@entity669 protein kinases and their substrates in XXXX @entity1778 cells.

@entity1 @entity981 @entity1072 @entity3052 @entity1778 @entity669 @entity1860
We have quantitated @entity669 protein kinase (TPK) activity in particulate and cytosolic fractions from @entity1 leukemic cells. Slowly proliferating cells from @entity1 with @entity1072 ( @entity1072 ) had levels of TPK similar to those of quiescent normal lymphocytes. Cells from @entity1 with @entity981 ( @entity981 ), @entity3052 ( @entity3052 ) and @entity1860 ( @entity1860 ) contained markedly lower levels of TPK activity, similar to the levels in phytohaemagglutinin-stimulated (proliferating) normal lymphocytes and in bone marrow cells. This suggested that TPK is part of a mechanism for transducing growth signals and is down-regulated following signal transmission. We also identified endogenous substrates for TPK in leukemic cells. Particulate fractions from @entity981 , @entity1072 and @entity3052 cells contained substrates identical to those previously detected in normal lymphocytes. In particular, a 38kD substrate thought to be involved in early stages of growth signal transduction in normal lymphocytes was found in all samples of these groups examined. Cytosolic fractions from these groups of @entity1778 cells contained higher molecular weight substrates not found in resting or proliferating normal lymphocytes or bone marrow cells. In contrast, TPK substrates in both particulate and cytosolic fractions from @entity1860 cells resembled those of normal bone marrow cells in that only proteins with molecular weight below 40kD were labelled on @entity669 . We conclude that leukemic cells do not contain higher levels of TPK than do normal hemopoietic cells. Qualitative differences in TPK species or in their substrates may result in aberrant regulation of proliferation in leukemic cells. However, we cannot exclude the possibility that additional TPK substrates detected in leukemic cells were a feature of the normal equivalent hematopoietic cells from which the @entity1778 cells were derived.
