Active Mek2 as a regulatory scaffold that promotes Pin1 binding to BPGAP1 to suppress BPGAP1-induced acute Erk activation and cell migration

Abstract

BPGAP1 is a multidomain Rho GTPase-activating protein (RhoGAP) that promotes Erk activation and cell motility. However, the molecular mechanism of how these two processes are linked and regulated remains unclear. Here, we show that the RhoGAP domain of BPGAP1 interacts with the peptidyl-prolyl cis/trans isomerase (PPI) Pin1, leading to enhanced GAP activity towards RhoA. BPGAP1 also interacted with wild-type and constitutively active Mek2, but not with its kinase-dead mutant. However, only active Mek2 could bind Pin1, acting as a scaffold to bridge Pin1 and BPGAP1 in a manner that involves the release of an autoinhibited proline-rich motif, 186-PPLP-189, proximal to the RhoGAP domain. This allows the non-canonical 186-PPLP-189 and 256-DDYGD-260 motifs of the proline-rich region and RhoGAP domain of BPGAP1 to become accessible to concerted binding by the WW and PPI domains of Pin1, respectively. Interestingly, Pin1 knockdown led to ‘super-induction’ of BPGAP1-induced acute, but not chronic, Erk activation upon epidermal growth factor stimulation, in a process independent of GAP modulation. Reintroducing Pin1, but not its catalytic or non-binding mutants, reversed the effect and inhibited cell migration induced by coexpression of BPGAP1 and active Mek2. Thus, Pin1 regulates BPGAP1 function in Rho and Erk signalling, with active Mek2 serving as a novel regulatory scaffold that promotes crosstalk between RhoGAP, Pin1 and Erk in the regulation of cell migration.

Structural basis for the allosteric inhibitory mechanism of human kidney-type glutaminase (KGA) and its regulation by Raf-Mek-Erk signaling in cancer cell metabolism

“…Plasmid purification, transfection, cell proliferation assay, and immuno precipitation experiments were performed as previously described (28,29). Details are provided in SI Text.…”

Interleukin-1β production in human monocytes/macrophages is differentially regulated by MEK1 upon sterile and infectious inflammatory conditions

“…Although MEK1 and MEK2 activities are rarely distinguished in the literature, growing evidence indicates that MEK1 and MEK2 may be differentially regulated and exert non-redundant functions [42][43][44][45][46][47][48][49][50][51]. That MEK1 and MEK2 play different roles in the regulation of several cellular processes implies that either substrate other than ERK1/2 might be differentially phosphorylated by MEK1 and MEK2, or MEK1/2 functions that do not directly require kinase activity, or both [29,52]. However, ERK1/2 is still the only substrates of MEK1/2 identified to date.…”

“…However, ERK1/2 is still the only substrates of MEK1/2 identified to date. Noticeably, in studies revealing different functions of MEK1 and MEK2, MEK2 is often characterized as an important element in cross-talk between two pathways involving direct interaction between active MEK2 and other signaling molecules [29,30,53]. It has also been described that MEK2 may exert activity independently of ERK1/2 phosphorylation [29,30,53].…”

“…In the latter studies, MEK2 is likely to display protein scaffold activity promoting Pin1 binding to BPGAP1 and membrane localization of PI3Kδ, respectively. In the study by Pan et al [29] the scaffold activity of MEK2 aimed at diminishing the activation of ERK1/2. The present study does not prove a role of regulatory scaffold for MEK2, it only establishes that there is a pathway initiated by MEK2 that leads to IL-1β production in LPS-activated human monocytes.…”

“…More recently, it was shown that active MEK2 may function as a regulatory scaffold protein promoting a crosstalk between different transduction pathways [29], further demonstrating that MEK1 and MEK2 may display non-redundant functions in spite of identical downstream substrates. We also highlighted a non-redundant role of MEK1 and MEK2 in human monocytes activated by interferon-β.…”