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A Rodriguez-Peña

Publications and source records attributed to A Rodriguez-Peña.

10 recordsLinked to original sources
PubMed2000

Pleiotrophin signals increased tyrosine phosphorylation of beta beta-catenin through inactivation of the intrinsic catalytic activity of the receptor-type protein tyrosine phosphatase beta/zeta.

Pleiotrophin (PTN) is a platelet-derived growth factor-inducible, 18-kDa heparin-binding cytokine that signals diverse phenotypes in normal and deregulated cellular growth and differentiation. To seek the mechanisms of PTN signaling, we studied the interactions of PTN with the receptor protein tyrosine phosphatase (RPTP) beta/zeta in U373-MG cells. Our results suggest that PTN is a natural ligand for RPTP beta/zeta. PTN signals through "ligand-dependent receptor inactivation" of RPTP beta/zeta and disrupts its normal roles in the regulation of steady-state tyrosine phosphorylation of downstream signaling molecules. We have found that PTN binds to and functionally inactivates the catalytic activity of RPTP beta/zeta. We also have found that an active site-containing domain of RPTP beta/zeta both binds beta-catenin and functionally reduces its levels of tyrosine phosphorylation when added to lysates of pervanidate-treated cells. In contrast, an (inactivating) active-site mutant of RPTP beta/zeta also binds beta-catenin but fails to reduce tyrosine phosphorylation of beta-catenin. Finally, in parallel to its ability to inactivate endogenous RPTP beta/zeta, PTN sharply increases tyrosine phosphorylation of beta-catenin in PTN-treated cells. The results suggest that in unstimulated cells, RPTP beta/zeta is intrinsically active and functions as an important regulator in the reciprocal control of the steady-state tyrosine phosphorylation levels of beta-catenin by tyrosine kinases and phosphatases. The results also suggest that RPTP beta/zeta is a functional receptor for PTN; PTN signals through ligand-dependent receptor inactivation of RPTP beta/zeta to increase levels of tyrosine phosphorylation of beta-catenin to initiate downstream signaling. PTN is the first natural ligand identified for any of the RPTP family; its identification provides a unique tool to pursue the novel signaling pathway activated by PTN and the relationship of PTN signaling with other pathways regulating beta-catenin.

Blotting, Western↗
PubMed1996

Evidence for the existence of at least two timing mechanisms that contribute to oligodendrocyte generation in vitro.

We have been studying oligodendrocyte generation in vitro to obtain insights into how the timely generation of these cells might be regulated. Our studies suggest the existence of timing mechanisms quite different from those of existing models, wherein it is proposed that timely oligodendrocyte generation is associated with synchronous and symmetric differentiation controlled by cell-intrinsic biological clocks. Our results are most consistent with the hypothesis that the propensity of a clone of dividing oligodendrocyte type-2 astrocyte (O-2A) progenitors initially to generate at least one oligodendrocyte may be regulated by cell-intrinsic mechanisms, but that cell-extrinsic signals regulate the extent of further oligodendrocyte generation. In cultures of embryonic rat cortex grown in the presence of platelet-derived growth factor (PDGF), oligodendrocytes appeared in a timely manner in the absence of clonal differentiation. In contrast with previous suggestions, the presence or absence of thyroid hormone (T3) did not alter the probability of individual clones of O-2A progenitors generating at least one oligodendrocyte in vitro at a time equal to the rat's day of birth. Instead, T3 increased the proportion of oligodendrocytes generated within clones. For postnatally derived progenitor cells, the initial appearance of oligodendrocytes also was followed by further asymmetric generation of these cells, with the ratio of progenitors to oligodendrocytes within clones being regulated by environmental signals. T3 and ciliary neurotrophic factor increased oligodendrocyte generation, while neurotrophin-3 (NT-3) suppressed oligodendrocyte generation. Also in contrast to previous reports, NT-3 was not required for the promotion of extensive division of O-2A progenitor cells by PDGF.

