Cooperative signaling between alpha(6)beta(4) integrin and ErbB-2 receptoris required to promote phosphatidylinositol 3-kinase-dependent invasion

We previously demonstrated that beta(4) integrin subunit overexpression inc reases in vitro invasiveness of NIH3T3 cells that have been transformed by ErbB-2 oncogene. We used this model to identify domains within the large be ta(4) cytoplasmic domain that are involved in the interaction of alpha(6)be ta(4) with ErbB-2, invasion, and phosphatidylinositol 3-kinase (PI3K) activ ation. For this purpose, we expressed deletion mutants of beta(4) that lack ed either all or portions of the beta(4) cytoplasmic domain in NIH3T3/ErbB- 2 cells. me also used an ecto-domain mutant in which most of the extracellu lar domain of beta(4) was replaced with a c-Myc tag, These transfectants we re examined for their ability to invade Matrigel and their ability to activ ate PI3K, as well as for the ability of alpha(6)beta(4) to co-immunoprecipi tate with ErbB-2, The results obtained revealed that a region of the beta(4 ) cytoplasmic domain between amino acids 854 and 1183 is critical for the a bility of alpha(6)beta(4) integrin to increase invasion. Interestingly, the extracellular domain of beta(4) is not necessary for alpha(6)beta(4) to st imulate invasion. The association of alpha(6)beta(4) with ErbB-2 is depende nt upon the beta(4) cytoplasmic domain and can occur in the absence of alph a(6)beta(4) heterodimerization, Finally, we observed strong activation of P I3K with beta(4) wild type and with those beta(4) deletion mutants that wer e able to stimulate invasion upon the expression in NIH3T3/ErbB-2 cells, In conclusion our results establish that there is cooperation between alpha(6 )beta(4) and ErbB-2 in promoting PI3K-dependent invasion and implicate a sp ecific region of the beta(4) cytoplasmic domain (amino acids 854-1183) in t his event.