C1‐TEN is a negative regulator of the Akt/PKB signal transduction pathway and inhibits cell survival, proliferation, and migration

Abstract

We have previously identified C1 domain-containing phosphatase and TENsin homologue (C1-TEN) as being an intracellular binding partner for Axl receptor tyrosine kinase (RTK). C1-TEN is a tensin-related protein that houses an N-terminal region with predicted structural similarity to PTEN. Here, we report our observations on the effects of ectopic expression of C1-TEN in HEK293 cells, which resulted in profound molecular and phenotypic changes. Stable expression of C1-TEN altered cellular morphology, with less cell spreading and weaker filamentous actin staining. Cells overexpressing C1-TEN were inhibited greatly in their proliferation and migration rates as compared with mock-transfected cells. Furthermore, serum starvation-induced apoptosis caused a twofold increase in caspase 3 activity in C1-TEN-overexpressing cells vs. mock cells. In addition, C1-TEN-overexpressing cells showed a markedly reduced phosphorylation of Akt/PKB kinase and its substrate GSK3, as well as reduced Akt enzymatic activity. No such effects on JNK were observed. Also, serum-stimulated activation of Akt was delayed in C1-TEN-overexpressing cells, while no difference in profile of ERK activation was observed. Furthermore, cells expressing a C1-TEN mutant where the putative phosphatase active site cysteine at position 231 was substituted for a serine displayed full restoration of both cell proliferation and Akt activation. In conclusion, C1-TEN appears to be a novel intracellular phosphatase that negatively regulates the Akt/PKB signaling cascade, and is similar to its relative PTEN in this respect. However, the particular domain organization of C1-TEN may enable it to regulate RTK and other signaling complexes that are linked to Akt/PKB signaling in a unique manner.

TAM Receptor Tyrosine Kinases: Biologic Functions, Signaling, and Potential Therapeutic Targeting in Human Cancer

“…A second phosphorylation-mediated mechanism of receptor downregulation is receptor dephosphorylation by protein tyrosine phosphatases. The putative tyrosine phosphatase C1-TEN has been shown to bind Axl and overexpression of C1-TEN correlates with reduced cell survival, proliferation, and migration of 293 cells (Hafizi et al, 2002(Hafizi et al, , 2005b. Although neither enzymatic activity of C1-TEN nor direct dephosphorylation of Axl have been demonstrated, these results are consistent with C1-TEN-mediated Axl inactivation.…”

Akt is negatively regulated by the MULAN E3 ligase

“…PI3K induces Akt phosphorylation/activation, whereas PTEN inhibits Akt activation through the dephosphorylation of phosphatidylinositol-3,4,5-triphosphate, which is generated from phosphatidylinositol-4,5-bisphosphate by PI3K [2,4,11]. Negative regulators, such as C1 domain-containing PTEN, carboxy-terminal modulator protein, Trb3, and Keratin K10, are also reported to inactivate Akt [12][13][14][15].…”

Akt–PDK1 Complex Mediates Epidermal Growth Factor-induced Membrane Protrusion through Ral Activation

“…PDK1 phosphorylates Akt at Thr 308 , which causes a charge-induced conformational change, allowing Akt for substrate binding and an increased rate of catalysis. Akt is further activated by the phosphorylation of Ser 473 , which can be catalyzed by various kinases, including PDK2, DNA-PK, mammalian target of rapamysin, rictor complex, integrin linked kinase, and protein kinase C␤II (Feng et al, 2004;Kawakami et al, 2004;Fayard et al, 2005;Sarbassov et al, 2005 It has been demonstrated that PI3K plays an essential role in the epidermal growth factor (EGF)-induced membrane protrusion by regulating not only Akt (Higuchi et al, 2001;Nishita et al, 2004;Hafizi et al, 2005) but also Rac and Ral GTPases (Tian et al, 2002;Gavard et al, 2004;Nishita et al, 2004;Takaya et al, 2004). However, the mechanism by which Akt regulates the cytoskeletal remodeling and the relationship to Ral and Rac has been still remains elusive.…”

“…It has been demonstrated that PI3K plays an essential role in the epidermal growth factor (EGF)-induced membrane protrusion by regulating not only Akt (Higuchi et al, 2001;Nishita et al, 2004;Hafizi et al, 2005) but also Rac and Ral GTPases (Tian et al, 2002;Gavard et al, 2004;Nishita et al, 2004;Takaya et al, 2004). However, the mechanism by which Akt regulates the cytoskeletal remodeling and the relationship to Ral and Rac has been still remains elusive.…”

“…PtdIns(3,4,5)P 3 is dephosphorylated to yield PtdIns(4,5)P 2 by a tumor suppressor protein, phosphatase and tensin homolog deleted in chromosome 10 (PTEN), which is frequently mutated or deleted in various human cancers (Sulis and Parsons, 2003). The resulting PTEN deficiency causes accumulation of PtdIns(3,4,5)P 3 in cells, and, as a consequence, an increase in cell motility in fibroblasts (Liliental et al, 2000;Higuchi et al, 2001;Hafizi et al, 2005). Another dephosphorylated derivative of PtdIns (3,4,5)P 3 is PtdIns(3,4)P 2 produced by phosphoinositide 5-phosphatases, including Src homology 2-containing inositol-5-phosphatase (SHIP).…”