FoxN1-dependent thymic epithelial cells promote T-cell leukemia development

Abstract

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy of thymocytes. The role of thymic microenvironmental cells and stromal factors in thymocyte malignant transformation and T-ALL development remains little explored. Here, using the TEL-JAK2 transgenic (TJ2-Tg) mouse model of T-ALL, which is driven by constitutive JAK/STAT signaling and characterized by the acquisition of Notch1 mutations, we sought to identify stromal cell alterations associated with thymic leukemogenesis. Immunofluorescence analyses showed that thymic lymphomas presented epithelial areas characterized by keratin 5 and keratin 8 expression, adjacently to keratin-negative, epithelialfree areas. Both keratin-positive and -negative areas stained conspicuously with ER-TR7 (a fibroblast marker), laminin, and CD31 (an endothelial cell marker). Besides keratin 5, keratin-positive areas were also labeled by the Ulex Europaeus agglutinin-1 medullary thymic epithelial cell (TEC) marker. To assess whether TECs are important for T-ALL development, we generated TJ2-Tg mice heterozygous for the FoxN1 transcription factor nude null mutation. In contrast to nude homozygous mice, which lack thymus and thymocytes, heterozygous mutant mice present only mild thymocyte maturation defects. In TJ2-Tg;Foxn1 +/nu compound mice both emergence of malignant cells in pre-leukemic thymi and overt T-ALL onset were significantly delayed. Moreover, in transplantation assays leukemic cell expansion in the thymus of recipient Foxn1 +/nu mice was reduced as compared to control littermates.These results indicate that FoxN1 insufficiency impairs specifically thymic leukemogenesis but not thymocyte development. SummaryIn a mouse model of T-ALL, several cellular alterations were detected in thymic lymphomas, including altered epithelial distribution and increased proportion of fibroblasts or endothelial cells. Reduced dosage of FoxN1, a thymic epithelial transcription factor, delayed leukemogenesis in these mice.not peer-reviewed)

NF-κB-dependent RANKL expression in a mouse model of immature T-cell leukemia

“…RANKL in leukemic T cells may activate and modulate specific RANK-expressing microenvironmental cells, such as osteoclasts in the bone marrow microenvironment. TJ2-Tg leukemia arises in the thymus, leading to the development of lymphomas characterized by progressive alterations in epithelial cell composition [21]. Since medullary thymic epithelial cells (mTECs) express RANK and differentiate in response to RANKL [9,33], it is possible that RANKL expression by leukemic cells influences mTEC function.…”

“…RANKL-RANK signaling was also shown to mediate interactions between T cells and DCs, thus favoring T-cell proliferation and DC function and survival [10]. DCs are present in thymic lymphomas from TJ2-Tg mice [21], and are therefore potential targets of RANKL-expressing leukemic cells. Future studies should address the potential role for RANKL-RANK signaling in T-cell leukemia.…”

“…EµSRα-TEL-JAK2 (B6.Cg-Tg(Emu-ETV6/JAK2)71Ghy) transgenic (TJ2-Tg) mice, previously provided by Dr. Jacques Ghysdael (Institut Curie, France), were described before [20,21]. C57BL/6J mice were purchased from Harlan Laboratories (C57BL/6JRccHsd substrain) and bred locally.…”

“…Single-cell suspensions were stained with fluorochrome-labeled antibodies as previously described [21] and detected in a FACS Calibur flow cytometer (BD Biosciences, San Jose, CA, USA) or sorted using a FACSAria I (BD Biosciences). Fluorescein isothiocyanate (FITC)-, Rphycoerythrin (PE)-, or PE-cyanin 5 (PE-Cy5)-conjugated antibodies specific for RANKL (IK22/5), CD69 (H1.2F3), CD4 (GK1.5), and CD8 (53-6.7) (BioLegend, San Diego, CA USA) were used.…”

ET-1 regulates the human umbilical vein endothelial cell cycle by adjusting the ERβ/FOXN1 signaling pathway

“…It is predominantly expressed with thymic epithelial cells and is an important transcriptional regulator (20,21). FOXN1 plays an important regulatory role in tumors, immunodeficiency, and epithelial cell growth (22,23). Investigating the function and molecular regulation mechanisms of ET-1, ERβ, and FOXN1 in disease models will provide new targets and means for clinical treatment.…”