CXCL12 secretion by bone marrow stromal cells is dependent on cell contact and mediated by connexin-43 and connexin-45 gap junctions


The chemokine CXCL12 is essential for the function of hematopoietic stem and progenitor cells. Here we report that secretion of functional CXCL12 from human bone marrow stromal cells (BMSCs) was a cell contact–dependent event mediated by connexin-43 (Cx43) and Cx45 gap junctions. Inhibition of connexin gap junctions impaired the secretion of CXCL12 and homing of leukocytes to mouse bone marrow. Purified human CD34+ progenitor cells did not adhere to noncontacting BMSCs, which led to a much smaller pool of immature cells. Calcium conduction activated signaling by cAMP–protein kinase A (PKA) and induced CXCL12 secretion mediated by the GTPase RalA. Cx43 and Cx45 additionally controlled Cxcl12 transcription by regulating the nuclear localization of the transcription factor Sp1. We suggest that BMSCs form a dynamic syncytium via connexin gap junctions that regulates CXC12 secretion and the homeostasis of hematopoietic stem cells.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Secretion of functional CXCL12 in the bone marrow correlates with expression of Cx43 and Cx45 and gap-junction activity.
Figure 2: CXCL12 secretion is cell contact dependent, but CXCL12 production is not.
Figure 3: Cx43 and Cx45 gap junctions directly regulate CXCL12 secretion.
Figure 4: Cx43 and Cx45 regulate Cxcl12 transcription by localizing Sp1 to the nucleus.
Figure 5: Calcium internalization controls the secretion of CXCL12 from BMSCs.
Figure 6: Calcium internalization results in more cAMP and PKA activation, which in turn induces the secretion of CXCL12 from BMSCs via RalA.
Figure 7: Maintenance of CD34+CD38 primitive properties by stromal networks.


  1. 1

    Scadden, D.T. The stem-cell niche as an entity of action. Nature 441, 1075–1079 (2006).

    CAS  Article  Google Scholar 

  2. 2

    Sugiyama, T., Kohara, H., Noda, M. & Nagasawa, T. Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches. Immunity 25, 977–988 (2006).

    CAS  Article  Google Scholar 

  3. 3

    Nie, Y.C., Han, Y.C. & Zou, Y.R. CXCR4 is required for the quiescence of primitive hematopoietic cells. J. Exp. Med. 205, 777–783 (2008).

    CAS  Article  Google Scholar 

  4. 4

    Broxmeyer, H.E. et al. Stromal cell-derived factor-1/CXCL12 directly enhances survival/antiapoptosis of myeloid progenitor cells through CXCR4 and Gai proteins and enhances engraftment of competitive, repopulating stem cells. J. Leukoc. Biol. 73, 630–638 (2003).

    CAS  Article  Google Scholar 

  5. 5

    Nagasawa, T. et al. Defects of B-cell lymphopoiesis and bone-marrow myelopoiesis in mice lacking the CXC chemokine PBSF/SDF-1. Nature 382, 635–638 (1996).

    CAS  Article  Google Scholar 

  6. 6

    Peled, A. et al. Dependence of human stem cell engraftment and repopulation of NOD/SCID mice on CXCR4. Science 283, 845–848 (1999).

    CAS  Article  Google Scholar 

  7. 7

    Glimm, H., Tang, P., Clark-Lewis, I., von Kalle, C. & Eaves, C. Ex vivo treatment of proliferating human cord blood stem cells with stroma-derived factor-1 enhances their ability to engraft NOD/SCID mice. Blood 99, 3454–3457 (2002).

    CAS  Article  Google Scholar 

  8. 8

    Dar, A., Kollet, O. & Lapidot, T. Mutual, reciprocal SDF-1/CXCR4 interactions between hematopoietic and bone marrow stromal cells regulate human stem cell migration and development in NOD/SCID chimeric mice. Exp. Hematol. 34, 967–975 (2006).

    CAS  Article  Google Scholar 

  9. 9

    Dar, A. et al. Chemokine receptor CXCR4-dependent internalization and resecretion of functional chemokine SDF-1 by bone marrow endothelial and stromal cells. Nat. Immunol. 6, 1038–1046 (2005).

