Transglutaminase 2 Is Needed for the Formation of an Efficient Phagocyte Portal in Macrophages Engulfing Apoptotic Cells

Abstract

Transglutaminase 2 (TG2), a protein cross-linking enzyme with many additional biological functions, acts as coreceptor for integrin β3. We have previously shown that TG2−/− mice develop an age-dependent autoimmunity due to defective in vivo clearance of apoptotic cells. Here we report that TG2 on the cell surface and in guanine nucleotide-bound form promotes phagocytosis. Besides being a binding partner for integrin β3, a receptor known to mediate the uptake of apoptotic cells via activating Rac1, we also show that TG2 binds MFG-E8 (milk fat globulin EGF factor 8), a protein known to bridge integrin β3 to apoptotic cells. Finally, we report that in wild-type macrophages one or two engulfing portals are formed during phagocytosis of apoptotic cells that are characterized by accumulation of integrin β3 and Rac1. In the absence of TG2, integrin β3 cannot properly recognize the apoptotic cells, is not accumulated in the phagocytic cup, and its signaling is impaired. As a result, the formation of the engulfing portals, as well as the portals formed, is much less efficient. We propose that TG2 has a novel function to stabilize efficient phagocytic portals.

Over-expression of integrin β3 can partially overcome the defect of integrin β3 signaling in transglutaminase 2 null macrophages

“…In context with our 276 previous observations [18] macrophages of this TG2 subline also 277 did not concentrate integrin ␤ 3 around the apoptotic cells (Fig. 2f).…”

“…1a) and TG2 null cells had fibrob-235 lastoid forms [18], and Rac1 was located in the cytoplasm in the 236 perinuclear region [18], in non-engulfing macrophages of the TG2 237 subline a clear recruitment of Rac1 to the periphery could be 238 detected (Fig. 1b).…”

“…were elevated in all types of TG2 null macrophages, as compared to 256 the wild-types. However, while RhoG-GTP levels were not elevated 257 in the TG2 null macrophages [18], in the macrophages from the TG2 258 null subline an elevated RhoG-GTP level was detected (Fig. 2c).…”

“…2e). macrophages [18]. But in the macrophages of this subline increased 273 expression of integrin ␤ 3 could maintain an elevated Rac1 level.…”

Tissue transglutaminase contributes to the all-trans-retinoic acid–induced differentiation syndrome phenotype in the NB4 model of acute promyelocytic leukemia

“…24 TG2 has been shown to influence the phagocytosis of apoptotic corps by macrophages, most probably through its interaction with integrins and MFG-E8. 25 Impairment of neutrophil function by the reduction of TG2 could, in principle, result from the compromise of one or more of the aforementioned processes. The unexpected comprehensiveness of phenotypic changes in TG2-KD NB4, however, suggest these do not represent isolated instances of interference with the molecular machinery of specific granulocyte tasks (phagocytosis, adherence, migration), rather a break-up of the blueprint for the granulocytespecific molecular apparatus as a whole.…”