Presumed pseudokinase VRK3 functions as a BAF kinase

Abstract

Vaccinia-related kinase 3 (VRK3) is known as a pseudokinase that is catalytically inactive due to changes in motifs that are essential for kinase activity. Although VRK3 has been regarded as a genuine pseudokinase from structural and biochemical studies, recent reports suggest that VRK3 acts as an active kinase as well as a signaling scaffold in cells. Here, we demonstrate that VRK3 phosphorylates the nuclear envelope protein barrier-to-autointegration factor (BAF) on Ser4. Interestingly, VRK3 kinase activity is dependent upon its N-terminal regulatory region, which is excluded from the determination of its crystal structure. Furthermore, the kinase activity of VRK3 is involved in the regulation of the cell cycle. VRK3 expression levels increase during interphase, whereas VRK1 is enriched in late G2 and early M phase. Ectopic expression of VRK3 induces the translocation of BAF from the nucleus to the cytoplasm. In addition, depletion of VRK3 decreases the population of proliferating cells. These data suggest that VRK3-mediated phosphorylation of BAF may facilitate DNA replication or gene expression by facilitating the dissociation of nuclear envelope proteins and chromatin during interphase.

Comparative Interactomes of VRK1 and VRK3 with Their Distinct Roles in the Cell Cycle of Liver Cancer

“…In the network analysis, 12 common potential interacting proteins, 29 VRK1-interacting candidate proteins, and 11 VRK3-interacting candidate proteins were identified. Consistent with previous findings (Gorjanacz et al, 2007; Park et al, 2015), BAF was identified in both VRK1 and VRK3 interactomes (Fig. 2C).…”

“…Indeed, VRK3 was initially reported to be a pseudokinase (Nichols and Traktman, 2004). However, we confirmed the kinase activity of VRK3 by demonstrating the VRK3-mediated phosphorylation of BAF at Ser 4 (Park et al, 2015). CDK5/p35 complex was identified as a regulator of VRK3 by phosphorylating VRK3 at Ser 108, which resulted in increase of its affinity to VHR (Song et al, 2016a).…”

“…VRK1 phosphorylates BAF at three sites, Ser4 and/or Thr2/Thr3, for the progression of mitosis (Nichols et al, 2006). VRK3 phosphorylates BAF at Ser4 for DNA replication during interphase (Park et al, 2015). We also identified 10 novel VRK1- or VRK3-interacting candidate proteins involved in the cell cycle, including cyclin B1 (CCNB1), centriolin (CTNRN), and spindlin-1 (SPIN1) (Fig.…”

“…During mitosis, VRK1 phosphorylates BAF in Ser 4, Thr 2 and Thr 3, which results in nuclear envelope disassembly required for the progression of mitosis (Gorjanacz et al, 2007; Nichols et al, 2006). During interphase, phosphorylation of BAF on Ser 4 by VRK3 promoted the disassembly of BAF, LEM proteins, and chromatin, which might result in the DNA replication (Park et al, 2015). Interaction of BAF with both VRK1 and VRK3 may imply the functional links during the specific biological processes.…”

Nuevas funciones de la quinasa humana VRK1 en la respuesta al daño en el ADN y la estructura de la cromatina

“…Inicialmente, se consideró que sólo las quinasas VRK1 y VRK2 eran catalíticamente activas, ya que VRK3 era una pseudoquinasa con mutaciones en aminoácidos clave en el dominio catalítico y que era incapaz de unir ATP (136). Sin embargo, estudios más recientes demuestran la capacidad que tiene VRK3 de fosforilar sustratos siguiendo un mecanismo no canónico, al igual que ocurre con otras pseudoquinasas (137).…”