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Biomedical subjects

J F Whitfield

Publications and source records attributed to J F Whitfield.

At least 145 records · Page 8Linked to original sources
PubMed1985

The widely-distributed tumour protein, oncomodulin, is a normal constituent of human and rodent placentas.

Oncomodulin, first found in tumours, turns out to be a highly conserved oncodevelopmental protein in human and rodent placentas. The human and rat placental oncomodulins were visualised immunohistochemically. The placental oncomodulins are identical to each other, and to tumour oncomodulin with respect to amino acid composition, chromatographic elution and the pattern of the peptides released by trypsin action.

Amino Acids↗
PubMed1985

1 alpha,25-Dihydroxyvitamin D3 enables regenerating liver cells to make functional ribonucleotide reductase subunits and replicate DNA in thyroparathyroidectomized rats.

Between 16 and 20 h after partial (70%) hepatectomy (HPX) in normal rats, the remaining liver cells accumulate ribonucleotide reductase subunits, assemble these into active holoenzyme, and initiate DNA replication. These late prereplicative activities did not occur in most of the liver cells remaining after HPX in rats which had been thyroparathyroidectomized (TPTX) 72 h previously. However, one intraperitoneal injection of 400 or 600 ng 1 alpha,25-dihydroxyvitamin D3/100 g body weight at the time of HPX enabled the remaining liver cells in such TPTX rats to make functional ribonucleotide reductase subunits, assemble these subunits into active CDP-reducing holoenzymes, and replicate their DNA, though they started to do so 4 to 16 h later than in normal animals.

Animals↗
PubMed1984

The mitogenic activity of pp60v-src, the oncogenic protein product of the src gene of avian sarcoma virus, is independent of external serum growth factors.

The oncogenic pp60v-src product of ASV (avian sarcoma virus) is shown to be a potent endogenous mitogen, which, unlike mitogens such as PDGF (platelet derived growth factor), is able to stimulate host cell proliferation without the help of other growth factors. Thus, NRK rat cells, infected with a temperature-sensitive ASV mutant which produces an abnormally thermolabile pp60v-src, became proliferatively quiescent at a pp60v-src-inactivating 40 degrees C in medium containing either 0.2% calf serum or no serum at all. Adding PDGF stimulated the quiescent tsASV-NRK cells at 40 degrees C to initiate DNA replication in medium containing 0.2% serum, but not in serum-free medium. By contrast, activating internal pp60v-src by dropping the temperature to a permissive 36 degrees C stimulated these quiescent cells to transit G1, initiate DNA replication and to enter mitosis even in serum-free medium. Thus, relative to PDGF, endogenous pp60v-src behaves as a complete mitogen.

Animals↗
PubMed1984

Colchicine prevents the translation of mRNA molecules transcribed immediately after proliferative activation of hepatocytes in regenerating rat liver.

A dual-labelling technique has been used to establish that partial hepatectomy has no effect on the degradation of poly (A)+mRNA and confirms that the increased incorporation of precursor into mRNA during early prereplicative development reflects an actual increase in mRNA biosynthesis. Simultaneous studies on the changes in nuclear RNA metabolism support the conclusion that an increase in gene transcription does occur. Colchicine, at concentrations known to disrupt microtubules, has no effect on this increase in gene transcription but prevents the translation of the gene products by promoting polysome disaggregation transiently during a critical stage of prereplicative development. Studies with mefenamic acid and hydrocortisone, specific inhibitors of prostaglandin metabolism, have ruled out any involvement of prostaglandins in the induction of prereplicative mRNA synthesis.

Animals↗
PubMed1984

Prereplicative changes in the soluble calmodulin of isoproterenol-activated rat parotid glands.

Cells of rat parotid glands were maximally stimulated to initiate DNA synthesis by injecting into the animal a single dose of 25 to 150 mg of isoproterenol/kg of body weight. During the 18- to 21-hr prereplicative period following injection of the highest dose of the drug, there were two predominant and transient redistributions of calmodulin from the bound to the soluble form, which tripled the level of soluble calmodulin at 3 hr and again at 18 hr just before the initiation of DNA synthesis. A small (50%) increase in total calmodulin was observed only during the early (3-h) prereplicative surge of soluble calmodulin. The late, pre-DNA-synthetic surge of soluble calmodulin and the initiation of DNA synthesis were both prevented in rats that lacked their parathyroid-thyroid gland complex and had been hypocalcemic for 48 or 72 hr. Unlike the effect of high doses of isoproterenol, low doses (e.g., 25 mg/kg body weight) of the beta-adrenergic drug could maximally stimulate DNA synthetic activity without the later pre-DNA-synthetic surge of soluble calmodulin, suggesting that any apparent correlation between the level of calmodulin and DNA synthesis may be spurious and that an actual increase in the level of soluble calmodulin just before the onset of DNA synthesis was not a prerequisite for DNA synthetic activity in parotid cells.

