R. Taichman et al., EVIDENCE THAT PROTEIN-TYROSINE KINASE P56-LCK REGULATES THE ACTIVITY OF PHOSPHATIDYLINOSITOL-3'-KINASE IN INTERLEUKIN-2-DEPENDENT T-CELLS, The Journal of biological chemistry, 268(27), 1993, pp. 20031-20036
The relative levels of phosphatidylinositol-3'-kinase (PI3K) activity
were measured in interleukin-2 (IL-2)-dependent helper (HT-2) and cyto
lytic (CTLL-2) T-cell clones that had been stably transfected with exp
ression plasmids encoding either the normal p56-Lck kinase or a mutant
version of this kinase, p56-Lck(Y505F), that has constitutively high
levels of kinase activity. Stimulation of untransfected T-cells or of
transfected T-cells containing increased levels of normal p56-Lck resu
lted in an approximate doubling of the relative amounts of total cellu
lar PI3K activity. In contrast, T-cells producing the activated versio
n of p56-Lck contained levels of PI3K activity comparable to or slight
ly higher than those found IL-2-stimulated control cells, even in the
absence of IL-2. Assessments of the relative levels of PI3K activity i
n immunoprecipitates prepared with the use of anti-phosphotyrosine-spe
cific antibodies revealed constitutively high levels of anti-phosphoty
rosine-immunoprecipitable PI3K activity in T-cells containing p56-Lck(
Y505F), as opposed to T-cells containing normal p56-Lck where increase
s in anti-PY-immunoprecipitable PI3K activity were IL-2-inducible. IL-
2 stimulation of T-cells containing the normal p56-Lck kinase resulted
in marked increases in the relative amounts of PI3K activity and p85
that were coimmunoprecipitated when using anti-p56-Lck antibodies. In
contrast, PI3K activity and the p85 subunit of PI3K could be coimmunop
recipitated from T-cells producing the activated p56-Lck(Y505F) kinase
even in the absence of IL-2 stimulation, implying constitutive associ
ation of PI3K with the activated Lck kinase. Taken together with previ
ous studies showing that IL-2 induces rapid increases in the activitie
s of both p56-Lck and PI3K in T-cells, these findings suggest that p56
-Lck lies immediately upstream of PI3K in a signal transduction cascad
e initiated by the binding of IL-2 to its specific receptor on T-lymph
ocytes.