Phosphorylation of iRhom2 at the plasma membrane controls mammalian TACE-dependent inflammatory and growth factor signalling

Abstract

Proteolytic cleavage and release from the cell surface of membrane-tethered ligands is an important mechanism of regulating intercellular signalling. TACE is a major shedding protease, responsible for the liberation of the inflammatory cytokine TNFα and ligands of the epidermal growth factor receptor. iRhoms, catalytically inactive members of the rhomboid-like superfamily, have been shown to control the ER-to-Golgi transport and maturation of TACE. Here, we reveal that iRhom2 remains associated with TACE throughout the secretory pathway, and is stabilised at the cell surface by this interaction. At the plasma membrane, ERK1/2-mediated phosphorylation and 14-3-3 protein binding of the cytoplasmic amino-terminus of iRhom2 alter its interaction with mature TACE, thereby licensing its proteolytic activity. We show that this molecular mechanism is responsible for triggering inflammatory responses in primary mouse macrophages. Overall, iRhom2 binds to TACE throughout its lifecycle, implying that iRhom2 is a primary regulator of stimulated cytokine and growth factor signalling.DOI: http://dx.doi.org/10.7554/eLife.23968.001

FRMD8 promotes inflammatory and growth factor signalling by stabilising the iRhom/ADAM17 sheddase complex

“…2D). These phenotypes partially phenocopy the loss of iRhoms 136 (Christova et al, 2013, Grieve et al, 2017, consistent with FRMD8 being needed for iRhoms 137 to act as positive regulators of ADAM17. 138…”

“…These experiments demonstrate that FRMD8 binds to the cytoplasmic N-terminal 195 region of iRhom2, which has previously been shown to be required to stabilise ADAM17 at 196 the cell surface (Grieve et al, 2017). We therefore tested whether FRMD8 is necessary for 197 iRhom2 to stabilise ADAM17.…”

“…Among other 109 significant hits were several 14-3-3 proteins (eta, epsilon, gamma, sigma, theta, zeta/delta) 110 and MAPK1/3 (Fig. S1B), which we have previously reported to participate in the regulation 111 of inflammatory signalling by phosphorylation of iRhom2 (Grieve et al, 2017). The top hit by 112 a long way, however, was FRMD8 (Fig.…”

“…Moreover, an iRhom2 181 mutant, in which 15 conserved phosphorylation sites have been mutated to alanine 182 (iRhom2 pDEAD , Fig. S2C) (Grieve et al, 2017), did not abolish the interaction to FRMD8 (Fig. 183 2E), further demonstrating that the binding of FRMD8 to iRhom2 is independent of the 184 phosphorylation state of iRhom2.…”

“…Although the N-terminal cytoplasmic tail of iRhom2 177 contains multiple regulatory phosphorylation sites (Fig. S2B), the FRMD8 binding region 178 does not overlap with the sites required for phosphorylation-dependent 14-3-3 binding 179 (Grieve et al, 2017, Cavadas et al, 2017. Consistent with this, the interaction of FRMD8 180 with iRhom2 was not changed upon PMA stimulation (Fig.…”