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HkRP3 is a microtubule-binding protein regulating lytic granule clustering and NK cell killing
Hyoungjun Ham1, Walter Huynh2, Renee A Schoon3
1Department of Immunology, Mayo Graduate School, College of Medicine, Mayo Clinic, Rochester, MN 55905;
Abstract:
NK cells provide host defense by killing viral-infected and cancerous cells through the secretion of preformed lytic granules. Polarization of the lytic granules toward the target cell is dependent on an intact microtubule (MT) network as well as MT motors. We have recently shown that DOCK8, a gene mutated in a primary immunodeficiency syndrome, is involved in NK cell killing in part through its effects on MT organizing center (MTOC) polarization. In this study, we identified Hook-related protein 3 (HkRP3) as a novel DOCK8- and MT-binding protein. We further show that HkRP3 is present in lytic granule fractions and interacts with the dynein motor complex and MTs. Significantly, depletion of HkPR3 impaired NK cell cytotoxicity, which could be attributed to a defect in not only MTOC polarity, but also impaired clustering of lytic granules around the MTOC. Our results demonstrate an important role for HkRP3 in regulating the clustering of lytic granules and MTOC repositioning during the development of NK cell-mediated killing.
Insights
Hook-related protein 3 (HkRP3) is crucial for Natural Killer (NK) cell defense. This protein helps organize lytic granules and the microtubule organizing center (MTOC) for effective target cell killing.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Natural Killer (NK) cells are vital for host defense against viral infections and cancer.
- NK cell-mediated cytotoxicity relies on directed secretion of lytic granules, dependent on microtubule (MT) dynamics and MT motors.
- DOCK8, a protein implicated in primary immunodeficiency, influences NK cell MT organizing center (MTOC) polarization.
Purpose of the Study:
- To identify novel proteins involved in NK cell cytotoxicity and MTOC polarization.
- To investigate the role of Hook-related protein 3 (HkRP3) in NK cell function.
Main Methods:
- Co-immunoprecipitation assays to identify binding partners.
- Immunofluorescence microscopy to visualize protein localization and MTOC polarization.
- siRNA-mediated gene silencing to assess the functional impact of HkRP3 depletion.
- NK cell cytotoxicity assays.
Main Results:
- Hook-related protein 3 (HkRP3) was identified as a novel binding protein for DOCK8 and microtubules (MTs).
- HkRP3 localizes to lytic granules and interacts with the dynein motor complex and MTs.
- Depletion of HkRP3 significantly impairs NK cell cytotoxicity due to defects in MTOC polarity and lytic granule clustering.
Conclusions:
- HkRP3 plays a critical role in NK cell-mediated killing by regulating lytic granule clustering and MTOC repositioning.
- HkRP3 is a key mediator in the DOCK8- and MT-dependent pathway for NK cell cytotoxicity.
- These findings highlight HkRP3 as a potential therapeutic target for enhancing NK cell function.
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