AATYK: a novel tyrosine kinase induced during growth arrest and apoptosis of myeloid cells.

Apoptosis, or programmed cell death, is a process where developmental or environmental stimuli activate a genetic program to implement a series of events that culminate in cell death. To study the nature of genes that are induced during the apoptotic death of myeloid precursor cells, we utilized the 32Dcl3 cell line, which is derived from normal mouse bone marrow, is non-tumorigenic and diploid. These cells are strictly dependent on IL-3 for growth and apoptose when deprived of IL-3. However, when these cells are transferred to medium containing G-CSF, the cell number increases 4-5-fold and after 12 days the entire population is differentiated into granulocytes followed by apoptotic death. In our search for genes that are induced during apoptosis and/or terminal differentiation of 32Dcl3 cells, we identified a novel gene termed AATYK (Apoptosis Associated Tyrosine Kinase), whose expression is dramatically upregulated during IL-3 deprivation as well as G-CSF-induced terminal differentiation. In this report, we describe the sequence of the cDNA clone, derived from the mRNA transcript of this gene. These studies show that this gene encodes a protein with a tyrosine kinase domain at the N-terminal end and a proline-rich domain at the C-terminal end. We also report that the expression of this gene is blocked in v-abl or bcr-abl transformed myeloid cells which are unable to apoptose when grown in the absence of IL-3. However, AATYK expression is induced in 32D cells transformed by the v-abl gene when these cells are incubated in the presence of DMSO, which induces growth arrest and apoptotic death of the cells. On the other hand, DMSO fails to induce apoptosis or AATYK expression in 32D cells transformed by the bcr-abl oncogene, suggesting that AATYK expression may be a necessary pre-requisite for the induction of growth arrest and/or apoptosis of myeloid precursor cells.

Primary binding domain of bovine von Willebrand factor fragment expressed in E. coli.

Bovine vWF cDNA has been cloned from a bovine endothelial cell library. A fragment of this cDNA, corresponding to amino acid sequence Leu 469-Ser 723, called primary adhesion domain (PAD-1), and containing the binding sites for platelet glycoprotein Ib (GPIb), heparin and collagen, has been expressed in E. coli. The reduced and alkylated form of fragment PAD-1 inhibited native vWF binding to GPIb. Fragment PAD-1 bound to heparin and botrocetin in a specific and dose dependent manner as did the native vWF. In a solid-phase assay, fragment PAD-1 bound to calf skin collagen in contrast to a human vWF recombinant fragment (Ser 445-Val 733) which was inactive in the same assay. The studies presented in this paper demonstrated that the A1 domain of bovine vWF contained the GPIb, heparin, botrocetin as well as collagen binding sites and that integrity of the disulfide bond (Cys 509-Cys 695), did not seem to be essential for binding of bovine vWF fragment to GPIb.