Animals↗
PubMed1994

Characterization of the promoter region and flanking sequences of the neuron-specific gene RC3 (neurogranin).

RC3 encodes a thyroid hormone-dependent, calmodulin-binding, protein kinase C substrate (neurogranin, p17) present in the dendritic spines of discrete neuronal populations in the forebrain. Its physiological role could be related to synaptic plasticity, memory, and other processes. In the present work we have isolated and sequenced 2.4 kbp of genomic DNA upstream from the origin of transcription and determined its nucleotide sequence. The major features of the RC3 promoter are the absence of TATA and CAAT boxes and the presence of an Initiator sequence surrounding the cap site. By sequence analysis we identified several cis-acting regulatory elements, among them response elements for retinoic acid and steroid (glucocorticoids/progesterone) hormone receptors. An oligonucleotide containing the retinoic acid responsive element bound to retinoic acid receptors specifically in vitro and conferred retinoic acid regulation to a heterologous promoter after transfection in COS-7 cells. Retinoic acid and dexamethasone, respectively, increased activity of the RC3 promoter in neuroblastoma cells when a deletion construct containing the retinoic acid and the glucocorticoid responsive elements was cotransfected with retinoic acid receptor or glucocorticoid receptor expression vectors. When added together all-trans retinoic acid and dexamethasone had additive effects. Despite the fact that RC3 expression in vivo is thyroid hormone-dependent, no evidence for the presence of a thyroid hormone responsive element was found within the 2.4 kbp flanking region analyzed and thyroid hormone did not increase reporter activity after cotransfection of suitable constructs with thyroid hormone receptor expression vectors. Our results suggest that the expression of RC3 in vivo could be subject to complex physiological signals, including retinoids and steroid hormones in addition to thyroid hormones.

Amino Acid Sequence↗
PubMed1993

Neonatal hypothyroidism affects the timely expression of myelin-associated glycoprotein in the rat brain.

Congenital hypothyroidism strongly affects myelination. To assess the role of thyroid hormone on myelin gene expression, we have studied the effect of hypothyroidism on the steady state levels of myelin-associated glycoprotein (MAG) and its mRNA in rat brain during the first postnatal month. As studied by immunoblot analysis of several brain regions, MAG increased from days 10-15 onwards, reaching constant levels by days 20-25. Hypothyroid samples showed a delay in the accumulation of MAG that was more severe in rostral regions, such as cortex and hippocampus. The effect of hypothyroidism on the accumulation of the protein correlated with mRNA levels. MAG mRNA started to accumulate in the cerebrum of normal animals by postnatal day 7, reaching maximal levels by day 20. Hypothyroid rats showed a delay of several days in the onset of mRNA expression, increasing thereafter at the same rate as in normal animals, and eventually reaching similar values. When individual brain regions were analyzed, we found strong regional differences in the effect of hypothyroidism. The cerebral cortex was most affected, with messenger levels lower than in normal animals at all ages. In more caudal regions differences between control and hypothyroid rats were evident only at the earlier stages of myelination, with spontaneous recovery at later ages. By run on analysis, we found no differences in transcriptional activities of the MAG gene in normal, hypothyroid, or T4-treated rats. Therefore, the effects of hypothyroidism on MAG mRNA and protein levels were most likely caused by decreased mRNA stability. We propose that thyroid hormone contributes to enhanced myelin gene expression by affecting the stability of newly transcribed mRNA in the early phases of myelination.

Aging↗
PubMed1993

Thyroid hormone regulation of RC3, a brain-specific gene encoding a protein kinase-C substrate.

