Hepatic cell cycle-related kinase shapes a metastatic-prone liver microenvironment via crosstalk between myeloid-derived suppressor cell and natural killer T cell

Ph.D.Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and characterized by sex disparity. The research team of my PhD mentor has previously identified that cell cycle-related kinase (CCRK), the latest family member of cyclin-dependent kinases (CDKs), functions as a direct target of aberrant androgen receptor signaling in driving the male predominance of HCC. Mechanistically, CCRK regulates multiple tumor cell-intrinsic pathways such as β-catenin/T cell factor, enhancer of zeste homolog 2 and nuclear factor-κB. As recent studies highlight the key role of CDKs in tumor immunity, I aimed to uncover the immunoregulatory role of CCRK in HCC in this study.Through a liver-specific CCRK inducible transgenic (TG) C57/BL6 mouse model, we found that hepatic induction of CCRK expression by tamoxifen could increase CD11b⁺Gr-1⁺Ly6G⁺Ly6Cˡᵒʷ polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) accumulation, specifically in male mice. Next, I investigated whether the altered liver immune environment affects tumorigenicity. Using an orthotopic HCC model, I found that CCRK TG mice developed significantly larger tumor compared to control mice with increased PMN-MDSCs accumulation in the liver which was positively correlated with tumor weight. Notably, PMN-MDSC depletion by a specific antibody abrogated the tumor growth in CCRK TG mice, suggesting that PMN-MDSC induction may form a tumor-supportive microenvironment to promote local hepatoma growth.In addition to primary HCC development, the liver microenvironment may also influence metastatic tumor growth. As a unique immune tolerant organ, liver is the most common metastatic site for various cancers, and metastasis leads to poor survival. Although this metastatic tropism may reflect the mechanical trapping of circulating tumor cells, the success of metastatic tumor outbreak is also dependent, at least in part, on the formation of a 'pro-metastatic' niche that supports the spread and outgrowth of tumor cells to the liver. Here I showed that compared to control mice, CCRK TG male mice exhibited enhanced liver metastasis when intrasplenically injected with mouse melanoma cell line B16F10 or colon cancer cell line MC38. Interestingly, the metastatic tumor weights were positively associated with liver-infiltrating PMN-MDSCs, which were accompanied by upregulation of MDSC-trafficking chemokine C-X-C motif chemokine 1 (Cxcl1). Further immune profiling showed that the proportion of anti-tumor natural killer T (NKT) cells was decreased in CCRK TG mice liver and were negatively correlated with tumor weight. Importantly, depletion of PMN-MDSCs restored NKT cell infiltration and suppressed metastasis to the liver, thus demonstrating a functional crosstalk between MDSC and NKT cells in liver metastasis. In support of the clinical relevance of our findings, I further found that CCRK and CXCL1 expression were concordantly upregulated in livers of colorectal cancer liver metastasis patients compared to healthy donors, which were accompanied by increased liver-infiltrating MDSC and decreased NKT cell proportions.Taken together, my findings suggest that hepatic CCRK expression creates a tumor growth- and metastasis-supportive liver microenvironment via enhancing MDSC-mediated immunosuppression, thus providing new mechanistic insights for cancer metastasis and therapeutic targets for intervention.肝细胞癌是恶性程度较高的癌症之一，而且高发于男性。我们实验室前期研究发现，细胞周期素依赖性激酶家族的最新成员细胞周期相关激酶（CCRK），通过异常激活雄激素受体通路导致男性更容易罹患肝细胞癌。细胞周期相关激酶可调控多个肿瘤细胞增殖相关通路，比如β-catenin/T cell factor, enhancer of zeste homolog 2 and nuclear factor-κB通路等。近年来，研究发现细胞周期素依赖性激酶家族在肿瘤免疫中发挥重要作用，因此本研究探索细胞周期相关激酶在肝细胞癌中的免疫调控作用。利用肝细胞特异表达细胞周期相关激酶的转基因小鼠模型，我们发现相比于对照小鼠，雄性转基因小鼠中CD11b⁺Gr-1⁺Ly6G⁺Ly6Cˡᵒʷ 多核型骨髓源性免疫抑制细胞明显增多，而且其相关的趋化因子CXC趋化因子1（Cxcl1）的转录明显增加。为了进一步研究这是否影响肿瘤生长，我们注射肝癌细胞到小鼠肝中，发现肿瘤在转基因小鼠中生长加快，且与多核型骨髓源性免疫抑制细胞数量呈正相关。抑制多核型骨髓源性免疫抑制细胞明显抑制肿瘤生长。这表明，细胞周期相关激酶诱导多核型骨髓源性免疫抑制细胞在肝脏聚集形成促进肿瘤生长的免疫微环境。除了促进肝癌发展，肝脏微环境也会影响癌症转移。肝脏的免疫耐受性导致多种癌症容易转移到肝。在小鼠脾中注射黑色素瘤细胞或者肠癌细胞后，转基因小鼠肝中转移瘤明显比对照小鼠大。转移瘤大小与肝中多核型骨髓源性免疫抑制细胞数量呈正相关。另外，抗肿瘤自然杀伤T细胞显著减少，并与转移瘤大小呈负相关。抑制多核型骨髓源性免疫抑制细胞显著减少肿瘤肝转移，同时恢复自然杀伤T细胞的浸润，预示着多核型骨髓源性免疫抑制细胞与自然杀伤T细胞之间存着相互作用。同时，肠癌肝转移的病人肝脏中细胞周期相关激酶和CXCL1的表达显著增加，伴随增多的骨髓源性免疫抑制细胞和减少的自然杀伤T细胞浸润。本研究证明肝中细胞周期相关激酶通过诱导骨髓源性免疫抑制细胞在肝中聚集，形成免疫抑制微环境，从而促进肝癌发展和肿瘤肝转移。这为开发治疗癌症转移的药物提供新的思路。Zeng, Xuezhen.Thesis Ph.D. Chinese University of Hong Kong 2019.Includes bibliographical references (leaves 127-142).Abstracts also in Chinese.Title from PDF title page (viewed on 22, December, 2020)