Natural Killer Cell Activation by Ubiquitin-specific Protease 6 Mediates Tumor Suppression in Ewing Sarcoma

Abstract

Ewing sarcoma (ES) is a rare and deadly pediatric bone cancer for which survival rates and treatment options have stagnated for decades. ES has not benefited from immunotherapy due to poor understanding of how its immune landscape is regulated. We recently reported that Ubiquitin-Specific Protease 6 (USP6) functions as a tumor suppressor in ES, and identified it as the first cell-intrinsic factor to modulate the ES immune tumor microenvironment (TME). USP6 induces intratumoral infiltration and activation of multiple innate immune lineages in xenografted nude mice. Here we report that natural killer (NK) cells are essential for its tumor-inhibitory functions, as NK cell depletion reverses USP6-mediated suppression of ES xenograft growth. USP6 expression in ES cells directly stimulates NK cell activation and degranulation in vitro, and functions by increasing surface levels of multiple NK-activating ligands. USP6 also induces surface upregulation of the receptor for the apoptosis-inducing ligand TRAIL, providing an additional route for enhanced sensitivity to NK killing. Furthermore, USP6-expressing ES and NK cells participate in a paracrine immunostimulatory feedforward loop, wherein interferon-gamma secreted by activated NK cells feeds back on USP6/ES cells to induce synergistic expression of chemokines CXCL9 and CXCL10. Remarkably, expression of USP6 in subcutaneous ES xenografts induces systemic activation and maturation of NK cells, and induces an abscopal response in which growth of distal tumors is inhibited, coincident with increased infiltration and activation of NK cells. This work reveals how USP6 reprograms the ES TME to enhance anti-tumor immunity, and may be exploited for future therapeutic benefit.

Advancements in osteosarcoma management: integrating immune microenvironment insights with immunotherapeutic strategies

“…Notably, the expression of USP6 in Ewing’s sarcoma has been shown to facilitate NK cell invasion and activation, thereby enhancing their tumor cell-killing potential and underscoring the positive impact of NK cell infiltration in impeding tumor growth ( Jain et al, 2023 ). Furthermore, USP6 also stimulates the secretion of immune-related chemokines, augmenting the infiltration and activation of NK cells and additional immunocytes, significantly impeding Ewing’s sarcoma progression ( Henrich et al, 2021 ).…”

“…Furthermore, studies by Jain et al observed that USP6 inhibits tumor growth in Ewing’s sarcoma by activating NK cells and inducing the expression of chemokines. USP6 increases the surface levels of NK cell activation ligands, enhancing the interaction between NK cells and Ewing’s sarcoma cells, thus augmenting the tumor-killing capability of NK cells and highlighting the significance of USP6 in regulating the TME ( Jain et al, 2023 ). Research by Pahl et al emphasized that LPS and IFN-γ-activated M1-type macrophages could inhibit osteosarcoma growth, with a similar effect observed when M1-type macrophages were activated with L-MTP-PE and IFN-γ.…”