With the refinement of algorithms for the identification of distinct motifs from sequence databases, especially those using secondary structure predictions, new protein modules have been determined in recent years. Calponin homology (CH) domains were identified in a variety of proteins ranging from actin cross-linking to signaling and have been proposed to function either as autonomous actin binding motifs or serve a regulatory function. Despite the overall structural conservation of the unique CH domain fold, the individual modules display a quite striking functional variability. Analysis of the actopaxin/ parvin protein family suggests the existence of novel (type 4 and type 5) CH domain families which require special attention, as they appear to be a good example for how CH domains may function as scaffolds for other functional motifs of different properties. ß

Recent studies have shown that the targeting of substrate adhesions by microtubules promotes adhesion site disassembly (Kaverina, I., O. Krylyshkina, and J.V. Small. 1999. J. Cell Biol. 146:1033–1043). It was accordingly suggested that microtubules serve to convey a signal to adhesion sites to modulate their turnover. Because microtubule motors would be the most likely candidates for effecting signal transmission, we have investigated the consequence of blocking microtubule motor activity on adhesion site dynamics. Using a function-blocking antibody as well as dynamitin overexpression, we found that a block in dynein–cargo interaction induced no change in adhesion site dynamics in Xenopus fibroblasts. In comparison, a block of kinesin-1 activity, either via microinjection of the SUK-4 antibody or of a kinesin-1 heavy chain construct mutated in the motor domain, induced a dramatic increase in the size and reduction in number of substrate adhesions, mimicking the effect observed after microtubule disruption by nocodazole. Blockage of kinesin activity had no influence on either the ability of microtubules to target substrate adhesions or on microtubule polymerisation dynamics. We conclude that conventional kinesin is not required for the guidance of microtubules into substrate adhesions, but is required for the focal delivery of a component(s) that retards their growth or promotes their disassembly.

A sequence motif of about 100 amino acids, termed the`calponin homology domain' has been suggested to confer actin binding to a variety of cytoskeletal and signalling molecules. Here we analyse and compare the sequences of all calponin homology domain-containing proteins identified to date. We propose that single calponin homology domains do not confer actin-binding per se and that the actin-binding motifs of crosslinking proteins, which comprise two disparate calponin homology domains, represent a unique protein module.z 1998 Federation of European Biochemical Societies.

The Caenorhabditis elegans unc-87 gene product is essential for the maintenance of the nematode body wall muscle where it is found colocalized with actin in the I band. The molecular domain structure of the protein reveals similarity to the C-terminal repeat region of the smooth muscle actin-binding protein calponin. In this study we investigated the in vitro function of UNC-87 using both the full-length recombinant molecule and several truncated mutants. According to analytical ultracentrifugation UNC-87 occurs as a monomer in solution. UNC-87 cosedimented with both smooth and skeletal muscle F-actin, but not with monomeric G-actin, and exhibited potent actin filament bundling activity. Actin binding was independent of the presence of tropomyosin and the actin cross-linking proteins filamin and ␣-actinin. Consistent with its actin bundling activity in vitro, UNC-87 tagged with green fluorescent protein associated with and promoted the formation of actin stress fiber bundles in living cells. These data identify UNC-87 as an actin-bundling protein and highlight the calponin-like repeats as a novel actin-binding module.The interaction of actin and myosin to produce force is an essential prerequisite for a variety of cellular processes including muscle contraction (1), cell motility, and anchorage (2). The organization of contractile and motile systems based on actin relies on a large family of actin-associated proteins that regulate and define the assembly of actin into filaments and then into filament arrays (3, 4). To date, more than 60 different proteins directly interacting with actin have been identified, but the majority of F-actin-binding proteins populate partially overlapping regions on the filament (5, 6). Despite the large number of actin-binding proteins, functional diversity is reflected by a limited number of basic structural modules (7). Most actin cross-linking proteins exhibit two independent actin-binding domains, each individual actin-binding domain commonly composed of a tandem arrangement of the calponin homology domain module (8) and other modular elements defining the distance between and the relative orientation of the two actin-binding domains, often involving parallel or antiparallel dimerization (7).We have shown recently that a unique sequence motif found in the C-terminal third of the calponin (CaP) 1 molecule and other members of the CaP family of actin-associated proteins (9), namely a 23-amino acid residue repeat, which we will refer to from now on as the CLIK-23 repeat, forms an independent actin-binding site (10). This finding was corroborated by Mino et al. (11) who demonstrated the direct interaction of a peptide corresponding to the first CaP repeat with actin in vitro. A survey of the available data bases identified other proteins with CLIK-23 repeats, in particular the Caenorhabditis elegans body wall muscle protein UNC-87 that exhibits seven tandem CLIK-23 repeats (12). A protein with a similar molecular structure has also been described by Irvine et al. (13) in the filar...

