Inhibition of PDK-1 activity causes a reduction in cell proliferation and survival

Abstract

3-Phosphoinositide-dependent kinase-1 (PDK-1) was identified by its ability to phosphorylate and activate protein kinase B (PKB) in vitro [1,2] and can phosphorylate and activate additional protein kinases in the AGC family in vitro [3-6]. Its role in vivo has, however, only begun to be addressed. We used antisense oligonucleotides directed against PDK-1 expression to explore the role of PDK-1 in human glioblastoma cells (U87-MG), which express a mutant PTEN allele. Reduction in PDK-1 levels resulted in inhibition of PKB activity, and a reduction in phosphorylation on Thr308 and Ser473 of PKB. p70 S6 kinase (p70(S6K)) activity was also reduced. Cell proliferation was dramatically inhibited following treatment with PDK-1 antisense oligonucleotides, due to a combination of decreased cell doubling and an increase in apoptosis. This is in contrast to direct inhibition of phosphoinositide 3-OH kinase (PI 3-kinase), which results in G1 arrest with no effect on apoptosis. This study confirms both PKB and p70(S6K) as in vivo substrates for PDK-1. The effect of acute PDK-1 loss on cell proliferation and survival suggests the involvement of PI 3-kinase dependent and independent signaling events, and implicates PDK-1 as a potential therapeutic target for human neoplasms.

Differential Regulation of Akt Kinase Isoforms by the Members of the TCL1 Oncogene Family

“…Phosphorylation of Thr-308, which is dependent on PDK1, is thought to be prerequisite for Akt activation (29). Antisense PDK1 oligonucleotide has been shown to inhibit phosphorylation of both Thr-308 and Ser-473 of Akt (37). However, recent studies using PDK1Ϫ/Ϫ cells suggest that phosphorylation of Ser-473 may be independent from Thr-308 phosphorylation (38).…”

Involvement of PI3K/Akt pathway in cell cycle progression, apoptosis, and neoplastic transformation: a target for cancer chemotherapy

“…This suggested that T157 of p27 Kip1 is important for nuclear localization and Cdk-2 inhibition. Furthermore, T157 is located within the nuclear localization sequence of p27 Kip1 (amino acids [151][152][153][154][155][156][157][158][159][160][161][162][163][164][165][166] and is contained in a putative Akt consensus phosphorylation site (RXXRXXT 157 D). Using breast cell lines as a model, it was shown that Akt could phosphorylate p27 Kip1 on T157 both in vitro and in vivo.…”

“…150 Similar results were obtained from studies of antisense oligonucleotides targeted to PDK1. 151 Earlier in this review, it was discussed that PI3K is a known downstream substrate of the GTPase Ras. Disruption of Ras activity may also be effective for inhibition of the PI3K/Akt pathway.…”

Phosphorylation of TNF-α converting enzyme by gastrin-releasing peptide induces amphiregulin release and EGF receptor activation

“…7-hydroxystaurosporine (UCN-01) inhibits PDK1 nonselectively and has been reported to abrogate tumor cell growth and promote apoptosis (52,53). PDK1 antisense oligonucleotides have shown to reduce glioblastoma cell proliferation and survival (54).…”