# Calreticulin-mediated protein folding in health and disease

> **NIH NIH R01** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2022 · $458,052

## Abstract

Abstract
Calreticulin (CRT) is a calcium-binding endoplasmic reticulum (ER) chaperone that is important for the folding
of many N-linked glycoproteins. It is best known for its function in the assembly of major histocompatibility
complex (MHC) class I (MHC-I) molecules, which present peptide antigens to CD8+ T cells for protective
immunity against cancers and infections. Recent studies show that somatic frameshift mutations that alter the
C-terminus of CRT are one class of driver mutations in myeloproliferative neoplasms (MPN). A 52 base-pair
deletion mutant CRTDel52 and a 5 base-pair insertion mutant CRTIns5 are recurrent mutations in essential
thrombocythemia (ET), primary myelofibrosis (PMF) and post-ET myelofibrosis (MF). It is our overall
hypothesis that the changes to the sequence and charge of the C-terminal domains of CRT induced by the
mutations enable both megakaryocyte transformation and immune system evasion in MPN. Although
oncogenic transformation in megakaryocytes requires both mutated CRT and the thrombopoietin
receptor/myeloproliferative leukemia protein (Mpl), the molecular mechanisms of mutant CRT-mediated
constitutive activation of Mpl are unknown. CRT is known to be important for ER calcium storage and cellular
calcium signaling, but precisely how MPN mutations alter these processes is not understood. The human
MHC-I locus is highly polymorphic. While it is known that MPN-linked mutant CRTs are ineffectively
incorporated into the MHC-I peptide-loading complex (PLC), it is unknown whether MPN CRT mutants have
differential influences on the assembly of various MHC-I allotypes. Studies are proposed here to address these
gaps in knowledge. We present evidence that disulfide-linked dimers of CRTDel52 are important for Mpl
activation. The nature of CRTDel52 dimers and their complexes with Mpl will be elucidated using structural and
mutagenesis studies. The effects of CRT deficiency, haploinsufficiency and mutation upon cellular calcium
signaling will be examined. Based on the knowledge of variable dependencies on CRT for cell-surface
expression of MHC-I allotypes, we will examine whether MPN CRT mutants impair MHC class I assembly for
some allotypes, but alter assembly and peptide display for some other MHC-I allotypes. Such alterations could
be exploited for immunotherapeutic targeting of MPN. Finally, mutant CRT expression is also detectable in
blood monocytes of MPN patients, leading to predictions of alterations to antigen presenting cell (APC) calcium
signaling and phagocytosis, which will be examined. Taken together, these studies will further our
understanding of how mutations of a ubiquitous ER chaperone drive cell transformation, and influence the
fundamental immunological processes of antigen presentation and phagocytosis.

## Key facts

- **NIH application ID:** 10362228
- **Project number:** 2R01AI123957-06A1
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** MALINI RAGHAVAN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $458,052
- **Award type:** 2
- **Project period:** 2016-03-10 → 2026-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10362228

## Citation

> US National Institutes of Health, RePORTER application 10362228, Calreticulin-mediated protein folding in health and disease (2R01AI123957-06A1). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10362228. Licensed CC0.

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