Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.22.54 (calpain 3)
 430 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fractionation of a cytosolic extract of HeLa cells revealed the existence of a highly active protein tyrosine kinase. Chromatographic fractionation of the extract resulted in partial purification of a single enzymatic activity that coeluted with a 94-kDa polypeptide. In vitro phosphorylation of the isolated enzyme showed that p94 was the only polypeptide phosphorylated and only the tyrosine residue(s) was (were) modified. The fractionated enzyme (p94 kinase) also phosphorylated a number of other nonspecific substrates exclusively on tyrosine residues. Unlike other protein tyrosine kinases that have been characterized, p94 kinase is relatively insensitive to inhibition by the isoflavone genistein. Using two different antisera, we provided evidence that the HeLa p94 kinase is most likely the FER gene product, which was previously shown to be expressed in a wide variety of cell types. These results represent the first biochemical characterization of the cellular FER gene product and also provide a basis for studying the biochemistry of tyrosine kinase function in HeLa cells.
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PMID:Identification and characterization of a cytosolic protein tyrosine kinase of HeLa cells. 155 92

p94(fer) is a cytoplasmic and nuclear tyrosine kinase whose function has been linked to cell growth. p94(fer) accumulates at different levels in various cell types and is not detected in pre-B, pre-T and T-cells (Halachmy, S., Bern, O., Schreiber, L., Carmel, M., Sharabi, Y., Shoham, J., Nir, U., 1997. p94(fer) facilitates cellular recovery of gamma irradiated pre-T cells. Oncogene 14, 2871-2880). The fer RNA, encoding p94fer, is transcribed from the FER locus in human rat and mouse. In the present work, a Fer gene transcription initiation point was determined, and the Fer promoter was cloned. A DNA genomic fragment, extending 3698bp upstream of the fer RNA start site, was isolated, sequenced and functionally characterized. A transient transfection assay, carried out in fibroblastic cell lines, revealed the presence of the Fer promoter within the cloned genomic fragment. The Fer promoter contains neither an obvious 'TATA' element nor a putative initiator sequence, but is composed of positive and negative, cis-acting elements. Negative regulation was found to be the main cause for dysfunctioning of the Fer promoter in a T-cell leukemia cell line (Jurkat). The minimal Fer promoter that is still active in fibroblasts consists of an AP1 binding site located 14bp upstream of the fer transcription initiation point. This minimal promoter was not active in the Jurkat T-cell leukemia cells and did not bind AP1 in these cells. Three additional AP1 sites were identified in functional sequences of the Fer promoter. Thus, the availability of AP1 activity may contribute as well to the modulation of the Fer promoter activity. The presumed regulatory role of AP1 in modulating the Fer promoter activity implies a link between cell growth and the Fer gene expression level. Indeed, exposure of fibroblasts to low serum growth conditions reduced the cellular level of the fer RNA.
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PMID:Role of positive and negative regulation in modulation of the Fer promoter activity. 1060 2

p94(fer) and p51(ferT) are two tyrosine kinases which share identical SH2 and kinase domains but differ in their N-terminal regions. While p94(fer) is expressed in most mammalian cells, the accumulation of p51(ferT) is restricted to meiotic spermatocytes. Here we show that the different N-terminal tails of p94(fer) and p51(ferT) direct different autophosphorylation states of these two kinases in vivo. N-terminal coiled-coil domains cooperated to drive the oligomerization and autophosphorylation in trans of p94(fer). Moreover, the ectopically expressed N-terminal tail of p94(fer) could act as a dominant negative mutant and associated with the endogenous p94(fer) protein in CHO cells. This increased significantly the percentage of cells residing in the G0/G1 phase, thus suggesting a role for p94(fer) in the regulation of G1 progression. Unlike p94(fer), overexpressed p51(ferT) was not autophosphorylated in COS1 cells. However, removal of the unique N-terminal 43 aa of p51(ferT) or the replacement of this region by a parallel segment from p94(fer) endowed the modified p51(ferT) with the ability to autophosphorylate. The unique N-terminal sequences of p51(ferT) thus interfere with its ability to autophosphorylate in vivo. These experiments indicate that the N-terminal sequences of the FER tyrosine kinases direct their different cellular autophosphorylation states, thereby dictating their different cellular functions.
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PMID:N-terminal sequences direct the autophosphorylation states of the FER tyrosine kinases in vivo. 1099 46