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F F Bolander

Publications and source records attributed to F F Bolander.

At least 19 recordsLinked to original sources
PubMed2002

Prolactin activation of mammary nitric oxide synthase: molecular mechanisms.

Prolactin (PRL) is capable of stimulating both calcium and nitric oxide (NO) accumulation in mammary epithelial cells within 15min. A calcium ionophore was also able to stimulate NO levels to an extent similar to that generated by PRL. Furthermore, maximal concentrations of PRL and the ionophore were not additive, suggesting that they were both using the same pathway, i.e. calcium. Finally, the depletion of intracellular calcium completely abrogated the effect of PRL on NO production. No other pathway known to affect NO synthase (NOS) influenced the action of PRL. Specifically, manipulations of protein phosphatase 2B, protein kinase B (PKB), protein kinase C (PKC), and arginine transport did not alter the activation of NOS by PRL. Therefore, the ability of PRL to stimulate NO production at 15min can be completely explained by its ability to elevate intracellular calcium.

Animals↗
PubMed2001

The role of nitric oxide in the biological activity of prolactin in the mouse mammary gland.

In mouse mammary epithelial cells, prolactin transiently elevates nitric oxide (NO) to a maximum of 6 nmol/mg protein at 15 min, after which levels fall rapidly. This stimulation can be achieved by as little as 100 ng prolactin/ml and can be mimicked by 100 microg sodium nitroprusside/ml. NO is both necessary and sufficient to mediate the prolactin-induced redistribution of its receptor from internal pools to the cell surface. NO can also enhance DNA synthesis stimulated by submaximal prolactin concentrations (50 ng/ml), but it is not necessary at pharmacological prolactin concentrations (1 microg/ml). In contrast, NO completely inhibits alpha-lactalbumin production. In summary, prolactin transiently elevates NO to enhance DNA synthesis and suppress premature differentiation; thereafter, NO declines, DNA synthesis ceases and differentiation proceeds. This data suggest that NO may mediate some of the effects of prolactin on growth in the mammary gland.

Animals↗
PubMed2000

Rapid hormonal regulation of N-acetylglucosamine transferase I.

Previous studies have shown that, in unstimulated mammary epithelial cells from virgin mice, prolactin receptors are retained intracellularly because of their incomplete N-glycosylation. Activation of the nitric oxide/cGMP pathway stimulates Nacetylglucosamine (NAG) transferase I activity, completion of terminal glycosylation, and redistribution of the receptors to the cell surface. In this study, it was shown that nitric oxide could stimulate the phosphorylation of NAG transferase I in intact cells and that the cGMP-dependent protein kinase (PKG) could directly phosphorylate the purified enzyme. Furthermore, this modification was associated with enhanced enzymatic activity. Conversely, this stimulation of activity was blocked in intact cells by coincubation with a PKG inhibitor and reversed in the immunoprecipitated enzyme by alkaline phosphatase treatment. Kinetic analysis revealed that this effect on enzyme activity was due to an increase in V(max) without any change in K(m). Therefore, it appears that the nitric oxide/cGMP pathway activates NAG transferase I via direct phosphorylation by PKG.

Animals↗
PubMed1999

Regulation of prolactin receptor glycosylation and its role in receptor location.

In unstimulated mammary epithelial cells from virgin mice, the prolactin receptor exists as two isoforms: a 78 and a 70 kDa species. Both proteins are reduced to a single 61 kDa molecule after N-glycanase F treatment, indicating that their size difference is solely a result of carbohydrate content. Membrane fractionation experiments reveal that the smaller species is exclusively intracellular, while the larger one is located on the cell surface. Nitric oxide (NO) stimulates the migration of prolactin receptors from an internal pool to the plasmalemma in only 30 min and this redistribution is associated with an increase in molecular weight. Redistribution is blocked by swainsonine, but not by castanospermine or 1-deoxymannojirimycin, suggesting that the glycosylation step involved with translocation is either alpha-mannosidase II or N-acetylglucosamine (NAG) transferase I. The former is unaffected by NO but the activity of the latter is doubled 30 min after exposure to NO. These data suggest that prolactin receptors are retained intracellularly because of their incomplete N-glycosylation and that NO triggers their redistribution by stimulating the completion of this process, in part by increasing NAG transferase I activity.

Animals↗
PubMed1998

Transduction pathways involved in rapid hormone receptor regulation in the mammary epithelium.