RC3 is a brain-specific mRNA expressed in discrete neuronal groups of the forebrain that encodes a 78-amino acid protein, also called neurogranin, a calmodulin-binding, protein kinase-C substrate. Expression of RC3 mRNA was studied in normal and hypothyroid animals during the first month of life. Hypothyroid rats were produced by administration of methyl-mercapto-imidazol to the pregnant dams and subsequent surgical thyroidectomy on postnatal day 5 of the neonates. As studied by slot-blotting of total cerebrum poly(A)+ RNA, RC3 mRNA accumulates in normal brain from the fifth to seventh postnatal day, reaching maximal levels around days 10-12. RC3 mRNA accumulation in hypothyroid animals was blunted, and the maximal levels attained were about 30-50% of normal values. The effect of hypothyroidism on steady state mRNA levels was also observed by Northern blotting of RNA from cerebral cortex and striatum. As studied by immunoblotting using a polyclonal antibody, hypothyroidism also led to clear decreases in the amount of the RC3 protein in extracts from cerebral cortex, striatum, and hippocampus. A single administration of 10 micrograms T4 to hypothyroid rats on postnatal day 12 led to a steady increase in striatal RC3 mRNA from levels that were about 40% of normal to about 70% of normal at 16 h and 115% of normal at 48 h. In contrast to the effect on RC3, hypothyroidism did not affect developmental expression of the mRNA encoding GAP-43, another brain protein kinase-C substrate of axonal localization. RC3 is, thus, one of the few known neuronal genes whose expression is influenced by thyroid hormone in the brain. Thyroid hormone is required for an appropriate level of expression, not for the developmentally programmed timing of expression of the RC3 gene.

Animals↗
PubMed1992

Adult rat brain is sensitive to thyroid hormone. Regulation of RC3/neurogranin mRNA.

The mammalian brain is considered to be poorly responsive to thyroid hormone after the so called "critical periods" of brain development, which occur in the rat before postnatal days 15-20. In a previous work (Muñoz, A., A. Rodriguez-Peña, A. Perez-Castillo, B. Ferreiro, J.G. Sutcliffe, and J. Bernal. 1991. Mol. Endocrinol. 5:273-280) we have identified one neuronal gene, RC3, whose expression is influenced by early neonatal hypothyroidism and thyroid hormone treatment. In the present work we show that adult-onset hypothyroidism leads to a reversible decrease of RC3 mRNA. Rats thyroidectomized on postnatal day 40 and killed three months later showed a decreased RC3 mRNA concentration in the cerebral cortex and striatum. The same effect was observed in animals made hypothyroid on postnatal day 32 and killed on postnatal day 52. RC3 expression was normal when hypothyroid animals were treated with T4 five days before being killed. In contrast, the mRNA encoding myelin proteolipid protein showed no changes in either experimental situation. RC3 mRNA levels were not affected by food restriction demonstrating that the effect of hypothyroidism was not related to the lack of weight gain. The control of RC3 mRNA is so far the only molecular event known to be regulated by thyroid hormone once the critical periods of brain development are over and could represent a molecular correlate for the age-independent, reversible alterations induced by hypothyroidism in the adult brain.

Age Factors↗
PubMed1991

Effects of neonatal hypothyroidism on rat brain gene expression.

To define at the molecular biological level the effects of thyroid hormone on brain development we have examined cDNA clones of brain mRNAs and identified several whose expression is altered in hypothyroid animals during the neonatal period. Clones were identified with probes prepared by subtractive or differential hybridization, and those corresponding to mRNAs altered in hypothyroidism were further studied by Northern blot analysis. Using RNA prepared from whole brains, no effect of hypothyroidism was found on the expression of the astroglial gene coding for glial fibrillary acidic protein. Among genes of neuronal expression, no significant alterations were found in the steady state levels of mRNAs coding for neuron-specific enolase, microtubule-associated protein-2, Tau, or nerve growth factor. N-CAM mRNA increased slightly in hypothyroid brains. In contrast a 2- to 3-fold decrease was found in the mRNA coding for a novel neuronal gene, RC3. This is the first neuronal gene known to be significantly altered at the mRNA level by thyroid hormone deprivation. The abundance of the mRNAs for the major myelin proteins proteolipid protein, myelin basic protein, and myelin-associated glycoprotein, expressed by oligodendrocytes, were also decreased in hypothyroid brains. Developmental studies on RC3 and myelin-associated glycoprotein expression indicated that the corresponding mRNAs accumulate in the brain of normal rats during the first 15-20 days of neonatal life. A similar accumulation occurred in hypothyroid brains, but at much reduced levels. The results demonstrate that thyroid hormone controls the steady state levels of particular mRNAs during brain development.

