Acute myeloblastic leukemia with active tyrosine protein kinase

Tyrosine protein kinase inhibition and cancer

The various aspects of the research on tyrosine protein kinase inhibition and its connections with cancer are presented. The emphasis was made on the theoretical low toxic side effects of specific tyrosine protein kinase inhibitors. Particularly, the strategy of finding peptidic substrate-derived inhibitors or modulators is discussed, with an almost complete compendium of the tyrosine protein kinase peptidic substrates published so far. A series of data has been gathered that may serve as a basis for the discovery of selective and specific tyrosine protein kinase inhibitors by screening on molecular and cellular models. The potential of SH2 domain-interfering agents are also presented as a promising route to new anticancer compounds.

Tyrosine protein kinase activity in normal and leukaemic human blood cells

Tyrosine protein kinase (TPK) activity was measured in subcellular fractions of normal granulocytes, lymphocytes and monocytes, and acute and chronic myeloid and lymphoid leukaemic cells. Of several tested tyrosine-containing substrates, poly (glutamic acid: tyrosine = 4:1) (S1) proved to be the best synthetic substrate. High cytosolic TPK activity was found in every cell type. Different TPKs may exist in various cell fractions, as was indicated by the difference in Km values for S1 in cell fractions of normal granulocytes and lymphocytes. No significant difference was found in total TPK activity between normal and leukaemic cells, indicating that total TPK activity is not related to the leukaemic process itself. A highly significant difference was found in membrane fractions in normal granulocytes and M1-M2 AML cells versus normal monocytes and M4-M5 AML cells, suggesting an association between TPK activity and monocytic differentiation in these cell fractions.

Purification of the LSTRA tyrosine protein kinase (p56lck)

p56lck, a p60src related tyrosine protein kinase was recently described in a murine lymphoma cell line (LSTRA), in several human lymphomas and in normal peripheral lymphocytes. We have purified p56lck to homogeneity by electrofocusing followed by two-step SDS/polyacrylamide gel electrophoresis. The pure protein was identical to the p56 characterized in LSTRA cells and used to raise antibodies in rabbits. This simple procedure is applicable for the rapid purification of minor proteins.

Correlation between phosphorylation and kinase activity of a tyrosine protein kinase: p56lck

P56lck is the product of a cellular oncogene highly expressed in lymphoid cells. Tyrosine kinase activity was measured by using an exogenous substrate: polyamino acid glutamic acid-tyrosine (4:1) (PGT). Different levels of phosphorylation of p56lck were achieved by the utilisation of SH reagents and different lengths of incubation time. The phosphorylation of PGT was proportional to the level of phosphorylation of p56lck. Identical results were obtained with crude membrane preparations and with p56lck partially purified on immunecomplexes.

The amino terminal region of the p56 lck from LSTRA exerts negative modulation on the tyrosine kinase activity

High levels of tyrosine kinase activity have been detected in the murine lymphoma LSTRA (p56). The functional domains of this kinase have been studied by the use of antibodies generated against peptides from the amino terminal region and from the tyrosine autophosphorylation site. The amino terminal antibody had higher affinity for the p56 than the antibody directed against the phosphotyrosine site. However, the phosphorylation of exogenous substrate by p56 was lower when the tyrosine kinase was immunocomplexed by the antibody against the amino terminal region than when the kinase was complexed by the phosphorylation site antibody. This suggests that in the N-terminal region exist structures which modulate the tyrosine kinase activity of the p56.