Dual mechanism of intercellular communication in HOBIT osteoblastic cells: a role for gap-junctional hemichannels.
Intercellular communication allows tissue coordination of cell metabolism and sensitivity to extracellular stimuli. Paracrine stimulation and cell-to-cell coupling through gap junctions induce the formation of complex cellular networks, which favors the intercellular exchange of nutrients and second messengers. Intercellular Ca2+ signaling was investigated in human osteoblast-like initial transfectant (HOBIT) cells, a human osteoblastic cell line in which cells retain most of the osteoblastic differentiation markers. HOBIT cells express connexin43 (Cx43) clustered at the cell-to-cell boundary and display functional intercellular coupling as assessed by the intercellular transfer of Lucifer yellow. Mechanical stimulation of a single cell induced a wave of increased Ca2+ that was radially propagated to surrounding cells. Treatment of cells with thapsigargin blocked mechanically induced signal propagation. Intercellular Ca2+ spreading and dye transfer were inhibited by 18alpha-glycyrrhetinic acid (18-GA), showing the involvement of gap junctions in signal propagation. Pretreatment of cells with suramin or with apyrase decreased the extent of wave propagation, suggesting that ATP-mediated paracrine stimulation contribute to cell-to-cell signaling. The functional expression of gap-junctional hemichannels was evidenced in experiments of Mn2+ quenching, extracellular dye uptake, and intracellular Ca2+ release, activated by uptake of inositol 1,4,5-trisphosphate (InsP3) from the external medium. Gap-junctional hemichannels were activated by low extracellular Ca2+ concentrations and inhibited by 18-GA. A role for Cx hemichannels in adenosine triphosphate (ATP) release and paracrine stimulation is suggested.
Romanello
M
M
Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, Università di Trieste, Italy.
D'Andrea
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000328:Adult; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D002450:Cell Communication; D002460:Cell Line; D002461:Cell Line, Transformed; D018031:Connexin 43 / Q000032:analysis; D017630:Connexins / Q000032:analysis / Q000037:antagonists & inhibitors*; D017629:Gap Junctions / Q000378:metabolism*; D006034:Glycyrrhetinic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D058919:Purinergic P2 Receptor Antagonists; D000097002:Gap Junction beta-1 Protein
D000255:Adenosine Triphosphate; D002118:Calcium; D018031:Connexin 43; D017630:Connexins; D006034:Glycyrrhetinic Acid; D015544:Inositol 1,4,5-Trisphosphate; D008345:Manganese; D058919:Purinergic P2 Receptor Antagonists; D000097002:Gap Junction beta-1 Protein; C119129:18alpha-glycyrrhetinic acid