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Oncogenic CALR Mutant C-terminus Mediates Dual Binding to the Thrombopoietin Receptor Triggering Complex Dimerization and Activation

ABSTRACT: Calreticulin (CALR) is a master lectin chaperone that guides the proper folding of integral membrane proteins in the endoplasmic reticulum. In healthy cells, CALR transiently and non-specifically interacts with thousands of immature N-glycosylated proteins through its N-terminal glycan-binding domain. Conversely, frameshift mutants of CALR turn into rogue cytokine by acquiring the ability to stably and specifically interact with the Thrombopoietin Receptor (TpoR). Strikingly, this interaction induces activation of TpoR leading to myeloproliferative neoplasms, blood cancers resulting from the overproduction of blood cells. Using a multidisciplinary approach, we unveil how the CALR frameshift mutations result in structural overhaul of the entire protein and identify the structural basis of its acquired specificty for TpoR. We further describe the mechanisms by zhich complex formation triggers TpoR dimerization and activation. In addition, we provide the first complete dynamic conformational footprints of both wild-type and mutant CALR and identify novel potentially targetable sites.

INSTRUMENT(S): Synapt MS

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Permanent Cell Line Cell

DISEASE(S): Acute Leukemia

SUBMITTER: Nicolas Papadopoulos

LAB HEAD: Stefan N. Constantinescu

PROVIDER: PXD034131 | Pride | 2023-04-11

REPOSITORIES: Pride

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			Action	DRS
	CALR-TpoR.fasta	Fasta
	CALR_DEL52_D1D4_MATURE.zip	Other
	CALR_DEL52_D1D4_VS_D1D4.DnX	Other
	CALR_DEL52_TPORD1D2_IMMATURE.zip	Other
	CALR_DEL52_alone.zip	Other

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Calreticulin mutated hematopoietic cells are vulnerable to ATR-CHK1 pathway inhibition

Project description:Disease frameshift mutations of calreticulin (CALR) are the second most prevalent driver mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF). To identify potential targeted therapies for CALR mutated myeloproliferative neoplasms, we aimed to search for small molecule drugs that selectively inhibit the growth of CALR mutated cells using high-throughput drug screening. We investigated 89,172 compounds using isogenic cell lines and identified several hits targeting the ATR-CHK1 pathway. The selective inhibitory effect of these candidate compounds was validated in a co-culture assay of CALR mutated and wild type cells. Of the tested hit compounds, CHK1 inhibitors potently depleted CALR mutated cells, allowing CALR wild type cell dominance in the co-culture over time. Neither CALR deficient cells nor JAK2V617F mutated cells showed hypersensitivity to the drug treatment, suggesting that the vulnerability to ATR-CHK1 inhibition is specifically caused by the oncogenic activation by the mutant CALR. CHK1 inhibitors induced replication stress in CALR mutated cells revealed by elevated pan-nuclear staining for γH2AX and hyperphosphorylation of RPA2. They also promoted S-phase cell cycle arrest and blocked the completion of DNA replication in CALR mutated cells. Transcriptomic and phosphoproteomic analyses revealed a replication stress signature caused by the oncogenic CALR mutation, suggesting an intrinsic vulnerability of these cells to CHK1 perturbation. This study indicates that ATR-CHK1 pathway is a potential therapeutic target in CALR mutated hematopoietic cells.

2021-09-07 | PXD026803 | Pride

The stem/progenitor landscape is reshaped in a mouse model of essential thrombocythaemia and causes excess megakaryocyte production

Project description:Frameshift mutations in CALR (calreticulin) are associated with essential thrombocythaemia (ET), but the stages at and mechanisms by which mutant CALR drives transformation remain incompletely defined. Here, we use single-cell approaches to examine the haematopoietic stem/progenitor cell (HSPC) landscape in a mouse model of mutant CALR-driven ET. We identify a trajectory linking HSCs with megakaryocytes, and prospectively identify a novel intermediate population that is overrepresented in the disease state. We also show that mutant CALR drives transformation primarily from the earliest stem cell compartment, with some contribution from megakaryocyte progenitors. Finally, relative to wild-type HSCs, mutant CALR HSCs showed increases in JAK-STAT signalling, the unfolded protein response, cell cycle, and a previously undescribed upregulation of cholesterol biosynthesis. Overall, we have identified a novel megakaryocyte-biased cell population that is increased in a mouse model of ET and described transcriptomic changes linking CALR mutations to increased HSC proliferation and megakaryopoiesis.

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CALR frameshift mutations accelerate maturation of megakaryocytes in MPN patient-derived iPS cells

Project description:CALR frameshift mutations accelerate maturation of megakaryocytes in MPN patient-derived iPS cells

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Expression analysis of Clostridium acetobutylicum ATCC 824 grown on different carbohydrates

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Targeting the CALR Interactome in Myeloproliferative Neoplasms

Project description:Mutations in the endoplasmic reticulum (ER) chaperone calreticulin (CALR) are common in myeloproliferative neoplasm (MPN) patients, activate the thrombopoietin receptor (MPL), and mediate constitutive JAK/STAT signaling. The mechanisms by which CALR mutations cause myeloid transformation are incompletely defined. We employed mass spectrometry proteomics to identify novel CALR-mutant interacting proteins. Mutant CALR caused mislocalization of binding partners and increased recruitment of FLI1, ERP57 and CALR to the MPL promoter to enhance transcription. CALR 52 mutant was also found to increase genome-wide recruitment of Fli1 to the chromatin. Overall, these results show that type 1 CALR mutant modulates Fli1 cellular localization and recruitment.

