Regular Article
Effects of cAMP on Intercellular Coupling and Osteoblast Differentiation

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Abstract

Bone-forming cells are organized in a multicellular network interconnected by gap junctions. Direct intercellular communication via gap junctions is an important component of bone homeostasis, coordinating cellular responses to external signals and promoting osteoblast differentiation. The cAMP pathway, a major intercellular signal transduction mechanism, regulates osteoblastic function and metabolism. We investigated the effects of this second messenger on junctional communication and on the expression of differentiation markers in human HOBIT osteoblastic cells. Increased levels of cAMP induce posttranslational modifications (i.e., phosphorylations) of connexin43 and enhancement of gap junction assembly, resulting in an increased junctional permeance to Lucifer yellow and to a positive modulation of intercellular Ca2+ waves. Increased intercellular communication, however, was accompanied by a parallel decrease of alkaline phosphatase activity and by an increase of osteocalcin expression. cAMP-dependent stimulation of cell-to-cell coupling induces a complex modulation of bone differentiation markers.

References (28)

  • Y. Wang et al.

    Clustering of Cx43 cell-to-cell channels into gap junction plaques: Regulation by cAMP and microfilaments

    J. Cell. Sci.

    (1995)
  • P.P. Metha et al.

    Transcription of the gene for the gap junctional protein connexin43 and expression of functional cell-to-cell channels are regulated by cAMP

    Mol. Biol. Cell

    (1992)
  • P.C. Schiller et al.

    Parathyroid hormone up-regulation of connexin 43 gene expression in osteoblasts depends on cell phenotype

    J. Bone Min. Res.

    (1997)
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