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M Jaramillo

Publications and source records attributed to M Jaramillo.

30 records · Page 2Linked to original sources
PubMed1991

Multiple mRNAs encode the murine translation initiation factor eIF-4E.

All eukaryotic cellular mRNAs (except organellar) possess at their 5' end the structure m7GpppX (where X is any nucleotide) termed the "cap." The cap structure facilitates the melting of mRNA 5' secondary structure through the action of initiation factor-4F (eIF-4F) in conjunction with eIF-4B. eIF-4F consists of three subunits of which one, eIF-4E (eIF-4E has recently been designated eIF-4 alpha according to the Nomenclature Committee of the International Union of Biochemistry (NC-IUB) (Safer, B. (1989) Eur. J. Biochem. 186, 1-3)), contains the cap binding site. Several lines of evidence suggest that eIF-4E regulates the rate of translation initiation. Consequently, changes in cellular eIF-4E levels could control growth and differentiation. To investigate the possibility that eIF-4E expression is regulated, we studied the pattern of eIF-4E expression in several cell lines. Here, we show the existence of multiple mRNAs for eIF-4E that are generated by differential polyadenylation. In addition, we show tissue-specific differences in eIF-4E mRNA expression and utilization of polyadenylation sites.

Animals↗
PubMed1991

RNA unwinding in translation: assembly of helicase complex intermediates comprising eukaryotic initiation factors eIF-4F and eIF-4B.

Ribosome binding to mRNA requires the concerted action of three initiation factors, eIF-4A, eIF-4B, and eIF-4F, and the hydrolysis of ATP in a mechanism that is not well understood. Several lines of evidence support a model by which these factors bind to the 5' end of mRNA and unwind proximal secondary structure, thus allowing 40S ribosomal subunits to bind. We have previously used an unwinding assay to demonstrate that eIF-4A or eIF-4F in combination with eIF-4B functions as an RNA helicase. To elucidate the molecular mechanism of RNA unwinding, we used a mobility shift electrophoresis assay which allows the simultaneous analysis of unwinding and complex formation between these factors and RNA. eIF-4F forms a stable complex (complex A) with duplex RNA in the absence of ATP. Addition of eIF-4B results in the formation of a second complex (complex B) of slower mobility in the gel. In the presence of ATP, both complexes dissociate, concomitant with the unwinding of the duplex RNA. We present evidence to suggest that unwinding occurs in a processive as opposed to distributive manner. Thus, we conclude that helicase complexes that are formed in the absence of ATP on duplex RNA translocate processively along the RNA in an ATP-dependent reaction and melt secondary structure. These helicase complexes therefore represent intermediates in the unwinding process of mRNA that could precede ribosome binding.

Base Sequence↗
PubMed1991

Modulation of the mitogenic activity of eukaryotic translation initiation factor-4E by protein kinase C.

Eukaryotic initiation factor-4E (eIF-4E) binds to the cap structure of eukaryotic mRNAs and is a component of the cap-binding protein complex eIF-4F. eIF-4E is present in cells in limiting concentrations and is phosphorylated both in vivo and in vitro by protein kinase C (PKC). Recently, eIF-4E has been implicated as an intracellular transducer of extracellular growth signals; microinjection of recombinant eIF-4E into quiescent NIH 3T3 cells induced DNA synthesis. In the present report, the mitogenic activity of eIF-4E was examined after coinjection with PKC. Recombinant eIF-4E was phosphorylated by PKC at the same amino acid that is phosphorylated in cultured cells and reticulocytes in response to phorbol ester. At limiting concentrations of eIF-4E, coinjection with PKC induced a fivefold increase in the mitogenic activity of eIF-4E. Injection of PKC alone or coinjection of eIF-4E with cAMP-dependent protein kinase (PKA) or the Raf protein had no effect. These results suggest that the mitogenic activity of eIF-4E is enhanced by PKC-specific phosphorylation and that phosphate addition is a rate-limiting step in eIF-4E activity.

Animals↗
PubMed1990

Translation initiation factors that function as RNA helicases from mammals, plants and yeast.

Ribosome binding to eukaryotic mRNAs requires the concerted action of three eukaryotic initiation factors: eIF-4A, eIF-4B and eIF-4F as well as the hydrolysis of ATP. These initiation factors are implicated in the unwinding of mRNA 5' secondary structure and have been isolated from mammals, yeast and wheat germ. We used an RNA unwinding assay to compare the activities of these factors from the different species. We also measured the inter-species interchangeability of these factors in the unwinding reaction. In mammals, it has been previously shown that a combination of rabbit reticulocyte eIF-4F and -4B or eIF-4A and -4B were active in the RNA unwinding assay. In wheat germ, the combination of eIF-4A and eIF-4F resulted in RNA unwinding in a reaction that was stimulated by eIF-4B. Mammalian eIF-4A was able to substitute in this system. We also show that yeast eIF-4A is able to effectively substitute for mammalian eIF-4A in duplex RNA unwinding in combination with mammalian eIF-4B, while wheat-germ eIF-4A was only partially able to substitute. Taken together, these results suggest that initiation factor requirements for RNA unwinding are largely similar in mammals, yeast and plants.

