The F-Actin-Binding MPRIP Forms Phase-Separated Condensates and Associates with PI(4,5)P2 and Active RNA Polymerase II in the Cell Nucleus.

Can Balaban,Martin Sztacho,Pavel Hozák,Michaela Blažíková

doi:10.3390/cells10040848

Can Balaban, Martin Sztacho + Show 2 more

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https://doi.org/10.3390/cells10040848

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Abstract

Here, we provide evidence for the presence of Myosin phosphatase rho-interacting protein (MPRIP), an F-actin-binding protein, in the cell nucleus. The MPRIP protein binds to Phosphatidylinositol 4,5-bisphosphate (PIP2) and localizes to the nuclear speckles and nuclear lipid islets which are known to be involved in transcription. We identified MPRIP as a component of RNA Polymerase II/Nuclear Myosin 1 complex and showed that MPRIP forms phase-separated condensates which are able to bind nuclear F-actin fibers. Notably, the fibrous MPRIP preserves its liquid-like properties and reforms the spherical shaped condensates when F-actin is disassembled. Moreover, we show that the phase separation of MPRIP is driven by its long intrinsically disordered region at the C-terminus. We propose that the PIP2/MPRIP association might contribute to the regulation of RNAPII transcription via phase separation and nuclear actin polymerization.

Highlights

Myosin phosphatase rho-interacting protein (MPRIP) was first described as a cytoskeletal protein involved in the regulation of stress fibers [1,2,3]
We show that MPRIP localizes to PIP2-containing nuclear structures, forms complex with RNA polymerase II (RNAPII) and MYO1C-an isoform of NM1-and undergoes liquid–liquid phase separation (LLPS)
The MPRIP protein was previously described as a cytoplasmic protein localizing to

Summary

Introduction

Myosin phosphatase rho-interacting protein (MPRIP) was first described as a cytoskeletal protein involved in the regulation of stress fibers [1,2,3]. Its binding to F-actin stress fibers is mediated by the N-terminal region which contains two Pleckstrin Homology (PH) domains [7,8]. These PH domains possess a lipid binding site where the positively charged residues (i.e., Lysine and Arginine) enable the binding of the negatively charged inositol head group of the phosphatidylinositol phosphates (PIPs) [9]. We proposed a model where PIP2 localizes into discrete nuclear areas where it regulates processes such as transcription and splicing [12].

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