    CAS  Article  Google Scholar 

  10. 10

    Ponomaryov, T. et al. Induction of the chemokine stromal-derived factor-1 following DNA damage improves human stem cell function. J. Clin. Invest. 106, 1331–1339 (2000).

    CAS  Article  Google Scholar 

  11. 11

    Kortesidis, A. et al. Stromal-derived factor-1 promotes the growth, survival, and development of human bone marrow stromal stem cells. Blood 105, 3793–3801 (2005).

    CAS  Article  Google Scholar 

  12. 12

    Petit, I. et al. G-CSF induces stem cell mobilization by decreasing bone marrow SDF-1 and up-regulating CXCR4. Nat. Immunol. 3, 687–694 (2002).

    CAS  Article  Google Scholar 

  13. 13

    Kollet, O. et al. HGF, SDF-1, and MMP-9 are involved in stress-induced human CD34+ stem cell recruitment to the liver. J. Clin. Invest. 112, 160–169 (2003).

    CAS  Article  Google Scholar 

  14. 14

    Giepmans, B.N.G. Gap junctions and connexin-interacting proteins. Cardiovasc. Res. 62, 233–245 (2004).

    CAS  Article  Google Scholar 

  15. 15

    Evans, W.H., De Vuyst, E. & Leybaert, L. The gap junction cellular internet: connexin hemichannels enter the signalling limelight. Biochem. J. 397, 1–14 (2006).

    CAS  Article  Google Scholar 

  16. 16

    Rosendaal, M., Green, C.R., Rahman, A. & Morgan, D. Up-regulation of the connexin43+ gap junction network in haemopoietic tissue before the growth of stem cells. J. Cell Sci. 107, 29–37 (1994).

    CAS  PubMed  Google Scholar 

  17. 17

    Cancelas, J.A. et al. Connexin-43 gap junctions are involved in multiconnexin-expressing stromal support of hemopoietic progenitors and stem cells. Blood 96, 498–505 (2000).

    CAS  PubMed  Google Scholar 

  18. 18

    Mendez-Ferrer, S. et al. Mesenchymal and haematopoietic stem cells form a unique bone marrow niche. Nature 466, 829–834 (2010).

    CAS  Article  Google Scholar 

  19. 19

    Reaume, A.G. et al. Cardiac malformation in neonatal mice lacking connexin43. Science 267, 1831–1834 (1995).

    CAS  Article  Google Scholar 

  20. 20

    Flenniken, A.M. et al. A Gja1 missense mutation in a mouse model of oculodentodigital dysplasia. Development 132, 4375–4386 (2005).

    CAS  Article  Google Scholar 

  21. 21

    Presley, C.A. et al. Bone marrow connexin-43 expression is critical for hematopoietic regeneration after chemotherapy. Cell Commun. Adhes. 12, 307–317 (2005).

    CAS  Article  Google Scholar 

  22. 22

    Krieger, N.S., Frick, K.K. & Bushinsky, D.A. Mechanism of acid-induced bone resorption. Curr. Opin. Nephrol. Hypertens. 13, 423–436 (2004).

    CAS  Article  Google Scholar 

  23. 23

    Adams, G.B. et al. Stem cell engraftment at the endosteal niche is specified by the calcium-sensing receptor. Nature 439, 599–603 (2006).

    CAS  Article  Google Scholar 

  24. 24

    Bergh, J.J., Xu, Y.H. & Farach-Carson, M.C. Osteoprotegerin expression and secretion are regulated by calcium influx through the L-type voltage-sensitive calcium channel. Endocrinology 145, 426–436 (2004).

    CAS  Article  Google Scholar 

  25. 25

    Cartin, L., Lounsbury, K.M. & Nelson, M.T. Coupling of Ca2+ to CREB activation and gene expression in intact cerebral arteries from mouse: roles of ryanodine receptors and voltage-dependent Ca2+ channels. Circ. Res. 86, 760–767 (2000).

    CAS  Article  Google Scholar 

  26. 26

    Willoughby, D. & Cooper, D.M.F. Organization and Ca2+ regulation of adenylyl cyclases in cAMP microdomains. Physiol. Rev. 87, 965–1010 (2007).

