Protein kinase C fusion proteins are paradoxically loss of function in cancer

Van, An-Angela N.; Kunkel, Maya T.; Baffi, Timothy R.; Lordén, Gema; Antal, Corina E.; Banerjee, Sourav; Newton, Alexandra C.

doi:10.1016/j.jbc.2021.100445

Cited by 24 publications

(29 citation statements)

References 86 publications

(139 reference statements)

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“…Evidence for the importance of PKC as a tumor suppressor is provided by reanalysis of the tumor promotion mechanism of phorbol esters including DAG and PMA. Such tumor promoters have recently been shown to deplete PKC populations, indicating that their well-established tumor promotion activity actually stems from loss of PKC as a tumor suppressor (41)(42)(43). Due to the variety and complexity of cancer mechanisms, it is plausible that PKC activity may act as either a tumor/cancer promoter or suppressor depending on the cellular context.…”

Section: Discussionmentioning

confidence: 99%

“…Overall, the findings reveal a novel, bimodal regulatory system in which (i) moderate levels of a Ca 2+ -activated, conventional PKC can stimulate PI3K/PIP3 signaling in cells by phosphorylating MARCKS and releasing sequestered PIP2, while (ii) high levels of PKC are proposed to act as a brake on downstream PIP3 signaling by competitively blocking PDK1:AKT1 heterodimer formation and cis PDK1 phosphoactivation of AKT1. Notably, the latter inhibition of PDK1 by high levels of PKC provides a simple molecular explanation for the recent discovery that PKC acts as a tumor suppressor in cells (41)(42)(43).…”

Section: Introductionmentioning

confidence: 99%

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Single Molecule Studies and Kinase Activity Measurements Reveal Regulatory Interactions between the Master Kinases Phosphoinositide-Dependent-Kinase-1 (PDK1), Protein Kinase B (AKT1/PKB) and Protein Kinase C (PKCα)

Gordon

Ziemba

Falke

2021

Preprint

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Leukocyte migration is controlled by a leading edge chemosensory pathway that generates the regulatory lipid PIP3, a growth signal, thereby driving leading edge expansion up attractant gradients toward sites of infection, inflammation, or tissue damage. PIP3 also serves as an important growth signal in growing cells and oncogenesis. The kinases PDK1, AKT1/PKB and PKCα are key components of a plasma membrane-based PIP3 and Ca2+ signaling circuit that regulates these processes. PDK1 and AKT1 are recruited to the membrane by PIP3, while PKCα is recruited to the membrane by Ca2+. All three of these master kinases phosphoregulate an array of protein targets. For example, PDK1 activates AKT1, PKCα and other AGC kinases by phosphorylation at key sites. PDK1 is known to form PDK1:AKT1 and PDK1:PKCα heterodimers stabilized by a PIF interaction between the PDK1 PIF pocket and the PIF motif of the AGC binding partner. Here we present the first, to our knowledge, single molecule studies of full length PDK1 and AKT1 on target membrane surfaces, as well as their interaction with full length PKCα. The findings show that membrane-bound PDK1:AKT1 and PDK1:PKCα heterodimers form under physiological conditions, and are stabilized by PIF interaction. PKCα exhibits 8-fold higher PDK1 affinity than AKT1, thus PKCα competitively displaces AKT1 from PDK1:AKT1 heterodimers. Ensemble activity measurements under matched conditions reveal that PDK1 activates AKT1 via a cis mechanism by phosphorylating an AKT1 molecule in the same PDK1:AKT1 heterodimer, while PKCα acts as a competitive inhibitor of this phosphoactivation reaction by displacing AKT1 from PDK1. Overall, the findings provide new insights into molecular and regulatory interactions of the three master kinases on their target membrane, and suggest that the recently described tumor suppressor activity of PKC may arise from its ability to downregulate PDK1-AKT1 phosphoactivation in the PIP3-PDK1-AKT1-mTOR pathway linked to cell growth and oncogenesis.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Single Molecule Studies and Kinase Activity Measurements Reveal Regulatory Interactions between the Master Kinases Phosphoinositide-Dependent-Kinase-1 (PDK1), Protein Kinase B (AKT1/PKB) and Protein Kinase C (PKCα)

Gordon

Ziemba

Falke

2021

Preprint

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“…This hypothesis proposes that TIM phosphorylation by mTORC2 facilitates binding of PDK1 to monomerized PKC by exposing the C-tail, initiating the conformational switches leading to autophosphorylation at the hydrophobic motif. Unphosphorylated PKC is thermally unstable Parker, 1996, 1997;Edwards and Newton, 1997) and rapidly degraded in the cell (Baffi et al, 2019;Van et al, 2021); thus, dimerization may aide in stabilizing/protecting nascent PKC during processing. Biophysical assays showed that phosphorylation of the TIM and turn motif sites dissociates the PKC dimer, initiating the cascade of processing phosphorylations that yields a catalytically-competent kinase (Baffi et al, 2021a).…”

