SHED-Dependent Oncogenic Signaling of the PEAK3 Pseudo-Kinase

Abstract

The PEAK1 and Pragmin/PEAK2 pseudo-kinases have emerged as important components of the protein tyrosine kinase pathway implicated in cancer progression. They can signal using a scaffolding mechanism that involves a conserved split helical dimerization (SHED) module. We recently identified PEAK3 as a novel member of this family based on structural homology; however, its signaling mechanism remains unclear. In this study, we found that, although it can self-associate, PEAK3 shows higher evolutionary divergence than PEAK1/2. Moreover, the PEAK3 protein is strongly expressed in human hematopoietic cells and is upregulated in acute myeloid leukemia. Functionally, PEAK3 overexpression in U2OS sarcoma cells enhanced their growth and migratory properties, while its silencing in THP1 leukemic cells reduced these effects. Importantly, an intact SHED module was required for these PEAK3 oncogenic activities. Mechanistically, through a phosphokinase survey, we identified PEAK3 as a novel inducer of AKT signaling, independent of growth-factor stimulation. Then, proteomic analyses revealed that PEAK3 interacts with the signaling proteins GRB2 and ASAP1/2 and the protein kinase PYK2, and that these interactions require the SHED domain. Moreover, PEAK3 activated PYK2, which promoted PEAK3 tyrosine phosphorylation, its association with GRB2 and ASAP1, and AKT signaling. Thus, the PEAK1-3 pseudo-kinases may use a conserved SHED-dependent mechanism to activate specific signaling proteins to promote oncogenesis.

Oncogenic Signalling of PEAK2 Pseudokinase in Colon Cancer

“…Several groups including ours have linked PEAK1_3 pseudokinases to cancer (i.e., PEAK1/Sgk269, PEAK2/Pragmin/SgK223/NACK, and PEAK3/C19orf35) [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. These pseudo-kinases belong to signalling proteins that regulate cell adhesion and proliferation induced by growth and adhesive cues [ 10 , 14 ].…”

“…Notably, their aberrant tumour expression often leads from epithelial cell to mesenchyme transition, which plays critical roles in cancer cell dissemination and therapeutic resistance [ 13 , 20 , 21 , 22 , 23 , 24 ]. PEAK3 is overexpressed in acute myeloid leukaemia and promotes leukaemic cell growth [ 16 ].…”

“…They display a classical protein kinase fold but are catalytically inactive because of an inaccessible nucleotide binding site occluded by an inhibitory triad. Importantly, they contain a Split HElical Dimerization (SHED) domain flanking the pseudokinase, which regulates PEAKs’ self-association ( Figure 1 B) [ 11 , 12 , 15 , 16 , 17 ]. This SHED module is essential for their scaffolding activity of signalling hubs and their oncogenic activity [ 12 , 16 , 17 ].…”

“…Importantly, they contain a Split HElical Dimerization (SHED) domain flanking the pseudokinase, which regulates PEAKs’ self-association ( Figure 1 B) [ 11 , 12 , 15 , 16 , 17 ]. This SHED module is essential for their scaffolding activity of signalling hubs and their oncogenic activity [ 12 , 16 , 17 ]. While protumour functions for PEAK1 were reported in CRC [ 26 ], the oncogenic role of PEAK2 in this cancer was not clearly established.…”

Structural insights into regulation of the PEAK3 pseudokinase scaffold by 14-3-3

“…Reminiscent of the signal switching effect that PEAK1 has on the EGF-induced Shc1 proteome, the PEAK3 interactome is also altered by EGF stimulation, suggesting that PEAK3 has a dynamic role in signaling 13 . Importantly, in osteosarcoma and acute myeloid leukemia (AML) cell lines, overexpression of PEAK3 results in elevated AKT activity and increased cell growth 14 .…”