One of the primary mechanisms of tumor cell immune evasion is the loss of antigenicity, which arises due to lack of immunogenic tumor antigens as well as dysregulation of the antigen processing machinery. In a screen for small-molecule compounds from herbal medicine that potentiate T cell–mediated cytotoxicity, we identified atractylenolide I (ATT-I), which substantially promotes tumor antigen presentation of both human and mouse colorectal cancer (CRC) cells and thereby enhances the cytotoxic response of CD8⁺ T cells. Cellular thermal shift assay (CETSA) with multiplexed quantitative mass spectrometry identified the proteasome 26S subunit non–ATPase 4 (PSMD4), an essential component of the immunoproteasome complex, as a primary target protein of ATT-I. Binding of ATT-I with PSMD4 augments the antigen-processing activity of immunoproteasome, leading to enhanced MHC-I–mediated antigen presentation on cancer cells. In syngeneic mouse CRC models and human patient–derived CRC organoid models, ATT-I treatment promotes the cytotoxicity of CD8⁺ T cells and thus profoundly enhances the efficacy of immune checkpoint blockade therapy. Collectively, we show here that targeting the function of immunoproteasome with ATT-I promotes tumor antigen presentation and empowers T cell cytotoxicity, thus elevating the tumor response to immunotherapy.

Immune evasion is a pivotal event in tumor progression. To eliminate human cancer cells, current immune checkpoint therapy is set to boost CD8⁺ T cell–mediated cytotoxicity. However, this action is eventually dependent on the efficient recognition of tumor-specific antigens via T cell receptors. One primary mechanism by which tumor cells evade immune surveillance is to downregulate their antigen presentation. Little progress has been made toward harnessing potential therapeutic targets for enhancing antigen presentation on the tumor cell. Here, we identified MAL2 as a key player that determines the turnover of the antigen-loaded MHC-I complex and reduces the antigen presentation on tumor cells. MAL2 promotes the endocytosis of tumor antigens via direct interaction with the MHC-I complex and endosome-associated RAB proteins. In preclinical models, depletion of MAL2 in breast tumor cells profoundly enhanced the cytotoxicity of tumor-infiltrating CD8⁺ T cells and suppressed breast tumor growth, suggesting that MAL2 is a potential therapeutic target for breast cancer immunotherapy.

Immune checkpoint blockade immunotherapy delivers promising clinical results in colorectal cancer (CRC). However, only a fraction of cancer patients develop durable responses. The tumor microenvironment (TME) negatively impacts tumor immunity and subsequently clinical outcomes. Therefore, there is a need to identify other checkpoint targets associated with the TME. Early-onset factors secreted by stromal cells as well as tumor cells often help recruit immune cells to the TME, among which are alarmins such as IL-33. The only known receptor for IL-33 is stimulation 2 (ST2). Here we demonstrated that high ST2 expression is associated with poor survival and is correlated with low CD8 ⁺ T cell cytotoxicity in CRC patients. ST2 is particularly expressed in tumor-associated macrophages (TAMs). In preclinical models of CRC, we demonstrated that ST2-expressing TAMs (ST2 ⁺ TAMs) were recruited into the tumor via CXCR3 expression and exacerbated the immunosuppressive TME; and that combination of ST2 depletion using ST2 -KO mice with anti–programmed death 1 treatment resulted in profound growth inhibition of CRC. Finally, using the IL-33trap fusion protein, we suppressed CRC tumor growth and decreased tumor-infiltrating ST2 ⁺ TAMs. Together, our findings suggest that ST2 could serve as a potential checkpoint target for CRC immunotherapy.

Park jointly notified the JCI of data falsification in Figures 2B and 6D and misconduct findings against Xiongbin Lu and Hanchen Xu. In accordance with the investigation committee's recommendation, the JCI is retracting this article.

The mechanosensitive PIEZO family channels, PIEZO1 and PIEZO2, are essential for mechanotransduction and play roles in many cellular processes, including cell volume regulation, tissue development, touch sensation, and proprioception. Emerging evidence suggests roles for PIEZO channels in cancer biology; however, direct mechanistic evidence in breast cancer remains limited. They have been shown to promote proliferation, epithelial-to-mesenchymal transition (EMT), and migration; however, these roles are varied and context-dependent. In breast cancer specifically, the two PIEZO channels may play opposing and complex roles in tumor progression, the tumor microenvironment (TME), and the tumor immune microenvironment (TIME), potentially impacting therapeutic response and prognosis. Where breast cancer-specific mechanistic data are lacking, we integrate findings from other tumor types to generate testable hypotheses relevant to breast cancer. In this review, we will explore the importance of PIEZO channels in breast cancer development, progression, and therapeutic response, and explore therapeutics and potential strategies to improve patient outcomes.