J. Biol. Chem., Vol. 268, Issue 4, 2304-2306, Feb, 1993
Cell cycle-specific activation of the PTK72 protein-tyrosine kinase in B lymphocytes
DL Burg, ML Harrison and RL Geahlen
Department of Medicinal Chemistry and Pharmacognosy, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Indiana 47907-1333.
The engagement of cell-surface antigen receptors on B lymphocytes by
anti-IgM antibodies leads to the rapid tyrosine phosphorylation and
activation of the protein-tyrosine kinase, PTK72. High concentrations of
anti-IgM, which promote cell cycle entry and progression through G1, result
in a biphasic change in the state of tyrosine phosphorylation of PTK72. An
initial, rapid increase is seen within 5 min, which slowly declines to the
level found in resting cells over a period of 9 h. A second increase is
then observed 18-30 h following the initial stimulation. Low concentrations
of anti-IgM, which promote cell cycle entry but not progression through G1,
result only in the initial, rapid phosphorylation. The polyclonal mitogens
lipopolysaccharide and dextran sulfate, which stimulate both cell cycle
entry and progression to late G1, result only in the second, late phase of
tyrosine phosphorylation. This second phase of elevated tyrosine
phosphorylation is cell cycle- dependent, as demonstrated by its appearance
in cells blocked at G1/S and absence in cells blocked at G2/M. The increase
in the tyrosine phosphorylation of PTK72 is accompanied by an increase in
its activity with no change in its concentration. These data suggest a
possible second role for PTK72 in the commitment of activated B cells to
proliferation.
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