High CO₂ leads to Na, K-ATPase endocytosis via c-Jun amino-terminal kinase-induced LMO7b phosphorylation

The c-Jun amino-terminal kinase (JNK) plays a role in inflammation, proliferation, apoptosis, and cell adhesion and cell migration by phosphorylating paxillin and ß-catenin. JNK phosphorylation downstream of AMP-activated protein kinase (AMPK) activation is required for high CO₂ (hypercapnia)-induced Na, K-ATPase endocytosis in alveolar epithelial cells. Here, we provide evidence that during hypercapnia, JNK promotes the phosphorylation of LMO7b, a scaffolding protein, in vitro and in intact cells. LMO7b phosphorylation was blocked by exposing the cells to the JNK inhibitor SP600125 and by infecting cells with dominant-negative JNK or AMPK adenovirus. The knockdown of the endogenous LMO7b or overexpression of mutated LMO7b with alanine substitutions of five potential JNK phosphorylation sites (LMO7b-5SA) or only Ser-1295 rescued both LMO7b phosphorylation and the hypercapnia-induced Na, K-ATPase endocytosis. Moreover, high CO₂ promoted the colocalization and interaction of LMO7b and the Na, K-ATPase α₁ subunit at the plasma membrane, which were prevented by SP600125 or by transfecting cells with LMO7b-5SA. Collectively, our data suggest that hypercapnia leads to JNK-induced LMO7b phosphorylation at Ser-1295, which facilitates the interaction of LMO7b with Na, K-ATPase at the plasma membrane promoting the endocytosis of Na, K-ATPase in alveolar epithelial cells.