Single Molecule Investigation Of Cisplatin Induced Apoptosis

Cisplatin is one of the most widely used clinical medicines in chemotherapy.Its anticancer function is attributed to the formation of crosslinks between cisplatin and DNA molecules.These cisplatin-DNA adducts are able to influence the DNA replication and transcription,and finally induce apoptosis.In this work,we study the mechanism of cisplatin induced apoptosis in vivo and in vitro.The main contents of our thesis are listed as follow:(1)Torsion is actively maintained in eukaryotic and prokaryotic chromosomes,and plays key roles in biological functions of DNA.We investigate the effect of torsion on cisplatin induced DNA condensation with torsion-constrained and unconstrained DNA systems,using an atomic force microscope.We find that there are two stages in the cisplatin-induced DNA condensation process under torsional constraint.At the early stage,the low torsion will accelerate DNA condensation by promoting the formation of micro-loops or intersection structures;while at the later stage,the increasing torsion will slow it down by preventing the further crosslinking of cisplatin and DNA since the DNA molecule becomes more rigid.Our results show the important role of torsion in cisplatin-induced DNA condensation and shed new light on the mechanism of cisplatinDNA interaction.(2)Apoptosis is a process of programmed cell death.During which the cell morphology is dramatically changed,with signaling molecules transported between different organelles within the cells.We study the dynamics of intracellular transport in cisplatin induced apoptotic cells,by using the single-particle tracking method and single-cell apoptosis detection technique.We find that both directed and diffusive motions of endocytic vesicles are accelerated in early apoptotic cells.With careful elimination of other factors involved in the intracellular transport,the reason for the acceleration is attributed to the elevation of intracellular adenosine triphosphate(ATP)concentration.Both the elevated ATP concentration and accelerated intracellular transport occur before the caspase activation during the early apoptosis.Above all,we find that the accelerated intracellular transport is critical for apoptosis,and apoptosis is obviously delayed when the dynamics of intracellular transport is regulated back to normal level.Our results demonstrate that the transport dynamics play a critical role in apoptotic process,and shed light on the apoptosis mechanism from a physical perspective.