The
PTEN (phosphatase and
tensin homolog)
phosphatase is unique in mammals in terms of its
tumor suppressor activity, exerted by dephosphorylation of the
lipid second messenger PIP(3) (phosphatidylinositol 3,4,5-trisphosphate), which activates the
phosphoinositide 3-kinase/Akt/mTOR (
mammalian target of rapamycin) oncogenic pathway. Loss-of-function mutations in the PTEN gene are frequent in human
cancer and in the germline of patients with PTEN
hamartoma tumor-related syndromes (PHTSs). In addition, PTEN is mutated in patients with
autism spectrum disorders (ASDs), although no functional information on these mutations is available. Here, we report a comprehensive in vivo functional analysis of human PTEN using a heterologous yeast reconstitution system. Ala-scanning mutagenesis at the catalytic loops of PTEN outlined the critical role of residues within the P-catalytic loop for PIP(3)
phosphatase activity in vivo. PTEN mutations that mimic the P-catalytic loop of mammalian PTEN-like
proteins (TPTE, TPIP,
tensins and
auxilins) affected PTEN function variably, whereas
tumor- or PHTS-associated mutations targeting the PTEN P-loop produced complete loss of function. Conversely, Ala-substitutions, as well as
tumor-related mutations at the WPD- and TI-catalytic loops, displayed partial activity in many cases. Interestingly, a
tumor-related D92N mutation was partially active, supporting the notion that the PTEN Asp92 residue might not function as the catalytic general
acid. The analysis of a panel of ASD-associated hereditary PTEN mutations revealed that most of them did not substantially abrogate PTEN activity in vivo, whereas most of PHTS-associated mutations did. Our findings reveal distinctive functional patterns among PTEN mutations found in
tumors and in the germline of PHTS and ASD patients, which could be relevant for
therapy.