No abstract

Chronic myelogenous leukemia (CML) is IntroductionBcr-Abl proteins result from chromosomal translocations that lead to the fusion of parts from the breakpoint cluster region (bcr) gene on chromosome 22 to sequences of the c-abl gene on chromosome 9. Although both genes encode for protein kinases, [1][2][3] it is thought that mainly the activation of the tyrosine kinase activity encoded in the fragment of the c-abl gene is important for the development of a human disease termed chronic myelogenous leukemia (CML). [4][5][6] The bcr portion of the bcr-abl fusion gene is thought to contribute to the course of the disease by providing an oligomerization domain, which resides in a coiled-coil region at the N-terminus of the Bcr protein, 7 but also by antagonizing the Abl kinase activity. 8 State-of-the-art therapies for CML patients currently include cytostatic drugs, ␣-interferon and its derivatives, as well as bone marrow or stem cell transplantation for younger patients. 6,9 However, the current treatment options are not yet satisfactory with respect to the long-term survival of the patients.During the last decade, a tremendous number of studies have unraveled many aspects of the intracellular signal-transduction events resulting from the chromosomal translocations that lead to the formation of Bcr-Abl proteins. It is therefore hoped that specific signal-transduction inhibitors will eventually complement the spectrum of therapeutic choices for CML. 10 As in many other cancers, the central mitogenic cascade, which leads via the small GTPase Ras to the activation of mitogen-activated protein kinases (MAPKs), 11 has gained much attention in this respect. Activation of Ras and MAPK was also observed for the Tel-Abl (ETV6-Abl) fusion protein, a leukemic protein similar to Bcr-Abl, which uses instead of Bcr the Ets family protein Tel (ETV6) to oligomerize the Abl kinase. 12,13 Numerous reports link Bcr-Abl directly to the adapter proteins Shc and Grb2, which are signal transducers upstream of Ras and are known to recruit the Ras-activating exchange factor SoS toward the intracellular sites where Ras is located. [14][15][16][17][18][19] Despite the large number of studies obtained with different established cell lines, no clear picture of how these data relate to the situation in human patients' cells has yet emerged. This is in part because, despite considerable efforts, so far it has not been possible to generate animal models that convincingly mimic human CML. 20,21 Signal-transduction-based strategies, which are often still in an experimental state, have so far mainly targeted Bcr-Abl on the protein or RNA level. A prominent example is the new tyrosine kinase inhibitor compound CGP57148B (recently renamed STI571), which showed promising results in first clinical trials. 22 Despite this positive result, it is already obvious that the development of resistance to STI571 will become a problem at least in some cases. 23 To overcome this obstacle, in CML therapy as 21 In this report, we tested whether cell-penetrating hig...

Bcr-Abl contributes prominently to the development of most chronic myeloid leukemias (CMLs). Prior work has identified the adapter protein CRKL as a major substrate of the Bcr-Abl tyrosine kinase. CRKL can also bind via its first SH3 domain [SH3(1)] to specific sequences in Bcr-Abl. Cell-penetrating peptides were developed that bind with high affinity and selectivity to the SH3(1) domain of CRKL. They disrupt Bcr-Abl-CRKL complexes and strongly reduce the proliferation of primary CML blast cells and cell lines established from Bcr-Abl-positive patients. Activation-specific antibodies against phosphorylated MAP kinase (MAPK) showed that MAPK activity is down-regulated in blast cells treated with the CRKLSH3(1) blocker peptides. We conclude that the Bcr-Abl-CRKL complexes are largely dependent on the CRKLSH3(1) domain, that the central mitogenic cascade is down-regulated as a consequence of the disruption of CRKLSH3(1) interactions, and that CRKL therefore contributes to the proliferation of CML blast cells.