Interaction of surfactant protein A with the intermediate filaments desmin and vimentin

Biochemistry. 2008 May 6;47(18):5127-38. doi: 10.1021/bi800070u. Epub 2008 Apr 12.

Abstract

Surfactant protein A (SP-A), a member of the collectin family that modulates innate immunity, has recently been involved in the physiology of reproduction. Consistent with the activation of ERK-1/2 and COX-2 induced by SP-A in myometrial cells, we reported previously the presence of two major proteins recognized by SP-A in these cells. Here we identify by mass spectrometry one of these SP-A targets as the intermediate filament (IF) desmin. In myometrial preparations derived from desmin-deficient mice, the absence of binding of SP-A to any 50 kDa protein confirmed the identity of this SP-A-binding site as desmin. Our data based on partial chymotrypsin digestion of pure desmin suggested that SP-A recognizes especially its rod domain, which is known to play an important role during the assembly of desmin into filaments. In line with that, electron microscopy experiments showed that SP-A inhibits in vitro the polymerization of desmin filaments. SP-A also recognized in vitro polymerized filaments in a calcium-dependent manner at a physiological ionic strength but not the C1q receptor gC1qR. Furthermore, Texas Red-labeled SP-A colocalized with desmin filaments in myometrial cells. Interestingly, vimentin, the IF characteristic of leukocytes, is one of the major proteins recognized by SP-A in protein extracts of U937 cells after PMA-induced differentiation of this monocytic cell line. Interaction of SP-A with vimentin was further confirmed using recombinant vimentin in solid-phase binding assays. The ability of SP-A to interact with desmin and vimentin, and to prevent polymerization of desmin monomers, shed light on unexpected and wider biological roles of this collectin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Cell Extracts
  • Cells, Cultured
  • Desmin / deficiency
  • Desmin / genetics
  • Desmin / metabolism*
  • Desmin / ultrastructure
  • Humans
  • Intermediate Filaments / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Microscopy, Electron
  • Osmolar Concentration
  • Protein Binding
  • Pulmonary Surfactant-Associated Protein A / chemistry
  • Pulmonary Surfactant-Associated Protein A / metabolism*
  • Pulmonary Surfactant-Associated Protein A / ultrastructure
  • Rats
  • Tandem Mass Spectrometry
  • Vimentin / metabolism*

Substances

  • Cell Extracts
  • Desmin
  • Pulmonary Surfactant-Associated Protein A
  • Vimentin
  • Calcium