Heterotrimeric Gαq11 Co-Immunoprecipitates With Surface-Anchored GRP78 From Plasma Membranes of α2M*-stimulated Macrophages

We have previously shown that a traction of newly expressed GRP78 is trans located to the cell surface in association with the co-chaperone MTJ-1. Proteinase and methylamine-activated alpha M-2 (alpha M-2) bind to cell surface-associated GRP78 activating phosphoinositide-specific phospholipase C coupled to a pertussis toxin-insensitive heterotrimeric G protein, generating IP3/calcium signaling. We have now studied the association of pertussis toxin-insensitive G alpha q11, with GRP78/MTJ-1 complexes in the plasma membranes of alpha M-2 stimulated macrophages. When GRP78 was immunoprecipitated from plasma membranes of macrophages stimulated with alpha M-2*, G alpha q11, and MTJ-1 were co-precipitated. Likewise G alpha q11 and GRP78 co-immunoprecipitated with MTJ-1 while GRP78 and MTJ-1 co-immunoprecipiatated with G alpha q11. Silencing GRP78 expression with GRP78 dsRNA or MTJ-1 with MTJ-1 dsRNA greatly reduced the levels of G alpha q11 co-precipitated with GRP78 or MTJ-1. In conclusion, we show here that plasma membrane-associated GRP78 is coupled to pertussis toxin-insensitive G alpha q11 and forms a ternary signaling complex with MTJ-1 (C) 2008 Wiley-Liss, Inc.