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Whole-genome CRISPR screening identifies N-glycosylation as an essential pathway and a potential novel therapeutic target in CALR-mutant MPN (Whole Genome CRISPR Screen).

Project description:Calreticulin (CALR) mutations are frequent, disease-initiating events in myeloproliferative neoplasms (MPN). Although the biological mechanism by which CALR mutations cause MPN has been elucidated, there currently are no clonally selective therapies for CALR-mutant MPN. To identify unique genetic dependencies in CALR-mutant MPN, we performed a whole-genome CRISPR knockout depletion screen in mutant CALR-transformed hematopoietic cells. We found that genes in the N-glycosylation pathway (amongst others) were differentially depleted in mutant CALR-transformed cells as compared with control cells. Using a focused pharmacological screen targeting unique vulnerabilities uncovered in the CRISPR screen, we found that chemical inhibition of N-glycosylation impaired the growth of mutant CALR-transformed cells in vitro. We treated Calr-mutant knockin mice with the N-glycosylation inhibitor, 2-deoxy-glucose (2-DG), and found a preferential sensitivity of Calr-mutant cells to 2-DG as compared to wild-type cells, and a normalization of key MPN disease features. These findings advance the development of clonally selective treatments for CALR-mutant MPN.

2022-09-21 | GSE203456 | GEO

Whole-genome CRISPR screening identifies N-glycosylation as an essential pathway and a potential novel therapeutic target in CALR-mutant MPN (Pooled CRISPR Screen).

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Physical interaction between mutant calreticulin and the thrombopoietin receptor is required for transformation of hematopoietic cells

Project description:Somatic mutations in calreticulin (CALR) are present in approximately 40% of patients with myeloproliferative neoplasms (MPN). However, the mechanism by which mutant CALR is oncogenic is unknown. Here, we demonstrate that a megakaryocytic-specific MPN phenotype is induced when mutant CALR is over-expressed in mice and that the thrombopoietin receptor, MPL is required for mutant CALR driven transformation. Whole transcriptome analysis reveals enrichment of STAT signatures in mutant CALR transformed cells and JAK2 inhibitor treatment abrogates STAT activation. Employing extensive mutagenesis-based structure-function analysis we demonstrate that the positively charged amino acids within the mutant CALR C-terminus are required for cellular transformation through facilitating physical interaction between mutant CALR and MPL. Together, our findings elucidate a novel mechanism of cancer pathogenesis.

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Calreticulin Ins5 and Del52 mutations impair unfolded protein and oxidative stress responses in K562 cells expressing CALR mutants.

Project description:Somatic mutations of calreticulin (CALR) have been described in approximately 30-40% of JAK2 and MPL unmutated Essential Thrombocythemia and Primary Myelofibrosis patients. CALR is an endoplasmic reticulum (ER) chaperone responsible for proper protein folding and calcium retention. Recent data demonstrated that the TPO receptor (MPL) is essential for the development of CALR mutant-driven Myeloproliferative Neoplasms (MPNs). However, the precise mechanism of action of CALR mutants haven't been fully unraveled. In this study, we showed that CALR mutants impair the ability to respond to the ER stress and reduce the activation of the pro-apoptotic pathway of the unfolded protein response (UPR). Moreover, our data demonstrated that CALR mutations induce increased sensitivity to oxidative stress, leading to increase oxidative DNA damage. We finally demonstrated that the downmodulation of OXR1 in CALR-mutated cells could be one of the molecular mechanisms responsible for the increased sensitivity to oxidative stress mediated by mutant CALR. Altogether, our data identify novel mechanisms collaborating with MPL activation in CALR-mediated cellular transformation. CALR mutants negatively impact on the capability of cells to respond to oxidative stress leading to genomic instability and on the ability to react to ER stress, causing resistance to UPR-induced apoptosis.

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HIF-1-regulated expression of calreticulin promotes breast tumorigenesis and progression through Wnt/β-catenin pathway activation

Project description:Calreticulin (CALR) is a multi-functional protein that participates in various cellular processes, which include calcium homeostasis, cell adhesion, protein folding and cancer progression. However, the role of CALR in breast cancer is unclear. Here we report that CALR is overexpressed in breast cancer compared with normal tissue, and its expression is correlated with patient mortality and stemness indices. CALR expression was increased in mammosphere cultures, CD24-CD44+ subsets and ALDH+ subsets, which are enriched for breast cancer stem cells (BCSCs). Additionally, CALR knockdown led to BCSC depletion, which impaired tumor initiation and metastasis, and enhanced chemosensitivity in vivo. Chromatinimmunoprecipitation and reporter assays revealed that hypoxia-inducible factor 1 (HIF-1) directly activated CALR transcription in hypoxic breast cancer cells. CALR expression was correlated with Wnt/β-catenin pathway activation and an activator of Wnt/β-catenin signaling abrogated the inhibitory effect of CALR knockdown on mammosphere formation. Taken together, our results demonstrate that CALRfacilitates breast cancer progression by promoting the BCSC phenotype through Wnt/β-catenin signaling in a HIF-1-dependent manner, and suggest that CALR may represent a novel target for breast cancer therapy.

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