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P Coulombe

Publications and source records attributed to P Coulombe.

At least 19 recordsLinked to original sources
PubMed2001

p27 cytoplasmic localization is regulated by phosphorylation on Ser10 and is not a prerequisite for its proteolysis.

The activity of the cyclin-dependent kinase inhibitor p27 is controlled by its concentration and subcellular localization. However, the mechanisms that regulate its intracellular transport are poorly understood. Here we show that p27 is phosphorylated on Ser10 in vivo and that mutation of Ser10 to Ala inhibits p27 cytoplasmic relocalization in response to mitogenic stimulation. In contrast, a fraction of wild-type p27 and a p27(S10D)-phospho-mimetic mutant translocates to the cytoplasm in the presence of mitogens. G1 nuclear export of p27 and its Ser10 phosphorylation precede cyclin-dependent kinase 2 (Cdk2) activation and degradation of the bulk of p27. Interestingly, leptomycin B-mediated nuclear accumulation accelerates the turnover of endogenous p27; the p27(S10A) mutant, which is trapped in the nucleus, has a shorter half-life than wild-type p27 and the p27(S10D) mutant. In summary, p27 is efficiently degraded in the nucleus and phosphorylation of Ser10 is necessary for the nuclear to cytoplasmic redistribution of a fraction of p27 in response to mitogenic stimulation. This cytoplasmic localization may serve to decrease the abundance of p27 in the nucleus below a certain threshold required for activation of cyclin-Cdk2 complexes.

Alanine↗
PubMed2000

Differential regulation of p27(Kip1) expression by mitogenic and hypertrophic factors: Involvement of transcriptional and posttranscriptional mechanisms.

Platelet-derived growth factor-BB (PDGF-BB) acts as a full mitogen for cultured aortic smooth muscle cells (SMC), promoting DNA synthesis and cell proliferation. In contrast, angiotensin II (Ang II) induces cellular hypertrophy as a result of increased protein synthesis, but is unable to drive cells into S phase. In an effort to understand the molecular basis for this differential growth response, we have examined the downstream effects of PDGF-BB and Ang II on regulators of the cell cycle machinery in rat aortic SMC. Both PDGF-BB and Ang II were found to stimulate the accumulation of G(1) cyclins with similar kinetics. In addition, little difference was observed in the expression level of their catalytic partners, Cdk4 and Cdk2. However, while both factors increased the enzymatic activity of Cdk4, only PDGF-BB stimulated Cdk2 activity in late G(1) phase. The lack of activation of Cdk2 in Ang II-treated cells was causally related to the failure of Ang II to stimulate phosphorylation of the enzyme on threonine and to downregulate p27(Kip1) expression. By contrast, exposure to PDGF-BB resulted in a progressive and dramatic reduction in the level of p27(Kip1) protein. The time course of p27(Kip1) decline was correlated with a reduced rate of synthesis and an increased rate of degradation of the protein. Importantly, the repression of p27(Kip1) synthesis by PDGF-BB was associated with a marked attenuation of Kip1 gene transcription and a corresponding decrease in Kip1 mRNA accumulation. We also show that the failure of Ang II to promote S phase entry is not related to the autocrine production of transforming growth factor-beta1 by aortic SMC. These results identify p27(Kip1) as an important regulator of the phenotypic response of vascular SMC to mitogenic and hypertrophic stimuli.

Angiotensin II↗
PubMed1994

Genetic bases of epidermolysis bullosa simplex and epidermolytic hyperkeratosis.

Keratins are the major structural proteins of the epidermis. Analyzing keratin gene sequences, appreciating the switch in keratin gene expression that takes place as epidermal cells commit to terminally differentiate, and elucidating how keratins assemble into 10-nm filaments have provided the foundation that has led to the discoveries of the genetic bases of two major classes of human skin diseases. In this report, we review the cell biology and human genetics of these diseases, epidermolysis bullosa simplex and epidermolytic hyperkeratosis. Both of these diseases are epidermal disorders of keratin, typified by cell fragility as a consequence of defects in the mechanical strength of basal epidermolysis bullosa simplex or suprabasal epidermolytic hyperkeratosis cells.

Cell Differentiation↗
PubMed1984

Ready evaluation of lung alveolar toxic damage with histological sections morphometry.

