Lnk controls mouse hematopoietic stem cell self-renewal and quiescence through direct interactions with JAK2

Abstract

In addition to its role in megakaryocyte production, signaling initiated by thrombopoietin (TPO) activation of its receptor, myeloproliferative leukemia virus protooncogene (c-Mpl, or Mpl), controls HSC homeostasis and self-renewal. Under steady-state conditions, mice lacking the inhibitory adaptor protein Lnk harbor an expanded HSC pool with enhanced self-renewal. We found that HSCs from Lnk -/-mice have an increased quiescent fraction, decelerated cell cycle kinetics, and enhanced resistance to repeat treatments with cytoablative 5-fluorouracil in vivo compared with WT HSCs. We further provide genetic evidence demonstrating that Lnk controls HSC quiescence and self-renewal, predominantly through Mpl. Consistent with this observation, Lnk -/-HSCs displayed potentiated activation of JAK2 specifically in response to TPO. Biochemical experiments revealed that Lnk directly binds to phosphorylated tyrosine residues in JAK2 following TPO stimulation. Of note, the JAK2 V617F mutant, found at high frequencies in myeloproliferative diseases, retains the ability to bind Lnk. Therefore, we identified Lnk as a physiological negative regulator of JAK2 in stem cells and TPO/Mpl/JAK2/Lnk as a major regulatory pathway in controlling stem cell self-renewal and quiescence.

LNK mutation studies in blast-phase myeloproliferative neoplasms, and in chronic-phase disease with TET2, IDH, JAK2 or MPL mutations

“…LNK is a negative regulator of thrombopoietinFthrombopoietin receptor (MPL)-mediated JAK2 activation; LNK-deficient mice exhibit increased number of megakaryocytes with increased ploidy, 5 increased number of erythrocyte progenitors, 6 as well as an expanded hematopoietic stem cell pool with enhanced self renewal. 7 LNK has been shown to down regulate signaling downstream of MPLW515L and JAK2V617F in vitro. 8,9 Indeed, in a transduction-transplant murine model, LNK deficiency accelerates and exacerbates MPN development induced by TEL-JAK2 and JAK2V617F.…”

Lnk Deletion Reinforces the Function of Bone Marrow Progenitors in Promoting Neovascularization and Astrogliosis Following Spinal Cord Injury

“…Lnk is an adaptor protein expressed in KSL cells and believed to negatively regulate the key signaling pathways for the proliferation of KSL cells such as stem cell factor (SCF) signaling and thrombopoietin signaling [10][11][12]. In Lnk-deficient mice, the proliferation of KSL cells is upregulated and the number of KSL cells in bone marrow is increased compared to that in wild-type mice [10].…”

Regulation of Hematopoietic Stem Cell Fate: Self-Renewal, Quiescence and Survival

“…Furthermore, Lnk-deficient HSCs show higher levels of symmetric proliferation in response to thrombopoietin (TPO) in ex vivo culture than wildtype HSCs (Seita et al, 2007). Biochemical analyses revealed that Lnk directly binds to phosphorylated tyrosine residues in JAK2 after TPO stimulation (Bersenev et al, 2008). Therefore, Lnk is a physiologic negative regulator of JAK2 in HSCs, and TPO/cMpl/JAK2/Lnk constitute a major regulatory pathway controlling HSC quiescence and selfrenewal.…”