Panoply™ Human CDK8 Knockdown Stable Cell Line

Triple-negative breast cancer (TNBC) is an aggressive malignancy that accounts for approximately 15% of all breast cancers. Current standard treatments include surgery and chemotherapy, but the prognosis remains poor, highlighting the urgent need for new therapeutic strategies. Recent computational modeling studies have shown a negative correlation between recurrence-free survival in breast cancer patients and the levels of cyclin-dependent kinase 8 (CDK8). CDK8 is known to play a role in the cytotoxicity of natural killer (NK) cells, but its function in TNBC progression and immune cell recognition or evasion has not been investigated. Here, researchers used an orthotopic breast cancer mouse model to study the tumor-intrinsic role of CDK8 in TNBC. Knockdown of CDK8 in TNBC cells inhibited recurrence after tumor resection and prevented metastasis. In the absence of CDK8, epithelial-mesenchymal transition (EMT) was suppressed, and immune-mediated tumor cell clearance was enhanced. CDK8 drives the EMT process in TNBC cells in a kinase activity-independent manner. In vivo experiments confirmed that CDK8 is a key regulator of NK cell-mediated immune evasion in TNBC. The study also showed that CDK8 is involved in regulating the immune checkpoint inhibitor programmed death-ligand 1 (PD-L1). The CDK8-PD-L1 axis exists in both mouse and human TNBC cells, highlighting the importance of CDK8-driven immune cell evasion in these highly aggressive breast cancer cells.

CDK8 deficiency was associated with reduced expression of MHC class I genes H2-K1 and H2-D1 (Figure 1A), which was confirmed by flow cytometry (Figure 1B). Flow cytometry also confirmed that in CDK8 knockdown cells, the protein level of the activating natural killer cell 2D receptor (NKG2D) ligand retinoic acid early transcript 1 (RAE1) was decreased, while the expression of intercellular adhesion molecule 1 (ICAM-1) was upregulated (Figure 1C, D). Transcriptome analysis of CDK8 knockdown E0771 cells revealed reduced expression of the Cd274 gene, which encodes PD-L1 (a ligand of PD-1, an important immune checkpoint protein). The researchers confirmed that CDK8 deficiency leads to decreased PD-L1 protein levels in E0771 cells (Figure 1E). These data suggest that CDK8 is a regulator of NK cell-mediated recognition of triple-negative breast cancer (TNBC) cells. Therefore, they performed in vitro cytotoxicity experiments using IL-2-expanded splenic NK cells. CDK8 knockdown made the E0771 cell line more susceptible to NK cell-mediated cytotoxicity (Figure 1F), while treatment of E0771 cells with SnxB for 48 hours (SnxB inhibits CDK8/CDK19 kinase activity) did not alter NK cell killing of E0771 cells. Therefore, CDK8 in TNBC cells blocks NK cell-mediated tumor recognition in a kinase-independent manner.

Figure 1. Loss of CDK8 enhances TNBC's visibility to NK cells. (Knab V M, et al., 2021)