Fluctuations in AKT and PTEN Activity Are Linked by the E3 Ubiquitin Ligase cCBL

3-Poly-phosphoinositides (PIP₃) regulate cell survival, division, and migration. Both PI3-kinase (phosphoinositide-3-kinase) and PTEN (Phosphatase and tensin-homolog in chromosome 10) control PIP₃ levels, but the mechanisms connecting PI3-kinase and PTEN are unknown. Using non-transformed cells, the activation kinetics of PTEN and of the PIP₃-effector Akt were examined after the addition of growth factors. Both epidermal growth factor and serum induced the early activation of Akt and the simultaneous inactivation of PTEN (at ~5 min). This PIP₃/Akt peak was followed by a general reduction in Akt activity coincident with the recovery of PTEN Phosphatase activity (at ~10-15 min). Subsequent Akt peaks and troughs followed. The fluctuation in Akt activity was linked to that of PTEN; PTEN reconstitution in PTEN-null cells restored Akt fluctuations, while PTEN depletion in control cells abrogated them. The analysis of PTEN activity fluctuations after the addition of growth factors showed its inactivation at ~5 min to be simultaneous with its transient ubiquitination, which was regulated by the ubiquitin E3 Ligase cCBL (casitas B-lineage lymphoma proto-oncogene). Protein-protein interaction analysis revealed cCBL to be brought into the proximity of PTEN in a PI3-kinase-dependent manner. These results reveal a mechanism for PI3-kinase/PTEN crosstalk and suggest that cCBL could be new target in strategies designed to modulate PTEN activity in Cancer.