Phosphorylation of synaptic GTPase-activating protein (synGAP) by polo-like kinase (Plk2) alters the ratio of its GAP activity toward HRas, Rap1 and Rap2 GTPases

Abstract

SynGAP is a Ras and Rap GTPase-activating protein (GAP) found in high concentration in the postsynaptic density (PSD) fraction from mammalian forebrain where it binds to PDZ domains of PSD-95. Phosphorylation of pure recombinant synGAP by Ca/calmodulin-dependent protein kinase II (CaMKII) shifts the balance of synGAP's GAP activity toward inactivation of Rap1; whereas phosphorylation by cyclin-dependent kinase 5 (CDK5) has the opposite effect, shifting the balance toward inactivation of HRas. These shifts in balance contribute to regulation of the numbers of surface AMPA receptors, which rise during synaptic potentiation (CaMKII) and fall during synaptic scaling (CDK5). Polo-like kinase 2 (Plk2/SNK), like CDK5, contributes to synaptic scaling. These two kinases act in concert to reduce the number of surface AMPA receptors following elevated neuronal activity by tagging spine-associated RapGAP protein (SPAR) for degradation, thus raising the level of activated Rap. Here we show that Plk2 also phosphorylates and regulates synGAP. Phosphorylation of synGAP by Plk2 stimulates its GAP activity toward HRas by 65%, and toward Rap1 by 16%. Simultaneous phosphorylation of synGAP by Plk2 and CDK5 at distinct sites produces an additive increase in GAP activity toward HRas (∼230%) and a smaller, non-additive increase in activity toward Rap1 (∼15%). Dual phosphorylation also produces an increase in GAP activity toward Rap2 (∼40-50%), an effect not produced by either kinase alone. As we previously observed for CDK5, addition of Ca/CaM causes a substrate-directed doubling of the rate and stoichiometry of phosphorylation of synGAP by Plk2, targeting residues also phosphorylated by CaMKII. In summary, phosphorylation by Plk2, like CDK5, shifts the ratio of GAP activity of synGAP to produce a greater decrease in active Ras than in active Rap, which would produce a shift toward a decrease in the number of surface AMPA receptors in neuronal dendrites.

SynGAP splice variants display heterogeneous spatio‐temporal expression and subcellular distribution in the developing mammalian brain

“…The activity of SynGAP toward small GTPases is considered to be its key functional role, with the other domains and sequence motifs being involved in regulating it. For instance, the C2 domain is key in the GAP activity toward Rap GTPases (Pena et al, 2008) and phosphorylation determines substrate specificity, as CaMK2α promotes RapGAP activity while CDK5 and PLK2 stimulate RasGAP activity (Walkup, Sweredoski, Graham, Hess, & Kennedy, 2018; Walkup et al, 2015). The exact role of sequences such as the pleckstrin homology (PH) domain, the SH3‐binding, or poly‐histidine motifs in the function of SynGAP are not yet understood.…”

Loss of PLK2 induces acquired resistance to temozolomide in GBM via activation of notch signaling

“…Besides these kinases which function as oncogenes, there are also a portion of tumor-suppressing kinases promotes aggressive biological behaviors of GBM via eliminated expression or inactivation. Serine/threonine-protein kinase polo like kinase 2 (PLK2) is a key regulator participates in centriole duplication [9], G1/S phase transition [10] and synaptic plasticity [11]. Benetatos et al [12] report that PLK2 expression is significantly suppressed in acute myeloid leukemias.…”

Modelling the Functions of Polo-Like Kinases in Mice and Their Applications as Cancer Targets with a Special Focus on Ovarian Cancer

“…It is found in a rather tissue-specific manner compared to PLK1 [ 19 , 56 ]. Attention has been drawn to participation in development, especially of the mammary gland epithelium [ 57 , 58 ] and to non-catalytic roles in the adult nervous system, where it is highly expressed and associated with the control of neuronal activity and synaptic function [ 59 , 60 , 61 , 62 ] repressing synaptic hyperactivity [ 63 ]. Mitosis-associated kinase activity is seen in centriole duplication, were PLK2 is localized during early G1 phase [ 64 , 65 ].…”