Article

Lnk negatively regulates self-renewal of hematopoietic stem cells by modifying thrombopoietin-mediated signal transduction.

Laboratory of Stem Cell Therapy, Center for Experimental Medicine, University of Tokyo, 4-6-1 Shirokanedai, Tokyo 108-8639, Japan.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 02/2007; 104(7):2349-54. DOI: 10.1073/pnas.0606238104
Source: PubMed

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.

0 Bookmarks
 · 
102 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cardiovascular disease has become the main factor of death and birth defects in the world and also in Iran. New clinical studies have shown that early diagnosis of patients with coronary artery disease (CAD) can contribute to effective prevention or therapeutic structures, which reduce mortality or the next chance of cardiovascular events, and increase the quality of life. Most studies on CAD disease and its genetic risk factors so far, have been done excluding the Iranian population. PubMed was used to search for all relevant studies published on or before 2013 and rs3184504 was selected for association study for CAD. A total of 200 subjects with 100 cases and 100 controls were ultimately included in the analysis. Blood samples were collected and after DNA extraction the DNA analysis was performed by TaqMan Probe Real Time PCR to evaluate the association between candidate variant with the disease and some blood biochemical factors. Our study demonstrated that there was not a direct association between rs3184504 C>T variant with risk of CAD in Iranian population, whereas, there is a significant association between this variant with increased blood LDL and diastolic blood pressure. Further molecular analysis and other disease association studies are necessary in the Iranian population.
    International journal of molecular and cellular medicine. 01/2014; 3(3):157-65.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Throughout life, hematopoietic stem cells (HSCs) sustain the blood cell supply through their capacities for self-renewal and multilineage differentiation. These processes are regulated within a specialized microenvironment termed the 'niche'. Here, we show a novel mechanism for regulating HSC function that is mediated by nephroblastoma overexpressed (Nov/CCN3), a matricellular protein member of the CCN family. We found that Nov contributes to the maintenance of long-term repopulating (LTR) activity through association with integrin αvβ3 on HSCs. The resultant β3 integrin outside-in signaling is dependent on thrombopoietin (TPO), a crucial cytokine involved in HSC maintenance. TPO was required for Nov binding to integrin αvβ3, and stimulated Nov expression in HSCs. However, in the presence of IFNγ, a cytokine known to impair HSC function, not only was TPO-induced expression of Nov suppressed, but the LTR activity was conversely impaired by TPO-mediated ligation of integrin αvβ3 with exogenous ligands, including Nov, as well. Thus, Nov/integrin αvβ3-mediated maintenance of HSCs appears to be modulated by simultaneous stimulation by other cytokines. Our finding suggests that this system contributes to the regulation of HSCs within the bone marrow niche.
    International journal of hematology 02/2014; · 1.17 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: LNK (SH2B3) is an adaptor protein studied extensively in normal and malignant hematopoietic cells. In these cells, it downregulates activated tyrosine kinases at the cell surface resulting in an antiproliferative effect. To date, no studies have examined activities of LNK in solid tumors. In this study, we found by in silico analysis and staining tissue arrays that the levels of LNK expression were elevated in high-grade ovarian cancer. To test the functional importance of this observation, LNK was either overexpressed or silenced in several ovarian cancer cell lines. Remarkably, overexpression of LNK rendered the cells resistant to death induced by either serum starvation or nutrient deprivation, and generated larger tumors using a murine xenograft model. In contrast, silencing of LNK decreased ovarian cancer cell growth in vitro and in vivo. Western blot studies indicated that overexpression of LNK upregulated and extended the transduction of the mitogenic signal, whereas silencing of LNK produced the opposite effects. Furthermore, forced expression of LNK reduced cell size, inhibited cell migration and markedly enhanced cell adhesion. Liquid chromatography-mass spectroscopy identified 14-3-3 as one of the LNK-binding partners. Our results suggest that in contrast to the findings in hematologic malignancies, the adaptor protein LNK acts as a positive signal transduction modulator in ovarian cancers.Oncogene advance online publication, 7 April 2014; doi:10.1038/onc.2014.34.
    Oncogene 04/2014; · 8.56 Impact Factor

Full-text (2 Sources)

Download
14 Downloads
Available from
Jun 4, 2014