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R A Lockshin

Publications and source records attributed to R A Lockshin.

At least 19 recordsLinked to original sources
PubMed1990

Programmed cell death: new thoughts and relevance to aging.

Cell death is a common phenomenon in developmental biology, and recent data suggest that it is as tightly regulated as mitosis. For numerous systems endocrine and neuronal factors are required to maintain viability of cells, as are specific diffusible and other unknown factors deriving from intimate cell-to-cell contact; and, in some instances, specific hormones or other circulating factors induce spontaneous self-destruction by the targeted cells. Some cells such as thymocytes may be primed to self-destruct and hence activate specific enzymes. In others, the doomed cell up-regulates a limited number of genes just before it dies. Of these genes, several are known but are not considered to cause cell death; others are under investigation. Although the situation is clearest for developmental biology, it appears that the presumptively random loss of cells in senescence results from invocation of the same mechanisms. Understanding and control of these mechanisms could conceivably lead either to protection against cell loss or specific induction of lysis in malignant cells.

Aging↗
PubMed1990

Diverse secretory patterns of clusterin by epididymis and prostate/seminal vesicles undergoing cell regression after orchiectomy.

Nucleotide sequence analysis of the complimentary DNAs (cDNA) and N-terminal amino acid sequence analysis have shown that clusterin is equivalent to sulfated glycoprotein-2 (SGP-2), testosterone-repressed prostate protein-2 (TRPP-2), and androgen-repressed protein (ARP) in the rat, as well as serum/seminal plasma protein, SP-40,40, in the human. In view of its widespread presence in various species, a specific RIA was established to quantify the tissue distribution of this protein. Rat clusterin is present in almost all organ tissues examined, including testis, epididymis, serum, liver, prostate, seminal vesicles, and uterus. Displacement curves generated using cytosols prepared from these organs were parallel to those obtained using purified rat clusterin and crude Sertoli cell-enriched culture medium. Immunoreactive clusterin was also visualized in these organ extracts by immunoblots. Studies on the tissue distribution of immunoreactive clusterin using RIA revealed that the concentration of clusterin in the epididymis of adult rats was 6- and 10-fold higher than that in the serum and testis, respectively and is 50- to 100-fold higher in the liver, spleen, kidney, brain, ventral prostate, seminal vesicles, and uterus. A study of the distribution of clusterin in various compartments of the epididymis indicated its concentration in the caput epididymis was almost 3-fold higher than that in the corpus and cauda epididymis. After orchiectomy, the concentrations of clusterin in the ventral prostate and seminal vesicles increased as much as 100- and 10-fold and peaked at day 4 after surgery, respectively; daily injection of dihydrotestosterone (DHT) beginning at day 3 after orchiectomy reduced the concentrations of clusterin and restored them to a normal level. A different pattern was noted in the epididymis after orchiectomy; the concentration of clusterin in the caput epididymis decreased with time; however, daily injection of DHT beginning at day 3 increased the caput epididymal clusterin concentration and restored it to a normal level. The concentration of clusterin was not altered in the corpus or cauda epididymis after castration and/or DHT administration. Also, the serum and liver clusterin levels did not change with time after orchiectomy. These observations suggest that clusterin will be a valuable marker to monitor the diverse effects of androgen withdrawal in the male reproductive tract. We conclude that clusterin may be a multifunctional protein in view of its broad tissue distribution and association with numerous physiological and pathological conditions.

Amino Acid Sequence↗
PubMed1989

Testins are structurally related Sertoli cell proteins whose secretion is tightly coupled to the presence of germ cells.

Previous studies from this laboratory have shown that Sertoli cell-enriched culture medium contained two immunologically and structurally related proteins designated CMB-22 and CMB-23 with Mr of 37,000 and 40,000, respectively. We have now demonstrated that both CMB-22 and CMB-23 are monomeric proteins with the following NH2-terminal amino acid sequences: CMB-22, NH2-TPDPSLDVEWNEWRTKHGKTYNMNEERLKR; CMB-23, NH2-XAPXPDPSLDVEXNEXRTK. These sequences are virtually identical except that CMB-23 has three extra NH2 terminus amino acids of X-A-P. Comparison of these sequences with those in the Protein Identification Resource revealed that they are unique proteins. CMB-22 and CMB-23 are highly concentrated in testes and their levels in this tissue increase with age. Studies using [35S]methionine incorporation and immunoprecipitation demonstrated that Sertoli cells synthesize and secrete these proteins in vitro. Because they seem not to have been isolated previously, are concentrated in and synthesized by the testes, and are structurally related, we propose that CMB-22 and CMB-23 be designated testin I and testin II, respectively. The distribution of these proteins in biological fluids were compared with those of testibumin and rat androgen binding protein (rABP), two other Sertoli cell proteins. The results suggest that testins, unlike testibumin and rABP, are not transported to the epididymis. Although the amount of testins secreted by Sertoli cells in vitro is similar to that of testibumin and rABP, the concentrations in testis and rete testis fluid are several orders of magnitude less than that of testibumin and rABP. These observations suggest that the secretion of these proteins in vivo might be suppressed by germ cells. The fact that 10 times more testins are secreted by tubules from immature rats than by those from adult rats and that there is an increase in the testicular content of testins following a single dose of busulfan, which depleted the germ cells from the seminiferous epithelium, supports this hypothesis. Thus, the secretion of testins by Sertoli cells appears to be tightly coupled to the presence of germ cells; there is an inverse relationship between the amount of testins in the testis and the number of germ cells. These results suggest that testins are unique testicular proteins that can be used to study Sertoli cell-germ cell interactions in the seminiferous epithelium.

