Intracellular single-chain antibody inhibits integrin VLA-4 maturation and function

A single-chain antibody construct was prepared containing the V_H and V_L regions of anti-(integrin α⁴) antibody HP1/2, an interchain linker and a KDEL endoplasmic reticulum retention sequence. Intracellular expression of this single-chain antibody caused cell-surface expression of α⁴β₁ integrin to be decreased by 80% on selected RD cells and by 65–100% on selected Jurkat cells, relative to mock transfectants. Immunoprecipitation from single-chain-antibody-transfected cells showed that the single-chain antibody was complexed with the integrin α⁴ and β₁ subunits, and the diminished sizes of α⁴ and β₁ were consistent with impaired maturation. Furthermore, cell adhesion to α⁴β₁ ligands [VCAM-1 (vascular cell adhesion molecule-1), FN40 (40 kDa chymotryptic fragment of fibronectin) and CS1] was greatly impaired in both RD and Jurkat cells, and cell spreading on immobilized FN40 protein was almost completely eliminated. Thus we conclude that intracellular single-chain antibodies may be used to reduce or eliminate cell-surface expression of a specific integrin, with specific functional consequences. This approach should be generally applicable to other integrin subunits.