A Dominant Jurkat T Cell Mutation That Inhibits LFA-1-Mediated Cell Adhesion Is Associated with Increased Cell Growth

LFA-1 exists in a low avidity state on resting leukocytes and is believed to adopt a high avidity state when the cells are exposed to a stimulus. Current evidence supports both aggregation of LFA-1 on the cell surface and conformational changes in the reversible acquisition of a high avidity state. We studied this regulation by selecting a Jurkat T cell clone, J-lo1.3, that expresses LFA-1 yet fails to bind to purified ICAM-1 despite treatment of the cells with PMA or Mn2+. Several lines of evidence demonstrated the absence of any changes within LFA-1 itself. LFA-1 protein purified from the J-lo1.3 clone and the wild-type Jurkat clone, Jn.9, were found to be functionally equivalent. The cDNA sequences encoding the LFA-1 alpha- and beta-chains from J-lo1.3 were identical with the published sequences except for nine base pairs. However, these differences were also found in a Jurkat mutant with a constitutively avid phenotype, J+hi1.19 or the wild-type Jn.9 genomic or cDNA. Fusion of J-lo1.3 with Jn.9 yielded hybrids that exhibited the J-lo1.3 adhesion phenotype, which indicated a dominant mutation in J-lo1.3. This phenotype was relatively specific for LFA-1 among all integrins expressed by Jurkat. Interestingly, the J-lo1.3 cells had a 1.2-fold faster doubling time than did the Jn.9 cells. Reversion of J-lo1.3 to the wild-type adhesion phenotype by mutagenesis and selection also decreased the growth rate. These data support a connection between cellular growth and cellular adhesion in lymphocytes.