Deregulated expression and/or activity of Protein Tyrosine Kinases (PTKs) and their downstream signaling proteins are now widely recognized as oncogenesis-driving mechanisms that are amenable to targeted therapies. Studies by the PI and others have established the Cbl family of ubiquitin ligases (E3s) as physiological negative regulators of PTK signaling. Cbl proteins interact with PTKs and their effectors to promote their ubiquitination resulting in degradation-dependent or degradation-independent negative regulation of PTK signaling. Consistent with the importance of this mechanism in PTK regulation, mutations of Cbl that cluster in regions (linker region and RING finger) essential for E3 activity have now been identified in a subset of patients with myeloproliferative neoplasms and leukemia. Notably, most patients show acquired Uniparental Disomy with mutant Cbl allele replacing the wildtype allele. These findings lead us to our working hypotheses that Cbl is a tumor suppressor and that mutant Cbl proteins attain transforming properties due dominant-negative inhibition of endogenous Cbl proteins together with a gain-of-function trait that is selected for in cancer. Based on biochemical studies in previous funding cycles of this grant and work by others, we hypothesize the following molecular mechanisms for oncogenesis by Cbl mutants: The E3-deficient Cbl mutants produce dominant-negative inhibition of Cbl and related Cbl-b by competing for binding to activated target PTKs. Mutant Cbl proteins also serve as supra- molecular scaffolds to juxtapose the associated hyperactive PTKs with mutant Cbl-bound signaling intermediates to create a gain of function oncogenic cascade. This combination of dominant-negative and GOF mechanisms is hypothesized to allow the mutant Cbl proteins to establish a PTK-dependent oncogenic signaling cascade. In this renewal application, we will leverage our vast expertise and unique resources to test this model using molecular, biochemical, cellular and animal-based analyses. We will use engineer oncogenic Cbl mutant proteins that cannot interact with upstream PTKs through the TKB domain or with other signaling effectors through their C-terminal regions. In vitro and in vivo oncogenesis studies of these engineered proteins in hematopoietic stem/progenitor cells derived from wildtype, Cbl-null, Cbl-b-null and Cbl/Cbl-b-null backgrounds (which are available) will help test the role of key structural domains of mutant Cbl in establishing dominant-negative and gain-of-function mechanisms to drive oncogenesis. The engineered mutants and hematopoietic stem/progenitor cells expressing these, together with cells from an available Cbl RING Finger Knock-In mouse model, will be used to identify PTK and signaling protein partners that are required for mutant Cbl oncogenesis. Multi-pronged overexpression, knock-down/knockout, dominant-negative protein expression and chemical inhibition approaches will validate the role of identified Cbl partners in oncogenesis. Successful accomplishment of the proposed goals will help bring together the conceptual frameworks established during the previous cycles of this grant together with recent advances in the field to elucidate the mechanisms by which Cbl mutations contribute to human cancer and provide a conceptual and experimental framework for novel options towards targeted therapy of patients with Cbl mutations and related malignancies.

Public Health Relevance

Loss of genes that suppress the tendency of normal cells to become cancerous (tumor supressor genes) and mutation of genes that lead to the formation of oncogenes serve as drivers of human cancer. Our laboratory studies a group of proteins, the Cbl protein family, that control the levels and activity of receptors on normal cells that help our cells receive and process external signals, and they function as molecular brakes. Recent studies have identified loss of normal Cbl and accumulation of mutant Cbl protein in a subset of human leukemias, indicating that normal Cbl functions as a tumor suppressor and the mutant version as an oncogene. Based on our prior and ongoing molecular, cellular and animal studies, further studies are proposed to decipher the exact molecular mechanisms of cancer induced by mutations of Cbl proteins. The lessons learned here are hoped to open avenues for designing new drugs to treat human cancers in which Cbl mutants serve as drivers of cancer. The insights generated here could also help understand mechanisms of oncogenesis in other prevalent cancers in which protein tyrosine kinases (which are targeted by Cbl proteins) are deregulated.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Cancer Molecular Pathobiology Study Section (CAMP)
Program Officer
Hildesheim, Jeffrey
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Nebraska Medical Center
Internal Medicine/Medicine
Schools of Medicine
United States
Zip Code
Luan, Haitao; Mohapatra, Bhopal; Bielecki, Timothy A et al. (2018) Loss of the Nuclear Pool of Ubiquitin Ligase CHIP/STUB1 in Breast Cancer Unleashes the MZF1-Cathepsin Pro-oncogenic Program. Cancer Res 78:2524-2535
Iseka, Fany M; Goetz, Benjamin T; Mushtaq, Insha et al. (2018) Role of the EHD Family of Endocytic Recycling Regulators for TCR Recycling and T Cell Function. J Immunol 200:483-499
Lv, Kaosheng; Jiang, Jing; Donaghy, Ryan et al. (2017) CBL family E3 ubiquitin ligases control JAK2 ubiquitination and stability in hematopoietic stem cells and myeloid malignancies. Genes Dev 31:1007-1023
Olou, Appolinaire A; Sarkar, Aniruddha; Bele, Aditya et al. (2017) Mammalian ECD Protein Is a Novel Negative Regulator of the PERK Arm of the Unfolded Protein Response. Mol Cell Biol 37:
Nadeau, Scott A; An, Wei; Mohapatra, Bhopal C et al. (2017) Structural Determinants of the Gain-of-Function Phenotype of Human Leukemia-associated Mutant CBL Oncogene. J Biol Chem 292:3666-3682
Mohapatra, Bhopal; Zutshi, Neha; An, Wei et al. (2017) An essential role of CBL and CBL-B ubiquitin ligases in mammary stem cell maintenance. Development 144:1072-1086
Bhattacharyya, Sohinee; Rainey, Mark A; Arya, Priyanka et al. (2016) Endocytic recycling protein EHD1 regulates primary cilia morphogenesis and SHH signaling during neural tube development. Sci Rep 6:20727
Cypher, Luke R; Bielecki, Timothy Alan; Huang, Lu et al. (2016) Corrigendum to CSF-1 receptor signalling is governed by pre-requisite EHD1 mediated receptor display on the macrophage cell surface [Cell Signalling 2016 Sep.; 28(9): 1325-35]. Cell Signal 28:1933
An, Wei; Mohapatra, Bhopal C; Zutshi, Neha et al. (2016) VAV1-Cre mediated hematopoietic deletion of CBL and CBL-B leads to JMML-like aggressive early-neonatal myeloproliferative disease. Oncotarget 7:59006-59016
William, Basem M; An, Wei; Feng, Dan et al. (2016) Fasudil, a clinically safe ROCK inhibitor, decreases disease burden in a Cbl/Cbl-b deficiency-driven murine model of myeloproliferative disorders. Hematology 21:218-24

Showing the most recent 10 out of 107 publications