A Phosphoinositide Interacting Protein Coordinates Stress Precursor Activities.

Unlabelled: Samd14 is crucial for cell signaling and survival in mouse models of acute anemia. Samd14 has an N-terminal actin capping protein (CP) and a C-terminal sterile alpha motif (SAM) to coordinate stem cell factor/Kit and erythropoietin receptor signaling pathways during terminal differentiation of red blood cell precursors. Here we present new findings that Samd14 expression is needed to maintain balanced autophagy in red blood cell precursors following acute anemia. Autophagy gene signatures and protein levels are markedly altered within the context of acute anemia when red blood cell precursors accelerate the process of erythropoiesis. Samd14 interacted via its SAM domain with phosphatidylinositol 3-phosphate (PI3P) which is an integral component of endosomal and autophagic membranes. We tested PI3Ps role in red blood cell differentiation using a small molecule inhibitor of the Class III PI 3-kinase VPS34, which is the sole kinase responsible for PI3P genesis. SAR405 treatment blocked red blood cell formation. In the absence of Samd14, higher doses of VPS34 inhibition were required to block erythroid differentiation. Given the critical roles of autophagy in normal differentiation, Samd14's stress-dependent activation and roles in autophagy suggest that this mechanism is needed to maintain progenitor levels and balance the production of healthy, mature red blood cells.

Key Points: Autophagy genes/proteins are deregulated in red blood cell progenitors after hemolysis-induced acute anemia.The anemia-activated Samd14 protein interacts with the PI3P lipid moiety which is integral to endosomal and autophagic membrane functions.VPS34 inhibition blocks terminal erythroid maturation in a Samd14-dependent manner.