Paxillin is a 68-kDa focal adhesion protein that is phosphorylated on tyrosine residues in fibroblasts in response to transformation by v-src, treatment with platelet-derived growth factor, or cross-linking of integrins. Paxillin has been shown to have binding sites for the SH3 domain of Src and the SH2 domain of Crk in vitro and to coprecipitate with two other focal adhesion proteins, vinculin and focal adhesion kinase (p125fak). After preliminary studies showed that paxillin was a substrate for the hematopoietic oncogene p210BCR/ABL, we investigated the role of this protein in hematopoietic cell transformation and signal transduction. A full-length length cDNA encoding human paxillin was cloned, revealing multiple protein domains, including four tandem LIM domains, a proline-rich domain containing a consensus SH3 binding site, and three potential Crk-SH2 binding sites. The paxillin gene was localized to chromosome 12q24 by fluorescence in situ hybridization analysis. A chicken paxillin cDNA was also cloned and is predicted to encode a protein approximately 90% identical to human paxil-lin. Paxillin coprecipitated with p210BCR/ABL and multiple other cellular proteins in myeloid cell lines, suggesting the formation of multimeric complexes. In normal hematopoietic cells and myeloid cell lines, tyrosine phosphorylation of paxillin and coprecipitation with other cellular proteins was rapidly and transiently induced by interleukin-3 and several other hematopoietic growth factors. The predicted structure of paxillin implicates this molecule in protein-protein interactions involved in signal transduction from growth factor receptors and the BCR/ABL oncogene fusion protein to the cytoskeleton.

Acquired deficiency of factor X occurs in patients with systemic amyloid lightchain (AL) amyloidosis, presumably due to adsorption of factor X to amyloid fibrils. Of 368 consecutive patients with systemic AL amyloidosis evaluated at Boston Medical Center, 32 patients (8.7%) had factor X levels below 50% of normal. Eighteen of these patients (56%) had bleeding complications, which were more frequent and severe in the 12 patients below 25% of normal; 2 episodes were fatal. Ten factor X-deficient patients received high-dose melphalan chemotherapy followed by autologous stem cell transplantation. Of 7 patients alive 1 year after treatment, 4 had a complete hematologic response, and all 4 experienced improvement in their factor X levels. One of 2 additional patients with partial hematologic responses had improvement in factor X. Thus, aggressive treatment of the underlying plasma cell dyscrasia in AL amyloidosis can lead to the amelioration of amyloid-related factor X deficiency. (Blood. 2001;97: 1885-1887)

Nelarabine is a novel nucleoside with significant cytotoxic activity against malignant T cells. DLT is neurologic. Phase II and III trials in patients with T-cell malignancies are encouraged.

The BCR/ABL oncogene causes human chronic myelogenous leukemia (CML), a myeloproliferative disease characterized by massive expansion of hematopoietic progenitor cells and cells of the granulocyte lineage. When transfected into murine hematopoietic cell lines, BCR/ABL causes cytokine-independence and enhances viability. There is also growing evidence that p210 BCR/ABL affects cytoskeletal structure. p210 BCR/ABL binds to actin, and several cytoskeletal proteins are tyrosine phosphorylated by this oncoprotein. Also, at least one aspect of cytoskeletal function is abnormal, in that the affinity of ␤ 1 integrins for fibronectin is altered in CML cells. However, isolated changes in ␤ 1 integrin function would be unlikely to explain the clinical phenotype of CML. We used time-lapse video microscopy to study cell motility and cell morphology on extracellular cell matrix protein-coated surfaces of a series of cell lines before and after transformation by BCR/ABL . BCR/ABL was associated with a striking increase in spontaneous motility, membrane ruffling, formation of long actin extensions (filopodia) and accelerated the rate of protrusion and retraction of pseudopodia on fibronectin-coated surfaces. Also, while untransformed cells were sessile for long periods, BCR/ABLtransformed cells exhibited persistent motility, except for brief periods during cell division. Using cell lines transformed by a temperature-sensitive mutant of BCR/ABL, these kinetic abnormalities of cytoskeletal function were shown to require BCR/ABL tyrosine kinase activity. Similar abnormalities of cytoskeletal function on fibronectin-coated surfaces were observed when hematopoietic progenitor cells purified by CD34 selection from patients with CML were compared with CD34 positive cells from normal individuals. Interestingly, ␣ -interferon treatment was found to slowly revert the abnormal motility phenotype of BCR/ABL -transformed cells towards normal. The increase in spontaneous motility and other defects of cytoskeletal function described here will be useful biological markers of the functional effects of BCR/ABL in hematopoietic cells. ( J. Clin. Invest.