WAVE3 phosphorylation regulates the interplay between PI3K, TGF-β, and EGF signaling pathways in breast cancer

Abstract

Both TGF-β and the PI3K-AKT signaling pathways are known activators of various intracellular pathways that regulate critical cellular functions, including cancer cell survival and proliferation. The interplay between these two oncogenic pathways plays a major role in promoting the initiation, growth, and progression of tumors, including breast cancers. The molecular underpinning of the inter-relationship between these pathways is, however, not fully understood, as is the role of WAVE3 phosphorylation in the regulation of tumor growth and progression. WAVE3 has been established as a major driver of the invasion–metastasis cascade in breast cancer and other tumors of epithelial origin. WAVE3 phosphorylation downstream of PI3K was also shown to regulate cell migration. Here we show that, in addition to PI3K, WAVE3 tyrosine phosphorylation can also be achieved downstream of TGF-β and EGF and that WAVE3 tyrosine phosphorylation is required for its oncogenic activity. Our in vitro analyses found loss of WAVE3 phosphorylation to significantly inhibit cell migration, as well as tumorsphere growth and invasion. In mouse models for breast cancer, loss of WAVE3 phosphorylation inhibited tumor growth of two aggressive breast cancer cell lines of triple-negative subtype. More importantly, we found that WAVE3 phosphorylation is also required for the activation of PI3K, TGF-β, and EGF signaling and their respective downstream effectors. Therefore, our study identified a novel function for WAVE3 in the regulation of breast cancer development and progression through the modulation of a positive feedback loop between WAVE3 and PI3K-TGF-β-EGF signaling pathways.

Phosphorylation of the proline-rich domain of WAVE3 drives its oncogenic activity in breast cancer

“…Our published studies have also shown that phosphorylation of WAVE3 at four tyrosine residues (Fig. 1 A) can be achieved upon stimulation with PDGF and activation of phosphatidylinositol 3-kinase (PI3K) signaling pathway 15 , 16 . Furthermore, we have also shown that the PRD domain of WAVE3 is required for the oncogenic activity of WAVE3 by activating the CSC phenotype in TNBC cells 14 .…”

“…We used STR DNA fingerprinting analysis for regular authentication of cells that we used for this study. WAVE3-deficient (WAVE3-KO) cells were produced using lentiviral transduction as described 14 , 15 . For each BC cell line, we used two different and verified WAVE3-specific sgRNAs and a scrambled sgRNA i.e., nonsilencing sgRNA 14 , 15 .…”

“…Subsequent recruitment of Rho GTPase Rac1 to the WRC releases WAVE3 from this complex 11 , which becomes free to bind to the actin nucleator Arp2/3 complex and activate actin polymerization 9 , 12 , 13 . Recent studies from our group have however identified a function for WAVE3 that may be independent of its traditional relationship with the WRC, Arp2/3 complex and actin polymerization 14 , 15 .…”

“…Post-translational modifications (PTMs) of proteins plays a major role in driving the oncogenic activity in several cancer types including BC. Several studies have shown that PTM of WAVE3 through its tyrosine phosphorylation was critical for that WAVE3-mediated regulation of tumor progression and metastasis of TNBC 15 – 17 . Phosphorylation of WAVE3 at four tyrosine residues (Y151, Y248, Y337, and Y486) is mediated by the non-receptor tyrosine kinase c-Abl, downstream of PI3K 16 .…”

“…Phosphorylation of WAVE3 at four tyrosine residues (Y151, Y248, Y337, and Y486) is mediated by the non-receptor tyrosine kinase c-Abl, downstream of PI3K 16 . A more recent study has shown that the oncogenic activity of WAVE3 in BC is significantly enhanced as a result of tyrosine phosphorylation 15 . Two of the four tyrosine residues of WAVE3, Y248 and Y337, reside within the PRD domain.…”