TGF? receptor endocytosis and Smad signaling require synaptojanin1, PI3K-C2?-, and INPP4B-mediated phosphoinositide conversions.

ABSTRACT: Phosphoinositide conversion regulates a diverse array of dynamic membrane events including endocytosis. However, it is not well understood which enzymes are involved in phosphoinositide conversions for receptor endocytosis. We found by small interfering RNA (siRNA)-mediated knockdown (KD) that class II PI3K ?-isoform (PI3K-C2?), the 5'-phosphatase synaptojanin1 (Synj1), and the 4'-phosphatase INPP4B, but not PI3K-C2?, Synj2, or INPP4A, were required for TGF?-induced endocytosis of TGF? receptor. TGF? induced rapid decreases in PI(4,5)P₂ at the plasma membrane (PM) with increases in PI(4)P, followed by increases in PI(3,4)P₂, in a TGF? receptor kinase ALK5-dependent manner. TGF? induced the recruitment of both synaptojanin1 and PI3K-C2? to the PM with their substantial colocalization. Knockdown of synaptojanin1 abolished TGF?-induced PI(4,5)P₂ decreases and PI(4)P increases. Interestingly, PI3K-C2? KD abolished not only TGF?-induced PI(3,4)P₂ increases but also TGF?-induced synaptojanin1 recruitment to the PM, PI(4,5)P₂ decreases, and PI(4)P increases. Finally, the phosphoinositide conversions were necessary for TGF?-induced activation of Smad2 and Smad3. These observations demonstrate that the sequential phosphoinositide conversions mediated by Synj1, PI3K-C2?, and INPP4B are essential for TGF? receptor endocytosis and its signaling.

SUBMITTER: Aki S 

PROVIDER: S-EPMC7183790 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature