Clathrin-associated SCYL2 contributes to the activation of PI3K/AKT signaling and tumorigenesis through PTEN phosphorylation in adult T-cell leukemia/lymphoma

Inactivation of PTEN by post-translational modifications causes aberrant amplification of the PI3K/AKT signaling pathway in many tumors. PTEN is a tumor suppressor phosphatase that is frequently phosphorylated at conserved serine/threonine residues (S380, T382, and T383 clusters) in the C-terminal tail of ATL and various solid cancer cells. Here, we identify SCY1-like protein 2 (SCYL2), with a protein kinase-like domain, as a novel PTEN-binding protein; however, the mechanism by which SCYL2 regulates PTEN phosphorylation remains unclear. SCYL2-associated complex phosphorylates PTEN at STT, and SCYL2 downregulation has anti-tumor effects in ATL via inhibition of the PI3K/AKT signaling pathway by dephosphorylating PTEN at STT. SCYL2 reportedly binds to the clathrin heavy chain (CHC), which regulates cytoplasmic vesicle formation, trafficking, and signaling pathways. Our results indicate that SCYL2 expression induces the binding of CHC to PTEN. Furthermore, the inhibition of clathrin-coated vesicles (CCVs) by CHC downregulation or inhibition suppresses cell survival by reducing phosphorylated PTEN at the STT, suggesting that SCYL2 enhances PTEN phosphorylation through CCVs as a signaling platform. Our results indicate that SCYL2/CHC complex plays a pivotal role in regulating the PI3K/AKT signaling pathway through PTEN phosphorylation, thus leading to tumor development and may be a promising novel target for treating tumors.