Amino Acid Sequence↗
PubMed1989

Selenium modulates peroxidation in the absence of glutathione peroxidase in Musca domestica.

Adult houseflies fed a low-selenium diet showed a 73% decrease in total Se compared to those given 1.0 ppm Se in their drinking water. This decrease was associated with a 84.4% increase in thiobarbituric acid reactants and a 16.3% increase in conjugated dienes. These increases were unrelated to activities of glutathione S-transferases, superoxide dismutases and catalase and to levels of reduced and oxidized glutathione, all of which were unaltered by Se deficiency. Since houseflies lack glutathione peroxidase, Se apparently modulates peroxidation in these animals independent of the antioxidant enzymes and glutathione.

Animals↗
PubMed1989

Selenium-independent glutathione peroxidase activity associated with glutathione S-transferase from the housefly, Musca domestica.

1. A glutathione S-transferase having Se-independent glutathione peroxidase activity was isolated from 100,000 g supernatant from housefly homogenate. 2. The specific activity of the partially purified Se-independent glutathione peroxidase was 1776 nmol NADPH oxidized/min/mg protein, representing an 87-fold purification. 3. The Mr of this enzyme was estimated to be 37,000 and 26,000 by gel filtration chromatography and gel electrophoresis, respectively. 4. Selenium-dependent glutathione peroxidase activity could not be detected in this same supernatant. 5. Se-independent glutathione peroxidase activity should be considered in future studies of the insect antioxidant defense system.

Animals↗
PubMed1988

Programmed cell death: dying cells synthesize a co-ordinated, unique set of proteins in two different episodes of cell death.

Intersegmental muscles of the tobacco hornworm, Manduca sexta, degenerate promptly after the ecdysis of the moth. Protein content of the growing, static, and degenerating muscle was evaluated by two-dimensional electrophoresis; RNA was isolated from the muscle and translated, and the translation products likewise analyzed by two-dimensional electrophoresis. Growing and static muscles synthesize predominantly myofibrillar proteins, and small cytosolic proteins constitute a vanishingly small proportion of the proteins identified even by silver staining. When the muscle begins to degenerate, a large number of smaller proteins is seen on the gels. Many of these are apparently fragments of the myofibrillar proteins, but over 30 can be recognized as new translation products. Most of the translation products are found in two regions, one ranging from 20 to 40 kDa and with a pI of 6.5-6.9; and the other approx. 50-70 kDa and pI 5.8-6.2. The pattern is identical in two separate instances of degeneration.

Aging↗
PubMed1987

The effect of selenium deficiency on peroxidative injury in the house fly, Musca domestica. A role for glutathione peroxidase.

Selenium-dependent glutathione peroxidase activity is documented for the first time in insects. Reduction in glutathione peroxidase activity in the cytosol of adult house flies by lowering selenium in the diet results in significant increases in peroxidative injury. Catalase activity, while higher in low-selenium flies than in selenium-supplemented flies, does not prevent lipid peroxidation. The discovery of glutathione peroxidase activity in insects eliminates an anomaly which partially limited the usefulness of these animals as models for the study of the antioxidant defense system.

Animals↗
PubMed1979

Programmed cell death. electrophysiological and ultrastructural correlations in metamorphosing muscles of lepidopteran insects.

Individual spontaneously degenerating fibers of moths have been examined successively by electrophysiological and ultrastructural techniques. The correlations observed by this method have revealed two phases of lysis. The first lytic phase begins at or before the ecdysis of the moth. It is characterized by a probable but occult respiratory lesion, normal movement of the ions across the plasma membrane, and limited degradation of myofilaments and autophagy of mitochondria. There are nevertheless early degenerative changes in the Z-band and a slight swelling of the T system. The second lytic phase is introduced, at approximately 15 hr after ecdysis, by collapse of the tracheal airways. The collapse of the tracheae is followed within 2 or 3 hr by a drastic reduction of input resistance, depolarization of the fiber, and loss of contractility. The rate of proteolysis increases, and the remaining myofilaments lose all structural identity by the twentieth hour. During this period of rapid change, the electron density of the reticular portion of the dyads decreases before a compactive process increases their opacity. Neural elements degenerate secondarily. The early lytic phases are apparently non-lysosomal for the myofilaments, although organelles such as mitochondria, ribosomes, and glycogen are destroyed in autophagic vacuoles. Elimination of oxygen and collapse of the resting potential, with the presumed equilibration of intracellular ionic content, provokes a rapid dissolution of the myofilament, with continued autophagic elimination of the organelles.

Animals↗