The Tumor Suppressor PTEN Is Phosphorylated by the Protein Kinase CK2 at Its C Terminus

Abstract

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...

Loss of Mel-18 induces tumor angiogenesis through enhancing the activity and expression of HIF-1α mediated by the PTEN/PI3K/Akt pathway

“…PTEN can be ubiquitinated and degradaded by several ubiquitin E3 ligases, such as NEDD4 and the X-linked inhibitor of apoptosis protein Wang et al, 2007;Van Themsche et al, 2009). Phosphorylation of PTEN by casein kinase 2 or GSK3b also controls PTEN stability by promoting ubiquitination (Torres and Pulido, 2001;Al-Khouri et al, 2005). Unlike casein kinase 2 and GSK3b, ROCK1-mediated PTEN phosphorylation at S380 upregulates the stablilty of PTEN (Vemula et al, 2010).…”

La protéine kinase CK2, une enzyme qui cultive la différence

“…La protéine PTEN est phosphorylée par CK2 sur son extrémité régu-latrice carboxy-terminale. Cette phosphorylation règle négativement l'activité de la phosphatase en bloquant son intégration dans un complexe macromoléculaire nécessaire pour son adressage à la membrane plasmique [34]. En neutralisant PTEN, la CK2 potentialise l'action essentielle de la PI3K et de la PKB (protéine kinase B) pour assurer la survie cellulaire.…”

“…Le produit du gène suppresseur de tumeur PTEN antagonise l'action anti-apoptotique de la PI3K [33]. La phosphorylation de PTEN par CK2 entraîne une inhibition de son activité phosphatase [34]. TNFα: tumor necrosis factor α; FRZ: récep-teur frizzled; Dsh: dishevelled; GSK3β: glycogen synthase kinase 3β; Fas L: Fas ligand; Fas R: récépteur de Fas L; PI3K: phosphatidylinositol 3-kinase; Cyt C: cytochrome C; PKB: protéine kinase B, IKK: IκB-kinase.…”

Post-translational regulation of PTEN

“…A cluster of phosphorylation sites (S370, S380, T382, T383 and S385) on its conserved but structurally flexible C-terminal regions was mapped, and casein kinase 2 was shown to be able to phosphorylate these sites (Vazquez et al, 2000;Torres and Pulido, 2001). On the basis of these studies and the crystal structure of PTEN (Lee et al, 1999), an attractive model has been raised: phosphorylation of these sites keeps PTEN in the cytoplasm and thus inactive (in terms of its lipid phosphatase activity); but after dephosphorylation, the C2 domain of PTEN is probably more exposed allowing translocation of PTEN to the plasma membrane to antagonize PI3K-Akt signaling.…”

“…For example, as mentioned above, PTEN phosphorylation (Vazquez et al, 2000;Torres and Pulido, 2001;Maccario et al, 2007) and its multiple associating proteins (Tolkacheva et al, 2001;Okahara et al, 2004) have been suggested to regulate its protein stability, presumably via ubiquitin-mediated proteasomal degradation. In addition, deregulation of PTEN protein stability control might be involved in cancer development, as we discussed earlier.…”