In this experiment we aimed at developping a method of ready evaluation of lung alveolar toxic damage using morphometric measurements. Swiss-Webster mice were treated with different doses of diquat (i.p.) and the left lung was fixed at 0, 3, and 5 days after treatment. The technique of morphometry of histological sections embedded in glycol methacrylate (GMA) was used to quantify possible modifications of alveolar cells. Quantitative evaluation includes: alveolar macrophages, polymorphonuclear cells, type II and intermediate pneumocytes. The results indicate a lung dose-dependent response, observed in both inflammatory and epithelial regeneration components of the alveolar primary reaction. This method could be used to readily evaluate the pulmonary toxic potential of any substance.

Animals↗
PubMed1984

Thyroid hormones modulate ornithine decarboxylase in the immature rat cerebellum.

In this study, we measured ornithine decarboxylase (ODC) activity as a potential parameter to evaluate the response of the developing rat brain to thyroid hormones. In cerebellum, neonatal hyperthyroidism (40 micrograms thyroxine/100 g body weight daily from birth) increased ODC activity at 2 and 5 days of age and then accelerated its developmental decline. Conversely, ODC activity was decreased in 2- and 5-day-old hypothyroid rats (propylthiouracil to the mother), but it was not significantly different from normal thereafter. No significant differences were observed in the forebrain following either treatment. In hypothyroid rat cerebellum, a single injection of triiodothyronine (T3, 100 micrograms/100 g 18 h before sacrifice) increased significantly ODC activity at all ages. A dose-response study showed that 0.5 micrograms T3/100 g is sufficient to obtain maximal stimulation. Finally, administration of antiserum against rat growth hormone had no significant effect on ODC response to T3. These results show that ODC is a useful marker of thyroid state and tissue response in the neonatal rat cerebellum.

Aging↗
PubMed1983

Pituitary nuclear triiodothyronine receptors during development in the rat.

Studies were undertaken to measure the pituitary nuclear triiodothyronine (T3) binding capacity (BC) during development in the rat. BC was measured in 0.4 M NaCl-solubilized receptors in 5-, 14-, 20-, 27-, 30-, 40-, 50-day-old rats and in adult animals. Results indicate that BC is lower in 5-day-old rats than in adult animals (0.397 +/- 0.02 vs. 0.797 +/- 0.06 pmol T3/mg protein) (mean +/- SE) (P less than 0.01). Hypothyroidism, induced during the neonatal period or in the adult animal, results in a significant decrease in BC (P less than 0.01) when compared with control rats. However, treatment of hypothyroid animals with T3 (0.4 micrograms/100 g body wt) for a period of 7-14 days significantly increased BC as compared with hypothyroid rats without apparent changes in Ka. The relative affinities of various thyroid hormone analogues for the nuclear receptor were also measured in the adult animal. The affinities of these analogues are in the following order: TRIAC greater than L-T3 greater than D-T3 greater than L-T4 greater than D-T4 greater than DIMIT greater than L-T2 greater than rT3. The present findings demonstrate the presence of high affinity nuclear T3 binding sites in the pituitary of neonatal rat and could thus account for the effects of thyroid hormones on GH synthesis and TSH secretion observed in these animals.

Aging↗
PubMed1983

Pituitary receptors during development in the rat. I. TRH binding capacity.

In order to study the role of thyroid releasing hormone (TRH) in the control of thyroid stimulating hormone (TSH) secretion during the neonatal period, we measured the binding of [3H]-TRH to pituitary homogenate of rats at various stages of development. In 2-day-old animals, the number of [3H]-TRH binding sites were similar to that of adult male animals (23 +/- 8 fmole/mg protein versus 21 +/- 7 fmole/mg protein, respectively). Between 5-21 days of age, the number of [3H]-TRH binding sites was significantly higher than that of adult animals (P less than 0.01). Hypothyroidism induced a 2-fold increase in the number of [3H]-TRH binding sites in all the age groups studied. This effect was reversed by administration of L-T4 (0.4 microgram/g body weight for 3 days). These studies thus indicate that TRH binding sites are present during the neonatal period in the rat and suggest that TRH may be an important modulator of TSH secretion during this period in the rat and that these effects are mediated by postreceptor mechanisms.

Age Factors↗
PubMed1982

Influence of tetraiodothyronine on hearing maturation in rats.

