Oncogenic Signalling of PEAK2 Pseudokinase in Colon Cancer

View from the PEAKs: Insights from structural studies on the PEAK family of pseudokinases

The PEAK family of pseudokinase scaffolds, comprising PEAK1 (originally termed SgK269), PEAK2 (SgK223, the human orthologue of rat Pragmin) and PEAK3 (C19orf35), have emerged as important regulators and integrators of cellular signaling and also play oncogenic roles in a variety of human cancers. These proteins undergo both homo- and heterotypic association that act to diversify signal output. Recently, structural and functional characterization of PEAK3 and its protein-protein interactions have shed light on PEAK signaling dynamics and the interdependency of PEAK family members, how PEAK dimerization regulates the binding of downstream effectors, and how 14-3-3 binding acts to regulate PEAK3 signal output. These important advances form the basis of this review.

Feed-forward stimulation of CAMK2 by the oncogenic pseudokinase PEAK1 generates a therapeutically 'actionable' signalling axis in triple negative breast cancer

The PEAK family of pseudokinases, comprising PEAK1-3, are signalling scaffolds that play oncogenic roles in several poor prognosis human cancers, including triple negative breast cancer (TNBC). However, therapeutic targeting of pseudokinases is challenging due to their lack of catalytic activity. To address this, we screened for PEAK1 effectors by affinity purification and mass spectrometry, identifying calcium/calmodulin-dependent protein kinase 2 (CAMK2)D and CAMK2G. PEAK1 promoted CAMK2D/G activation in TNBC cells via a novel feed-forward mechanism involving PEAK1/PLCγ1/Ca 2+ signalling and direct binding via a consensus CAMK2 interaction motif in the PEAK1 N-terminus. In turn, CAMK2 phosphorylated PEAK1 to enhance association with PEAK2, which is critical for PEAK1 oncogenic signalling. To achieve pharmacologic targeting of PEAK1/CAMK2, we repurposed RA306, a second generation CAMK2 inhibitor under pre-clinical development for treatment of cardiovascular disease. RA306 demonstrated on-target activity against CAMK2 in TNBC cells and inhibited PEAK1-enhanced migration and invasion in vitro . Moreover, RA306 significantly attenuated TNBC xenograft growth and blocked metastasis in a manner mirrored by CRISPR-mediated PEAK1 ablation. Overall, these studies establish PEAK1 as a critical cell signalling nexus, identify a novel mechanism for regulation of Ca 2+ signalling and its integration with tyrosine kinase signals, and identify CAMK2 as a therapeutically 'actionable' target downstream of PEAK1.