DEFECTIVE EXPRESSION OF BETA-1-INTEGRINS IN CELLS WITH CONSTITUTIVELYACTIVE ALPHA-L-BETA-2-INTEGRINS

We have investigated a potential relationship between expression of be ta 1-integrins and adhesiveness of the beta 2-integrin LFA-1 (alpha L beta 2, CD11a/CD18). By an approach of random mutagenesis and selectio n we established clones from the human acute lymphatic leukemia cell l ine HPB-ALL with (i) constitutively active LFA-1 and (ii) with no appa rent integrin-beta 1 cell surface expression. Thirty seven of 42 clone s selected for activated LFA-1 were found to have lost apparent integr in-beta 1 expression. Conversely, 7 of 21 clones selected for lack of beta 1 expression were found to have activated LFA-1. Since this point ed toward a possible coupling between beta 1 expression and LFA-1 acti vity, we further analyzed at which level beta 1 expression was blocked . We focused on one clone, HAP4, with activated LFA-I and no detectabl e beta 1 cell surface expression and found, surprisingly, that it expr essed wild-type levels of beta 1 mRNA and, in Western blots of whole c ell lysates, apparently normal levels of beta 1 protein. However, in a ddition to beta 1 of the expected molecular weight, HAP4 expressed a u nique 48-kDa band recognized by the polyclonal anti-beta 1 antiserum. Immunoprecipitation experiments revealed that the epitope recognized b y the anti-beta 1 antibody 4B4 was hidden or lost. The alpha 4-chain w as found in its precursor form but it did not associate with any beta- chain, and it was not processed to its mature form. Instead alpha 4-ch ains were eventually degraded. Taken together this showed that beta 1- chains were produced but not properly processed in HAP4. From this we propose that HAP4 is deficient in a gene product required both for pro per beta 1 folding and for repression of LFA-1 adhesiveness. (C) 1997 Academic Press.