The DNA synthesis of leukemic (L2C) guinea pig B lymphocytes involves a permanent activation of protein kinase C without corresponding phosphoinositide hydrolysis.
L2C B lymphocytes have a constant high DNA synthesis due to their continuous proliferative state. The addition of polymyxin B (PmB), a rather selective inhibitor of protein kinase C, stopped (3H)thymidine incorporation with an IC50 of 10 microM when added 18 h before measuring DNA synthesis. Interestingly, PmB inhibition of DNA synthesis was suppressed when 4 nM 12-O-tetradecanoylphorbol-13-acetate was added along with PmB, indicating that PmB may act through inhibition of protein kinase C. In the node and spleen lymphocytes of normal guinea pigs, protein kinase C activity was entirely cytosolic and was eluted at 0.12 M NaCl when adsorbed on DEAE-cellulose. In L2C leukemic lymphocytes, total protein kinase C activity was of the same order of magnitude, but 20% of it was associated with the membrane fraction. The lipid-dependent activity, eluted at 0.12 M NaCl from cytosolic and membrane fractions, was suppressed by staurosporine with an IC50 of 10-40 nM and by polymyxin B with an IC50 of 2-6 microM. Phosphoinositide metabolism was studied in the transformed cells. Incorporation of 32Pi into polyphosphoinositides was considerable, whereas much more time was required for a tiny incorporation of inositol. We detected no release of radioactive inositol triphosphate. Taken together, these results suggest that protein kinase C function is indispensible for triggering L2C leukemic lymphocyte proliferation. The causes of this permanent activation merit further investigation.
Vial
H J
HJ
CNRS UA 530, Université de Montpellier, France.
Parant
M R
MR
Marie
J S
JS
Laurent
A M
AM
Le Peuch
C J
CJ
D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology / Q000378:metabolism*; D002051:Burkitt Lymphoma / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002848:Chromatography, DEAE-Cellulose; D000242:Cyclic AMP / Q000037:antagonists & inhibitors; D004247:DNA / Q000096:biosynthesis*; D004789:Enzyme Activation; D005260:Female; D006168:Guinea Pigs; D006868:Hydrolysis; D010712:Phosphatidic Acids / Q000096:biosynthesis; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000096:biosynthesis / Q000378:metabolism*; D010743:Phospholipids / Q000032:analysis; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000201:enzymology / Q000378:metabolism
D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D010743:Phospholipids; D004247:DNA; D000242:Cyclic AMP; D011493:Protein Kinase C