In line with activation of PI3-kinase (PI3K) by other receptor tyrosine kinases, PI3K recruited to the activated NTRK1 receptor via IRS1 and/or IRS2 (Miranda et al. 2001) is thought to phosphorylate 1-phosphatidyl-1D-myo-inositol 4,5-bisphosphate, commonly known as PtdIn(4,5)P2 or PIP2, at the plasma membrane producing the second messenger PtdIns(3,4,5)P3, also named PIP3, as evidenced by increased PIP3 levels (Miranda et al. 2001) and increased activating phosphorylation of AKT1 (Tsuchiya et al. 2014) upon stimulation of cells with the NTRK1 ligand NGF.