Thyroid hormones are essential to the maturation of the central nervous system and sensory organs. Hypothyroidism induced various kinds of neural retardation, including hearing deficits. Despite careful attention to replacement therapy in human neonatal hypothyroidism, psychological disorders and cerebellar malfunction may occur in later life and may be related to overdoses. Brain stem response audiometry (BSRA) is used in this study as an indicator of acoustic pathway maturation in newborn rats. Normal litters are compared to tetraiodothyronine (T4)-overtreated rats from birth to day 12 of life. Onset of hearing and acoustic maturation are accelerated in treated animals as compared to controls (p less than 0.0001). Differences between groups progressively vanish after cessation of T4 administration. However, as long as 4 months later, small differences are still present, leading one to suspect a permanent change in the functioning of the acoustic pathways.

Animals↗
PubMed1982

Thyroid hormones, malnutrition, and biochemical composition of developing rat lung.

We studied the effects of thyroid hormones and malnutrition on protein, DNA, and phospholipid content of the developing rat lung during the first month of life. Neonatal hypothyroidism significantly decreases the lung phospholipid content by 30-45% between 5 and 30 days of age whether the results are expressed per milligram DNA or per gram tissue. Administration of thyroxine for 3 days to hypothyroid rats increases significantly (20%) their total phospholipid content, mainly through its preferential effect on phosphatidylcholine (50% increase). Adult animal response to thyroid hormones is markedly different from that observed in young rats for most parameters examined. In malnourished rats, lung tissue phospholipids are decreased per cell but not per unit cell mass after 11 days of age. These results show that hypothyroidism has a specific effect on lung phospholipids during the neonatal period.

Animals↗
PubMed1982

Characterization of nuclear 3,5,3'-triiodothyronine receptors in the developing rat lung: effects of hypo- and hyperthyroidism.

In this study, we measured the changes in binding characteristics of T3 to its nuclear receptor in lungs of rats from 2 days of age to adulthood. In all ages studied, we found a single class of binding sites with a mean Ka of 1.16 +/- 0.05 x 10(10) M-1. The specificity of the nuclear receptor, as judged by the relative affinities of thyroid hormone analogs, is in general agreement with data previously reported for lung and other organs. A significant decrease in the maximum binding capacity of the lung T3 receptor occurs between 30 and 40 days of age: 0 to 30 days, 0.208 +/- 0.005 pmole T3/mg protein; 40 days to adulthood, 0.111 +/- 0.007 pmole T3/mg protein. Our experiments showed that this reduction is not due to differential recovery of nuclei or efficiency of extraction at various ages. The relative saturation of the nuclear receptor increases from 26% at 2 days of age to 48% in the adult animal. Thyroid status has no significant effect on the nuclear T3 binding capacity of developing rat lung up to 11 days of age. However, hyperthyroidism substantially increased the binding capacity in lungs of adult animals (0.157 +/- 0.009 versus 0.108 +/- 0.006 pmole T3/mg protein), without a corresponding reduction in hypothyroidism (0.116 +/- 0.007 pmole T3/mg protein). These findings suggest that thyroid hormones play a yet unspecified important role in lung physiology during the first month of life in the rat.

Age Factors↗
PubMed1982

Effects of neonatal hyperthyroidism on the development of the hypothalamic-pituitary-thyroid axis in the rat.

The acute and latent effects of neonatal hyperthyroidism (NH) on the hypothalamic-pituitary-thyroid axis were studied in the rat after treatment of newborn animals with L-T4 (0.4 microgram/g BW, daily) for a period of 12 days. NH was associated with a permanent reduction in body weight in both male and female rats, in addition to a delay in the attainment of peak concentrations of hypothalamic TRH and pituitary and serum TSH. Serum TSH, T4, and T3 concentrations also were significantly and permanently reduced in NH animals (P less than 0.01) after cessation of L-T4 treatment. The serum TSH secretory response to 1 microgram synthetic TRH also was evaluated in 120-day-old control and NH rats, before and after the administration of L-T4 (0.6 microgram/100 g BW for 7 days) or propylthiouracil (0.05% in the drinking water for 14 days). In the baseline state, adult NH rats had a net secretory response similar to that of controls (189.0 +/- 31.3 vs. 227.0 +/- 29.3 microgram/ml . min). Administration of T4 significantly decreased while propylthiouracil treatment significantly increased the net TSH secretory response of NH rats compared to similarly treated control rats. These data are compatible with the hypothesis that NH leads to a permanent resetting of the regulatory set-point for pituitary TSH secretion and to increased sensitivity to the feedback inhibitory effects of thyroid hormones.

