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Tumor markers are gene products which signal the occurrence of tumors in different organs as well as their response to surgery and chemotherapy. The discovery of tumor markers occurred after the demonstration of tumor-specific transplantation antigens in chemically or virally induced tumors in syngenic rodents. The history of currently used tumor markers began in the 1940s, the first discovered being alpha-fetoprotein in 1956, followed by that of carcinoembryonic antigen in 1965. Since then the range of tumor markers has widened continously. Their chemical structure and genetics is now well known. Some may play part in tumor growth and development of metastases. The potential uses of tumor markers are general or high risk population screening, adjunct in diagnosis of cancer, preoperative indicator of tumor burden, indicator of therapeutic success, evidence of postoperative recurrences and use in tumor localization. However, there is no ideal tumor marker fulfilling all the criteria. Isotope-labeled anti-carcinoembryonic antigen antibodies and small molecular E-selectin inhibitors could play a role in the molecular radio- and chemotherapy of colon and pancreatic carcinomas.

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My desire as a young endocrinologist to improve my clinical skills through a better knowledge of hormone chemistry led me to serendipitous discoveries and unexpected horizons. The first discovery, published in 1967, revealed that peptide hormones are derived from endoproteolytic cleavages of larger precursor polypeptides. It was the foundation of the prohormone theory. Initially thought to apply to a few hormones, the theory rapidly extended to many proteins, including neuropeptides, neurotrophins, growth and transcription factors, receptors, extracellular matrix proteins, bacterial toxins, and viral glycoproteins. Its endoproteolytic activation mechanism has become a fundamental cellular process, affecting many biological functions. It implied the existence of specific endoproteolytic enzymes. These proprotein convertases were discovered in 1990. They have been shown to play a wide range of important roles in health and disease. They have opened up novel therapeutic avenues. Inactivation of PCSK9 to reduce plasma cholesterol is currently the most promising. To make this good thing even better, I recently discovered in a French Canadian family a potent PCSK9 (Gln152His) mutation that significantly lowers plasma cholesterol and should confer cardiovascular longevity. The discovery helped me to complete the loop: "From the bedside to the bench and back to the bedside."

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Studies of the biosynthesis of insulin in a human insulinoma beginning in 1965 provided the first evidence for a precursor of insulin, the first such prohormone to be identified. Further studies with isolated rat islets then confirmed that the precursor became labeled more rapidly than insulin and later was converted to insulin by a proteolytic processing system located mainly within the secretory granules of the beta cell and was then stored or secreted. The precursor was designated "proinsulin" in 1967 and was isolated and sequenced from beef and pork sources. These structural studies confirmed that the precursor was a single polypeptide chain which began with the B chain of insulin, continued through a connecting segment of 30-35 amino acids and terminated with the A chain. Paired basic residues were identified at the sites of excision of the C-peptide. Human proinsulin and C-peptide were then similarly obtained and sequenced. The human C-peptide assay was developed and provided a useful tool for measuring insulin levels indirectly in diabetics treated with insulin. The discovery of other precursor proteins for a variety of peptide hormones, neuropeptides, or plasma proteins then followed, with all having mainly dibasic cleavage sites for processing. The subsequent discovery of a similar biosynthetic pathway in yeast led to the identification of eukaryotic families of specialized processing subtilisin-like endopeptidases coupled with carboxypeptidase B-like exopeptidases. Most neuroendocrine peptides are processed by two specialized members of this family - PC2 and/or PC1/3 - followed by carboxypeptidase E (CPE). This brief report concentrates mainly on the role of insulin biosynthesis in providing a useful early paradigm of precursor processing in the secretory pathway.

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The discovery of glucagon-like peptide 1 (GLP-1) began more than two decades ago with the observations that anglerfish islet proglucagon messenger RNAs (mRNAs) contained coding sequences for two glucagon-related peptides arranged in tandem. Subsequent analyses revealed that mammalian proglucagon mRNAs encoded a precursor containing the sequence of pancreatic glucagon, intestinal glicentin and two glucagon-related peptides termed GLP-1 and GLP-2. Multidisciplinary approaches were then required to define the structure of biologically active GLP-1 7-36 amide and its role as an incretin, satiety hormone and, most recently, a neuroprotective peptide. This historial perspective outlines the use of traditional recombinant DNA approaches to derive the GLP-1 sequence and highlights the challenges and combination of clinical and basic science approaches required to define the physiology and pathophysiology of bioactive peptides discovered through genomics.

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The discoverers of secretin already thought of the existence of a chemical excitant for the internal secretion of the pancreas. Numerous experiments have been performed and published between 1906 and 1935 testing the effect of injected or ingested duodenal ("secretin") extracts on fasting or elevated blood glucose levels of normal or diabetic animals and humans with contradictory results. In 1940, after a series of negative dog experiments performed by an opinion leader, the existence of an incretin was considered questionable and further research stopped for more than 20 years. However, after the development of the radio-immunoassay, the incretin-concept has been revived in 1964, showing that significantly more insulin was released after ingestion of glucose than after intravenous injection. The possibility that nerves or one of the known gut hormones were responsible for the incretin effect could be ruled out. In 1970, glucose dependent insulinotropic polypeptide (GIP), and finally, in 1985 glucagon-like peptide 1 (GLP-1) and its truncated form GLP-1(7-36) were recognized as true incretins. Thereafter, multiple antidiabetic qualities and the therapeutic perspectives of GLP-1(7-36) and its analogues and mimetics have been demonstratred.

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An account of work on the biosynthesis of secondary metabolites up to 1965 is presented. The earliest suggestions for three of the four major pathways were speculative; for the isoprene rule, hypotheses date to 1877, for the polyketide rule to 1907, and for a role for amino acids in alkaloid biosynthesis to 1910. The fourth major pathway based on intermediates of the shikimic acid pathway has a much shorter history because shikimic acid itself was only identified as a primary metabolite in 1951. In addition to speculation, biomimetic syntheses were carried out in which chemists attempted to duplicate possible biosynthetic pathways in vitro. The classic example was Robinson's synthesis of tropinone in 1917. Direct examination of secondary metabolite biosynthesis was possible with the use of the isotopic tracer technique. This methodology, applied extensively to primary metabolism beginning in 1935 and to secondary metabolism from about 1950, was facilitated by the increasing availability of the 14C isotope. With the use of isotopes as tracers, the broad outlines of secondary metabolite biosynthesis, reviewed here, were established in the period 1950 to 1965.

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