Akt Forms an Intracellular Complex with Heat Shock Protein 90 (Hsp90) and Cdc37 and Is Destabilized by Inhibitors of Hsp90 Function

Basso, Andrea; Solit, David B.; Chiosis, Gabriela; Giri, Banabihari; Tsichlis, Philip N.; Rosen, Neal

doi:10.1074/jbc.m206322200

Cited by 576 publications

(496 citation statements)

References 53 publications

(43 reference statements)

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“…This conclusion is based on the notion that Cdc37 only binds to partially unfolded kinase molecules. However, we note that previous studies have observed enzymatically active preparations of Akt to contain Cdc37 [23]. Therefore it is also possible that NPM-ALK affects expression of an Akt binding protein that displaces Cdc37.…”

Section: Discussionmentioning

confidence: 71%

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Akt shows variable sensitivity to an Hsp90 inhibitor depending on cell context

Theodoraki

Kunjappu

Sternberg

et al. 2007

Experimental Cell Research

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Hsp90 inhibitors are currently in clinical trials for cancer therapy based on their ability to promote proteasomal degradation of oncogenic protein kinases and nuclear receptors. Results from recent studies suggest that cancer cells are more sensitive to these inhibitors than cells from healthy tissues. We analyzed an immortalized cell line Ba/F3, for sensitivity to the Hsp90 inhibitor geldanamycin in the absence and presence of the oncogenic tyrosine fusion kinase NPM-ALK expressed from a retroviral vector. Our results showed that NPM-ALK expression makes Akt and Cdk4 more resistant to degradation in the presence of geldanamycin, and there was a slightly reduced amount of apoptosis. The mechanism underlying the effect of NPM-ALK on Akt stability was probed by comparison of the turnover of the kinase after translation inhibition and geldanamycin treatment. We observed that Akt was degraded more rapidly in the presence of GA than upon translation inhibition without NPM-ALK expression. This suggests that NPM-ALK protects the mature kinase. Furthermore, Akt failed to bind to the Cdc37 chaperone in cells expressing NPMALK, which also correlates with increased Akt stability.

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Section: Discussionmentioning

confidence: 71%

“…Previous studies have shown that Hsp90 and Cdc37 can interact with Akt even after folding [23]. However, it seems unclear from the studies described above, whether this population is degraded in the presence of GA. We investigated by immunoprecipitation whether NPM-ALK expression affected binding of either chaperone to mature Akt or Cdk4 (Fig.…”

Section: Resultsmentioning

confidence: 94%

Akt shows variable sensitivity to an Hsp90 inhibitor depending on cell context

Theodoraki

Kunjappu

Sternberg

et al. 2007

Experimental Cell Research

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“…An attractive hypothesis is the existence of cofactors working in conjunction with TM phosphorylation. Akt-binding proteins, such as Hsp90 (Sato et al, 2000;Basso et al, 2002), TRB3 and PAK (Du et al, 2003;Du and Tsichlis, 2005;Higuchi et al, 2008), have been reported to regulate negatively or positively the phosphorylation status of Akt. It would be interesting to evaluate the relationship between their binding ability and TM phosphorylation.…”

Section: Regulation Of A-loop Phosphorylation Via Tm Phosphorylation mentioning

confidence: 99%

Turn motif phosphorylation negatively regulates activation loop phosphorylation in Akt

