vivo, acting as a tumor suppressor gene. Researchers further discovered that CSF1R is a novel tumor-dependent receptor whose activation state determines whether it can function as a tumor suppressor or an oncogene. In CRC tumors, CSF1R is highly expressed in TAMs, and its expression is associated with poor prognosis in CRC patients. In a co-culture system, CSF1R-expressing CRC cells compete with M2-like macrophages for CSF1R ligands, leading to CSF1R activation and reduced cell proliferation in macrophages. Blocking CSF1R using PLX3397 can eliminate M2 tumor-associated macrophages (TAMs) and enhance CD8+ T cell infiltration, thereby effectively inhibiting tumor growth and metastasis and improving the efficacy of chemotherapy and immunotherapy. These results indicate that CSF1R is a newly discovered dependent receptor in CRC, and its expression is silenced. This silencing prevents its ligand from activating CSF1R expressed on M2 TAMs. Therefore, CSF1R expression may be a potential target for clearing M2 TAMs and treating CRC.

To determine the effect of CSF1R activation on CRC cells, researchers stimulated the receptor with CSF1 and IL34 and examined downstream cellular CSF1R signaling pathways. CSF1R was successfully activated after treatment with IL34 and CSF1, and its downstream Akt and Erk signaling pathways were also activated in CSF1R-overexpressing DLD1 and HCT116 cells (Figure 1A). CSF1 and IL34 significantly promoted the proliferation of CSF1R-overexpressing DLD1 and HCT116 cells in a concentration-dependent manner. However, they did not promote the growth of empty vector-expressed DLD1 and HCT116 cells with low CSF1R expression to an equivalent extent (Figure 1B). Data from the Cancer Cell Line Encyclopedia (CCLE) database showed that CACO2 had a relatively high level of endogenous CSF1R mRNA expression in the CRC cell line. CSF1 and IL34 may enhance the proliferation of CACO2 cells, consistent with results in DLD1 and HCT116 cells ectopically expressing CSF1R (Figure 1C), indicating that endogenous CSF1R retains oncogene activity even when its ligand is available and activates the receptor. In summary, these properties suggest that CSF1R is a ligand-dependent receptor that is silenced in colorectal cancer (CRC). Ligand-dependent receptors lacking ligands tend to be cleaved by caspases in their intracellular domains, a prerequisite for triggering tumor cell apoptosis. Researchers also found increased activity of pro-apoptotic caspases 3/7 in CSF1R-overexpressing DLD1, HCT116, and CT26 cells, which CSF11 and IL34 could reverse (Figure 1D).

Figure 1. CSF1R activation by CSF1 and IL34 promotes CRC cell proliferation and reduces proapoptotic caspase 3/7 activity. (Zhu M, et al., 2022)