Biomedical subjects

Koichi Okumura

Publications and source records attributed to Koichi Okumura.

5 recordsLinked to original sources

PubMed2006

PCAF modulates PTEN activity.

The PTEN protein has a single catalytic domain possessing both lipid phosphoinositol and protein phosphatase activities. The lipid phosphoinositol phosphatase activity is essential for PTEN to block the cell cycle in the G1 phase and thereby to suppress tumor formation and progression (Cantley, L. C., and Neel, B. G. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 4240-4245), although the mechanisms governing PTEN activity under normal and neoplastic growth conditions remain unclear. Here, we report that PTEN interacts physically and functionally with PCAF, a histone acetyltransferase that regulates gene transcription through interaction with p300/CBP and various sequence-specific transcription factors (Nakatani, Y. (2001) Genes Cells 6, 79-86). Expression of PCAF results in increased acetylation of lysine residues (Lys125 and Lys128) within the catalytic cleft of PTEN, a structure essential for phosphatidylinositol 3,4,5-trisphosphate specificity (Lee, J. O., Yang, H., Georgescu, M. M., Di Cristofano, A., Maehama, T., Shi, Y., Dixon, J. E., Pandolfi, P., and Pavletich, N. P. (1999) Cell 99, 323-334). The acetylation of PTEN caused by PCAF expression depends on the presence of growth factors. Reduction of endogenous PCAF activity using shRNA results in a loss of PTEN acetylation in response to growth factors and restores the ability of PTEN to down-regulate phosphatidylinositol 3-kinase signaling and to induce G1 cell cycle arrest. The retention of phosphatidylinositol 3-kinase/AKT signaling and cell cycle regulatory activities of acetylation-resistant PTEN K125R and K128R mutants in the presence of enforced PCAF expression suggest a causal relationship. Together, these findings indicate a mechanism of PTEN regulation that forges a link between distinct cancer-relevant pathways central to the control of growth factor signaling and gene expression.

Acetylation↗

PubMed2005

TOR complex 2 integrates cell movement during chemotaxis and signal relay in Dictyostelium.

Dictyostelium cells form a multicellular organism through the aggregation of independent cells. This process requires both chemotaxis and signal relay in which the chemoattractant cAMP activates adenylyl cyclase through the G protein-coupled cAMP receptor cAR1. cAMP is produced and secreted and it activates receptors on neighboring cells, thereby relaying the chemoattractant signal to distant cells. Using coimmunoprecipitation and mass spectrometric analyses, we have identified a TOR-containing complex in Dictyostelium that is related to the TORC2 complex of Saccharomyces cerevisiae and regulates both chemotaxis and signal relay. We demonstrate that mutations in Dictyostelium LST8, RIP3, and Pia, orthologues of the yeast TORC2 components LST8, AVO1, and AVO3, exhibit a common set of phenotypes including reduced cell polarity, chemotaxis speed and directionality, phosphorylation of Akt/PKB and the related PKBR1, and activation of adenylyl cyclase. Further, we provide evidence for a role of Ras in the regulation of TORC2. We propose that, through the regulation of chemotaxis and signal relay, TORC2 plays an essential role in controlling aggregation by coordinating the two essential arms of the developmental pathway that leads to multicellularity in Dictyostelium.

Amino Acid Sequence↗

PubMed2005

PTEN: a novel anti-oncogenic function independent of phosphatase activity.

The PTEN gene is an important tumor suppressor mutated in a number of cancers. To date, its growth regulatory properties have been intimately linked to its ability to act as a protein and phosphoinositol phosphatase. Inactivation of the enzymatic activity of PTEN is primarily due to direct mutation of its amino-terminal catalytic domain but approximately 20% of mutations are in the carboxy-terminus, which regulates membrane localization, protein stability, cellular migration and p53 function. We identified a novel protein that interacts with this domain, the v-jun transcriptional target, MSP58. Binding of MSP58 to PTEN results in the suppression of MSP58-mediated transformation. However, this PTEN effect does not require its catalytic activity, suggesting additional mechanisms of PTEN action.

Animals↗

PubMed2005

Cellular transformation by the MSP58 oncogene is inhibited by its physical interaction with the PTEN tumor suppressor.

The PTEN (phosphatase and tensin homologue) tumor suppressor protein contains a single catalytic domain with both lipid and protein phosphatase activities. The remaining C-terminal half of the PTEN protein plays a role in its stability and is mutated in many clinical cancer samples. Here, we report that the PTEN C-terminal domain physically interacts with the forkhead-associated domain of the oncogenic MSP58 protein and that this interaction requires PTEN Thr-366. We further show that while MSP58 transforms Pten-/- mouse embryo fibroblasts (MEFs), concurrent introduction of wild-type PTEN causes a dramatic reduction in the number of MSP58-induced transformed foci. This PTEN-mediated inhibition of cellular transformation requires physical interaction as evidenced by the failure of PTEN(T366A) point mutation (residing within the MSP58 interaction domain) to suppress MSP-58-driven transformation. These observations, together with the capacity of catalytically inactive PTEN mutant (G129R) to suppress MSP58 oncogenicity, support the view that the C-terminal region of PTEN directly provides a previously uncharacterized biological function in its ability to regulate cellular transformation.

Animals↗

PubMed2004

c-Jun and Sp1 family are critical for retinoic acid induction of the lamin A/C retinoic acid-responsive element.

The expression of A-type lamins, subdivided into lamin A and C, is developmentally regulated. Retinoic acid (RA)-induced differentiation of P19 embryonic carcinoma cells, in which A-type lamins are absent, increases the expression of lamin A/C. We previously showed, using P19 cells as a model system, that the lamin A/C promoter has a retinoic acid-responsive element (L-RARE), and that Sp1 and Sp3 bind the CACCC box of the L-RARE. In this study, we report that Sp1, Sp3, and c-Jun increase transactivation of the L-RARE during RA treatment. Sp1 and Sp3 regulate the lamin A/C promoter in Sp1-deficient SL2 cells and contribute to RA-dependent activation in GAL4-based transcriptional assays. Overexpression of c-Jun causes transactivation of a chimeric promoter consisting of four tandem L-RARE repeats fused with the luciferase gene in P19 cells. c-Jun also transactivates a reporter construct with five tandem GAL4-binding sites, only when co-expressed with either GAL4-Sp1 or Sp3 fusion proteins. Furthermore, we detect a physiological interaction between c-Jun with Sp1/Sp3 in RA-treated cells. Our data suggest that Sp1, Sp3, and c-Jun play an important role in gene expression through the L-RARE during RA treatment.

Animals↗