A novel bivalent interaction mode underlies a non-catalytic mechanism for Pin1-mediated Protein Kinase C regulation

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    Pin1 as an essential prolyl cis/trans isomerase has attracted considerable attention because this enzyme family is implicated in cancer and neurodegenerative diseases. However, the requirement for its catalytic function remains a matter of dispute. The authors provide solid evidence that Pin1 modulates the activity of an important cell signaling kinase, Protein Kinase C, by a non-catalytic mechanism, acting as a chaperone to regulate the stability of this kinase.

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Abstract

Regulated hydrolysis of the phosphoinositide phosphatidylinositol(4,5)-bis-phosphate to diacylglycerol and inositol-1,4,5-P 3 defines a major eukaryotic pathway for translation of extracellular cues to intracellular signaling circuits. Members of the lipid-activated protein kinase C isoenzyme family (PKCs) play central roles in this signaling circuit. One of the regulatory mechanisms employed to downregulate stimulated PKC activity is via a proteasome-dependent degradation pathway that is potentiated by peptidyl-prolyl isomerase Pin1. Here, we show that contrary to prevailing models, Pin1 does not regulate conventional PKC isoforms α and βII via a canonical cis-trans isomerization of the peptidyl-prolyl bond. Rather, Pin1 acts as a PKC binding partner that controls PKC activity via sequestration of the C-terminal tail of the kinase. The high-resolution structure of Pin1 complexed to the C-terminal tail of PKCβII reveals that a novel bivalent interaction mode underlies the non-catalytic mode of Pin1 action.

Specifically, Pin1 adopts a compact conformation in which it engages two conserved phosphorylated PKC motifs, the turn motif and hydrophobic motif, the latter being a non-canonical Pin1-interacting element. The structural information, combined with the results of extensive binding studies and in vivo experiments suggest that non-catalytic mechanisms represent unappreciated modes of Pin1-mediated regulation of AGC kinases and other key enzymes/substrates.

Impact statement

Integrated biophysical, structural, and in vivo approaches demonstrate a non-canonical and non-isomerizable binding motif-dependent mode of protein kinase C regulation by the peptidyl-prolyl isomerase Pin1 in mammalian cells.

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  1. Author Response

    Reviewer #1 (Public Review):

    Reviewer 1: The structural part of this work is interesting, as it is the first structure of Pin1 with a ligand that bridges both domains. They might want to underline this - all other structures in the PDB have a single domain complex, but never both domains by a single longer peptide.

    Done. We have highlighted the novelty of the structure in the abstract, introduction (page 5); and discussion (section “The Pin1-PKC interface is described by a novel bivalent interaction mode”, page 24).

    Reviewer 1: I would however question the static representation of this structure - the 90{degree sign} kink in the peptide when complexed is probably one single snapshot, but I hardly believe the PPIase/WW domain orientation to be static. Unless the authors have additional information to stand by this …

  2. eLife assessment

    Pin1 as an essential prolyl cis/trans isomerase has attracted considerable attention because this enzyme family is implicated in cancer and neurodegenerative diseases. However, the requirement for its catalytic function remains a matter of dispute. The authors provide solid evidence that Pin1 modulates the activity of an important cell signaling kinase, Protein Kinase C, by a non-catalytic mechanism, acting as a chaperone to regulate the stability of this kinase.

  3. Reviewer #1 (Public Review):

    When writing a short review on the function of Pin1 some 15 years ago (Lippens et al., Febs J 2007), we concluded the introduction by the following sentence: "..., it seems that further analysis is required to determine whether binding or catalysis is the primary mechanism through which Pin1 affects cell cycle progression." In the present manuscript, the authors provide experimental evidence for the Pin1/PKC interaction that tips the balance towards interaction and not catalysis.

    Their main data concern the interaction between the V5 domains of two PKC isoenzymes (alpha and betaII) and Pin1. This V5 domain can be further separated into a Turn Motif (TM) and a Hydrophobic Motif (HM), that both can be phosphorylated on specific positions. Phosphorylation in the TM occurs on a TPP motif, and in agreement with …

  4. Reviewer #2 (Public Review):

    Chen, Dixit et al. report on the first structure of a bivalent interaction between a natural interaction partner of Pin1: the C-terminal tail of PKC phosphorylated at two sites. The biggest strength of the paper is the impressive amount of NMR-based structural data that is sound and clearly reported. The authors strive to propose a novel non-catalytic mechanistic role for Pin1 that is supported by cell culture models and somewhat by the interaction assays, however, in my eyes, they fell short in proving their mechanistic hypothesis. Nevertheless, the potential ways Pin1 may modulate PKC's activity is nicely discussed.