No abstract

Cancer metastasis can occur at the early stage of tumor development when a primary tumor is at the microscopic size. In particular, the interaction of malignant cells with other cell types including cancer-associated fibroblasts (CAF) in promoting metastasis at the early stage of tumor development remains largely unknown. Here, we investigated the role of CAFs in facilitating the initial events of cancer metastasis when primary tumors were at microscopic sizes. Multicolor-coded cancer cells and CAFs were coimplanted into the transparent zebrafish body and metastasis at a single-cell level was monitored in living animals. Healthy fibroblasts, tumor factor-educated fibroblasts, and CAFs isolated from various tumors were tested for their ability to facilitate metastasis. We showed that CAFs promoted cancer cell metastasis at the very early stage during primary tumor development. When a primary tumor was at the microscopic size consisting of a few hundred cells, CAFs were able to hijack cancer cells for dissemination from the primary site. Surprisingly, a majority of metastatic cancer cells remained in tight association with CAFs in the circulation. Furthermore, stimulation of non-metastasis-promoting normal fibroblasts with TGF-B, FGF-2, HGF, and PDGF-BB led to acquisition of their metastatic capacity. Cancer metastasis occurs at the very early stage of tumor formation consisting of only a few hundred cells. CAFs are the key cellular determinant for metastasis. Our findings provide novel mechanistic insights on CAFs in promoting cancer metastasis and targeting CAFs for cancer therapy should be aimed at the early stage during cancer development. .

• The NF-kB subunits p52 and RelB increase IRF4 promoter activity and expression in PTCL cells.• A positive feedback loop involving CD30, NF-kB, and IRF4 drives PTCL cell proliferation and can be blocked by NF-kB inhibitors.Peripheral T-cell lymphomas (PTCLs) are generally aggressive non-Hodgkin lymphomas with poor overall survival rates following standard therapy. One-third of PTCLs express interferon regulatory factor-4 (IRF4), a tightly regulated transcription factor involved in lymphocyte growth and differentiation. IRF4 drives tumor growth in several lymphoid malignancies and has been proposed as a candidate therapeutic target. Because direct IRF4 inhibitors are not clinically available, we sought to characterize the mechanism by which IRF4 expression is regulated in PTCLs. We demonstrated that IRF4 is constitutively expressed in PTCL cells and drives Myc expression and proliferation. Using an inhibitor screen, we identified nuclear factor kB (NF-kB) as a candidate regulator of IRF4 expression and cell proliferation. We then demonstrated that the NF-kB subunits p52 and RelB were transcriptional activators of IRF4. Further analysis showed that activation of CD30 promotes p52 and RelB activity and subsequent IRF4 expression. Finally, we showed that IRF4 transcriptionally regulates CD30 expression. Taken together, these data demonstrate a novel positive feedback loop involving CD30, NF-kB, and IRF4; further evidence for this mechanism was demonstrated in human PTCL tissue samples. Accordingly, NF-kB inhibitors may represent a clinical means to disrupt this feedback loop in IRF4-positive PTCLs. (Blood. 2015; 125(20):3118-3127) Introduction Peripheral T-cell lymphomas (PTCLs) are aggressive non-Hodgkin lymphomas (NHLs) characterized by poor overall survival rates. [1][2][3] Most patients are treated with anthracycline-based chemotherapy regimens originally designed for B-cell lymphomas. Five-year overall survival rates vary somewhat by subtype but average ;35%. The possibility of individualized targeted therapy holds promise, but advances have been hindered by the fact that few therapeutic targets have been identified and validated in PTCLs. Our group's approach to this challenge has been to characterize the genetics of PTCLs to identify novel biomarkers and therapeutic targets. We have focused particularly on chromosomal translocations, which have played a major role in identifying diagnostic, prognostic, and theranostic biomarkers in hematologic neoplasms in general (eg, BCR-ABL) and PTCLs specifically (ALK rearrangements). 4,5 We previously discovered a recurrent translocation in PTCL, t(6;14)(p25.3;q11.2), that juxtaposes the interferon regulatory factor-4 (IRF4) and T-cell receptor-a (TRA) genes and is associated with increased IRF4 expression. 6 Because TRA translocation partners typically function as oncogenes in T-cell malignancies, we postulated that IRF4 plays an oncogenic role in PTCLs.7 IRF4 is a tightly regulated transcription factor involved in growth and differentiation of normal T and B lymp...