PP2A-B′ holoenzyme substrate recognition, regulation and role in cytokinesis

Abstract

Protein phosphatase 2A (PP2A) is a major Ser/Thr phosphatase; it forms diverse heterotrimeric holoenzymes that counteract kinase actions. Using a peptidome that tiles the disordered regions of the human proteome, we identified proteins containing [LMFI]xx[ILV]xEx motifs that serve as interaction sites for B′-family PP2A regulatory subunits and holoenzymes. The B′-binding motifs have important roles in substrate recognition and in competitive inhibition of substrate binding. With more than 100 novel ligands identified, we confirmed that the recently identified LxxIxEx B′α-binding motifs serve as common binding sites for B′ subunits with minor variations, and that S/T phosphorylation or D/E residues at positions 2, 7, 8 and 9 of the motifs reinforce interactions. Hundreds of proteins in the human proteome harbor intrinsic or phosphorylation-responsive B′-interaction motifs, and localize at distinct cellular organelles, such as midbody, predicting kinase-facilitated recruitment of PP2A-B′ holoenzymes for tight spatiotemporal control of phosphorylation at mitosis and cytokinesis. Moroever, Polo-like kinase 1-mediated phosphorylation of Cyk4/RACGAP1, a centralspindlin component at the midbody, facilitates binding of both RhoA guanine nucleotide exchange factor (epithelial cell transforming sequence 2 (Ect2)) and PP2A-B′ that in turn dephosphorylates Cyk4 and disrupts Ect2 binding. This feedback signaling loop precisely controls RhoA activation and specifies a restricted region for cleavage furrow ingression. Our results provide a framework for further investigation of diverse signaling circuits formed by PP2A-B′ holoenzymes in various cellular processes.

Proper chromosome alignment depends on BRCA2 phosphorylation by PLK1

“…Why is BRCA2 required for PP2A interaction with pBUBR1 and, is this regulated by PLK1? It has been reported that BRCA2 fragment from aa 1001 to aa 1255 (BRCA2 1001-1255 ) comprising a PP2A-B56 binding motif, binds to the B56 subunit of PP2A; in addition, the phosphorylation of positions 2 and 8 of this motif enhances the binding to B56 37 . In BRCA2, these positions are occupied by serines that are targets for PLK1.…”

PP2A‐B56 binds to Apc1 and promotes Cdc20 association with the APC/C ubiquitin ligase in mitosis

“…Crucially, the activity of PP2A-B55d fluctuates during the cell cycle, via the PP2A-B55d/ENSA/Greatwall pathway, and is high in interphase and low in mitosis [18][19][20]. More recent work suggests that PP2A-B56 achieves its functional specificity by binding to a LxxIxE short linear motif (SLiM) in which Glu (E) at position 6 is crucial, but position 1 (Leu) and position 4 (Ile) can be replaced by other hydrophobic residues, and phosphorylation or the enrichment of acidic residues within and downstream from the motif can increase PP2A-B56 binding [25][26][27]. In contrast, PP2A-B56 has been shown to be active during mitosis.…”

Reduction of protein phosphatase 2A (PP2A) complexity reveals cellular functions and dephosphorylation motifs of the PP2A/B′δ holoenzyme

“…Emerging evidence indicates that PSPs, including PP2A rely on short docking motifs in their substrates for recognition and dephosphorylation. Also referred to as short, linear interaction motifs (SLIMs), these degenerate, hydrophobic motifs are often distant from targeted phospho-Ser/Thr residues (13)(14)(15). We hypothesized that residues adjacent to sites targeted for dephosphorylation may also play a role in directing PP2A substrate selectivity (16).…”