Animals↗
PubMed1990

Translation initiation factors induce DNA synthesis and transform NIH 3T3 cells.

Several polypeptide factors that are essential for the initiation of protein synthesis bind to eukaryotic mRNAs and facilitate the formation of ribosome initiation complexes. Purified mRNA-binding translation initiation factors were microinjected into quiescent NIH 3T3 cells to study the possible growth-promoting role of these factors in living cells. We report that recombinant eIF-4E and rabbit reticulocyte eIF-4F induce a dose-dependent increase of DNA synthesis and morphologically transform NIH 3T3 cells. These results suggest that polypeptides involved in activating the rate-limiting step of protein synthesis (initiation complex formation) can be mitogenic and oncogenic when overexpressed in a cell by direct injection. Thus, eIF-4E and eIF-4F represent a class of proto-oncogenic proteins that is cytoplasmic, is involved in protein synthesis initiation, and is distinct from the proto-oncogenes that have been identified previously.

Animals↗
PubMed1988

A retrovirus expressing the 12S adenoviral E1A gene product can immortalize epithelial cells from a broad range of rat tissues.

An epithelial cell-transforming virus could be of great use, both in the culture of epithelial cell lines and in the study of carcinogenesis. Since the adenoviral E1A gene has been shown to partially transform some epithelial cells from primary rat cell cultures, we constructed retrovirus vectors containing either the 12S or 13S E1A cDNA sequences to facilitate the transfer of these genes into a variety of primary cell types. The 12S E1A virus induced proliferation and immortalization of epithelial cells in rat kidney, liver, heart, pancreas, and thyroid primary cultures. In the two cases tested, heart and liver cultures, E1A-immortalized cells were nontumorigenic, but could be completely transformed by subsequent introduction of the ras oncogene. To our surprise, the 13S virus had a greatly reduced immortalization potential. We discuss these data in light of the model of Spindler et al. (K. R. Spindler, C. Y. Eng, and A.-J. Berk, J. Virol. 53:742-750, 1985), in which the 12S E1A protein is required for the complete induction of the cellular DNA replication machinery in the quiescent human epithelial cells in which adenoviruses normally replicate.

Adenovirus Early Proteins↗
PubMed1988

HLA-DR gene expression in a proliferating human thyroid cell clone (12S).

We have used a retroviral vector carrying the adenovirus E1A oncogene and the neomycin phosphotransferase gene to establish a human thyroid-derived cell line that exhibits TSH-mediated cAMP generation as well as the differential expression of HLA class II antigens in response to recombinant gamma-interferon. Twenty-two-week gestation, histologically confirmed, human fetal thyroid was collagenase digested, cultured as a monolayer, and infected directly with 12S or 13S E1A-containing retrovirus constructs. Infected clones (n = 30) were selected in a hormone-supplemented medium containing bovine TSH (bTSH; 1 mU/ml), 10% fetal bovine serum, and 0.5 mg/ml G418 antibiotic. A rapidly growing clone (designated 12S) was chosen for detailed analysis over 18 months of continuous culture. The 12S clone was sensitive to less than 10 microU/ml bTSH when assessed by extracellular accumulation of cAMP, but TSH had no influence on 72-h incorporation of [3H]thymidine. Clone 12S responded to recombinant human gamma-interferon (1-10(4) U/ml) by induction of HLA DR alpha-chain-specific mRNA and the surface expression of HLA-DR antigen detected by fluorescein isothiocyanate-labeled monoclonal antibody to nonpolymorphic HLA-DR regions using flow cytometry. These studies indicate the potential for immortalizing human thyroid cells for use as targets of anti-TSH receptor immune responses and for long term studies of human throcyte HLA gene regulation.

Adult↗
PubMed1985

Induction of methotrexate release from rat hepatocytes in suspension by alpha-adrenergic agents: involvement of calcium and metabolic energy.

