Characterization of ATP-gated P2X7 receptors in fish provides new insights into the mechanism of release of the leaderless cytokine interleukin-1 beta.
Mammalian interleukin-1beta (IL-1beta) is produced as a biologically inactive precursor molecule, which is proteolytically cleaved to an active form by IL-1beta-converting enzyme (ICE) after the activation of P2X(7) receptor by extracellular ATP. The mechanism of IL-1beta release in non-mammalian vertebrates is largely unknown, although most of the IL-1beta gene sequences lack a conserved ICE recognition site. Here we have cloned the P2X(7) receptor from the bony fish seabream and compared agonist and antagonist profiles at this and other non-mammalian P2X(7) receptors expressed in HEK cells, as well in seabream SAF-1 cells expressing endogenous P2X(7) receptors. We used this information to further investigate the mechanisms of IL-1beta release induced by mammalian and fish P2X(7) receptors. Despite phosphatidylserine externalization and cell permeabilization in seabream leukocytes after the addition of high BzATP concentrations, IL-1beta remained unprocessed within the cell. However, activation of rat P2X(7) receptors ectopically expressed in HEK293 together with human ICE led to the specific secretion of unprocessed seabream IL-1beta. In contrast, neither seabream nor zebrafish P2X(7) receptors induced the secretion of mammalian or fish IL-1beta when expressed in HEK293, while a chimeric receptor harboring the ATP-binding domain of seabream P2X(7) and the intracellular region of its rat counterpart did so. These findings indicate that P2X(7) receptor-mediated activation of ICE and release of IL-1beta result from different downstream signaling pathways and suggest that although the mechanisms involved in IL-1beta secretion are conserved throughout evolution, distinct inflammatory signals have been selected for the secretion of this cytokine in different vertebrates.
López-Castejón
Gloria
G
Department of Cell Biology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain.
Young
Mark T
MT
Meseguer
José
J
Surprenant
Annmarie
A
Mulero
Victoriano
V
D000255:Adenosine Triphosphate / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D053583:Interleukin-1beta / Q000737:chemistry / Q000378:metabolism*; D015640:Ion Channel Gating / Q000276:immunology*; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals / Q000502:physiology*; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D058486:Receptors, Purinergic P2X7; D021541:Sea Bream / Q000378:metabolism*; D014981:Xenopus; D015027:Zebrafish
D053583:Interleukin-1beta; C546468:P2RX7 protein, human; C546470:P2rx7 protein, rat; D021382:Protein Sorting Signals; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D000255:Adenosine Triphosphate