Previous studies have shown that the envelope protein of the mouse mammary tumor virus (MMTV) rapidly upregulates prolactin (PRL) receptors by shifting them from internal pools to the cell surface and downregulates epidermal growth factor (EGF) receptors by inducing their internalization and degradation. This study shows that the effect on PRL receptors is mediated by the nitric oxide (NO)/cGMP pathway, since it can be mimicked by an NO donor or 8-bromo-cGMP and can be blocked by an NO synthase inhibitor. In contrast, the effect on EGF receptors is mediated by tyrosine phosphorylation and phosphatidylinositol 3-kinase (PI3K), since it can be blocked by either a tyrosine kinase inhibitor or by a PI3K inhibitor. Both of these pathways can be activated by a calcium ionophore and inhibited by calcium chelation. Therefore, it appears that the mouse mammary tumor virus envelope protein, like other retroviral envelope proteins, initially elevates cytoplasmic calcium, which can then stimulate both the NO/cGMP and the tyrosine phosphorylation/PI3K pathways, leading to PRL receptor upregulation and EGF receptor downregulation, respectively.

Androstadienes↗
PubMed1998

Regulation of mammary hormone receptor metabolism by a retroviral envelope protein.

In a previous study, the envelope protein (gp52) of the mouse mammary tumour virus (MMTV) was shown to facilitate mammary gland differentiation by increasing prolactin (PRL) receptors via increased receptor synthesis and via the redistribution of existing receptors from an internal pool. In this study, receptors for other hormones known to affect mammary gland metabolism were investigated. Epidermal growth factor (EGF) stimulates mammary epithelial growth and inhibits differentiation; its receptor is rapidly and dramatically down-regulated by gp52. This is accomplished by its internalization and by decreasing its half-life from 27 h to 2.4 h. Surprisingly, it also increased EGF receptor synthesis, although this effect was not great enough to overcome receptor down-regulation. In contrast, gp52 did not affect the distribution, half-life or synthesis of the insulin receptor. These results demonstrate that MMTV can enhance mammary differentiation by coordinately regulating several hormone receptors: specifically, it can increase the number of receptors for PRL, a differentiative hormone, while decreasing the number of receptors for EGF, a growth/anti-differentiative hormone.

Animals↗
PubMed1997

Second messengers induced by the envelope protein of a retrovirus.

The envelope protein (gp52) of the mouse mammary tumor virus (MMTV) can stimulate RNA synthesis via binding to its cellular receptor on mammary epithelium. This effect was mimicked by either nitric oxide (NO) or 8-bromo-cGMP and was blocked by an NO inhibitor. Furthermore, the effects of gp52 and 8-bromo-cGMP were not additive at maximal concentrations, suggesting that they were using the same signaling route. Finally, gp52 elevated cGMP levels in mammary epithelium. These data suggest that gp52 activates the following transduction pathway in this tissue: gp52-->NO synthase-->NO-->soluble guanylate cyclase cGMP RNA synthesis. In contrast to the mammary gland, gp52 inhibited RNA synthesis in the diaphragm. However, the effect was again mimicked by NO, blocked by an NO inhibitor, and the effects of gp52 and NO were not additive. Therefore, it appears that gp52 is using the NO-cGMP pathway in both tissues, but that muscle tissue may be more susceptible to the toxic effects of NO.

Animals↗
PubMed1997

The regulation of mammary prolactin receptor metabolism by a retroviral envelope protein.

In a previous study, infection with the mouse mammary tumor virus (MMTV) was shown to increase the sensitivity of the mammary epithelium toward prolactin (PRL); furthermore, this effect could be mimicked by the binding of the MMTV envelope protein (gp52) to its cell receptor. The present work has investigated the possibility that gp52-induced changes in the PRL receptor (PRLR) were responsible for this phenomenon. In vitro, gp52 doubled the PRLR concentration in the plasmalemma of mammary epithelium without affecting the affinity. The origins of these PRLRs were twofold: first, gp52 stimulated PRLR mRNA nearly fivefold, suggesting that some of the receptors were newly synthesized. Second, there was a redistribution of PRLRs within the mammary cell: PRLRs were shifted from an internal pool to the plasma membrane. This relocation was very rapid, occurring within 30 min. There did not appear to be any contribution from alterations in PRLR degradation, since the half-life of PRLR was not affected by gp52. In summary, the MMTV increases the PRL sensitivity of mouse mammary epithelium by elevating PRLRs through both enhanced synthesis and recruitment from microsomes.

