Characterization of ATP-gated P2X7 receptors in fish provides new insights into the mechanism of release of the leaderless cytokine interleukin-1 beta

Mol Immunol. 2007 Feb;44(6):1286-99. doi: 10.1016/j.molimm.2006.05.015. Epub 2006 Jul 11.

Abstract

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / physiology*
  • Amino Acid Sequence
  • Animals
  • Cell Line
  • Humans
  • Interleukin-1beta / chemistry
  • Interleukin-1beta / metabolism*
  • Ion Channel Gating / immunology*
  • Molecular Sequence Data
  • Protein Sorting Signals / physiology*
  • Rats
  • Receptors, Purinergic P2 / chemistry*
  • Receptors, Purinergic P2 / genetics
  • Receptors, Purinergic P2 / physiology*
  • Receptors, Purinergic P2X7
  • Sea Bream / metabolism*
  • Xenopus
  • Zebrafish

Substances

  • Interleukin-1beta
  • P2RX7 protein, human
  • P2rx7 protein, rat
  • Protein Sorting Signals
  • Receptors, Purinergic P2
  • Receptors, Purinergic P2X7
  • Adenosine Triphosphate