Despite the importance of integrins in epithelial cell biology surprisingly little is known about their regulation. It is known that they form hemidesmosomes (HDs), are actively involved in cell contacts during cell migration/invasion, and are key signaling molecules for survival and growth. However, there has been a distinct lack of understanding about what controls the dynamic integrin localization during cell activation and movement. Growth factors, such as EGF, are elevated during wound healing and carcinoma invasion leading to phosphorylation of ITGβ4 and the disassembly of the HD and mobilization of ITGβ4 to actin-rich protrusions. More recently the phosphorylation of a novel site on ITGβ4 (S1424) was found to be distinctly enriched on the trailing edge of migrating cells, suggesting a possible mechanism for the dissociation of ITGβ4 from HDs.

Arrestin family member proteins are involved in the regulation of cell surface proteins and vesicular trafficking. In this study, we find that over-expression of arrestin family member ARRDC3 causes internalization and proteosome-dependent degradation of ITGβ4, while decreased levels of ARRDC3 stabilizes ITGβ4 levels. These results lead us to a new mechanism of ITGβ4 internalization, trafficking and degradation. During migration, ARRDC3 co-localizes with ITGβ4 on the lagging edge of cells but has a distinct distribution on the leading edge of cells. Additional immuno co-precipitation experiments demonstrate that ARRDC3 preferentially binds to ITGβ4 when phosphorylated on S1424. Using confocal microscopy, we show that the expression pattern of ARRDC3 on the lagging edge of a migrating cell is identical to the expression pattern of ITGβ4-pS1424. We demonstrate that ARRDC3 expression represses cell proliferation, migration, invasion, growth in soft agar and tumorigenicity.

Collectively, our data reveals that ARRDC3 is a negative regulator of β4 integrin and demonstrates how this new pathway impacts biologic processes in stem cell and cancer biology. Additionally, as ARRDC3 is highly expressed in several tissues and conserved across species, our results are likely to be translated to other models.