Animals↗
PubMed1996

Requirements for mouse mammary tumour virus internalization in mouse mammary epithelial cells.

Methylamine, a lysosomotropic alkalinizing agent, blocked mouse mammary tumour virus (MMTV) infection in normal mouse mammary epithelium, suggesting that internalization and acidification are necessary for cell penetration. This mechanism was further supported by the fact that intact MMTV induced the translocation of its cellular binding protein from the plasmalemma to the microsomes; however, isolated gp52, the MMTV envelope protein that binds this receptor, did not redistribute the binding protein. These data suggest that either another viral component, in addition to gp52, is needed for cell entry or that internalization requires receptor aggregation, which only the multivalent viral envelope can induce.

Animals↗
PubMed1994

The effect of mouse mammary tumor virus receptor activation on mammary epithelial cell sensitivity toward prolactin.

Mammary epithelial cells infected with the mouse mammary tumor virus (MMTV) require less than one-half the concentration of prolactin to elicit alpha-lactalbumin production than uninfected tissue (EC50 = 89 +/- 10 ng/ml vs. 206 ng/ml, respectively). Furthermore, stimulating antibodies to the cellular receptor for MMTV halved the prolactin requirement of MMTV-tissue, while MMTV antibodies that sequestered secreted MMTV increased the prolactin requirement in MMTV+ tissue. These data suggest that the effect of MMTV on mammary epithelial sensitivity toward prolactin is being mediated by its interaction with a cell surface receptor.

Animals↗
PubMed1994

Regulation of the mouse mammary tumor virus receptor by phosphorylation and internalization in mammary epithelial cells.

The mouse mammary tumor virus enters mammary epithelial cells via a plasma membrane protein that binds to a viral envelope glycoprotein, gp52. In intact cells, this gp52 receptor can be phosphorylated by activators of protein kinase A and protein kinase C (PKC), but this modification does not occur in response to epidermal growth factor, whose receptor is a tyrosine kinase, or to gp52. Phosphorylation of the gp52 receptor rapidly leads to internalization and gradual loss of binding activity. Both the phosphorylation and the internalization induced by PKC are abolished by prior downregulation of this kinase. Although the physiological function of the gp52 receptor is unknown, its binding to gp52 can stimulate several biological activities, including amino acid accumulation. Receptor processing impairs this gp52-induced amino acid uptake, as well as viral infection, by depleting the binding protein at the cell surface. In contrast, PKC augments insulin-induced amino acid transport, and PKC downregulation abolishes the action of insulin, suggesting that insulin and gp52 utilize partially separate pathways leading to amino acid transport. These data further suggest that PKC may be involved in this insulin-stimulated activity.

Aminoisobutyric Acids↗
PubMed1991

Regulation of the mouse mammary tumor virus (MMTV) binding site in cultured mammary tissue.

The mouse mammary tumor virus (MMTV) initiates infection when the envelope protein, gp52, binds to a cell surface protein and triggers internalization. The hormonal regulation of this protein was studied both in vitro and in vivo. In mammary gland explant culture, levels of the MMTV binding protein were maintained only when prolactin was present in the medium. The further addition of progesterone induced levels to 164% of controls, while estradiol was without effect. These results were reproduced in ovariectomized mice which, in addition, demonstrated a need for estradiol in the maintenance of basal levels. Two growth-promoting agents were also tested in vitro: dibutyryl cAMP decreased levels to 31% of controls, while epidermal growth factor had no effect. Scatchard analyses revealed that all of these changes reflected alterations in binding protein concentration and not affinity. These results suggest that the expression of MMTV from mammary epithelium and the elevation of its binding protein are coordinated.

Animals↗
PubMed1991

Tissue distribution of the cellular binding protein for the mouse mammary tumour virus.

The envelope protein, gp52, of the mouse mammary tumour virus (MMTV) binds to a cell-surface receptor as a first step in infection. A protein with characteristics of this receptor was measured on freshly isolated cells using, as ligand, 125I-labelled gp52 purified from C3H/HeN mice. The gp52-binding protein was found in all mouse tissues examined, but was present at highest concentrations in the mammary gland and spleen where it reached 4.2 +/- 0.3 (S.E.M.) pmol/mg protein; the dissociation constant was 30 +/- 7 pM. Binding to mammary epithelium could be displaced by either the RIII or 34I-R strains of MMTV, and binding was blocked by antibodies to gp52. Levels in the liver and adrenal glands were only 25% of those in the mammary gland, while the concentrations in the ovary and salivary gland were intermediate. Scatchard analyses of the binding data suggested that there was only a single set of high-affinity binding sites. During late pregnancy and lactation, receptor levels in mammary epithelium rose threefold, while those in the liver and salivary gland were unchanged. This induction would result in the mammary gland having 12 times the gp52-binding protein than other tissues and may result in the preferential reinfection of this tissue during lactation, with subsequent tumour formation.

