PMID: 7538195May 1, 1995Paper

Camptothecin induction of a time- and concentration-dependent decrease of topoisomerase I and its implication in camptothecin activity

Molecular Pharmacology
D R Beidler, Y C Cheng

Abstract

Camptothecin (CPT) has been shown to induce protein-linked DNA breaks (PLDB), which are stabilized intermediates of topoisomerase I (TOP1) activity. Due to the reversible nature of PLDB and the need for replication fork movement for CPT toxicity, both the time of CPT exposure and TOP1 levels are determinants of CPT toxicity. Therefore, the effects of CPT exposure on TOP1 over time were examined in an established human cell line, KB. Using an in vivo KCl-SDS co-precipitation assay, it was determined that 1 hr of CPT exposure resulted in a concentration-dependent increase in PLDB that reached a maximum at 5 microM CPT. However, prolonged incubations with CPT revealed a concentration- and time-dependent decrease in CPT-induced PLDB formation. The most rapid loss of PLDB was within 6 hr. Neither aphidicolin nor cycloheximide cotreatments altered the PLDB decrease induced by CPT. Immunoblot analysis revealed a reduction in TOP1 protein upon CPT exposure, whereas RNA analysis revealed no changes, which suggested a post-transciptional mechanism of TOP1 down-regulation. The CPT-induced reduction was specific for TOP1, because actin and tubulin levels were unaltered by CPT exposure. Finally, clonogenic assays revealed a small but statis...Continue Reading

Related Concepts

Trending Feeds

COVID-19

Coronaviruses encompass a large family of viruses that cause the common cold as well as more serious diseases, such as the ongoing outbreak of coronavirus disease 2019 (COVID-19; formally known as 2019-nCoV). Coronaviruses can spread from animals to humans; symptoms include fever, cough, shortness of breath, and breathing difficulties; in more severe cases, infection can lead to death. This feed covers recent research on COVID-19.

Blastomycosis

Blastomycosis fungal infections spread through inhaling Blastomyces dermatitidis spores. Discover the latest research on blastomycosis fungal infections here.

Nuclear Pore Complex in ALS/FTD

Alterations in nucleocytoplasmic transport, controlled by the nuclear pore complex, may be involved in the pathomechanism underlying multiple neurodegenerative diseases including Amyotrophic Lateral Sclerosis and Frontotemporal Dementia. Here is the latest research on the nuclear pore complex in ALS and FTD.

Applications of Molecular Barcoding

The concept of molecular barcoding is that each original DNA or RNA molecule is attached to a unique sequence barcode. Sequence reads having different barcodes represent different original molecules, while sequence reads having the same barcode are results of PCR duplication from one original molecule. Discover the latest research on molecular barcoding here.

Chronic Fatigue Syndrome

Chronic fatigue syndrome is a disease characterized by unexplained disabling fatigue; the pathology of which is incompletely understood. Discover the latest research on chronic fatigue syndrome here.

Evolution of Pluripotency

Pluripotency refers to the ability of a cell to develop into three primary germ cell layers of the embryo. This feed focuses on the mechanisms that underlie the evolution of pluripotency. Here is the latest research.

Position Effect Variegation

Position Effect Variagation occurs when a gene is inactivated due to its positioning near heterochromatic regions within a chromosome. Discover the latest research on Position Effect Variagation here.

STING Receptor Agonists

Stimulator of IFN genes (STING) are a group of transmembrane proteins that are involved in the induction of type I interferon that is important in the innate immune response. The stimulation of STING has been an active area of research in the treatment of cancer and infectious diseases. Here is the latest research on STING receptor agonists.

Microbicide

Microbicides are products that can be applied to vaginal or rectal mucosal surfaces with the goal of preventing, or at least significantly reducing, the transmission of sexually transmitted infections. Here is the latest research on microbicides.