# Regulation of protein ubiquitination in hematopoietic cytokine signaling

> **NIH NIH R01** · CHILDREN'S HOSP OF PHILADELPHIA · 2020 · $549,992

## Abstract

Abstract
Hematopoietic stem and progenitor cell (HSPC) homeostasis is regulated by intricate cytokine receptor and
tyrosine kinase signaling pathways. Janus Kinase 2 (JAK2) is the key tyrosine kinase in the signaling pathway
of an array of hematopoietic receptors, including thrombopoietin (TPO) receptor (MPL) in hematopoietic stem
cells (HSCs) and granulocyte macrophage colony-stimulating factor receptor (GM-CSFR) in myeloid
progenitors. While JAK2 plays an essential role in hematopoietic development, uncontrolled JAK2 signaling
results in hematopoietic malignancies. Gain-of-function JAK2 mutations such as V617F are found in large
populations of patients with myeloproliferative neoplasms (MPNs), a clonal HSC disease. Genetically targeting
JAK2 abrogates MPN in mice; the JAK2V617F mutation is the driving mutation found in the HSCs of human MPN
patients. However, current FDA-approved JAK kinase inhibitors have low curative potential, indicating the need
for a better understanding of the regulation of JAK2 for efficient targeting. A number of E3 ubiquitin ligases for
JAK2 have been proposed, but none of them, when lost in vivo, increases JAK2 protein level in HSPCs,
expands HSC pool, or enhances multiple lineage hematopoiesis. Thus, the E3 ligase(s) regulating JAK2
turnover remain elusive. Through a series of biochemical and functional studies, we found that JAK2 stability is
regulated by the CBL family E3 ubiquitin ligases, c-CBL and CBL-b, via the adaptor protein LNK (also called
SH2B3). C-Cbl-/- mice phenocopy Lnk-/- mice, exhibiting an augmented HSPC pool with superior
transplantability and hypersensitivity to cytokines. Importantly, CBL loss-of-function mutations have been found
in a wide range of myeloid malignancies with the most frequent occurrence in chronic and juvenile
myelomonocytic leukemia (CMML and JMML), both of which bear poor prognosis. Here, we propose to define
the molecular basis underlying the regulation of JAK2 stability and signaling through this novel signaling axis,
CBL/LNK/JAK2, and exploit it for therapeutic strategies in treating myeloid neoplasms. The following specific
aims will be addressed: 1. Investigate mechanisms by which CBL regulates JAK2 ubiquitination, stability and
signaling in hematopoietic cell lines and HSPCs from Cbl deficient and Cbl E3 ligase inactive mouse models. 2.
Determine the influence of CBL on the stability of constitutively active JAK2 mutants and mutant JAK2-
mediated MPN development. 3. Determine the role of CBL in regulating JAK2 level and signaling in primary
human progenitors and explore therapeutic potential of JAK inhibition in treating murine and human myeloid
malignancies with CBL mutations. Collectively, our data point to a novel direct role of CBL-mediated JAK2
ubiquitination and degradation in cytokine signaling and hematopoiesis. The proposed studies will likely
provide mechanistic insights into the regulation of wild type JAK2 in normal HSPCs as well as JAK2 mutants in
MPNs. In ad...

## Key facts

- **NIH application ID:** 9850989
- **Project number:** 5R01HL133828-04
- **Recipient organization:** CHILDREN'S HOSP OF PHILADELPHIA
- **Principal Investigator:** Wei Tong
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $549,992
- **Award type:** 5
- **Project period:** 2017-04-18 → 2022-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9850989

## Citation

> US National Institutes of Health, RePORTER application 9850989, Regulation of protein ubiquitination in hematopoietic cytokine signaling (5R01HL133828-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9850989. Licensed CC0.

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