Hematopoietic Lineage Selective Roles for Trib Pseudokinases Post Bone Marrow Transplantation.

Abstract 2298

Trib's 1–3 are a homologous set of pseudokinases that (through their molecular actions as adaptors for E3 ubiquitin ligases, Akt and/or Mek/Erk) can exert diverse tissue and cellular effects. Upon ectopic expression, Trib2 promotes myeloid leukemia, and is elevated in its expression in melanoma. Trib3 can modulate insulin action, adipogenesis, and cardiomyopathy. Trib1 is implicated in inflammatory cytokine responses, and megakaryocytic leukemia. This illustrates the range of Trib functions, and also points to important regulatory roles for Tribs during hematopoiesis. To date the majority of Trib action studies have applied gain-of-function approaches. To gain new insight into hematopoietic roles of Trib2 and Trib3, we have generated novel knockout mouse models, and have employed a bone marrow transplant approach to assess possible effects of Trib2 or Trib3- deficiency on blood cell development. This approach also brings to bear the frequent requirement of physiological stress for the engagement of Trib pseudokinases. We assessed blood lineage reconstitution via hematological and flow cytometric analyses in irradiated (2 × 450 RAD) and bone marrow transplanted congenic recipient C57BL/B6.Ptprca, Ly-5.1 mice (5 × 10⁵ Trib2-KO, Trib3-KO or wild-type donor cells). In all experiments, full representation of donor derived Ly5.2 hematopoietic cells was confirmed in blood, bone marrow and spleen. Trib2-KO and Trib3-KO transplanted mice each exhibited skewed hematopoietic reconstitution profiles (as compared directly to wild-type BM transplanted controls). Trib2-KO transplanted mice exhibited persistently elevated lymphoid and WBC levels at week 6, 10 and 36 post BMT, and peripheral blood CD19+/B220+/Ly5.2+ B-cells also were elevated. In contrast, Trib3-KO transplanted mice exhibited sustained increases in reticulocyte production, together with heightened splenic erythropoiesis. Within a bone marrow transplantation context, findings reveal novel lineage- specific roles for Trib2 during lymphopoiesis, and for Trib3 during stress erythropoiesis.