The EGFR‐GEP100‐Arf6‐AMAP1 Signaling Pathway Specific to Breast Cancer Invasion and Metastasis^†

Abstract

Tumors are tissue-specific diseases, and their mechanisms of invasion and metastasis are highly diverse. In breast cancer, biomarkers that specifically correlate with the invasive phenotypes have not been clearly identified. A small GTPase Arf6 primarily regulates recycling of plasma membrane components. We have shown that Arf6 and its effector AMAP1 (DDEF1, DEF1, ASAP1 and centaurin β4) are abnormally overexpressed in some breast cancers and used for their invasion and metastasis. Overexpression of these proteins is independent of the transcriptional upregulation of their genes, and occurs only in highly malignant breast cancer cells. We recently identified GEP100 (BRAG2) to be responsible for the Arf6 activation to induce invasion and metastasis, by directly binding to ligand-activated epidermal growth factor receptor (EGFR). A series of our studies revealed that for activation of the invasion pathway of EGFR, it is prerequisite that Arf6 and AMAP1 both are highly overexpressed, and that EGFR is activated by ligands. Pathological analyses indicate that a significant large population of human ductal cancers may utilize the EGFR-GEP100-Arf6-AMAP1 pathway for their malignancy. Microenvironments have been highly implicated in the malignancy of mammary tumors. Our results reveal an aspect of the precise molecular mechanisms of some breast cancers, in which full invasiveness is not acquired just by intracellular alterations of cancer cells, but extracellular factors from microenvironments may also be necessary. Possible translation of our knowledge to cancer therapeutics will also be discussed.

Arf6 regulates tumour angiogenesis and growth through HGF-induced endothelial β1 integrin recycling

“…In addition, the well-known Arf6 effector phosphatidylinositol 4-phosphate 5-kinase 18 , which produces the versatile signalling lipid phosphatidylinositol 4,5-bisphosphate, regulates tethering of vesicles containing b1 integrin to the plasma membrane and/or fusion with it at the leading edge of migrating cells through the interaction of generated phosphatidylinositol 4,5-bisphosphate with the exocyst protein Exo70 (ref. 49). From these reports, it is likely that different pools of Arf6 are sequentially activated by distinct Arf6 GEFs and regulate different effectors at each step of b1 integrin recycling.…”

Overexpression of ARF1 is associated with cell proliferation and migration through PI3K signal pathway in ovarian cancer

“…It has been reported that ADP ribosylation factors (ARF), another family of small GTP-binding proteins, are closely related to cancer progression (9). Like all other GTPases, ARFs cycle between their inactive (GDP bound) and active (GTP bound) form.…”

Tumor responsiveness to statins requires overexpression of the ARF6 pathway

“…4,7 Moreover, these predictions were based on mRNA levels, and it should be noted that protein levels of ARF6 and AMAP1 are primarily determined post-transcriptionally. 6 Protein expression levels of EPB41L5 correlated well with its mRNA levels.…”

“…4 A series of our previous studies have shown that ARF6 and its signaling proteins, namely A Multi-domain ARF GAP Protein 1 (AMAP1, also called ASAP1/DDEF1) and Erythrocyte Membrane Protein Band 4.1 Like 5 (EPB41L5) are frequently overexpressed in different cancers. [4][5][6][7] Similar to RAS and RHO, ARF6 is a housekeeping small-GTPase, and primarily regulates recycling of plasma membrane components at cell peripheries. However, upon overexpression of ARF6, AMAP1, and EPB41L5, the ARF6-AMAP1-EPB41L5 pathway becomes crucial for the promotion of invasion and metastasis through enhanced integrin recycling and also becomes crucial for drug resistance by yet unidentified mechanisms.…”

“…However, upon overexpression of ARF6, AMAP1, and EPB41L5, the ARF6-AMAP1-EPB41L5 pathway becomes crucial for the promotion of invasion and metastasis through enhanced integrin recycling and also becomes crucial for drug resistance by yet unidentified mechanisms. [4][5][6][7] During invasion and metastasis, ARF6 is activated by GEP100, which is recruited to ligand-activated receptor tyrosine kinases (RTKs) such as epidermal growth factor receptor, hepatocyte growth factor receptor (also known as c-MET), and vascular endothelial cell growth factor receptor 2 8 or, alternatively, ARF6 is activated by EFA6, which binds to GTP-bound Ga12 that is released from G-protein-coupled receptors activated by lysophosphatidic acid (LPA-GPCR). 7 ARF6 is acylated but not prenylated.…”