The tumor suppressor phosphatase PTEN regulates cell migration, growth, and survival by dephosphorylating phosphatidylinositol second messengers and signaling phosphoproteins. PTEN possesses a C-terminal noncatalytic regulatory domain that contains multiple putative phosphorylation sites, which could play an important role in the control of its biological activity. The protein kinase CK2 phosphorylated, in a constitutive manner, a cluster of Ser/Thr residues located at the PTEN C terminus. PTEN-phosphorylated defective mutants showed decreased stability in comparison with wild type PTEN and were more rapidly degraded by the proteasome. Inhibition of PTEN phosphorylation by the CK2 inhibitor 5,6-dichloro-1-␤-D-ribofuranosyl-benzimidazole also diminished the PTEN protein content. Our results support the notion that proper phosphorylation of PTEN by CK2 is important for PTEN protein stability to proteasome-mediated degradation.The tumor suppressor gene PTEN (also named as MMAC1 or TEP-1) (1-3) encodes a phosphatase with enzymatic activity toward both protein substrates and the lipid second messenger, phosphatidylinositol-3,4,5-triphosphate (4 -6). PTEN regulates distinct signal transduction pathways, including the phosphatidylinositol 3-kinase/ protein kinase B cell survival-and integrin-triggered signaling pathways (for recent reviews, see . Structurally, PTEN protein is composed of an Nterminal dual specificity phosphatase-like enzyme domain and a C-terminal regulatory domain, which binds to phospholipid membranes (11). Mutations in the PTEN gene are present in a great number of tumors, as well as in the germ line cells of patients with several inherited cancer syndromes (reviewed in Refs. 12 and 13). The importance of PTEN catalytic activity in its tumor suppressor function is underscored by the fact that the majority of PTEN missense mutations detected in tumor specimens target the phosphatase domain and cause a loss in PTEN phosphatase activity. In addition, a large number of PTEN nonsense or frame-shift mutations found in tumors are targeted to the C-terminal domain of the protein, suggesting an important role for this domain in the regulation of the PTEN tumor suppressor activity. In this regard, the C-terminal region of PTEN has been shown to be important in the regulation of the stability and half-life of the molecule (14, 15). Also, the C-terminal PTEN amino acid sequence possesses a putative PDZ binding motif, which has been proposed to modulate PTEN functions by association to PDZ domain-containing proteins (16 -19). Finally, the C-terminal PTEN domain is rich in putative phosphorylation sites, and phosphorylation of the PTEN C terminus has been recently reported to affect PTEN protein stability and function (20); however, the kinase responsible for such phosphorylation remains unidentified.Protein kinase CK2 1 (formerly casein kinase II) is a highly conserved, ubiquitously expressed, messenger-independent serine/threonine-kinase that phosphorylates a wide variety of substrates involved in essential cel...

Protein kinases and phosphatases regulate the activity of extracellular signal‐regulated kinases 1 and 2 (ERK1/2) by controlling the phosphorylation of specific residues. We report the physical and functional association of ERK1/2 with the PTP‐SL and STEP protein tyrosine phosphatases (PTPs). Upon binding, the N‐terminal domains of PTP‐SL and STEP were phosphorylated by ERK1/2, whereas these PTPs dephosphorylated the regulatory phosphotyrosine residues of ERK1/2 and inactivated them. A sequence of 16 amino acids in PTP‐SL was identified as being critical for ERK1/2 binding and termed kinase interaction motif (KIM) (residues 224–239); it was shown to be required for phosphorylation of PTP‐SL by ERK1/2 at Thr253. Co‐expression of ERK2 with catalytically active PTP‐SL in COS‐7 cells impaired the EGF‐induced activation of ERK2, whereas a PTP‐SL mutant, lacking PTP activity, increased the ERK2 response to EGF. This effect was dependent on the presence of the KIM on PTP‐SL. Furthermore, ERK1/2 activity was downregulated in 3T3 cells stably expressing PTP‐SL. Our findings demonstrate the existence of a conserved ERK1/2 interaction motif within the cytosolic non‐catalytic domains of PTP‐SL and STEP, which is required for the regulation of ERK1/2 activity and for phosphorylation of the PTPs by these kinases. Our findings suggest that PTP‐SL and STEP act as physiological regulators of the ERK1/2 signaling pathway.

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.

The tumor suppressor phosphatase PTEN is a key regulator of cell growth and apoptosis that interacts with PDZ domains from regulatory proteins, including MAGI-1/2/3, hDlg, and MAST205. Here we identified novel PTEN-binding PDZ domains within the MAST205-related proteins, syntrophin-associated serine/threonine kinase and MAST3, characterized the regions of PTEN involved in its interaction with distinctive PDZ domains, and analyzed the functional consequences on PTEN of PDZ domain binding. Using a panel of PTEN mutations, as well as PTEN chimeras containing distinct domains of the related protein TPTE, we found that the PTP and C2 domains of PTEN do not affect PDZ domain binding and that the C-terminal tail of PTEN (residues 350 -403) provides selectivity to recognize specific PDZ domains from MAGI-2, hDlg, and MAST205. Binding of PTEN to the PDZ-2 domain from MAGI-2 increased PTEN protein stability. Furthermore, binding of PTEN to the PDZ domains from microtubule-associated serine/ threonine kinases facilitated PTEN phosphorylation at its C terminus by these kinases. Our results suggest an important role for the C-terminal region of PTEN in the selective association with scaffolding and/or regulatory molecules and provide evidence that PDZ domain binding stabilizes PTEN and targets this tumor suppressor for phosphorylation by microtubule-associated serine/ threonine kinases.Alterations in the function of the PTEN phosphatase tumor suppressor protein are of major relevance for the incidence of a wide variety of human cancers, as well as for the occurrence of inherited growth disorders, grouped as PTEN hamartoma tumor syndromes (1). Structurally, PTEN protein is composed of an N-terminal phosphatase catalytic domain and a C-terminal phospholipid-binding C2 domain; the integrity of both domains is required for full PTEN phosphatase activity and binding to membranes (2). The analysis of tumor specimens, tumor cell lines, and model organisms defective in PTEN protein expression has shown that the 3-phosphoinositide phosphatase activity of PTEN toward the phospholipid phosphatidylinositol 3,4,5-trisphosphate is crucial for the control of cell growth, cell cycle, cell motility and migration, and apoptosis (3-6). In addition, some PTEN biological functions have been attributed to its protein phosphatase activity (7-10), and a PTEN phosphatase independent effect on the regulation of p53 stability and transcriptional activity has been reported (11). A major level of regulation of PTEN functions is related with its phosphorylation status, which has been involved in maintaining PTEN protein stability and in the control of PTEN subcellular location and/or its association with regulatory molecules (12-21). In this regard, PTEN possesses a C-terminal tail (last 54 amino acids; residues 350 -403), which harbors at its far C terminus a functional PDZ domain-binding motif (residues Thr 401 -Lys 402 -Val 403 -COOH). PDZ domains are modular protein interaction domains that in most cases recognize C-terminal motifs on their target pr...

The transmembrane protein-tyrosinephosphatases (PTPases) LAR