Animals↗
PubMed1984

Partial characterization of the mitogenic action of pp60v-src, the oncogenic protein product of the src gene of avian sarcoma virus.

NRK cells infected with a temperature-sensitive, transformation-defective mutant of avian sarcoma virus (ASV), tsLA23, are transformed at 36 degrees C, but at 40 degrees C they behave as nontransformed cells because of the inactivation of the abnormally thermolabile pp60v-src product of the virus' transforming src gene. At 40 degrees C, these tsLA23-NRK cells were arrested in G1/G0 by severe serum deprivation. They were induced to enter G1, initiate DNA synthesis 7 or 10 hours later, and then divide as (1) nontransformed cells by adding serum or platelet-derived growth factor (PDGF) at 40 degrees C, or (2) transformed cells by lowering the temperature to a pp60v-src-activating 36 degrees C without adding exogenous growth factor(s). The level of pp60v-src kinase activity rose dramatically in these serum-deprived cells within 30 minutes of lowering the temperature to the permissive 36 degrees C, and it fell just as rapidly when the cells were returned to the restrictive 40 degrees C. As little as a 2-hour exposure to 36 degrees C, with an attendant 2-hour burst of pp60v-src kinase activity, was enough to stimulate serum-deprived tsLA23-NRK cells to transit G1 and initiate DNA replication, but not to divide. Much more prolonged pp60v-src activity was needed for these serum-deprived cells to complete their cycle and divide. The prereplicative development of quiescent tsLA23-NRK cells stimulated by serum or PDGF was accompanied by greatly increased protein synthesis and slightly decreased protein degradation, but the pp60v-src-stimulated cells progressed through G1 and initiated DNA replication without appreciably affecting the protein synthetic machinery of the cell. The cells stimulated by the mitogenic action of pp60v-src, like the cells stimulated by serum, needed to activate early prereplicative genes in order to initiate DNA replication. The needed RNA transcripts induced by serum and pp60v-src were produced with comparable efficiency, although it took longer for pp60v-src-stimulated cells to translate these transcripts and to initiate DNA replication, probably because of their unstimulated protein-synthetic machinery.

Animals↗
PubMed1984

The effect of serum on the calcium content of BALB/c 3T3 mouse cells.

Serum deprivation of sparse BALB/c 3T3 mouse cell cultures causes the cells to stop proliferating and increases the uptake of calcium from the medium, with the amount of calcium accumulated being proportional to the extent of reduction of the serum concentration in the medium. Serum addition stimulates the cells to start proliferating and rid themselves of the calcium accumulated during the period of serum deprivation.

Animals↗
PubMed1984

Relation between colony formation in calcium-deficient medium, colony formation in soft agar, and tumor formation by T51B rat liver cells.

T51B rat liver cells and several carcinogen-treated, carcinogen + saccharin-treated, or spontaneously altered clones of T51B cells were tested for their abilities to form colonies in calcium-deficient medium and soft agar and to produce tumors in athymic nude mice. Most (10 out of 11) of the clones which were derived from colonies in calcium-deficient medium were unable to form colonies in soft agar and 8 out of 11 were non-tumorigenic. Conversely, 6 out of 9 clones derived from colonies in soft agar were unable to multiply significantly in calcium-deficient medium and 5 of these 6 clones were also non-tumorigenic. Two of these 9 soft agar-growing clones were tumorigenic, one of which also proliferated in calcium-deficient medium, and the other of which acquired the ability to proliferate in calcium-deficient medium after it became able to form tumors in athymic nude mice. Thus, T51B rat liver cells gain the ability to grow in calcium-deficient medium and soft agar independently during the process of neoplastic transformation and neither characteristic by itself reliably predicts tumorigenicity.

