Tumor Cell Apoptosis Polarizes Macrophages—Role of Sphingosine-1-Phosphate

Abstract

Macrophage polarization contributes to a number of human pathologies. This is exemplified for tumor-associated macrophages (TAMs), which display a polarized M2 phenotype, closely associated with promotion of angiogenesis and suppression of innate immune responses. We present evidence that induction of apoptosis in tumor cells and subsequent recognition of apoptotic debris by macrophages participates in the macrophage phenotype shift. During coculture of human primary macrophages with human breast cancer carcinoma cells (MCF-7) the latter ones were killed, while macrophages acquired an alternatively activated phenotype. This was characterized by decreased tumor necrosis factor (TNF)-␣ and interleukin (IL) 12-p70 production, but increased formation of IL-8 and -10. Alternative macrophage activation required tumor cell death because a coculture with apoptosis-resistant colon carcinoma cells (RKO) or Bcl-2-overexpressing MCF-7 cells failed to induce phenotype alterations. Interestingly, phenotype alterations were achieved with conditioned media from apoptotic tumor cells, arguing for a soluble factor. Knockdown of sphingosine kinase (Sphk) 2, but not Sphk1, to attenuate S1P formation in MCF-7 cells, restored classical macrophage responses during coculture. Furthermore, macrophage polarization achieved by tumor cell apoptosis or substitution of authentic S1P suppressed nuclear factor (NF)-B signaling. These findings suggest that tumor cell apoptosis-derived S1P contributes to macrophage polarization.

Sphingosine 1-phosphate receptor 3 regulates recruitment of anti-inflammatory monocytes to microvessels during implant arteriogenesis

“…For example, IL-4 propagates T helper type 2 (TH2) (anti-inflammatory) immune responses by stimulating the proliferation of AMs (20), and S1P receptor signaling skews immune responses toward a TH2-cell response (27). Together, the recruitment and polarization of cells by angiocrine factors can spatially concentrate regenerative cells and enhance tissue repair, vascular remodeling, and implant integration.…”

Do not let death do us part: ‘find-me’ signals in communication between dying cells and the phagocytes

“…96 S1P can cause M2 polarization, leading to lower pro-inflammatory cytokines. Interestingly these actions are thought to be a consequence of S1P generation by SphK2, 97 and not SphK1(suggested to be responsible for the S1P find-me signal). Further analysis of the different sphingosine kinase members and their activity during cell death will be important for the understanding of S1P.…”

Heme Oxygenase-1 Contributes to an Alternative Macrophage Activation Profile Induced by Apoptotic Cell Supernatants

“…Nuclear extracts were prepared as described previously (Von Knethen and Brune, 2001) and an established EMSA method (Weigert et al, 2007) was used. Briefly, 10 g of nuclear protein was incubated for 30 min at room temperature with 2 g of poly(dI-dC) from Amersham Biosciences (Freiburg, Germany), 2 l of buffer D (20 mM HEPES/KOH, 20% glycerol, 100 mM KCl, 0.5 mM EDTA, 0.25% Nonidet P-40, 2 mM dithiothreitol [DTT], and 0.5 mM phenylmethylsulfonyl fluoride [PMSF], pH 7.9), 4 l of buffer F (20% Ficoll-400, 100 mM HEPES/KOH, 300 mM KCl, 10 mM DTT, and 0.5 mM PMSF, pH 7.9), 250 fmol of 5Ј-IRD700-labeled oligonucleotide (Metabion, Planegg-Martinsried, Germany), and in the case of competitive EMSA in addition with 2500 or 25,000 fmol of unlabeled oligonucleotide in a final volume of 20 l. Afterward samples were incubated on ice for 5 min.…”

“…Activation of S1P receptors exerts a powerful influence on a variety of immune cells and their responses (von Wenckstern et al, 2006). Moreover, S1P provoked M2 macrophage polarization either when added directly to cells (Hughes et al, 2008) or when being present in the supernatant of AC (Weigert et al, 2007).…”