Down‐regulation of monocytic VLA‐4 leads to a decreased adhesion to VCAM‐1

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Abstract
The α4β1 integrin VLA‐4 is expressed on practically all leukocytes, except on mature granulocytes. Here we show that in vitro treatment of monocytic cells with phorbol‐12‐myristate‐13‐acetate (PMA) leads to a selective decrease in the VLA‐4 α‐chain expression, both at the RNA and protein level. Meanwhile the expression of β1 and that of α5 another α‐chain associating with β1 was seen to increase. The decrease of α4 expression was restricted to monocytic cells, and was not observed on other VLA‐4‐positive cells tested (MOLT‐4 T cells and HOS sarcoma cells). The down‐regulation of the VLA‐4 α‐chain was followed by a decreased binding capacity of the cells to recombinant VCAM‐1. This data indicates that while previous findings show that the integrin‐dependent adhesion may rapidly be regulated by altering the avidity of the interacting molecules, their quantitative modulation also has a clear impact on adhesion.

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