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.

Enzasataurin Enhances ATRA-induced Differentiation of Acute Myeloid Leukemia Cells

“…The role of different PKC isozymes in granulocytic differentiation is quite controversial. For ATRA-induced granulocytic differentiation in HL-60 cells, PKCα and PKCβII are activated and positively regulate granulocytic differentiation [31]. However, Zauli G et al reported that only PKCα and PKCζ but neither PKCβII nor PKCβI showed signi cant modi cation upon ATRA treatment in HL-60 cells [32].…”

mTOR signaling for biological control and cancer

“…When active, mTORC2 is phosphorylated on Ser2481 (Copp et al, 2009) and is important for cell survival, metabolism, proliferation, and cytoskeletal organization. mTORC2 phosphorylates Protein Kinase Cα (PKC), which regulates cell proliferation, differentiation, apoptosis, and telomerase activities and is constitutively active in hematopoetic cancers, where it promotes cell proliferation and survival (Ikenoue et al, 2008; Yamada et al, 2010; Zhang et al, 2012). Knockdown of mTORC2 components disrupts cell morphology and actin polymerization (Loewith et al, 2002; Jacinto et al, 2004).…”

Protein kinase Cδ (PKCδ) involved in the regulation of pAkt1 (Ser473) on the release of mouse oocytes from diplotene arrest

“…17 Some studies have demonstrated that there are various PKC isoforms in the oocytes and zygotes. [19][20][21][22][23] However, little information is available on mouse oocytes. 18 Several studies have indicated that PKC may play a role on Akt in many cell function.…”

“…18 Several studies have indicated that PKC may play a role on Akt in many cell function. [19][20][21][22][23] However, little information is available on mouse oocytes.…”