Panoply™ Human CCR1 Over-expressing Stable Cell Line

The proteasome inhibitor bortezomib is a mainstay of treatment for the hematologic malignancy multiple myeloma (MM). However, intrinsic or acquired resistance to bortezomib, due to mechanisms that are not fully understood, remains a barrier to successful treatment for many patients. Previous studies have shown that elevated expression of the chemokine receptor CCR1 in MM plasma cells correlates with poor prognosis in newly diagnosed MM patients. Here, researchers hypothesized that the poor prognosis associated with CCR1 expression is partially due to CCR1-mediated reduced sensitivity of MM plasma cells to bortezomib. By overexpressing CCR1 or CRISPR-Cas9-mediated CCR1 knockout in MM cell lines, the researchers found that CCR1 expression significantly reduced sensitivity to bortezomib in vitro, independent of the CCR1 ligand CCL3. Furthermore, CCR1 knockout sensitized the human multiple myeloma cell line OPM2 to bortezomib in an intratibial MM model in NSG mice. In addition, CCR1 expression negatively regulates the expression of the unfolded protein response receptor IRE1 and its downstream target gene XBP1, suggesting that this pathway may be the cause of the reduced sensitivity of CCR1-expressing cells to bortezomib.

Previous studies have shown that decreased expression of genes involved in the ER stress response pathway is associated with bortezomib resistance. Therefore, the researchers hypothesized that elevated CCR1 expression might influence the sensitivity of multiple myeloma cells to bortezomib by modulating the ER stress response and subsequent induction of the UPR. First, the researchers assessed the effects of CCR1 on the expression of activating transcription factor 4 (ATF4), BiP (HSPA5), and X-box binding protein 1 (XBP1), which are transcriptionally activated via signalling downstream of the UPR receptors PERK, ATF6 and IRE1, respectively. Compared with the EV control, neither ATF4 nor HSPA5 was differentially expressed in CCR1 knockout OPM2 cells (Figure 1A) nor in CCR1-overexpressing 5TGM1 cells (Figure 1B). However, compared with the control, the total amount and spliceosomes of XBP1 were significantly increased in CCR1 knockout OPM2 cells, whereas they were significantly decreased in CCR1-overexpressing 5TGM1 cells (Figures 1A-B). Consistent with CCR1 regulation of IRE1 targets, the expression of ERN1 (the gene encoding IRE1) was significantly increased in CCR1 knockout OPM2 cells compared with controls, whereas its expression was decreased in CCR1-overexpressing 5TGM1 cells (Figure 1A-B).

Figure 1. CCR1 expression negatively regulates a target gene downstream of the IRE1 pathway but not genes downstream of the PERK and ATF6 pathways. (Zeissig M N, et al., 2024)