Influence of tyrosine residues Y705 and Y807 on the transforming potency of the v-fms oncogene product of feline sarcoma virus.

Cell transformation is characterized by overt changes in growth control and cell morphology. To study the role of tyrosine residues Y705 and Y807 of v-Fms of the McDonough strain of feline sarcoma virus in cell transformation we replaced them individually with phenylalanine residues. Cells expressing the mutant genes showed mitogenic properties similar to wild-type v-Fms transformed cells. However, the morphology of cells expressing the Y807F mutant remained the same as nontransformed cells. Four phosphoproteins of 190, 120, 55 and 50 kDa were detected in cells expressing the wild-type but were absent in cells expressing the mutant Y807F-v-fms gene.

Effects of atmospheric ammonia on vegetation--a review.

Atmospheric ammonia does not only cause acute injuries at vegetation close to the source, but significantly contributes to large scale nitrogen eutrophication and acidification of ecosystems because the amount of sources is high and after conversion to ammonium it can reach remote areas by long-range atmospheric transport. Besides having acute toxic potential, NH(3) and NH(4)(+) (= NH(y)) may disturb vegetation by secondary metabolic changes due to increased NH(y) uptake and assimilation leading to higher susceptibility to abiotic (drought, frost) and biotic (pests) stress. Prevention of damage to natural and semi-natural ecosystems will only be achieved if NH(3) emissions are drastically reduced. In this paper, the current knowledge on NH(y) emission, deposition, and its effects on vegetation and ecosystems are reviewed. Critical levels and critical loads for nitrogen deposition are discussed.

Reassessment of the v-fms sequence: threonine phosphorylation of the COOH-terminal domain.

The v-fms oncogene product of the McDonough strain of feline sarcoma virus is a member of the receptor tyrosine kinase family. Its cellular counterpart, the c-fms product, is the receptor for colony-stimulating factor 1 (CSF-1) of macrophages. We have reanalyzed the v-fms gene by direct sequencing of a biologically active clone. An additional A nucleotide was detected in position 2810 of the published v-fms sequence. The frameshift changed the COOH-terminal sequence of the v-fms protein from -R-937-G-P-P-L-COOH to -Q-937-R-T-P-P-V-A-R-COOH. Antibodies against a synthetic peptide representing this new sequence precipitated the v-fms proteins from transformed NRK cells as well as from feline sarcoma virus (McDonough)-infected feline fibroblasts. We show by tryptic peptide mapping that threonine 939 present in the new sequence is phosphorylated by a yet unknown serine/threonine kinase in vivo. In chicken fibroblasts expressing the v-fms gene, this phosphorylation clearly depended on the addition of exogenous CSF-1. Furthermore, addition of CSF-1 appeared to activate the serine/threonine kinase, as judged by phosphorylation of the synthetic peptide QRTPPVAR.

Transforming mechanism of the feline sarcoma virus encoded v-fms oncogene product.

The v-fms oncogene product encoded by the McDonough strain of feline sarcoma virus (SM-FeSV) is a transmembrane glycoprotein which belongs to the tyrosine kinase receptor family. The cellular counterpart, the c-fms product, is the receptor for macrophage colony stimulating factor (M-CSF or CSF-1). The v-fms and the c-fms product differ structurally only in seven point mutations and in their C-terminal domains. We have corrected the published sequence of the v-fms product and found that the new C-terminal end contains a threonine phosphorylation site (Thr939). This site is phosphorylated in vivo leading to an enhancement of the v-fms-specific tyrosine kinase activity. The extracellular domain of the v-fms product contains 11 N-glycosylation sites. Glycosylation and transport of the v-fms molecules to the plasma membrane are prerequisites for the transforming potential of the virus. Phosphorylation of the v-fms molecules in tyrosine, serine and threonine residues takes place only at the plasma membrane. Coexpression showed that the overexpression of M-CSF and c-fms in fibroblasts leads to cell transformation by an autocrine loop mechanism. This interaction between M-CSF and the c-fms protein also takes place at the plasma membrane. To study the v-fms transforming mechanisms, we have expressed the v-fms oncogene in chicken fibroblasts which are free of the cross-reactive M-CSF. The expression of the v-fms oncogene alone did not cause transformation. However, upon addition of M-CSF, these cells became completely transformed.(ABSTRACT TRUNCATED AT 250 WORDS)

Transformation of chicken fibroblasts by the v-fms oncogene.

