Functional Study of Mucin MUC1

描述（由申请人提供）：MUC1是一种肿瘤相关抗原，参与肿瘤发生、细胞信号传导和转录调节以及上皮表面保护。MUC1除广泛表达于上皮细胞外，也见于造血细胞；然而，MUC1在这些细胞中的功能仍然相当未知。我们发现，与野生型（WT） C57BL/6小鼠相比，C57BL/6小鼠的原代髓系祖细胞Muc1-/- (KO)缺乏Muc1导致CD11b+Gr1+细胞在GM-CSF和IL-4信号传导下扩增增加。从KO骨髓中扩增的CD11b+Gr1+细胞体外抑制T细胞增殖，而从WT中扩增的CD11b+Gr1+细胞体外抑制T细胞增殖，表明这些KO CD11b+Gr1+细胞是髓源性抑制细胞（MDSCs）。MDSCs有助于癌症中常见的免疫抑制；然而，它们从髓系祖细胞分化的机制仍然相对未知。最有趣的是，Muc1 KO小鼠能够更好地耐受异体肿瘤生长，在血液和肿瘤引流淋巴结中积累CD11b+Gr1+细胞。KO骨髓中CD11b+Gr1+ MDSCs的扩增伴随着β -catenin的下调，抑制β -catenin下调可逆转CD11b+Gr1+ MDSCs的扩增。我们的研究结果表明，Muc1需要调节髓系祖细胞向CD11b+Gr1+ MDSCs的分化。我们假设MUC1作为信号换能器在MDSC响应稳态干扰的分化中起关键作用。为了进一步表征Muc1在调节MDSC分化中的机制和功能作用，我们提出以下具体目标：(1)确定Muc1调控髓系祖细胞向CD11b+Gr1+ MDSCs分化的机制；(2)通过表征Muc1 KO荷瘤小鼠产生的MDSCs群体及其从骨髓发育到外周积累的过程，确定Muc1 KO小鼠产生MDSCs的功能意义；(3)利用造血或非造血区Muc1缺失或缺失的嵌合小鼠，确定在葡聚糖硫酸钠（DSS）诱导的结肠炎和结肠炎相关癌（CAC）期间，Muc1缺失对髓系发育的影响。MUC1是开发抗癌药物的一个特别有吸引力的靶点，它将被设计为靶向MUC1肿瘤，但也可能影响表达MUC1的造血细胞，我们的研究将有助于继续确定MUC1在造血中的作用。同时，进一步了解参与MDSC分化的信号通路（MUC1调控或其他）将使癌症和炎症药物更容易靶向这些通路。这些研究的结果应该让我们更清楚地了解MUC1在上皮和造血系统炎症和癌症信号通路中的作用。

DESCRIPTION (provided by applicant): MUC1 is a tumor-associated antigen involved in oncogenesis, regulation of cellular signaling and transcription and protection of epithelial surfaces. In addition to the widespread expression on epithelia, MUC1 is also found on hematopoietic cells; however, the function of MUC1 in these cells is still fairly unknown. We have found that the lack of Muc1 in primary myeloid progenitors from the C57BL/6 Muc1-/- (KO) mice resulted in an increased expansion of CD11b+Gr1+ cells under GM-CSF and IL-4 signaling, as compared to the wild type (WT) C57BL/6 mice. The CD11b+Gr1+ cells that were expanded in vitro from the KO bone marrow suppressed T cell proliferation in vitro while those from the WT did not, suggesting that these KO CD11b+Gr1+ cells were myeloid derived suppressor cells (MDSCs). MDSCs contribute to the immune suppression frequently seen in cancer; however, the mechanism by which they differentiate from myeloid progenitors is still relatively unknown. Most intriguingly, Muc1 KO mice were able to better tolerate allogeneic tumor growth, with an accumulation of CD11b+Gr1+ cells in the blood and tumor draining lymph nodes. The expansion of CD11b+Gr1+ MDSCs from KO bone marrow was accompanied by beta-catenin down regulation, and inhibition of beta-catenin down regulation could reverse the expansion of CD11b+Gr1+ MDSCs. Our findings indicate a need for Muc1 in modulating the differentiation of myeloid progenitors into CD11b+Gr1+ MDSCs. We hypothesize that MUC1 plays a critical role as a signal transducer in MDSC differentiation in response to a steady state disturbance. To further characterize the mechanistic and functional role of Muc1 in regulating MDSC differentiation, we propose the following specific aims: (1) To determine the mechanism by which Muc1 regulates the differentiation of myeloid progenitors into CD11b+Gr1+ MDSCs, (2) To determine functional significance of MDSCs generated in tumor-bearing Muc1 KO mice by characterizing MDSC populations generated as well as the process by which they develop from the bone marrow and accumulate in the periphery, (3) To determine the effect of a lack of Muc1 in myeloid development during dextran sodium sulfate (DSS)-induced colitis and colitis associated cancer (CAC) by using chimeric mice that lack or have Muc1 in the hematopoietic or non hematopoietic compartment. MUC1 is an especially attractive target for the development of anti-cancer agents, which would be designed to target MUC1 on carcinomas, but could also affect the hematopoietic cells expressing MUC1 and our studies would be useful in continuing to define the role of MUC1 in hematopoiesis. At the same time, furthering our understanding of the signaling pathways involved in MDSC differentiation (MUC1 regulated or otherwise) would enable the targeting of these pathways by drugs in cancer and inflammation more readily. Results from these studies should give us clearer insight into the role of MUC1 in the epithelium and hematopoietic system in both inflammation and cancer signaling pathways. PUBLIC HEALTH RELEVANCE: In this proposal we will study the function of MUC1, a cell-associated signaling mucin, in the maturation and expansion of a cell population (myeloid derived suppressor cells, MDSCs) that can suppress the immune system. Although MUC1 is well established as an oncogene in epithelial tissues, it appears to have different roles in hematopoietic tissues. This study will provide novel mechanistic and functional insights into the immunosuppressive microenvironment that can be found in inflammation and tumors. Further understanding of the signaling pathways involved in MDSC differentiation as well as increased insight into the role of MUC1 in the epithelium and hematopoietic systems in inflammation and cancer will enable us to target therapies more knowledgeably.