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R A Lockshin

Publications and source records attributed to R A Lockshin.

50 records · Page 3Linked to original sources
PubMedDate not supplied

Programmed cell death: early changes in metamorphosing cells.

Programmed cell death in intersegmental muscles and labial glands of Manduca sexta is a type II form of active cell death, in which lysosomal destruction of cytoplasm is a prominent and early feature, and the collapse of the nucleus is late and relatively modest until the bulk of the cytoplasm has been eroded. The prominent features of this collapse include an early expansion of the lysosomal compartment and a decrease in overall protein synthesis, while a small number of mRNAs persist or are upregulated. Energy resources appear to be adequate during the early stages of degeneration, and changes in levels of second messages likewise do not seem to be sufficiently dramatic to explain the failure of the tissue. There is some suggestion that DNA may not be completely intact long before the labial gland finally collapses, suggesting that it may fail under heavy load. Otherwise, we do not yet have an explanation for the precipitous drop in overall protein synthesis.

Animals↗
PubMedDate not supplied

Metabolic events during programmed cell death in insect labial glands.

The labial gland of Manduca sexta is a valuable system to study the mechanisms of programmed cell death since the death of the gland is nearly synchronous and, except for the anterior duct, involves all of the tissue. The gland degenerates in 5 days during pupation. Our previous work documents a drop in total protein synthesis as the gland degenerates. To evaluate potential causes of this altered protein synthesis, we monitored several parameters of metabolism in dying cells: levels of adenosine triphosphate to estimate the energy resources of the gland; reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide to assess mitochondrial respiration; levels of acid phosphatase to assay lysosomal enzyme activity; and concentrations of cyclic nucleotides and inositol triphosphate to monitor signaling. While protein synthesis fell precipitously on day 0, total adenosine triphosphate and mitochondrial respiration were unchanged until the cells underwent massive collapse on day 3. Lysosomal acid phosphatase increased during early metamorphosis, and ultimately the bulk of the cytoplasm was destroyed in autophagic vacuoles. Changes in the concentrations of second messengers were modest and late. The relationships between the metabolism and the collapse of the labial gland are under investigation.

Acid Phosphatase↗
PubMedDate not supplied

The induction of terminal differentiation markers by the cAMP pathway in human HaCaT keratinocytes.

The terminal differentiation of human epidermal keratinocytes is a complex morphological and biochemical shift from a mitotically active cell to an inert protein cross-linked envelope. This transition is a clearly predetermined cell death mechanism, but it is unlike many other programmed cell deaths in that it is not apoptotic. To explore and contrast the mechanism by which keratinocytes are committed to differentiation rather than apoptosis, we focused on the cyclic adenosine monophosphate (cAMP) signaling pathway using selective modulators of intracellular cAMP levels. Markers of differentiation were assayed by Western blotting. Raising intracelluar cAMP levels by treating HaCaT cells with forskolin, a diterpene, or with isobutylmethylxanthine, a phosphodiesterase inhibitor, and isoproterenol, a beta-adrenergic receptor agonist that selectively activates adenylate cyclase, increased the levels of the differentiation markers keratin K1 and K10, involucrin and transglutaminase. H89 and KT5720, both inhibitors of cAMP-dependent protein kinase, suppressed the expression of keratins K1 and K10. These observations are in line with the defined role for cAMP in the control of keratinocyte differentiation.

1-Methyl-3-isobutylxanthine↗