Target-Based Discovery of an Inhibitor of the Regulatory Phosphatase PPP1R15B

Abstract

SummaryProtein phosphorylation is a prevalent and ubiquitous mechanism of regulation. Kinases are popular drug targets, but identifying selective phosphatase inhibitors has been challenging. Here, we used surface plasmon resonance to design a method to enable target-based discovery of selective serine/threonine phosphatase inhibitors. The method targeted a regulatory subunit of protein phosphatase 1, PPP1R15B (R15B), a negative regulator of proteostasis. This yielded Raphin1, a selective inhibitor of R15B. In cells, Raphin1 caused a rapid and transient accumulation of its phosphorylated substrate, resulting in a transient attenuation of protein synthesis. In vitro, Raphin1 inhibits the recombinant R15B-PP1c holoenzyme, but not the closely related R15A-PP1c, by interfering with substrate recruitment. Raphin1 was orally bioavailable, crossed the blood-brain barrier, and demonstrated efficacy in a mouse model of Huntington’s disease. This identifies R15B as a druggable target and provides a platform for target-based discovery of inhibitors of serine/threonine phosphatases.

KRCC1: A potential therapeutic target in ovarian cancer

“…53 While, HDAC inhibitors are being rigorously pursued for clinical translation, 54 inhibitors of the PP1 phosphatase regulatory complexes are being developed. 55,56 In summary, we speculate that KRCC1 localizes PP1CC and HDAC1/2 to specific chromatin regions, which is instrumental in transcriptional regulation and in ameliorating DNA damage. In the absence of KRCC1, persistent DNA damage further sensitizes tumors to DNA damaging agents such as cisplatin as demonstrated in the animal model.…”

“…In addition, in recent years, chromatin modifying agents have gained attention since epigenetic modifications are at the forefront of several malignancies . While, HDAC inhibitors are being rigorously pursued for clinical translation, inhibitors of the PP1 phosphatase regulatory complexes are being developed . In summary, we speculate that KRCC1 localizes PP1CC and HDAC1/2 to specific chromatin regions, which is instrumental in transcriptional regulation and in ameliorating DNA damage.…”

Kinetochore phosphatases suppress autonomous kinase activity to control the spindle assembly checkpoint

“…If phosphatase regulation has generally evolved to restrain or extinguish localised kinase activity, as we shown here for the SAC, then this regulation could be therapeutically targeted to specifically elevate kinase activity in a range of conditions. Recent work has demonstrated that inhibition of a specific regulated phosphatase complex is both achievable and therapeutically valuable 47,48 .…”

Division of labour between different PP2A-B56 complexes during mitosis

“…Future studies such as this, which build upon the work presented here, may ultimately help to reveal novel ways to modulate the activity of specific PP2A-B56 complexes. The recent development of selective inhibitors of related PP1 regulatory isoforms to combat neurodegenerative diseases (Das et al, 2015;Krzyzosiak et al, 2018), provides a proof-ofconcept that successful targeting of specific phosphatase isoforms is both achievable and therapeutically valuable.…”