The dual role of protein kinase C in the regulation of telomerase activity in human lymphocytes

Sheng, Wei-Yun; Chien, Yu-Yi; Wang, Tzu-Chien V.

doi:10.1016/s0014-5793(03)00230-8

Cited by 31 publications

(29 citation statements)

References 42 publications

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“…PKC-dependent activity was also known to be required in the expression of telomerase activity in activated T lymphocytes [19,20]. In this case, PKC activity was shown to be required both for the induction of hTERT expression and for the post-transcriptional control of telomerase enzyme activity [21]. To further understand the role of PKC-dependent signaling in the expression of telomerase, we have employed U-73122 [22] as an inhibitor for phosphoinositide-specific phospholipase C (PLC) to examine the role of PLC, an up-stream effector of PKC, in the expression of telomerase activity.…”

Section: Introductionmentioning

confidence: 94%

“…The peripheral blood lymphocytes (PBL) were isolated and cultured as previously described [21]. Cells were grown at 37°C in a humidified incubator containing 5% CO 2 .…”

Section: Cell Culturementioning

confidence: 99%

“…The cell extracts used for determining telomerase activity were prepared as previously described [21]. The cell extracts used for determining glucose-6-phosphate dehydrogenase (G6PD) activity were prepared by suspending the cells in G-buffer [50 mM Tris-HCl, pH 7.4, 150 mM NaCl, 1 mM EDTA, 1 mM NaF, 1% NP-40, and 0.5% sodium deoxycholate] and sonicated on ice to disrupt the cells.…”

Section: Cell Extractsmentioning

confidence: 99%

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Potent inhibition of human telomerase by U-73122

et al. 2006

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SummaryTelomerase activity is repressed in normal human somatic cells, but is activated in most cancers, suggesting that telomerase may be an important target for cancer therapy. In this study, we report that U-73122, an amphiphilic alkylating agent that is commonly used as an inhibitor for phospholipase C, is also a potent and selective inhibitor of human telomerase. The inhibition of telomerase by U-73122 was attributed primarily to the pyrrole-2,5-dione group, since its structural analog U-73343 did not inhibit telomerase. In confirmation, we observed that telomerase was inhibited by N-ethylmaleimide, but not N-ethylsuccinimide. The IC 50 value of U-73122 for the in vitro inhibition of telomerase activity is 0.2 lM, which is comparable to or slightly more sensitive than that for phospholipase C. The inhibitory action of U-73122 on telomerase appears to be rather selective since the presence of externally added proteins did not protect the inhibition and the IC 50 values for the other enzymes tested in this study were at least an order of magnitude higher than that for telomerase. Furthermore, we demonstrate that U-73122 can inhibit telomerase in hematopoietic cancer cells. The potent and selective inhibition of telomerase by U-73122 raises the potential exploitation of this drug and other alkylating agents as telomerase inhibitor.

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Section: Introductionmentioning

confidence: 94%

“…The peripheral blood lymphocytes (PBL) were isolated and cultured as previously described [21]. Cells were grown at 37°C in a humidified incubator containing 5% CO 2 .…”

Section: Cell Culturementioning

confidence: 99%

Section: Cell Extractsmentioning

confidence: 99%

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Potent inhibition of human telomerase by U-73122

et al. 2006

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“…It has been demonstrated that telomerase in human breast cancer cells is regulated by PKC a through phosphorylation of hTERT (Li et al, 1998). PKC z has been reported to regulate telomerase activity through both transcription and post-transcriptional mechanisms in nasopharyngeal cancer cells and peripheral T lymphocytes during T-cell activation (Yu et al, 2001;Sheng et al, 2003). These results indicate that telomerase is regulated by various PKC isoenzymes, perhaps depending on the specific cell type or cell status.…”

