Loss of PTEN binding adapter protein NHERF1 from plasma membrane in glioblastoma contributes to PTEN inactivation.

Glioblastoma multiforme (GBM) is a severe brain malignancy with limited treatment and dismal prognosis. The tumor suppressor PTEN, a major inhibitor of the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway, is frequently deleted in GBM tumors. PTEN antagonizes PI3K by dephosphorylating PI3K phosphoinositide substrates at the plasma membrane. The PTEN binding adapter protein NHERF1/EBP50 is overexpressed in GBM but its effects on tumorigenesis have yet to be determined. Here, we show that NHERF1 is localized to the plasma membrane in normal astrocytes and to the cytoplasm of GBM tumor cells. This cytoplasmic shift paralleled an altered membrane distribution of wild-type PTEN with consecutive Akt activation. Membrane re-targeting of NHERF1 in GBM cells recruited PTEN to the membrane and suppressed Akt activation and cell proliferation. Conversely, NHERF1 depletion in GBM cells with membrane-localized NHERF1 increased cell proliferation and Akt activation. Our findings define a tumor suppressor role for NHERF1 at the plasma membrane, and reveal a novel mechanism for PI3K/Akt activation through PTEN inactivation caused by a loss of membrane-localized NHERF1.