BackgroundCharacterization of novel fusion genes in acute leukemia is important for gaining information about leukemia genesis. We describe the characterization of a new ETV6 fusion gene in acute myeloid leukemia (AML) FAB M0 as a result of an uncommon translocation involving chromosomes 12 and 15.MethodsThe ETV6 locus at 12p13 was shown to be translocated and to constitute the 5' end of the fusion product by ETV6 break apart fluorescence in situ hybridisation (FISH). To identify a fusion partner 3' rapid amplification of cDNA-ends with polymerase chain reaction (RACE PCR) was performed followed by cloning and sequencing.ResultsThe NTRK3 gene on chromosome 15 was found to constitute the 3' end of the fusion gene and the underlying ETV6-NTRK3 rearrangement was verified by reverse transcriptase PCR. No RNA of the reciprocal NTRK3-ETV6 fusion gene could be detected.ConclusionWe have characterized a novel ETV6-NTRK3 fusion transcript which has not been previously described in AML FAB M0 by FISH and RACE PCR. ETV6-NTRK3 rearrangements have been described in secretory breast carcinoma and congenital fibrosarcoma.

No abstract

Myeloid and lymphoid neoplasms with fibroblast growth factor receptor 1 (FGFR1) abnormalities, also known as 8p11 myeloproliferative syndrome (EMS), represent rare and aggressive disorders, associated with chromosomal aberrations that lead to the fusion of FGFR1 to different partner genes. We report on a third patient with a fusion of the translocated promoter region (TPR) gene, a component of the nuclear pore complex, to FGFR1 due to a novel ins(1;8)(q25;p11p23). The fact that this fusion is a rare but recurrent event in EMS prompted us to examine the localization and transforming potential of the chimeric protein. TPR-FGFR1 localizes in the cytoplasm, although the nuclear pore localization signal of TPR is retained in the fusion protein. Furthermore, TPR-FGFR1 enables cytokine-independent survival, proliferation, and granulocytic differentiation of the interleukin-3 dependent myeloid progenitor cell line 32Dcl3, reflecting the chronic phase of EMS characterized by myeloid hyperplasia. 32Dcl3 cells transformed with the TPR-FGFR1 fusion and treated with increasing concentrations of the tyrosine kinase inhibitors ponatinib (AP24534) and infigratinib (NVP-BGJ398) displayed reduced survival and proliferation with IC50 values of 49.8 and 7.7 nM, respectively. Ponatinib, a multitargeted tyrosine kinase inhibitor, is already shown to be effective against several FGFR1-fusion kinases. Infigratinib, tested only against FGFR1OP2-FGFR1 to date, is also efficient against TPR-FGFR1. Taking its high specificity for FGFRs into account, infigratinib could be beneficial for EMS patients and should be further investigated for the treatment of myeloproliferative neoplasms with FGFR1 abnormalities.

The classical pregnancy and tumor marker hCG has long been considered to be only accidentally expressed ectopically, e.g. by tumors. The biolo&al functions of low levels of hCG/3, hCGa and holo-hCG in the sera of nonpregnant healthy individuals remained unclear. Immunological analyses by our ultrasensitive time-resolved fluoroimmunoassays revealed a concentration gradient from < 5 pg hCGj?/ml in cubital vein serum versus up to 480 pg hCGj?/ml in the corresponding beni testicular hydrocele fluids. Moreover, hCGb and its cognate molecule luteinizing hormone/? (LHB) were present in cytosolic extracts of normal human testes. Both hCGj? and hLH#I are eutopically produced as proven by RT-l?CR and subsequent Southern and dot blot analyses. Thus, the view of a purely systemic hormonal function of hLH, and of hCG during pregnancy needs a reassessement as hCG@ and hLIQ3 are synthesized in the human testis and autocrine/paracrine actions seem to be likely.