Animals↗
PubMed1990

Differential characteristics of the thoracic and abdominal mammary glands from mice.

The anatomical and physiological characteristics of thoracic and abdominal mammary glands were investigated in order to understand why the incidence of mammary tumors is higher in the former. Epithelium in explants from both sets of glands required DNA synthesis, insulin, cortisol, and prolactin for full differentiation as measured by alpha-lactalbumin accumulation. The temporal pattern and magnitude of response were the same with respect to both DNA synthesis and differentiation; however, the epithelium in explants from the thoracic glands required concentrations of hormones for alpha-lactalbumin accumulation only one-half to one-third those from abdominal glands. Tumor distribution did not appear to correlate with mammary gland histology, size, or epithelial content.

Abdomen↗
PubMed1990

Developmental and hormonal regulation of a mouse mammary tumour virus glycoprotein in normal mouse mammary epithelium.

A radioimmunoassay was developed and validated for the major glycoprotein (gp58) of the mouse mammary tumour virus (MMTV). Using this assay, the expression of gp58 during pregnancy and lactation was found to parallel that for MMTV RNA. In particular, there was a very rapid induction in late pregnancy and a decline in late lactation, although some residual expression persisted well into involution. In cultures of normal mouse mammary tissue, induction of gp58 occurred after a 24-h lag period and began to reach a plateau after 3 days. Both the insulin and prolactin dose-response curves for gp58 resembled those for MMTV RNA; in contrast, the effects of steroid hormones on gp58 and MMTV RNA were disparate. Although progesterone stimulated the RNA, it only slightly increased gp58 levels; however, the presence of cortisol greatly augmented this stimulation, despite the inability of cortisol to induce RNA at physiological concentrations. These results suggest that insulin, prolactin and progesterone act primarily at the level of RNA accumulation in normal mammary epithelium, while cortisol affects some more distal event.

Animals↗
PubMed1990

Cyclic AMP and calcium in mouse mammary tumour virus expression: effects and post-transcriptional site of action.

The role of cyclic AMP (cAMP), calcium, calmodulin and protein kinase C (PKC) in the expression of both mouse mammary tumour virus (MMTV) RNA and an MMTV glycoprotein, gp58, was investigated in normal mammary epithelium in culture. None of these second messengers had any effect on MMTV RNA. Dibutyryl cAMP alone had no effect on gp58 levels but, at low concentrations (0.05-0.1 mM), it nearly doubled the induction seen with insulin, cortisol and prolactin; higher concentrations were inhibitory. Although a calcium ionophore (A23187), either alone or with hormones, was ineffective, a calcium channel blocker (verapamil) reduced hormonal induction of gp58 by 80%, and a calmodulin inhibitor (W-13) reduced it by 90%. Two PKC activators, a phorbol ester and a diacylglyceride, were ineffective alone, with hormones or with the calcium ionophore. The following conclusions can be made: (1) cAMP, calcium and calmodulin play an important role in MMTV expression, (2) these second messengers all act post-transcriptionally, since they do not affect MMTV RNA, and (3) PKC does not appear to have a role in MMTV production in normal mammary epithelium.

Animals↗
PubMed1989

The role of sex steroids in the expression of MMTV in the normal mouse mammary gland.

Infection with the mouse mammary tumor virus (MMTV) is associated with hyperplastic alveolar growth and subsequent tumorigenesis. The role of the sex steroids in the initial phase of this pathological chain of events is investigated in this study. In normal mammary epithelium, progesterone stimulates MMTV RNA expression both in vivo (2.6-fold) and in vitro (2.9-fold); although estradiol is ineffective alone, it does enhance the effect of progesterone (6.8- and 5.7-fold stimulation, respectively). These results suggest that the sex steroids may play an important role in inducing MMTV expression which can then lead to epithelial hyperplasia and, eventually, malignant transformation.

Animals↗