Animals↗
PubMed1985

Signalling mitogenesis in 3T3 cells: role of Ca2+-sensitive, phospholipid-dependent protein kinase.

Understanding the molecular mechanisms that control cell proliferation requires the identification of the early signals important for initiating a mitogenic response. In this context, the activation of Ca2+-sensitive, phospholipid-dependent protein kinase (protein kinase C), which is stimulated by diacylglycerols and serves as a major phorbol ester receptor, may play an important part in signalling mitogenesis. This conclusion is based on two main lines of evidence. Firstly, activation of protein kinase C in intact quiescent fibroblasts is one of the earliest events elicited by a variety of growth-promoting agents including serum, platelet-derived growth factor (PDGF), vasopressin and bombesin, as judged by the increase in the phosphorylation of a cellular protein characterized by an Mr of 80 000 and a pI of 5. Secondly, the synthetic diacylglycerol, 1-oleoyl-2-acetylglycerol, which directly competes with [3H]phorbol dibutyrate for binding to specific receptors in intact 3T3 cells and rapidly stimulates protein kinase C in these cells, is a potent mitogen for Swiss 3T3 cells, acting synergistically with other growth factors. We propose that activation of protein kinase C may be one of the early signals that mediate the mitogenic effects of a variety of growth factors and peptide hormones in quiescent fibroblastic cells.

Animals↗
PubMed1982

Are iodine-deficient rats euthyroid?

Inhabitants of many severe endemic goiter areas have low serum T4 and high circulating TSH, despite normal levels of T3. This situation may be produced experimentally chronically feeding rats a low iodine diet (LID). We fed rats a Remington-type LID and gave them 1% NaClO4 in their drinking water for 2 days. After this, the animals were divided into three groups. One group was fed LID, supplemented with 5 micrograms I/rat.day and was used as the control group. Another group was fed LID alone. The third group was fed LID and given 1% NaClO4 to drink. The latter treatment was used to induce severe hypothyroidism. Animals were killed 1, 2, 3, and 5 weeks after the onset of these treatment schedules. The following measurements were made on some or all groups of animals: body and thyroid weights; thyroidal I content; soluble labeled iodoprotein profile; thyroidal labeled iodoamino acid distribution pattern; plasma T4, T3, and TSH; pituitary GH content; and liver intramitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme activities. T4 and T3 concentrations were also measured in liver nuclei of the animals killed 5 weeks after the onset of treatment. As assessed from various indices of thyroid function, the LID rats became iodine deficient, although not as markedly as those given LID and ClO4-, The plasma T4 decreased to undetectable levels, and plasma TSH increased, whereas circulating T3 remained normal throughout in the LID rats. In rats given LID and ClO4-, plasma T4 decreased sooner than in rats given LID alone; plasma T3 levels also became undetectable, and TSH increased more markedly and sooner than in rats given LID alone. As measured at the end of 5 weeks of treatment, pituitary GH content, and liver alpha-glycerophosphate dehydrogenase and malic enzyme activities were lower in rats given LID than in the euthyroid LID- and I--treated controls. They were not, however, as markedly reduced as in the severely hypothyroid LID- and ClO4--treated rats. In spite of normal plasma T3 levels, the concentration of T3 in liver nuclei of the rats given LID alone was significantly lower than that of the LID- and I--treated controls. The results show that the thyrotrophs, somatotrophs, and livers of rats given LID alone are not like those of euthyroid rats despite normal circulating T3 levels. In iodine-deficient rats, there is a discrepancy between the measured indices of thyroid hormone action in the liver and the circulating T3 level, but not between biological activity and liver nuclear T3 concentration. It remains to be seen whether the same is true in the anterior pituitary.

Animals↗