CBL proteins are E3 ubiquitin ligases and adaptor proteins. The mammalian homologs – CBL, CBL-B and CBL-3 show broad tissue expression; accordingly, the CBL proteins play roles in multiple cell types. We have investigated the function of the CBL-B protein in hematopoietic cells and
fibroblasts.
The causative agent of chronic myeloid leukemia (CML) is BCR-ABL. This oncogenic fusion down-modulates CBL-B protein levels, suggesting that CBL-B regulates either the development or progression of CML. To assess the involvement of CBL-B in CML, bone marrow transduction and transplantation (BMT) studies were performed. Recipients of BCR-ABL-infected CBL-B(-/-) cells succumbed to a CML-like myeloproliferative disease with a longer latency than the wild-type recipients.
Peripheral blood white blood cell numbers were reduced, as were splenic weights. Yet despite the reduced leukemic burden, granulocyte numbers were amplified throughout the animals. As well, CBLB(-/-)
bone marrow (BM) cells possessed defective BM homing capabilities. From these results we
concluded that CBL-B negatively regulates granulopoiesis and that prolonged latency in our CBL-B(-/-) BMT animals was a function of perturbed homing.To develop an in vitro model to study CBL-B function we established mouse embryonic fibroblasts (MEFs) deficient in CBL-B expression. Transduction of the wild-type and CBL-B-deficient MEFs with BCR-ABL did not confer transformation; nevertheless, the role of CBL-B in fibroblasts was evaluated. The CBL-B(-/-) MEFs showed enhanced chemotactic migration toward serum in both Transwell migration and time-lapse video microscopy studies. The biochemical response to serum was
extensively evaluated leading to the development of a model. We predict that CBL-B deficiency either: (a) augments GRB2-associated binding protein 2 (GAB2) phosphorylation leading to enhanced
extracellular signal-regulated kinase (ERK) and protein kinase B (PKB / Akt) signaling, or (b) alleviates negative control of Vav3 resulting in stimulation of Rho effectors. In either case, our results reveal a
negative regulatory role for CBL-B in fibroblast migration.
The two studies detailed herein expand our knowledge of CBL-B function. They strongly
suggest that CBL-B can modulate granulocyte proliferation and point toward a role for CBL-B in the motility of numerous cell types.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/29946 |
| Date | 15 September 2011 |
| Creators | Badger-Brown, Karla Michelle |
| Contributors | Barber, Dwayne |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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