    CAS  Article  Google Scholar 

  27. 27

    Semerad, C.L. et al. G-CSF potently inhibits osteoblast activity and CXCL12 mRNA expression in the bone marrow. Blood 106, 3020–3027 (2005).

    CAS  Article  Google Scholar 

  28. 28

    Sacchetti, B. et al. Self-renewing osteoprogenitors in bone marrow sinusoids can organize a hematopoietic microenvironment. Cell 131, 324–336 (2007).

    CAS  Article  Google Scholar 

  29. 29

    Omatsu, Y. et al. The essential functions of adipo-osteogenic progenitors as the hematopoietic stem and progenitor cell niche. Immunity 33, 387–399 (2010).

    CAS  Article  Google Scholar 

  30. 30

    Grenier, A. et al. Presence of a mobilizable intracellular pool of hepatocyte growth factor in human polymorphonuclear neutrophils. Blood 99, 2997–3004 (2002).

    CAS  Article  Google Scholar 

  31. 31

    Spiegel, A. et al. Unique SDF-1-induced activation of human precursor-B ALL cells as a result of altered CXCR4 expression and signaling. Blood 103, 2900–2907 (2004).

    CAS  Article  Google Scholar 

  32. 32

    Evans, W.H. & Boitano, S. Connexin mimetic peptides: specific inhibitors of gap-junctional intercellular communication. Biochem. Soc. Trans. 29, 606–612 (2001).

    Article  Google Scholar 

  33. 33

    Maxeiner, S. et al. Deletion of connexin45 in mouse retinal neurons disrupts the rod/cone signaling pathway between AII amacrine and ON cone bipolar cells and leads to impaired visual transmission. J. Neurosci. 25, 566–576 (2005).

    CAS  Article  Google Scholar 

  34. 34

    Garcia-Moruja, C. et al. Functional characterization of SDF-1 proximal promoter. J. Mol. Biol. 348, 43–62 (2005).

    CAS  Article  Google Scholar 

  35. 35

    Mendez-Ferrer, S., Lucas, D., Battista, M. & Frenette, P.S. Haematopoietic stem cell release is regulated by circadian oscillations. Nature 452, 442–447 (2008).

    CAS  Article  Google Scholar 

  36. 36

    Montminy, M. Transcriptional regulation by cyclic AMP. Annu. Rev. Biochem. 66, 807–822 (1997).

    CAS  Article  Google Scholar 

  37. 37

    Rondaij, M.G. et al. Guanine exchange factor RalGDS mediates exocytosis of Weibel-Palade bodies from endothelial cells. Blood 112, 56–63 (2008).

    CAS  Article  Google Scholar 

  38. 38

    Ljubicic, S., Bezzi, P., Vitale, N. & Regazzi, R. The GTPase RalA regulates different steps of the secretory process in pancreatic beta-cells. PLoS ONE 4, e7770 (2009).

    Article  Google Scholar 

  39. 39

    Szumilas, P. et al. Effect of stem cell mobilization with cyclophosphamide plus granulocyte colony-stimulating factor on morphology of haematopoietic organs in mice. Cell Prolif. 38, 47–61 (2005).

    CAS  Article  Google Scholar 

  40. 40

    Kollet, O. et al. Osteoclasts degrade endosteal components and promote mobilization of hematopoietic progenitor cells. Nat. Med. 12, 657–664 (2006).

    CAS  Article  Google Scholar 

  41. 41

    Spiegel, A., Kalinkovich, A., Shivtiel, S., Kollet, O. & Lapidot, T. Stem cell regulation via dynamic interactions of the nervous and immune systems with the microenvironment. Cell Stem Cell 3, 484–492 (2008).

    CAS  Article  Google Scholar 

  42. 42

    Katayama, Y. et al. Signals from the sympathetic nervous system regulate hematopoietic stem cell egress from bone marrow. Cell 124, 407–421 (2006).

    CAS  Article  Google Scholar 

  43. 43

    Adams, G.B. & Scadden, D.T. The hematopoietic stem cell in its place. Nat. Immunol. 7, 333–337 (2006).