The v-fms oncogene of the McDonough strain of feline sarcoma virus (SM-FeSV) encodes a plasma-membrane-associated tyrosine kinase (gp140v-fms) which is closely related, both structurally and functionally, to the c-fms-specified receptor for the macrophage colony stimulating factor (CSF-1). In mammalian fibroblasts, the natural producers of CSF-1, expression of v-fms leads to cell transformation. To study the interaction between CSF-1 and gp140v-fms molecules in a cell system that does not produce endogenous cross-reactive CSF-1, we have expressed the entire v-fms gene as well as a nontransforming deletion mutant (SC2) in chicken embryo cells (CEC). For this purpose the avian retroviral vectors pDS3 and pREP, based on Rous sarcoma virus, were used to isolate recombinant virus particles. CEC infected with virus that carried the entire v-fms gene expressed high amounts of gp140v-fms, comparable to those in SM-FeSV transformed NRK cells. However, these CEC remained flat, retained their fibronectin network, and did not produce enhanced levels of plasminogen activator. The cells grew faster than control CEC for more than 8 weeks but failed to form colonies in soft agar. Within 2 days after addition of CSF-1 to the growth medium, a transformed cell phenotype was induced, as judged by loss of the fibronectin network, again with a growth rate fourfold faster than that of the parental cells and with colony formation in soft agar. Moreover, human CSF-1 caused a rapid tyrosine phosphorylation of v-fms molecules detectable within 5 min after addition of the growth factor. In contrast, CSF-1 had none of the above effects on cells that expressed the SC2 v-fms deletion mutant.

Detection of fms-oncogene-specific tyrosine kinase activity in human leukemia cells.

The c-fms protooncogene encodes the receptor for the colony-stimulating factor 1 of macrophages. Its transforming counterpart, the v-fms oncogene has previously been recognized as the transforming gene of the McDonough strain of feline sarcoma virus. We have isolated rabbit antisera against a 115-kDa recombinant polypeptide containing the 926 carboxy-terminal amino acids of the v-fms protein. All antibodies recognized the cytoplasmic domain of the v-fms protein, which is 95% homologous to the corresponding domain of human c-fms proteins. These sera were applied in a survey of various human cancer cell lines, such as peripheral blood mononuclear (HL60) and choriocarcinoma (BeWo) cells, as well as leukemic cells from 58 patients with acute myelocytic, chronic myelocytic or acute lymphocytic leukemias (AML, CML, ALL). Significantly enhanced levels of fms-specific tyrosine kinase activity were detected in 12-O-tetradecanoylphorbol-13-acetate-induced HL60 and in BeWo cells, and in 7 out of 24 samples from AML patients, whereas no activity could be detected in 9 ALL or in 25 CML cell preparations. The AML cells were classified according to the FAB criteria. The highest incidence of increased fms activity was found in cells assigned to the M4 class (four out of five cases). While no activity was found in material belonging to FAB classes M2 or M3, one of the two cases of the M5 class was kinase-positive. Interestingly, two out of seven cases of the M1 class cells exhibited enhanced levels of fms kinase. These data suggest that the determination of the fms kinase may be useful to subdivide the M1 class of the FAB classification into monocytic and non-monocytic precursor leukemia cells.

Inhibition of glycosylation processing alters the growth parameters of cells transformed by the oncogene of simian sarcoma virus.

Normal rat kidney (NRK) cells transformed by the v-sis oncogene of simian sarcoma virus (SSV) were treated with the glucosidase I inhibitor castanospermine. The inhibitor did not change cell morphology, but specific growth parameters such as serum- and anchorage-independence were lost.