Dataset Information

FAM122A ensures cell cycle interphase progression and checkpoint control by inhibiting B55⍺/PP2A through helical motifs

ABSTRACT: The Ser/Thr protein phosphatase 2A (PP2A) regulates the dephosphorylation of many phosphoproteins. Substrate recognition are mediated by B regulatory subunits. Here, we report the identification of a substrate conserved motif [RK]-V-x-x-[VI]-R in FAM122A, an inhibitor of B55α/PP2A. This motif is necessary for FAM122A binding to B55α, and computational structure prediction suggests the motif, which is helical, blocks substrate docking to the same site. In this model, FAM122A also spatially constrains substrate access by occluding the catalytic subunit. Consistently, FAM122A functions as a competitive inhibitor as it prevents substrate binding and dephosphorylation of CDK substrates by B55α/PP2A in cell lysates. FAM122A deficiency in human cell lines reduces the proliferation rate, cell cycle progression, and hinders G1/S and intra-S phase cell cycle checkpoints. FAM122A-KO in HEK293 cells attenuates CHK1 and CHK2 activation in response to replication stress. Overall, these data strongly suggest that FAM122A is a short helical motif (SHeM)-dependent, substrate-competitive inhibitor of B55α/PP2A that suppresses multiple functions of B55α in the DNA damage response and in timely progression through the cell cycle interphase

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Xavier Graña

LAB HEAD: Xavier Graña

PROVIDER: PXD052836 | Pride | 2024-08-10

REPOSITORIES: Pride

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			Action	DRS
	190228_Q2_Grana_293_Clone_5_Dox_1-1_Phospho.raw	Raw
	190228_Q2_Grana_293_Clone_5_Dox_1-2_Phospho.raw	Raw
	190228_Q2_Grana_293_Clone_5_Dox_2-1_Phospho.raw	Raw
	190228_Q2_Grana_293_Clone_5_Dox_2-2_Phospho.raw	Raw
	190228_Q2_Grana_293_Clone_5_NoDox_1-1_Phospho.raw	Raw

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FAM122A ensures cell cycle interphase progression and checkpoint control by inhibiting B55α/PP2A through helical motifs.

Wasserman Jason S JS Faezov Bulat B Patel Kishan R KR Kurimchak Alison M AM Palacio Seren M SM Glass David J DJ Fowle Holly H McEwan Brennan C BC Xu Qifang Q Zhao Ziran Z Cressey Lauren L Johnson Neil N Duncan James S JS Kettenbach Arminja N AN Dunbrack Roland L RL Graña Xavier X

Nature communications 20240710 1

The Ser/Thr protein phosphatase 2 A (PP2A) regulates the dephosphorylation of many phosphoproteins. Substrate recognition are mediated by B regulatory subunits. Here, we report the identification of a substrate conserved motif [RK]-V-x-x-[VI]-R in FAM122A, an inhibitor of B55α/PP2A. This motif is necessary for FAM122A binding to B55α, and computational structure prediction suggests the motif, which is helical, blocks substrate docking to the same site. In this model, FAM122A also spatially const ...[more]

PMID: 38982062

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Project description:The Ser/Thr protein phosphatase 2A (PP2A) is a highly conserved collection of heterotrimeric holoenzymes responsible for the dephosphorylation of many regulated phosphoproteins. Substrate recognition and the integration of regulatory cues are mediated by B regulatory subunits that are complexed to the catalytic subunit (C) by a scaffold protein (A). PP2A/B55 substrate recruitment was thought to be mediated by charge-charge interactions between the surface of B55a and its substrates. Challenging this view, we recently discovered a conserved SLiM [RK]-V-x-x-[VI]-R in a range of proteins, including substrates such as the retinoblastoma-related protein p107 and TAU (Fowle et al. eLife 2021;10:e63181). Here we report the identification of this SLiM in FAM122A, an inhibitor of B55a/PP2A. This conserved SLiM is necessary for FAM122A binding to B55a in vitro and in cells. Computational structure prediction with AlphaFold-Multimer predicts an interaction consistent with the mutational and biochemical data and supports a mechanism whereby FAM122A uses the 'SLiM' in the form of a short a-helix (helix 1) to dock to the B55a top groove, thereby blocking substrate binding to the same site. In this model, FAM122A also spatially constrains substrate access by occluding the catalytic subunit with a second a-helix immediately adjacent to helix 1. Consistently, FAM122A functions as a competitive inhibitor as it prevents the binding of substrates in in vitro competition assays and the dephosphorylation of CDK substrates by B55a/PP2A in cell lysates. The ablation of FAM122A in human cell lines reduces the rate of proliferation, progression through cell cycle transitions, and abrogates G1/S and intra-S phase cell cycle checkpoints. FAM122A-KO in HEK293 cells results in attenuation of CHK1 and CHK2 activation in response to replication stress. Overall, these data strongly suggest that FAM122A is a short helical motif (SHeM)-dependent, substrate-competitive inhibitor of B55a/PP2A that suppresses multiple functions of B55a in the DNA damage response and in timely progression through the cell cycle interphase.