The lysyl oxidase gene inhibits Ras signaling in transformed fibroblasts and 
breast cancer cells. Its activity was mapped to the 162 amino acid propeptide 
domain (LOX-PP) of the lysyl oxidase precursor protein. LOX-PP inhibited the 
Her-2/Ras signaling axis in breast cancer cells, and reduced the Her-2-driven 
breast tumor burden in a xenograft model. Since its mechanism of action is 
largely unknown, co-affinity-purification/mass spectrometry was performed and 
the "Cbl-interacting protein of 85-kDa" (CIN85) identified as an associating 
protein. CIN85 is an SH3-containing adapter protein that is overexpressed in 
invasive breast cancers. The CIN85 SH3 domains interact with c-Cbl, an E3 
ubiquitin ligase, via an unconventional PxxxPR ligand sequence, with the highest 
affinity displayed by the SH3-B domain. Interaction with CIN85 recruits c-Cbl to 
the AMAP1 complex where its ubiquitination activity is necessary for cancer 
cells to develop an invasive phenotype and to degrade the matrix. Direct 
interaction of LOX-PP with CIN85 was confirmed using co-immunoprecipitation 
analysis of lysates from breast cancer cells and of purified expressed proteins. 
CIN85 interaction with c-Cbl was reduced by LOX-PP. Domain specific CIN85 
regions and deletion mutants of LOX-PP were prepared and used to map the sites 
of interaction to the SH3-B domain of CIN85 and to an epitope encompassing amino 
acids 111 to 116 of LOX-PP. Specific LOX-PP point mutant proteins P111A and 
R116A failed to interact with CIN85 or to compete for CIN85 binding with c-Cbl. 
Structural modeling identified a new atypical PxpxxRh SH3-binding motif in this 
region of LOX-PP. The LOX-PP interaction with CIN85 was shown to reduce the 
invasive phenotype of breast cancer cells, including their ability to degrade 
the surrounding extracellular matrix and for Matrigel outgrowth. Thus, LOX-PP 
interacts with CIN85 via a novel SH3-binding motif and this association reduces 
CIN85-promoted invasion by breast cancer cells.