title: Akt and PKC are involved not only in upregulation of telomerase activity but also in cell differentiation-related function via mTORC2 in leukemia cells.
abstract: 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.
authors.affiliation: Department of Hematology, Medical Research Institute, Tokyo Women's Medical University, Tokyo, Japan. yamadao@lab.twmu.ac.jp
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamada
authors.forename: Kohji
authors.initials: K
authors.lastname: Ozaki
authors.forename: Mayuka
authors.initials: M
authors.lastname: Nakatake
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Kakiuchi
authors.forename: Masaharu
authors.initials: M
authors.lastname: Akiyama
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Mitsuishi
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Kawauchi
authors.forename: Rumiko
authors.initials: R
authors.lastname: Matsuoka
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics*; D002867:Chromones / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D019098:Telomerase / Q000378:metabolism*; D014157:Transcription Factors / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C493245:CRTC2 protein, human; D002352:Carrier Proteins; D002867:Chromones; D009025:Morpholines; C492571:RICTOR protein, human; D034741:RNA, Small Interfering; C463659:RPTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D014157:Transcription Factors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D019098:Telomerase