2011

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Akt, also known as protein kinase B, has a central role in various signaling pathways that regulate cellular processes such as metabolism, proliferation and survival. On stimulation, phosphorylation of the activation loop (Aloop) and hydrophobic motif (HM) of Akt by the kinase phosphoinositide-dependent kinase 1 (PDK1) and the mammalian target of rapamycin complex 2 (mTORC2), respectively, results in Akt activation. A well-conserved threonine in the turn motif (TM) is also constitutively phosphorylated by mTORC2 and contributes to the stability of Akt. The role of TM phosphorylation in HM and A-loop phosphorylation has not been sufficiently evaluated. Using starfish oocytes as a model system, this study provides the first evidence that TM phosphorylation has a negative role in A-loop phosphorylation. In this system, the maturation-inducing hormone, 1-methyladenine, stimulates Akt to reinitiate meiosis through activation of cyclin B-Cdc2. The phosphorylation status of Akt was monitored via introduction of exogenous human Akt (hAkt) in starfish oocytes. TM and HM phosphorylation was inhibited by microinjection of an anti-starfish TOR antibody, but not by rapamycin treatment, suggesting that both phosphorylation events depend on TORC2, as reported in mammalian cells. A single or double alanine substitution at each of three phosphorylation residues revealed that TM phosphorylation renders Akt susceptible to dephosphorylation on the A-loop. When A-loop phosphatase was inhibited by okadaic acid (OA), TM phosphorylation still reduced Aloop phosphorylation, suggesting that the effect is caused at least partially through reduction of sensitivity to PDK1. Negative regulation by TM phosphorylation was also observed in constitutively active Akt and was functionally reflected in meiosis resumption. By contrast, HM phosphorylation enhanced A-loop phosphorylation and achieved full activation of Akt via a mechanism at least partially independent of TM phosphorylation. These observations provide new insight into the mechanism controlling Akt phosphorylation in the cell.

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“…These results suggest that these three BH3- Bim and Bad, is also known to be a client of HSP-90. 27 Thus, 17-AAG may restore the Bim and Bad levels and their proapoptotic activity in bcr-abl-expressing cells. Indeed, treatment of K562 and BV173 cells with 17-AAG caused an increase in the levels of Bim, Bmf and Bik, Bad dephosphorylation and a faint reduction in the levels of antiapoptotic Mcl-1 (Figure 4b, c).…”

mentioning

confidence: 99%

Apoptosis-based dual molecular targeting by INNO-406, a second-generation Bcr-Abl inhibitor, and ABT-737, an inhibitor of antiapoptotic Bcl-2 proteins, against Bcr-Abl-positive leukemia

et al. 2007

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Bcr-Abl is the cause of Philadelphia-positive (Ph þ ) leukemias and also constitutes their principal therapeutic target, as exemplified by dramatic effects of imatinib mesylate. However, mono-targeting of Bcr-Abl does not always achieve complete leukemia eradication, and additional strategies those enable complete elimination of leukemic cells are desired to develop. Here we demonstrate that INNO-406, a much more active Bcr-Abl tyrosine kinase inhibitor than imatinib, augments the activities of several proapoptotic Bcl-2 homology (BH)3-only proteins (Bim, Bad, Bmf and Bik) and induces apoptosis in Ph þ leukemia cells via Bcl-2 family-regulated intrinsic apoptosis pathway. ABT-737, an inhibitor of antiapoptotic Bcl-2 and Bcl-X L , greatly enhanced the apoptosis by INNO-406, even in INNO-406-less sensitive cells with Bcr-Abl point mutations except T315I mutation. In contrast, co-treatment with INNO-406 and other pharmacologic inducers of those BH3-only proteins, such as 17-allylaminogeldanamycin, an heat shock protein-90 inhibitor, or PS-341, a proteasome inhibitor, did not further increase the BH3-only protein levels or sensitize leukemic cells to INNO-406-induced apoptosis, suggesting a limit to how much expression levels of BH3-only proteins can be increased by anticancer agents. Thus, double-barrelled molecular targeting for Bcr-Abl-driven oncogenic signaling and the cell protection by antiapoptotic Bcl-2 family proteins may be the rational therapeutic approach for eradicating Ph þ leukemic cells.

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Akt Forms an Intracellular Complex with Heat Shock Protein 90 (Hsp90) and Cdc37 and Is Destabilized by Inhibitors of Hsp90 Function

Cited by 576 publications

References 53 publications

Akt shows variable sensitivity to an Hsp90 inhibitor depending on cell context

Akt shows variable sensitivity to an Hsp90 inhibitor depending on cell context

Turn motif phosphorylation negatively regulates activation loop phosphorylation in Akt

Apoptosis-based dual molecular targeting by INNO-406, a second-generation Bcr-Abl inhibitor, and ABT-737, an inhibitor of antiapoptotic Bcl-2 proteins, against Bcr-Abl-positive leukemia

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