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Cell polarity in hematopoietic stem cell quiescence, signaling and fate determination

Althoff, Mark J
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1583999632089058

Abstract Details

2020, PhD, University of Cincinnati, Medicine: Cancer and Cell Biology.
Hematopoietic stem cells (HSC) self-renew and differentiate through changes in polarity. Polarity has been described as a major driver of asymmetric cell division, and in particular, Cdc42 allocation accurately predicts HSC asymmetric division potential. Few proteins responsible for establishing or maintaining cellular polarity (outside of Cdc42) have been investigated among HSC, and of those that have, many have been deemed functionally dispensable. Scribble is a multi-modular cytoplasmic scaffolding protein that coordinates the spatial organization of cell fate determinants and acts as a molecular hub for a variety of signaling proteins. The contributions of Scribble on cellular polarity establishment and maintenance in neuronal stem cells and epithelial cells is well characterized, however such mechanisms are yet to be defined in HSC. We discovered that Scribble controls HSC fate and function by acting as a molecular hub for signaling proteins like the Hippo pathway kinase, Lats1, and the effectors, Yap1 and Taz. The Hippo pathway controls proliferation and growth of multiple mammalian tissues, yet its role in HSC remains controversial. We found that Yap1 is predominantly polarized in the cytosol of HSC through a Scribble PDZ domain-mediated interaction. Deletion of Yap1 and Taz induces a loss of HSC quiescence, self-renewal and reconstitution following serial myeloablative 5-fluorouracil treatments, indicating a functional dependency for these effectors. We provide the first functional evidence that Scribble and Yap1 coordinate to control cytoplasmic Cdc42 activity, regulating both HSC quiescence and fate determination in vivo. Deletion of Scribble disrupted Yap1 co-polarization with Cdc42 and decreased Cdc42 activity, resulting in apoptosis of non-self-renewing daughter cells. This data suggests that Scribble/Yap1 co-polarization is indispensable for Cdc42-dependent activity on HSC asymmetric division and fate. The combined genetic loss of Scribble, Yap1 and Taz in HSC further decreases Cdc42 expression and activity, and is associated with transcriptional upregulation of Rac-specific guanine nucleotide exchange factors, and subsequent Rac activation and restoration of HSC fitness. Our data indicate that Scribble coordinates the cytosolic functions of Yap1 and Taz with Cdc42 activity and is required for HSC fate determination. We also identify a potential novel mechanism by which Scribble coordinates HSC activity in response to stress. Scribble deficient HSC retained cellular quiescence after interferons type I (IFN-I) stimulation. IFN-I are microenvironment cytokines produced during the physiological response mounted to combat a viral infection. In bone marrow hematopoiesis, IFN-I induce proliferation of HSC. Clinically, patients treated with IFN-I, as well as individuals suffering from IFN-I associated chronic disease, often exhibit sustained hematological cytopenias and HSC failure. The precise molecular mechanisms that govern HSC behavior in response to IFN-I are still unclear. Our data highlights that the deficiency of Scribble in HSC rendered them insensitive to IFN-I mediated activation. As a result, Scribble deficient HSC treated with IFN-I are functionally more fit, displaying increased competitive reconstitution abilities during serial transplantations. No discernible differences in Stat-1 (the major effector of IFN-I signaling) activity were observed when measuring phosphorylation status, nuclear translocation and transcriptional response within wild-type (Wt) and Scribble deficient HSC following IFN-I exposure. Ly6a transcript levels are appropriately upregulated following IFN-I stimulation, however the encoded stem cell antigen-1 (Sca-1) protein localization was significantly decreased on the membrane surface. These data provide compelling evidence for a role of Scribble in coordinating HSC endosomal membrane trafficking to drive IFN-I mediated HSC activation.
Jose Cancelas-Perez, M.D. (Committee Chair)
Marie-Dominique Filippi, Ph.D. (Committee Member)
Hartmut Geiger, Ph.D. (Committee Member)
Qing Richard Lu, Ph.D. (Committee Member)
Daniel Starczynowski, Ph.D. (Committee Member)
Yi Zheng, Ph.D. (Committee Member)
129 p.
Cellular Biology
Hematopoietic stem cells; hematopoiesis; Fate; Scribble; Polarity; Interferon

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Citations

  • Althoff, M. J. (2020). Cell polarity in hematopoietic stem cell quiescence, signaling and fate determination [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1583999632089058

    APA Style (7th edition)

  • Althoff, Mark. Cell polarity in hematopoietic stem cell quiescence, signaling and fate determination. 2020. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1583999632089058.

    MLA Style (8th edition)

  • Althoff, Mark. "Cell polarity in hematopoietic stem cell quiescence, signaling and fate determination." Doctoral dissertation, University of Cincinnati, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1583999632089058

    Chicago Manual of Style (17th edition)

ucin1583999632089058
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This open access ETD is published by University of Cincinnati and OhioLINK.
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