Sam68 impedes the recovery of arterial injury by augmenting inflammatory response

J Mol Cell Cardiol. 2019 Dec:137:82-92. doi: 10.1016/j.yjmcc.2019.10.003. Epub 2019 Oct 19.

Abstract

Objective: The role of Src-associated-in-mitosis-68-kDa (Sam68) in cardiovascular biology has not been studied. A recent report suggests that Sam68 promotes TNF-α-induced NF-κB activation in fibroblasts. Here we sought to dissect the molecular mechanism by which Sam68 regulates NF-κB signaling and its functional significance in vascular injury.

Approach and results: The endothelial denudation injury was induced in the carotid artery of Sam68-null (Sam68-/-) and WT mice. Sam68-/- mice displayed an accelerated re-endothelialization and attenuated neointima hyperplasia, which was associated with a reduced macrophage infiltration and lowered expression of pro-inflammatory cytokines in the injured vessels. Remarkably, the ameliorated vascular remodeling was recapitulated in WT mice after receiving transplantation of bone marrow (BM) from Sam68-/- mice, suggesting the effect was attributable to BM-derived inflammatory cells. In cultured Raw264.7 macrophages, knockdown of Sam68 resulted in a significant reduction in the TNF-α-induced expression of TNF-α, IL-1β, and IL-6 and in the level of nuclear phospho-p65, indicating attenuated NF-κB activation; and these results were confirmed in peritoneal and BM-derived macrophages of Sam68-/- vs. WT mice. Furthermore, co-immunoprecipitation and mass-spectrometry identified Filamin A (FLNA) as a novel Sam68-interacting protein upon TNF-α treatment. Loss- and gain-of-function experiments suggest that Sam68 and FLNA are mutually dependent for NF-κB activation and pro-inflammatory cytokine expression, and that the N-terminus of Sam68 is required for TRAF2-FLNA interaction.

Conclusions: Sam68 promotes pro-inflammatory response in injured arteries and impedes recovery by interacting with FLNA to stabilize TRAF2 on the cytoskeleton and consequently potentiate NF-κB signaling.

Keywords: Filamin a; Inflammation; Macrophage; NF-κB; Restenosis; Sam68; TNF-α.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • Carotid Arteries / pathology*
  • Cytokines / genetics
  • Cytokines / metabolism
  • Endothelium, Vascular / metabolism
  • Endothelium, Vascular / pathology
  • Filamins / metabolism
  • Gene Deletion
  • Hyperplasia
  • Inflammation / pathology*
  • Inflammation Mediators / metabolism
  • Macrophages / pathology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • NF-kappa B / metabolism
  • Neointima / pathology
  • RAW 264.7 Cells
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA-Binding Proteins / metabolism*
  • Tumor Necrosis Factor-alpha / pharmacology

Substances

  • Adaptor Proteins, Signal Transducing
  • Cytokines
  • Filamins
  • Inflammation Mediators
  • Khdrbs1 protein, mouse
  • NF-kappa B
  • RNA, Messenger
  • RNA-Binding Proteins
  • Tumor Necrosis Factor-alpha