Beta 1 ‐Integrins Control Spontaneous Adhesion and Motility of Human Progenitor Thymocytes and Regulate Differentiation‐Dependent Expression of the Receptor for Hyaluronan‐Mediated Motility

The functions of the receptor for hyaluronan‐mediated motility (RHAMM) and β 1 ‐integrin in adhesion and motility were analysed for human progenitor multinegative (CD3 −  4 −  8 −  19 − ) thymocytes (MN Thy). Both α 4 β 1 ‐ and α 5 β 1 ‐integrins are expressed by MN Thy, but only α 4 β 1 mediates fibronectin (FN)‐dependent adhesion and motility. Freshly isolated MN Thy lack expression of RHAMM and their motility is RHAMM independent. Prolonged surface expression of RHAMM on MN Thy is dependent upon FN. RHAMM expression, which occurs prior to surface expression of CD3/T‐cell receptor (TCR), was found to be inhibited by cross‐linking of α 4 ‐, α 5 ‐ and β 1 ‐integrins, as was the prolonged FN‐dependent phase of RHAMM expression. To confirm that RHAMM expression had been down‐regulated rather than rendered cryptic by treatment with immobilized anti‐integrin monoclonal antibody (MoAb), RHAMM mRNA levels were analysed. Transcription of RHAMM was decreased 7–12‐fold by treatment with immobilized anti‐α 4 or anti‐α 5 , and twofold by anti‐β 1 . Prior to expression of CD3/TCR and RHAMM, α 4 β 1 regulates migratory behaviour. After MN Thy differentiate to acquire CD3/TCR in vitro or in vivo , their motility becomes dependent upon both RHAMM and β 1 ‐integrins. Integrins play a direct role in FN‐dependent, RHAMM‐independent motility of MN Thy, and an indirect role in RHAMM‐dependent motility. This work shows that β 1 ‐integrins are primary mediators and regulators of fundamental cell behaviours required during migratory phases of T‐cell differentiation that occur prior to the expression of CD3/TCR.