The Membrane Proximal Region of the Integrin β Cytoplasmic Domain Can Mediate Oligomerization

Integrin-ligand binding generates many intracellular signals, including signals to initiate focal contact formation and to regulate cellular decisions concerning growth and differentiation. Oligomerization of the β subunit cytoplasmic domain appears to be required for many of these events. In order to study these processes, we have generated a novel chimeric protein, consisting of the chicken integrin β₁ cytoplasmic domain connected to the central rod domain of a neuronal intermediate filament, α-internexin. This chimeric protein, when expressed transiently in 293T cells, oligomerizes in a β cytoplasmic domain-dependent manner. This oligomerization requires the membrane proximal amino acids LLMII of the β₁ cytoplasmic domain, as demonstrated by deletion analysis. Therefore, the integrin β cytoplasmic domain in this system contains an oligomerization function, which may provide some insight as to the function of intact integrins in vivo.