Cell surface nucleolin interacts with and internalizes Bothrops asper Lys49 phospholipase A2 and mediates its toxic activity

Sci Rep. 2018 Jul 13;8(1):10619. doi: 10.1038/s41598-018-28846-4.

Abstract

Phospholipases A2 are a major component of snake venoms. Some of them cause severe muscle necrosis through an unknown mechanism. Phospholipid hydrolysis is a possible explanation of their toxic action, but catalytic and toxic properties of PLA2s are not directly connected. In addition, viperid venoms contain PLA2-like proteins, which are very toxic even if they lack catalytic activity due to a critical mutation in position 49. In this work, the PLA2-like Bothrops asper myotoxin-II, conjugated with the fluorophore TAMRA, was found to be internalized in mouse myotubes, and in RAW264.7 cells. Through experiments of protein fishing and mass spectrometry analysis, using biotinylated Mt-II as bait, we found fifteen proteins interacting with the toxin and among them nucleolin, a nucleolar protein present also on cell surface. By means of confocal microscopy, Mt-II and nucleolin were shown to colocalise, at 4 °C, on cell membrane where they form Congo-red sensitive assemblies, while at 37 °C, 20 minutes after the intoxication, they colocalise in intracellular spots going from plasmatic membrane to paranuclear and nuclear area. Finally, nucleolin antagonists were found to inhibit the Mt-II internalization and toxic activity and were used to identify the nucleolin regions involved in the interaction with the toxin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bothrops
  • Cell Membrane / metabolism
  • Cell Nucleus / metabolism
  • Crotalid Venoms / metabolism*
  • Crotalid Venoms / toxicity
  • Group II Phospholipases A2 / metabolism*
  • Group II Phospholipases A2 / toxicity
  • HeLa Cells
  • Humans
  • Hydrolysis
  • Intravital Microscopy
  • Mice
  • Microscopy, Confocal
  • Muscle Fibers, Skeletal
  • Neurotoxins / metabolism*
  • Neurotoxins / toxicity
  • Nucleolin
  • Phosphoproteins / antagonists & inhibitors
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism*
  • Primary Cell Culture
  • Protein Binding / drug effects
  • Protein Domains
  • RAW 264.7 Cells
  • RNA Interference
  • RNA-Binding Proteins / antagonists & inhibitors
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Reptilian Proteins / metabolism*
  • Reptilian Proteins / toxicity

Substances

  • Crotalid Venoms
  • Neurotoxins
  • Phosphoproteins
  • RNA-Binding Proteins
  • Reptilian Proteins
  • Group II Phospholipases A2
  • myotoxin II, Bothrops asper