Animals↗
PubMed1984

The presence in human tumours of a Mr 11,700 calcium-binding protein similar to rodent oncomodulin.

Oncomodulin is a parvalbumin-like calcium binding protein of Mr 11,700 from rodent tumours. An antiserum to rat oncomodulin cross-reacts with extracts of several human solid tumour tissues. When purified, this human immunoreactive protein binds calcium, and has a molecular weight and amino acid composition similar to the rodent protein. This protein was not found in normal adult human tissue.

Aged↗
PubMed1984

Changes in the cytoplasmic and nuclear activities of the ribonucleotide reductase holoenzyme and its subunits in regenerating liver cells in normal and thyroparathyroidectomized rats.

The level of the cytoplasmic ribonucleotide reductase nonheme-iron-containing L2 subunit in regenerating rat liver cells began rising about 2 h before the onset of DNA synthesis, rose sharply to a maximum level about 4 h before the DNA-synthetic activity reached its peak, and then stayed at this high level even after the cells had finished replicating their DNA. The cytoplasmic level of the CDP-specific, effector-binding L1 subunit and the holoenzyme activity began rising together about 2 h after the L2 subunit began increasing and at the same time as the DNA-synthetic activity, but subsequently rose much more slowly than the L2 subunit and continued rising even after the cells had finished making DNA. The nuclear level of the L2 subunit did not rise in the regenerating liver cells, but the nuclear level of the L1 subunit and the holoenzyme activity began rising together about the same time as the DNA-synthetic activity, peaked briefly 4-6 h before the peak DNA-synthetic activity, and dropped sharply back to the basal levels by the time the DNA-synthetic activity reached its peak, but then rose again slowly as the cells finished making DNA. Thyroparathyroidectomy 72 h before partial hepatectomy prevented the cytoplasmic and nuclear subunits and holoenzyme activity from rising and prevented most of the remaining liver cells from initiating DNA synthesis.

Animals↗
PubMed1983

Ca2+/phospholipid-dependent protein kinase activity correlates to the ability of transformed liver cells to proliferate in Ca2+-deficient medium.

Extracellular Ca2+-deprivation inhibited the proliferation of normal T51B rat liver cells and reduced (2-4 fold) the amount of EDTA/EGTA-extractable protein kinase C activity. By contrast, preneoplastic and neoplastic T51B rat liver cells were able to proliferate in Ca2+-deficient medium and retained all of their extractable protein kinase C activity.

Aflatoxin B1↗
PubMed1983

The calcium-dependence of the stimulation of neonatal rat hepatocyte DNA synthesis and division by epidermal growth factor, glucagon and insulin.

A low concentration (10(-11) mol/l) of epidermal growth factor (EGF) and/or an equimolar (10(-14) mol/l) mixture of glucagon and insulin stimulated DNA synthesis in hepatocytes in 4-day-old primary cultures of neonatal rat liver. EGF seems to have acted by inducing quiescent hepatocytes to begin cycling, while the glucagon-insulin combination seems to have acted mainly by shortening the cell cycle time. Incubation in low calcium medium blocked untreated hepatocytes in the G1 phase of their cycle and prevented EGF and the glucagon-insulin mixture from stimulating DNA synthesis. Nevertheless, hepatocytes in calcium-deficient medium did respond to these agents, as they reached a late stage of prereplicative development before being blocked: in fact, they initiated DNA synthesis soon after the addition of calcium. EGF, but not the glucagon-insulin combination, also enabled the already cycling hepatocytes (but not the newly activated ones) to overcome the block imposed by the extracellular calcium deficiency after a delay of several hours.

Animals↗
PubMed1983

The role of calmodulin in the proliferation of transformed and phenotypically normal tsASV-infected rat cells.

