Deficiency of ADAP/Fyb/SLAP-130 destabilizes SKAP55 in Jurkat T cells.
ADAP (adhesion and degranulation-promoting adaptor protein) and SKAP55 (Src kinase-associated phosphoprotein of 55 kDa) are T cell adaptors that mediate inside-out signaling from the T cell antigen receptor to integrins, giving rise to increased integrin affinity/avidity and formation of the immunological synapse between the T cell and the antigen-presenting cell. These two proteins are tightly and constitutively associated with one another, and their ability to interact is required for inside-out signaling. Here we show in an ADAP-deficient Jurkat T cell line that the co-dependence of ADAP and SKAP55 extends beyond their functional and physical interactions and show that SKAP55 protein is unstable in the absence of ADAP. Restoration of ADAP to the ADAP-deficient Jurkat T cell line restores SKAP55 expression by causing a 5-fold decrease in the rate of SKAP55 proteolysis. Inactivation of the Src homology 3 domain of SKAP55, which mediates the association between SKAP55 with ADAP, blocks the protective effect of ADAP. The half-life of SKAP55, in the absence of ADAP, is approximately 15-20 min, increasing to 90 min in the presence of ADAP. This is a remarkably rapid rate of turnover for a signaling protein and suggests the possibility that stimuli that signal for the stabilization of SKAP55 may play an important role in T cell adhesion and conjugate formation.
Huang
Yanping
Y
Laboratory of Cellular and Molecular Biology, NIA, National Institutes of Health, Intramural Research Program/Department of Health and Human Services, Baltimore, Maryland 21224, USA. HUANGY@email.chop.edu
Norton
Darrell D
DD
Precht
Patricia
P
Martindale
Jennifer L
JL
Burkhardt
Janis K
JK
Wange
Ronald L
RL
D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D001483:Base Sequence; D017931:DNA Primers; D006801:Humans; D019169:Jurkat Cells; D010750:Phosphoproteins / Q000502:physiology*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; C106957:FYB1 protein, human; D010750:Phosphoproteins; C108336:SKAP1 protein, human