title: Lnk negatively regulates self-renewal of hematopoietic stem cells by modifying thrombopoietin-mediated signal transduction.
abstract: One of the central tasks of stem cell biology is to understand the molecular mechanisms that control self-renewal in stem cells. Several cytokines are implicated as crucial regulators of hematopoietic stem cells (HSCs), but little is known about intracellular signaling for HSC self-renewal. To address this issue, we attempted to clarify how self-renewal potential is enhanced in HSCs without the adaptor molecule Lnk, as in Lnk-deficient mice HSCs are expanded in number >10-fold because of their increased self-renewal potential. We show that Lnk negatively regulates self-renewal of HSCs by modifying thrombopoietin (TPO)-mediated signal transduction. Single-cell cultures showed that Lnk-deficient HSCs are hypersensitive to TPO. Competitive repopulation revealed that long-term repopulating activity increases in Lnk-deficient HSCs, but not in WT HSCs, when these cells are cultured in the presence of TPO with or without stem cell factor. Single-cell transplantation of each of the paired daughter cells indicated that a combination of stem cell factor and TPO efficiently induces symmetrical self-renewal division in Lnk-deficient HSCs but not in WT HSCs. Newly developed single-cell immunostaining demonstrated significant enhancement of both p38 MAPK inactivation and STAT5 and Akt activation in Lnk-deficient HSCs after stimulation with TPO. Our results suggest that a balance in positive and negative signals downstream from the TPO signal plays a role in the regulation of the probability of self-renewal in HSCs. In general, likewise, the fate of stem cells may be determined by combinational changes in multiple signal transduction pathways.
authors.affiliation: Laboratory of Stem Cell Therapy, Center for Experimental Medicine, University of Tokyo, 4-6-1 Shirokanedai, Tokyo 108-8639, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Seita
authors.forename: Hideo
authors.initials: H
authors.lastname: Ema
authors.forename: Jun
authors.initials: J
authors.lastname: Ooehara
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamazaki
authors.forename: Yuko
authors.initials: Y
authors.lastname: Tadokoro
authors.forename: Akiko
authors.initials: A
authors.lastname: Yamasaki
authors.forename: Koji
authors.initials: K
authors.lastname: Eto
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takaki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Takatsu
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Nakauchi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002455:Cell Division / Q000187:drug effects*; D002478:Cells, Cultured; D016207:Cytokines; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D013926:Thrombopoietin / Q000494:pharmacology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D016207:Cytokines; D047908:Intracellular Signaling Peptides and Proteins; C490777:Lnk protein, mouse; D008565:Membrane Proteins; D011506:Proteins; D013926:Thrombopoietin; D011494:Protein Kinases