G protein α (Gα) is a negative regulator of kidney injury molecule-1-mediated efferocytosis.

Kidney injury molecule-1 (KIM-1) is a receptor for the "eat me" signal, phosphatidylserine, on apoptotic cells. The specific upregulation of KIM-1 by injured tubular epithelial cells (TECs) enables them to clear apoptotic cells (also known as efferocytosis), thereby protecting from acute kidney injury. Recently, we uncovered that KIM-1 binds directly to the α-subunit of heterotrimeric G protein (Gα) and inhibits its activation by reactive oxygen species during renal ischemia-reperfusion injury (Ismail OZ, Zhang X, Wei J, Haig A, Denker BM, Suri RS, Sener A, Gunaratnam L. 185: 1207-1215, 2015). Here, we investigated the role that Gα plays in KIM-1-mediated efferocytosis by TECs. We showed that KIM-1 remains bound to Gα and suppresses its activity during phagocytosis. When we silenced Gα expression using small interefering RNA, KIM-1-mediated engulfment of apoptotic cells was increased significantly; in contrast overexpression of constitutively active Gα (Gα) resulted in inhibition of efferocytosis. Inhibition of RhoA, a key effector of Gα, using a chemical inhibitor or expression of dominant-negative RhoA, had the same effect as inhibition of Gα on efferocytosis. Consistent with this, silencing Gα suppressed active RhoA in KIM-1-expressing cells. Finally, using primary TECs from Kim-1 and Kim-1 mice, we confirmed that engulfment of apoptotic cells requires KIM-1 expression and that silencing Gα enhanced efferocytosis by primary TECs. Our data reveal a previously unknown role for Gα in regulating efferocytosis and that renal TECs require KIM-1 to mediate this process. These results may have therapeutic implications given the known harmful role of Gα in acute kidney injury.