NRK cells infected with a temperature-sensitive, transformation-defective mutant of avian sarcoma virus (ASV), tsLA23, behaved as if nontransformed at a nonpermissive 40 degrees C and were rendered quiescent by serum deprivation. These serum-deprived cells were stimulated to start entering S phase about 7 hours after serum addition at 40 degrees C or about 9 hours after shifting the cultures to 36 degrees C, a temperature allowing the production of active viral pp60src and expression of the transformed phenotype. The transit of both serum- and temperature-stimulated tsLA23-NRK cells through later G1 was inhibited by the unrelated calmodulin antagonists W7 and R24571. The former drug was found to block the cells at a point in the cell cycle no more than 2 hours from the G1/S transition. The weaker calmodulin antagonist, W5, was less effective in impairing progression. Thus, calmodulin is likely required for the transit of both transformed and phenotypically normal tsLA23-NRK cells through the later stages of their G1 phases. Cells neoplastically transformed by ASV contain more calmodulin than uninfected, non-neoplastic cells. At the nonpermissive 40 degrees C, the calmodulin content of the tsLA23-NRK cells dropped to the non-neoplastic level. When these phenotypically nontransformed cells were enabled to reenter the cell cycle while still in low-serum medium by a 40 to 36 degrees C shift, they passed through the G1 and S phases and divided without a concomitant rise in the total calmodulin content. Thus, a calmodulin rise does not appear to be required for the expression of one characteristic of transformed cells, i.e., reduced requirement for exogenous growth factors.

Animals↗
PubMed1982

Isolation and purification of a new 105 kDa protein kinase from rat liver nuclei.

A protein kinase was purified from rat liver nuclei by affinity chromatography on poly(L-lysine)-agarose and protein kinase inhibitor-Sepharose 4B columns. The relative molecular weight of this protein kinase is 105000 (determined by 10% SDS-polyacrylamide slab gel electrophoresis, gel filtration on Sephadex G-200 and sedimentation velocity ultracentrifugation). Its pH optimum is between 8.0 and 9.0. It is active over a wide range of mg2+ concentrations, and its activity is stimulated by several small acidic proteins (calmodulin, lactalbumin, parvalbumin, protein kinase inhibitor and troponin C). The enzyme phosphorylates a variety of substrates including casein, histones, protamine and the synthetic basic polypeptides, poly(L-arginine) and poly(L-lysine).

Adenosine Triphosphate↗
PubMed1982

An early mitosis-determining event in regenerating rat liver and its possible mediation by prostaglandins or thromboxane.

Inhibitors of prostaglandin and thromboxane production such as mefenamic acid, hydrocortisone, and dexamethasone prevented a large proportion of the parenchymal cells of rat liver, proliferatively activated by a two-thirds partial hepatectomy, from entering mitosis without preventing them from initiating or completing DNA synthesis. This specific mitosis-inhibiting action was maximum when the drugs were present during the first few hours after partial hepatectomy. In contrast, indomethacin, another inhibitor of prostaglandin and thromboxane production, maximally inhibited both DNA synthetic and mitotic activities when present during the same early period of prereplicative development, which showed that it had an action not shared by the other inhibitors. Arachidonic acid completely reversed the hydrocortisone- or dexamethasone-induced inhibition of mitotic activity, but it did so only when it was injected between 2 and 3 hours after partial hepatectomy and glucocorticoid injection. Arachidonate's reversal of the hydrocortisone-induced inhibition did not occur in the presence of mefenamic acid. These observations indicate that there is an early, prostaglandin- or thromboxane-mediated, prereplicative process in proliferatively activated hepatocytes which determines their later entry into mitosis and which is separate from the early events leading to DNA synthesis.

Animals↗
PubMed1982

Rat liver ribonucleotide reductase: separation, purification, and properties of two nonidentical subunits.

Two nonidentical subunits of mammalian ribonucleotide reductase, L1 and L2, from regenerating rat liver have been extensively purified for the first time. They were separated by dATP-Sepharose affinity chromatography. Subunit L1, which bound to dATP-Sepharose, was eluted with 50 mM ATP and purified to homogeneity (as demonstrated by sodium dodecyl sulfate (SDS) - polyacrylamide gel electrophoresis) by molecular exclusion high-pressure liquid chromatography (HPLC). This subunit had an apparent relative mass (Mr) of 45 000 and a Km of 0.9 X 10(-4) for CDP. Subunit L2, which did not bind to dATP-Sepharose, was purified by pH 5.2 precipitation followed by chromatography on CM-Sephadex, molecular exclusion HPLC, and DEAE-cellulose. This subunit contained iron and had an apparent Mr of 120 000 by HPLC molecular exclusion chromatography, but showed two bands (Mr 75 000 and Mr 47 000) on SDS-polyacrylamide gel electrophoresis. Neither L1 nor L2 separately had any enzyme activity but when combined they reduced CDP to dCDP.

Animals↗