Pten Epsilon Suppresses Tumor Metastasis Through Regulation Of Filopodia Formation

PTEN is one of the most frequently mutated genes in malignancies and acts as a powerful tumor suppressor. Tumorigenesis is involved in multiple and complex processes including initiation, invasion, and metastasis. The complexity of PTEN function is partially attributed to PTEN family members such as PTEN alpha and PTEN beta. Here, we report the identification of PTEN epsilon (also named as PTEN5), a novel N-terminal-extended PTEN isoform that suppresses tumor invasion and metastasis. We show that the translation of PTEN epsilon/PTEN5 is initiated from the CUG(816) codon within the 5 ' UTR region of PTEN mRNA. PTEN epsilon/PTEN5 mainly localizes in the cell membrane and physically associates with and dephosphorylates VASP and ACTR2, which govern filopodia formation and cell motility. We found that endogenous depletion of PTEN epsilon/PTEN5 promotes filopodia formation and enhances the metastasis capacity of tumor cells. Overall, we identify a new isoform of PTEN with distinct subcellular localization and molecular function compared to the known members of the PTEN family. These findings advance our current understanding of the importance and diversity of PTEN functions.