β1-Integrins Mediate Ca2+-Signalling and T Cell Spreading via Divergent Pathways

Interaction of Jurkat T-lymphocytes with two extracellular matrix (ECM) proteins of the basement membrane, laminin or collagen type IV, combined with poly-L-lysine resulted in a strong adhesion, a highly increased intracellular Ca 2+ -concentration ([Ca 2+ ] i ), as compared to cells on laminin or collagen type IV alone and in spreading of the cells. The strong adhesion was independent of an increase in [Ca 2+ ] i , was not mediated by a β1-integrin, and was due to charge interaction between the positively charged polyaminoacid and the negatively charged cell surface. The latter was confirmed by substitution of poly-L-lysine by other positively charged polyaminoacids. In contrast, Ca 2+ -signalling and spreading of the cells adhering to laminin or collagen type IV combined with poly-L-lysine was completely blocked by anti-β1 mAb. However, spreading of the cells was independent of an increase in [Ca 2+ ] i suggesting divergent signal transduction pathways leading to Ca 2+ -signalling and spreading of the cells. We elucidated these signal transduction pathways by inhibition of key enzymes involved. The tyrosine kinase inhibitor genistein blocked Ca 2+ -signalling as well as spreading, whereas inhibitors of PKC (calphostin C, GF109203x), PLCγ (U73122) and PLA 2 (bromophenacyl-bromide (BPB), 3-[4-octadecyl)benzoyl]acrylic acid (OBAA)) selectively blocked spreading of the cells.