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confidence: 95%

hTERT phosphorylation by PKC is essential for telomerase holoprotein integrity and enzyme activity in head neck cancer cells

et al. 2006

Br J Cancer

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Telomerase activity is suppressed in normal somatic tissues but is activated in most cancer cells. We have previously found that all six telomerase subunit proteins, including hTERT and hsp90 are needed for full enzyme activity. Telomerase activity has been reported to be upregulated by protein kinase C (PKC), but the mechanism is not clear. In this study, we examined how PKC regulates telomerase activity in head and neck cancer cells. PKC inhibitor, bisindolylmaleimide I (BIS), inhibited telomerase activity but had no effect on the expressions of telomerase core subunits. RNA interference (RNAi) and in vitro phosphorylation studies revealed that PKC isoforms a, b, d, e, z specifically involved in telomerase regulation, and the phosphorylation target was on hTERT. Treatment with the hsp-90 inhibitor novobiocin dissociated hsp90 and hTERT as revealed by immunoprecipitation and immunoblot analysis and reduced telomerase activity. Treatment with the PKC activator SC-10 restored the association of hsp90 and hTERT and reactivate telomerase, suggesting that hTERT phosphorylation by PKC is essential for telomerase holoenzyme integrity and function. Analysis on clinical normal and tumour tissues reveal that the expressions of PKC a, b, d, e, z were higher in the tumour tissues, correlated with telomerase activity. Disruption of PKC phosphorylation by BIS significantly increased chemosensitivity to cisplatin. In conclusion, PKC isoenzymes a, b, d, e, z regulate telomerase activity in head and neck cancer cells by phosphorylating hTERT. This phosphorylation is essential for telomerase holoenzyme assembly, leading to telomerase activation and oncogenesis. Manipulation of telomerase activity by PKC inhibitors is worth exploring as an adjuvant therapeutic approach.

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“…Studies of protein phosphorylation have indicated that the up-regulation of telomerase activity during megakaryocytic differentiation and T lymphocyte activation is dependent on protein kinase C (PKC) (Counter et al 1998;Sheng et al 2003;Weng et al 1996). PI3K/Akt has also been proposed as a key signaling protein in telomerase regulation (Kawauchi et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Akt and PKC are involved not only in upregulation of telomerase activity but also in cell differentiation-related function via mTORC2 in leukemia cells

Ozaki

Nakatake

Kakiuchi

et al. 2010

Histochem Cell Biol

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We have shown previously that PI3K/Akt pathway is active after cell differentiation in HL60 cells. In the present study, we have investigated whether additional molecules, such as protein kinase C (PKC), are involved in the regulation, not only of telomerase, but also of leukemia cell differentiation. We show that PKC activates telomerase and is, itself, activated following VD3- or ATRA-induced differentiation of HL60 cells, as was observed for PI3K/Akt. To clarify the significance of PI3K/Akt and PKC pathway activation in leukemia cell differentiation, we examined the active proteins in either the downstream or upstream regulation of these pathways. In conjunction with the activation of Akt or PKC, mTOR and S6K were phosphorylated and the protein expression levels of Rictor were increased, compared with Raptor, following cell differentiation. Silencing by Rictor siRNA resulted in the attenuation of Akt phosphorylation on Ser473 and PKCα/βII phosphorylation, as well as the inhibition of Rictor itself, suggesting that Rictor is an upstream regulator of both Akt and PKC. In addition, in cells induced to differentiate by ATRA or VD3, Nitroblue-tetrazolium (NBT) reduction and esterase activity, were blocked either by LY294002, a PI3K inhibitor, or by BIM, a PKC inhibitor, without affecting cell surface markers such as CD11b or CD14. Intriguingly, the silencing of Rictor by its siRNA also suppressed the reducing ability of NBT following VD3-induced cell differentiation. Taken together, our results show that Rictor associated with mTOR (mTORC2) regulates the activity of both Akt and PKC that are involved in cell functions such as NBT reduction and esterase activity induced by leukemia cell differentiation.

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The dual role of protein kinase C in the regulation of telomerase activity in human lymphocytes

Cited by 31 publications

References 42 publications

Potent inhibition of human telomerase by U-73122

Potent inhibition of human telomerase by U-73122

hTERT phosphorylation by PKC is essential for telomerase holoprotein integrity and enzyme activity in head neck cancer cells

Akt and PKC are involved not only in upregulation of telomerase activity but also in cell differentiation-related function via mTORC2 in leukemia cells

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