Invasive potentials of
carcinomas greatly contribute to their
metastasis, which is a major threat in most
cancers. We have recently shown that Arf6 plays a pivotal role in
breast cancer invasive activities and identified AMAP1 as an effector of GTP-Arf6 in invasion. Expression of AMAP1 correlates well with invasive phenotypes of primary
tumors of the human breast. We also have shown that AMAP1 functions by forming a trimeric
protein complex with
cortactin and
paxillin. In this complex, AMAP1 binds to the src homology 3 (SH3) domain of
cortactin via its
proline-rich
peptide, SKKRPPPPPPGHKRT. SH3 domains are known to bind generally to the
proline-rich
ligands with a one-to-one stoichiometry. We found that AMAP1/
cortactin binding is very atypical in its stoichiometry and interface structure, in which one AMAP1
proline-rich
peptide binds to two
cortactin SH3 domains simultaneously. We made a cell-permeable
peptide derived from the AMAP1
peptide, and we show that this
peptide specifically blocks AMAP1/
cortactin binding, but not other canonical SH3/
proline bindings, and effectively inhibits
breast cancer invasion and
metastasis. Moreover, this
peptide was found to block invasion of other types of
cancers, such as
glioblastomas and lung
carcinomas. We also found that a small-molecule compound,
UCS15A, which was previously judged as a weak inhibitor against canonical SH3/
proline bindings, effectively inhibits AMAP1/
cortactin binding and
breast cancer invasion and
metastasis. Together with fine structural analysis, we propose that the AMAP1/
cortactin complex, which is not detected in normal mammary epithelial cells, is an excellent
drug target for
cancer therapeutics.