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Constitutive Activation of NF-kB Inducing Kinase (NIK) in the Mesenchymal Lineage Drives Spontaneous Soft Tissue Sarcoma

ABSTRACT: Aberrant NF-kB signaling fuels tumor growth in multiple human cancer types including both hematologic and solid malignancies. Chronic elevated alternative NF-kB signaling can be modeled in transgenic mice upon activation of a conditional NF-kB-inducing kinase (NIK) allele lacking the regulatory TRAF3 binding domain (NT3). Here, we report that expression of NT3 in the mesenchymal lineage with Osterix (Osx/Sp7)-Cre or Fibroblast Specific Protein (Fsp1)-Cre caused subcutaneous, soft tissue tumors. These tumors displayed significantly shorter latency and a greater multiple incidence rate in Fsp1-Cre;NT3 compared to Osx-Cre;NT3 mice, regardless of sex. Histological assessment revealed poorly differentiated solid tumors with some spindled patterns, as well as robust RelB (Relb) immunostaining, confirming activation of alternative NF-kB. Even though NT3 expression also occurs in the osteolineage in Osx-Cre;NT3 mice, we observed no bony lesions. The staining profiles and pattern of Cre expression in the two lines pointed to a mesenchymal tumor origin. Immunohistochemistry revealed that these tumors stain strongly for SMA (Acta2), although vimentin (Vim) staining was uniform only in Osx-Cre;NT3 tumors. Negative CD45 (Ptprc) and S100 immunostains precluded hematopoietic and melanocytic origins, respectively, while positive staining for CK19 (Krt19), typically associated with epithelia, was found in subpopulations of both tumors. Principal component, differential expression, and gene ontology analyses revealed that NT3 tumors are distinct from normal mesenchymal tissues and are enriched for NF-kB related biological processes. We conclude that constitutive activation of the alternative NF-kB pathway in the mesenchymal linage drives spontaneous sarcoma and provides a novel mouse model for NF-kB related sarcomas.

ORGANISM(S): Mus musculus

PROVIDER: GSE158479 | GEO | 2020/09/25

REPOSITORIES: GEO

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Project description:Studies from global loss-of-function mutants suggest that alternative NF-kB downstream of NF-kB inducing kinase (NIK) is a cell-intrinsic negative regulator of osteogenesis. However, the interpretation of the osteoblast and/or osteocyte contribution to the bone phenotype is complicated by simultaneous osteoclast defects in these models. Therefore, we turned to a transgenic mouse model to investigate the direct role of NIK in the osteolineage. Osx-Cre;NT3 animals (NT3-Cre+), which bear a constitutively active NIK allele (NT3) driven by Osx-Cre, were compared to their Cre-negative, Control (Ctrl) littermates. NT3-Cre+ mice had elevated serum P1NP and CTX levels. Despite this high turnover state, microCT showed that constitutive activation of NIK resulted in a net increase in basal bone mass in both cortical and cancellous compartments. Furthermore, NT3-Cre+ mice exhibited a greater anabolic response following mechanical loading compared to controls. We next performed RNA-Seq on non-loaded and loaded tibiae to elucidate possible mechanisms underlying the increased bone anabolism seen in NT3-Cre+ mice. Hierarchical clustering revealed two main transcriptional programs: one loading-responsive and the other NT3 transgene-driven. Gene ontology (GO) analysis indicated a distinct upregulation of receptor, kinase and growth factor activities including Wnts, as well as a calcium-response signature in NT3-Cre+ limbs. The promoters of these GO-term associated genes, including many known to be bone-anabolic, were highly enriched for multiple kB recognition elements (kB-RE) relative to the background frequency in the genome. The loading response in NT3-Cre+ mice substantially overlapped (>90%) with Ctrl. Surprisingly, control animals had 10-fold more differentially expressed genes (DEGs) in response to loading. However, most top DEGs shared between genotypes had a high incidence of multiple kB-RE in their promoters. Therefore, both transcriptional programs (loading-responsive and NT3 transgene-driven) are modulated by NF-kB. Our studies uncover a previously unrecognized role for NF-kB in the promotion of both basal and mechanically-stimulated bone formation.

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Constitutive Activation of NF-kB Inducing Kinase (NIK) in the Mesenchymal Lineage Drives Spontaneous Soft Tissue Sarcoma

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