Hepatocytes in suspension which have accumulated [3H]methotrexate release the antifolate compound into the medium upon exposure to alpha-adrenergic agents. In the presence of metabolic poisons, such as sodium azide, dinitrophenol, or dicumarol, the release of methotrexate is attenuated, indicating that integrity of the cellular metabolic apparatus is required for response to the hormonal stimulus. In the presence of millimolar concentrations of the organic acid, probenecid, release of cellular methotrexate may be reduced (1 mM probenecid) or eliminated (2 mM probenecid), suggesting the involvement of a "membrane carrier." Microtubule poisons such as vincristine, vinblastine, and griseofulvin do not modify epinephrine + isobutyl methyl xanthine (IBMX)-induced release of methotrexate. The involvement of calcium in release of methotrexate from the hepatocyte is substantiated by a dose-dependent response to the calcium ionophore, A23187, in the presence of calcium, with a lack of response in the absence of calcium. These effects of A23187 are not related to inhibition of methotrexate influx. Other putative "calcium antagonists" such as tetracaine, neomycin sulfate, and 3,4,5-trimethoxybenzoic acid [8-(diethylamino)octyl ester], do not interfere with epinephrine + IBMX-induced release of [3H]methotrexate, suggesting that these agents may not be effective probes of calcium flux in the liver cell.

1-Methyl-3-isobutylxanthine↗
PubMedDate not supplied

Comparison of photorefractive keratectomy and laser in situ keratomileusis for myopia of -6 D or less using the Nidek EC-5000 laser.

PURPOSE: We compared the efficacy, predictability, and safety of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for the surgical correction of low and moderate myopia. METHODS: A retrospective study was performed to evaluate uncorrected and spectacle-corrected visual acuity, and manifest refraction 1 year after PRK or LASIK. All procedures were done using an automatic microkeratome (Chiron Ophthalmic) and the Nidek EC-5000 excimer laser. RESULTS: PRK was performed in 75 eyes of 45 patients and LASIK in 133 eyes of 77 patients. Mean age for PRK patients was 32.8 years (range, 18 to 52 yr) and LASIK patients was 29.6 years (range, 18 to 49 yr). Mean preoperative spherical equivalent refraction for PRK patients was -3.28 D (range, -1.00 to -6.00 D) and LASIK, -3.86 D (range, -1.00 to -6.00 D). One year after surgery, mean spherical equivalent refraction for Group 1 (baseline, -1.00 to -3.00 D) PRK eyes was -0.18 +/- 0.61 D (range, -1.50 to +0.75 D) and for LASIK eyes, -0.08 +/- 0.61 D (range, -1.50 to +1.62 D), with no statistically significant difference. For Group 2 eyes (baseline, -3.25 to -6.00 D), mean spherical equivalent refraction for PRK eyes was -0.44 +/- 0.87 D (range, -2.00 to +2.12 D) and for LASIK eyes, -0.09 +/- 0.83 D (range, -1.50 to +1.75 D), with no statistically significant difference. The antilogarithm of the mean UCVA (antilogUCVA) in Group 1 for PRK was 0.79 +/- 0.21 (20/25) and for LASIK was 0.87 +/- 0.19 (20/23), with no statistically significant difference. The antilogUCVA in Group 2 for PRK eyes was 0.70 +/- 0.24 (20/28) and for LASIK eyes was 0.83 +/- 0.18 (20/24), with a statistically significant difference (0.7 vs. 0.83, P < .005). The percentage of eyes with a postoperative UCVA >20/40 in Group 1 for PRK was 91.5% (38 eyes) and for LASIK was 95% (50 eyes) (no statistically significant difference), and in Group 2 for PRK eyes, it was 82% (27 eyes) and 97.5% (78 eyes) for LASIK (statistically significant difference, P < .05). CONCLUSION: PRK and LASIK with the Nidek EC-5000 excimer laser are effective and safe for correcting low to moderate myopia, but LASIK eyes showed better results for moderate myopia in terms of uncorrected visual acuity.

Adolescent↗
PubMedDate not supplied

[Study of the left coronary trunk by 2-dimensional echocardiography in ischemic cardiopathy].

The study of the left main coronary artery (LMCA) obstruction is very important in view of the risk that it represents for coronarography, the high mortality that it has and its indication of early surgical treatment. For these reasons we studied LMCA obstruction by two-dimensional echocardiography (2-D Echo). The study was blind, prospective and included of 50 unselected patients with coronary artery disease proved by coronarography. The LMCA obstruction was recognized in 5 patients (10%) by 2-D Echo, in two of them it was seen as non-obstructive atheroma and in 3 as a significant obstruction. This LMCA correlated with angiographic findings. We had not false negatives. The patients with LMCA obstruction had higher frequency of positive treadmill test and anteroseptal myocardial infarction. Three patients had bypass surgery with good results. Two had not surgery, one of them died and the other one has angina and heart failure. The 2-D Echo is a useful procedure in the study of LMCA obstruction.

Adult↗