Section: Pkc: a Case Study In Tim Phosphorylationmentioning

confidence: 99%

mTOR Regulation of AGC Kinases: New Twist to an Old Tail

Baffi

Newton

2021

Mol Pharmacol

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The family of AGC kinases not only regulate cellular biology by phosphorylating substrates, but are themselves controlled by phosphorylation. Phosphorylation generally occurs at two conserved regions in these kinases: a loop near the entrance to the active site, termed the activation loop, that correctly aligns residues for catalysis, and a C-terminal tail whose phosphorylation at a site termed the hydrophobic motif stabilizes the active conformation.Whereas phosphorylation of the activation loop is well established to be catalyzed by the phosphoinositide-dependent kinase 1 (PDK1), the mechanism of phosphorylation of the C-tail hydrophobic motif has been controversial. For a subset of AGC kinases, which includes most protein kinase C (PKC) isozymes and Akt, phosphorylation of the hydrophobic motif in cells was shown to depend on mTORC2 over 15 years ago, yet whether by direct phosphorylation or by another mechanism has remained elusive. The recent identification of a novel and evolutionarily conserved phosphorylation site on the C-tail termed the TOR-Interaction Motif (TIM) has finally unraveled the mystery of how mTORC2 regulates its client kinases. mTORC2 does not directly phosphorylate the hydrophobic motif, rather it converts kinases such as PKC and Akt into a conformation that can ultimately autophosphorylate at the hydrophobic motif.Identification of the direct mTOR phosphorylation that facilitates auto-regulation of the C-tail hydrophobic motif revises the activation mechanisms of mTOR-regulated AGC kinases. This new twist to an old tail opens avenues for therapeutic intervention.Significance Statement: The enzyme mTORC2 has been an enigmatic regulator of AGC kinases such as protein kinase C (PKC) and Akt. The recent discovery of a motif named the TOR

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“…These priming phosphorylations are mediated by mTORC2 at a recently identified TOR Interaction Motif and adjacent turn motif on the C-tail, promoting phosphorylation by the phosphoinositide-dependent kinase 1 (PDK1) at the activation loop, in turn triggering an intramolecular autophosphorylation at another key regulatory site in the C-tail, the hydrophobic motif [ 11 ]. In the autoinhibited state, PKC is relatively resistant to dephosphorylation and subsequent degradation, and it has a half-time on the order of days [ 12 ]. This autoinhibited enzyme is transiently and reversibly activated by second messengers that recruit PKC to the plasma membrane where it is locked in an open and active conformation that can phosphorylate substrates and propagate downstream signaling.…”

Section: Pkc Maturation and Signalingmentioning

confidence: 99%

“…Downloaded from http://portlandpress.com/neuronalsignal/article-pdf/doi/10.1042/NS20210036/920816/ns-2021-0036c.pdf by guest on 27 September 2021 subsequent degradation, and it has a half-time on the order of days[12]. This autoinhibited enzyme is transiently and reversibly activated by second messengers that recruit PKC to the plasma membrane where it is locked in an open and active conformation that can phosphorylate substrates and propagate downstream signaling.…”

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confidence: 99%

Conventional protein kinase C in the brain: repurposing cancer drugs for neurodegenerative treatment?

Lordén

Newton

2021

Neuronal Signaling

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Protein Kinase C (PKC) isozymes are tightly regulated kinases that transduce a myriad of signals from receptor-mediated hydrolysis of membrane phospholipids. They play an important role in brain physiology, and dysregulation of PKC activity is associated with neurodegeneration. Gain-of-function mutations in PKCα are associated with Alzheimer’s disease and mutations in PKCγ cause spinocerebellar ataxia type 14. This article presents an overview of the role of the conventional PKCα and PKCγ in neurodegeneration and proposes repurposing PKC inhibitors, which failed in clinical trials for cancer, for the treatment of neurodegenerative diseases.

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Protein kinase C fusion proteins are paradoxically loss of function in cancer

Cited by 24 publications

References 86 publications

Single Molecule Studies and Kinase Activity Measurements Reveal Regulatory Interactions between the Master Kinases Phosphoinositide-Dependent-Kinase-1 (PDK1), Protein Kinase B (AKT1/PKB) and Protein Kinase C (PKCα)

Single Molecule Studies and Kinase Activity Measurements Reveal Regulatory Interactions between the Master Kinases Phosphoinositide-Dependent-Kinase-1 (PDK1), Protein Kinase B (AKT1/PKB) and Protein Kinase C (PKCα)

mTOR Regulation of AGC Kinases: New Twist to an Old Tail

Conventional protein kinase C in the brain: repurposing cancer drugs for neurodegenerative treatment?

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