    CAS  Article  Google Scholar 

  44. 44

    Arai, F. & Suda, T. Maintenance of quiescent hematopoietic stem cells in the osteoblastic niche. Ann. NY Acad. Sci. 1106, 41–53 (2007).

    CAS  Article  Google Scholar 

  45. 45

    Kiel, M.J. & Morrison, S.J. Uncertainty in the niches that maintain haematopoietic stem cells. Nat. Rev. Immunol. 8, 290–301 (2008).

    CAS  Article  Google Scholar 

  46. 46

    Zhang, J.W. & Li, L.H. Stem cell niche: Microenvironment and beyond. J. Biol. Chem. 283, 9499–9503 (2008).

    CAS  Article  Google Scholar 

  47. 47

    Chaytor, A.T., Evens, W.H. & Griffith, T.M. Central role of heterocellular gap junctional communication in endothelium-dependent relaxations of rabbit arteries. J. Physiol. 508, 561–573 (1998).

    CAS  Article  Google Scholar 

  48. 48

    Li, X. & Simard, J.M. Connexin45 gap junction channels in rat cerebral vascular smooth muscle cells. Am. J. Physiol. Heart Circ. Physiol. 281, H1890–H1898 (2001).

    CAS  Article  Google Scholar 

  49. 49

    Sorensen, C.M., Salomonsson, M., Braunstein, T.H., Nielsen, M.S. & Holstein-Rathlou, N.H. Connexin mimetic peptides fail to inhibit vascular conducted calcium responses in renal arterioles. Am. J. Physiol. Regul. Integr. Comp. Physiol. 295, R840–R847 (2008).

    CAS  Article  Google Scholar 

  50. 50

    Sorensen, C.M., Salomonsson, M., Braunstein, T.H., Nielsen, M.S. & Holstein-Rathlou, N.H. Connexin mimetic peptides fail to inhibit vascular conducted calcium responses in renal arterioles. Am. J. Physiol. Regul. Integr. Comp. Physiol. 295, R840–R847 (2008). First published July 9, 2008; doi:10.1152/ajpregu.00491.2007 ( Am. J. Physiol. Regul. Integr. Comp. Physiol. 298, R243 (2010).

    CAS  Article  PubMed  Google Scholar 

  51. 51

    Hozumi, K. et al. Delta-like 1 is necessary for the generation of marginal zone B cells but not T cells in vivo. Nat. Immunol. 5, 638–644 (2004).

    CAS  Article  Google Scholar 

Download references


We thank J. Von Maltzen and K. Willecke (Institute of Genetics Division of Molecular Genetics, University of Bonn, Bonn, Germany) for BMSCs with loxP-flanked Cx45 that express Cre from the myxovirus promoter; G. Lalli (King's College London) for plasmids encoding Myc tag alone or Myc-tagged dominant negative RalA; M. Segal for helping with real-time calcium imaging; R. Alon, N. Dekel and I.H. Oh for discussions; and C.M. Sorensen for advice on connexin mimetic peptides. Supported by the Israeli Science Foundation (ISF 544/09), the European Union (Advance Cell-based Therapies for the Treatment of Primary Immunodeficiency HEALTH-F5-2010-261387) and The Edith Arnoff Stein Professorial Chair in Stem Cell Research (T.L.).

Author information




A.S. designed and did the research, collected and analyzed data, and wrote the manuscript; T.I., G.D., A.K., K.G. and A.L. helped with designing and doing experiments; D.C. did and analyzed real time calcium imaging; Z.S. did dominant negative experiments; A.A. and A.N. supplied human bone marrow aspiration samples and mobilized blood samples from healthy donors; O.K. helped with designing experiments; R.S. designed the research; and T.L. designed the research and wrote the manuscript.

Corresponding author

Correspondence to Tsvee Lapidot.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–5 and Supplementary Tables 1–2 (PDF 2425 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Schajnovitz, A., Itkin, T., D'Uva, G. et al. CXCL12 secretion by bone marrow stromal cells is dependent on cell contact and mediated by connexin-43 and connexin-45 gap junctions. Nat Immunol 12, 391–398 (2011).

Download citation

Further reading