Animals↗
PubMed1981

Effect of neonatal thyroid deficiency on the catecholamine, substance P, and thyrotropin-releasing hormone contents of discrete rat brain nuclei.

The effects of neonatal thyroidectomy and thyroid hormone replacement therapy on the development of catecholamine-, TRH-, and substance P-containing neurons in discrete rat brain nuclei were studied. Newborn male rats were rendered hypothyroid by the injection of 125 muCi 131I and, after 45 days, were compared with normal littermate controls and 131I-injected animals subsequently maintained on T4 injections. The peptide or catecholamine content of discrete brain nuclei removed by punches of frozen brain slices was measured by RIA or radioenzymatic assay, respectively. The success of the thyroidectomy was verified by criteria of weight, length, plasma T4, and pituitary GH content. Animals receiving T4 replacement therapy were indistinguishable from normal littermates. Substance P was measured in 32 different brain nuclei and was significantly increased in 19 of these areas in hypothyroid animals. No changes in norepinephrine were detected, and the dopamine content of all but 3 brain nuclei was increased by thyroidectomy. The TRH concentration was drastically reduced in the median eminence of hypothyroid animals and also changed in 3 other extrahypothalamic areas. All of the changes seen in catecholamine, TRH, and substance P distribution in hypothyroid animals were completely reversed by T4 replacement therapy. These results demonstrate changes in brain peptide neurotransmitters during the hypothyroid state and open new vistas for comprehension of biochemical mechanisms underlying central nervous system malfunction.

Animals↗
PubMed1980

Minimal placental transfer of L-thyroxine (T4) in the rat.

Studies of L-thyroxine T4 kinetics and placental transfer were conducted in pregnant rats during the last days of gestation using radioiodine labeled and unlabeled T4. The maternal T4 secretion rate was 53.0 +/- 6.9 ng/hr/100 g body wt. The placental transfer rate was 0.463 +/- 0.196 x 10(-3)/hr at 18 days and 1.516 +/- 0.147 x 10(-3)/hr at 20 days. From these results, we calculated that at 20 days of gestation, 80 +/- 8 pg/hr were transfered to the fetus, less than 1% of the fetal production rate. Inasmuch as we have demonstrated that little placental transfer of T4 occurred during these studies, we conclude that the fetal rat hypothalamo-pituitary-thyroid axis develops autonomously.

Animals↗
PubMed1980

Effects of neonatal hypo- and hyperthyroidism on pituitary growth hormone content in the rat.

Thyroid hormones play an important role in growth and development. Therefore, we investigated the effects of neonatal hypo- and hyperthyroidism on pituitary GH content in the rat. In control rats, pituitary GH content increased from 4.16 +/- 0.34 at 2 days to 43.7 +/- 4.2 microgram/gland (mean +/- SE) at 15 days of age, with a t 1/2 of increment of 3.48 +/- 0.40 days. Between 18-60 days of age, pituitary GH content increased from 56.9 +/- 4.0 to 300 +/- 28 microgram/gland, with a t 1/2 of 18.2 +/- 1.5 days. The administration of T3 had no significant effect on the pituitary GH content of these animals. In neonatal hypothyroid rats, pituitary GH content was significantly lower than that of controls at 2 days of age (P < 0.01) and decreased from 8 days on, with a t 1/2 of 3.71 +/- 0.25 days. However, 24 h after the administration of T3 (100 microgram/100 g BW), pituitary GH content was significantly increased in these animals. Similarly, the administration of T3 (0.4 microgram/100 g BW) to 14-day-old hypothyroid rats restored the pituitary GH content to 70-80% of normal after 5 days of therapy. Conversely, hyperthyroidism induced in 14-day-old normal or hypothyroid rats resulted in a significant decrease in their pituitary GH contents after 5 days of treatment. Therefore, the present results indicate that during the neonatal period, thyroid hormones play a primary role in the control of GH accumulation in the pituitary. Furthermore, the lack of increase in pituitary GH content after the administration of T3 during development might suggest that the rate of formation of GH is already maximum during this period of life in the rat, or, alternatively, that the pituitary nuclear T3 receptors are near full saturation during development. Finally, a generally similar effect of T3 on pituitary GH response was observed in the neonatal rat as well as in the adult animal.

Aging↗