Panoply™ Human CD274 Knockdown Stable Cell Line

Programmed death ligand-1 (PD-L1, CD274 or B7-H1) is well known for its role in immune checkpoint regulation, but its function within tumor cells is less well understood. Here, researchers show that PD-L1 in the nucleus is essential for sister chromatid cohesion in cancer cells. In immunodeficient NSG mice, loss of PD-L1 inhibits cancer cell proliferation, in vitro clonogenicity, and in vivo tumor growth, independent of its role in immune checkpoints. Specifically, PD-L1 functions as a subunit of the cohesin complex, and its loss leads to the formation of multinucleated cells and causes defective sister chromatid cohesion. Mechanistically, PD-L1 can compensate for the loss of Sororin, whose expression is suppressed in cancer cells overexpressing PD-L1. PD-L1 competes with Wing Apart-Like (WAPL) for binding to PDS5B and ensures normal sister chromatid cohesion and separation. These findings suggest that nuclear PD-L1 plays an important role in cancer cells independent of its function in immune checkpoints.

Here, the researchers found that knocking down Sororin or PD-L1 alone significantly induced the formation of multinuclear cells. Depletion of both proteins simultaneously resulted in even more multinucleated cells when compared to individual knockdowns (Figure 1a). They also performed a cloning experiment and found that knocking down both PD-L1 and Sororin simultaneously resulted in a more significant inhibition of cloning than knocking down either protein alone (Figure 1b). Taken together, these results suggest that PD-L1 and Sororin may act independently. To further confirm the independent effects of PD-L1 and Sororin, the researchers overexpressed Sororin in PD-L1 knockdown MDA-MB-231 cells and found that the introduction of Sororin reduced the number of multinuclear cells caused by PD-L1 deficiency (Figure 1c). It was further observed that in PD-L1-deficient MDA-MB-231 cells, cell proliferation, colony formation, and sister chromatid adhesion were restored after Sororin was overexpressed (Figures 1d-g). The researchers also injected NSG mice with control cells, PD-L1 knockdown cells, and PD-L1 knockdown cells ectopically expressing Sororin. The results showed that the loss of PD-L1 significantly inhibited tumor growth, while the overexpression of Sororin alleviated this inhibition (Figure 1h), indicating that PD-L1 compensates for the function of Sororin in TNBC cells with low Sororin expression.

Figure 1. PD-L1 compensates for the loss of Sororin and regulates sister chromatid cohesion. (Yu J, et al., 2020)