Investigating the role of the polarity regulator Scribble in maintenance and polarity formation of hematopoietic stem cells.
Cell Biology
Final Report Abstract
Cell fate determinants regulate cell polarity and may influence self-renewal potential of hematopoietic stem cells. In model systems like drosophila melanogaster, Scribble and Llgl1 belong to the Scribble polarity complex and reveal tumor suppressor functions. In hematopoietic cells, genetic inactivation of Llgl1 leads to expansion of the stem cell pool and increases self-renewal capacity without conferring malignant transformation. In our work supported by this grant of the German Research Council (DFG) we provide first evidence that inactivation of Scribble results in functional impairment of hematopoietic stem cells (HSC) over serial transplantation and during stress. While loss of Scribble deregulates transcriptional downstream effectors involved in stem cell proliferation, cell signaling and cell motility, these effectors do not overlap with transcriptional targets of Llgl1. Binding partner analysis of Scribble in hematopoietic cells using tandem-affinity purification and mass-spectrometry confirms its role in cell signaling and cell motility but not for binding to polarity modules described in drosophila. We could validate these predicted functions in vitro and in vivo: Scrib-deficient hematopoietic stem- and progenitor cells failed in proper adhesion and revealed decreased migratory capacity. These effects were not seen in hematopoietic cells after inactivation of Llgl1. Finally, requirement of Scribble for self-renewal capacity also affects leukemia stem cell function. Thus, Scribble is a regulator of adult HSCs, essential for maintenance of HSCs during phases of cell stress. These results will be used to assess potential applications for translational / clinical use: (1) the modulation of Llgl1 as a possibility to expand human hematopoietic stem cells ex vivo, as loss of Llgl1 did not result in impaired motility, adhesion and migration or induction of neoplasia. (2) the possibility to use modulation of Scrib for therapeutic targeting of leukemia stem cell function in pre-clinical model systems. Given the extensive data on polarity complex formation in model systems such as drosophila melanogaster our hypothesis was based on the assumption that Scribble complex formation could be confirmed by interactome analysis in hematopoietic cells. However, while some polarity regulators appear to influence biology of hematopoietic cells (e.g. CDC42, Llgl1, Scrib) others such as Par-complex members Prkcz or Prkzi had not shown any influence on HSPC function. The surprising part of our analyses were the findings that in contrast to Llgl1, Scrib deletion results in loss of HSC function in vivo. Moreover, interactome analysis of Scrib and Llgl1 did not give any evidence for interaction or complex formation of these partners in hematopoiesis. Finally, the influence of Scrib on HSPC migration and adhesion appeared to be conserved, while these functions were not compromised in Llgl1 deficient cells.
Publications
- Evolutionarily Conserved Signaling Pathways: Acting in the Shadows of Acute Myelogenous Leukemia's Genetic Diversity. Clin Cancer Res. 2015 Jan 15;21(2):240-248
Heidel FH, Arreba-Tutusaus P, Armstrong SA, Fischer T
(See online at https://doi.org/10.1158/1078-0432.CCR-14-1436) - Diverging impact of cell fate determinants Scrib and Llgl1 on adhesion and migration of hematopoietic stem cells. J Cancer Res Clin Oncol. 2018 Aug 6
Dash BP, Schnöder TM, Kathner C, Mohr J, Weinert S, Herzog C, Godavarthy PS, Zanetti C, Perner F, Braun-Dullaeus R, Hartleben B, Huber TB, Walz G, Naumann M, Ellis S, Vasioukhin V, Kähne T, Krause DS and Heidel FH
(See online at https://doi.org/10.1007/s00432-018-2724-3) - The cell fate determinant Scribble is required for maintenance of hematopoietic stem cell function. Leukemia 2018 May;32(5):1211-1221
Mohr J, Dash BP, Schnoeder TM, Wolleschak D, Herzog C, Tubio Santamaria N, Weinert S, Godavarthy S, Zanetti C, Naumann M, Hartleben B, Huber TB, Krause DS, Kähne T, Bullinger L, Heidel FH
(See online at https://doi.org/10.1038/s41375-018-0025-0)
