The critical roles of tumor-initiating cells and the lymph node stromal microenvironment in human colorectal cancer extranodal metastasis using a unique humanized orthotopic mouse model.

Colorectal cancer (CRC) is the second-most common cause of cancer-related mortality. The most important prognostic factors are lymph node (LN) involvement and extranodal metastasis. Our objective is to investigate the interactions between CD133(+)CXCR4(+) (CXC receptor 4) colorectal cancer tumor-initiating cells (Co-TICs) and the LN stromal microenvironment in human CRC extranodal metastasis. We established a unique humanized orthotopic xenograft model. Luciferase-tagged CRC cell lines and human cancer cells were injected intrarectally into nonobese diabetic/SCID mice. Mesenteric LN stromal cells, stromal cell line HK, or CXCL12 knockdown HK (HK-KD-A3) cells were coinoculated with CRC cells. Tumor growth and metastasis were monitored by bioluminescent imaging and immunohistochemistry. We found that this model mimics the human CRC metastatic pattern with CRC cell lines or patient specimens. Adding LN stromal cells promotes CRC tumor growth and extranodal metastasis (P < 0.001). Knocking down CXCL12 impaired HK cell support of CRC tumor formation and extranodal metastasis. When HK cells were added, sorted CD133(+)CXCR4(+) Co-TICs showed increased tumor formation and extranodal metastasis capacities compared to unseparated and non-Co-TIC populations. In conclusion, both Co-TIC and LN stromal factors play crucial roles in CRC metastasis through the CXCL12/CXCR4 axis. Blocking Co-TIC/LN-stromal interactions may lead to effective therapy to prevent extranodal metastasis.

Usp18 promotes conventional CD11b+ dendritic cell development.

Dendritic cells (DCs) represent the key cells linking innate and adaptive immune responses. It is critical to understand the molecular factors regulating DC differentiation. Usp18 is an IFN-inducible member of the ubiquitin-specific protease family, which deconjugates ubiquitin-like modifier ISG15 from target proteins and competitively inhibits IFN-α/ß-induced JAK/STAT activation. This study demonstrates that the frequency of conventional CD11b(+) DCs in the spleen of Usp18(-/-) mice was significantly reduced, whereas the frequencies of conventional CD8(+) DCs and plasmacytoid DCs remained normal. In addition, Usp18(-/-) bone marrow (BM) cells generate DCs less efficiently in GM-CSF-supplemented culture, demonstrating a fundamental defect throughout the DC differentiation pathway. Usp18(-/-) BM cells were rescued by exogenous expression of either wild-type or deconjugation-inactive Usp18, and superimposition of an IFN-α/ß receptor knockout returned in vivo DC populations to normal, clearly showing that the defect seen is due solely to Usp18's effect on IFN signaling. Finally, Usp18(-/-) BM-derived DCs expressed high levels of SOCS1/SOCS3, known inhibitors of GM-CSF signaling, providing a mechanistic explanation for the phenotype. In conclusion, we have identified a novel role of Usp18 in modulating conventional CD11b(+) DC development via its inhibitory effect on type I IFN signaling.