zVAD-fmk and DEVD-cho induced late mitosis arrest and apoptotic expressions

Cell growth in human Chang liver cells was arrested in late mitosis with 600 microM zVAD-fmk. Associated cell death manifested cell shrinkage and phagocytic marking shown by phosphatidylserine (PS) externalization, in a dose-dependent manner. While low molecular weight internucleosomal ladder cleavages were suppressed, there were however high molecular weight DNA cleavages extending up to megabase level in association with chromatin condensation that appeared more marked than the staurosporine-induced positive-apoptosis control. Caspase-3 activity was suppressed. Specific caspase-3 inhibitor DEVD-cho also produced cell growth suppression with late mitosis arrest, and cell shrinkage which was expressed concomitantly with phagocytic PS marking in similar dose-dependent manners at 50 to 100 microM concentrations. Cell shrinkage, PS externalization, and high molecular weight DNA cleavages associated with chromatin condensation without 200 bp ladder fragmentations, were dissociated from caspase-3 activity. Anti-caspases inducing late mitosis arrest provided fresh insights into late mitosis progression.

G-band expression and megabase fragmentations in apoptosis

Apoptosis seems characterized by a cascade of megabase to 200-bp fragmentations and by a commitment to perish at the initial level. How that could be achieved seems unclear. Preferential cleavage of transcriptionally active chromatin by apoptotic nuclease activity has long been suggested. We show here the manifestation of self-inflicted G-banding patterns in mitotic chromosomes, or G-band expression, occurring concurrently with a pattern of megabase fragmentations in two apoptotic systems that we have established in human Chang liver cells using (a) staurosporine and (b) vanadyl(4) prepulsing. We further show that rare-cutting NotI and MluI restriction endonucleases with C-G dinucleotide sequence specificity had produced similar G-bandings and megabase fragmentations cascading down to the 200-bp ladder fragmentation that were also associated with the expression of characteristic apoptotic morphologies by the digested cells. CpG-specific methylation using the methylase SssI abolished the DNA fragmentation cascade, G-banding, and apoptotic expressions induced by NotI and MluI, implicating endonuclease cleavage of active chromatin, where CpG islands are concentrated, as the initiating event. Reproducing the G-bandings and megabase fragmentations by directly applying NotI and MluI endonucleases to fixed chromosomes and extracted genomic DNA, respectively, further confirmed the notion of endonucleolytic cleavage of active chromatin as the causation. Nuclease-digested light G-band regions of chromosomes appeared to be the chromosome sites providing the megabase fragments. Transcriptionally active genes of the genome are known to be preferentially cleaved by nuclease activity and are established as being concentrated in the light G-bandings that correspond to R-bandings, which are also known to be the sites of more frequent cytogenetic breakpoints. Manifestation of self-inflicted G-banding patterns (G-banding expression) in apoptosis would then imply cleavage of the transcriptionally active genes in every light G-band site of every chromosome in the genome. This must be suicidal.

Staurosporine induces telophase arrest and apoptosis blocking mitosis exit in human Chang liver cells

Staurosporine is a protein kinase inhibitor that is known to block G1/S and G2/M cell cycle transitions, resulting in the accumulation of G1 or G2 interphase cells, depending on the applied dosage. It is, however, not known to block mitosis (M-phase) progression. We show here that a 15 min prepulse with 500 nM staurosporine had caused mitotic cell arrest in human Chang liver cells, accumulating telophase cells distinguished by their doublet nuclei and cytokinetic constrictions. The arrested telophase cells perished by apoptosis. Telophase-specific cell cycle arrest and apoptosis are novel. Staurosporine targeting cytokinesis could provide insights into late mitosis where control mechanisms remain largely unknown.

Interphase and M-phase oral KB carcinoma cells are targetted in staurosporine-induced apoptosis

The effect of staurosporine, an antimicrobial agent and inhibitor of protein kinase C (PKC) on programmed cell death/apoptosis (PCD) was investigated in the human oral cavity epidermoid carcinoma KB cell line. Staurosporine-treated oral KB carcinoma cells exhibited morphological features characteristic of apoptosis such as (a) cell shrinkage and increased nuclear fluorescence (quantitated by image analysis with laser scanning confocal microscopy), (b) nuclear condensation and fragmentation observed under fluorescence microscopy with propidium-iodide-DNA staining and (c) chromatin condensation seen under transmission electron microscopy. Specific terminal deoxynucleotidyl transferase (TdT)-mediated labeling of 3'OH ends of DNA breaks in staurosporine-treated cells confirmed DNA fragmentation. In addition, we show the concomitant existence of M-phase PCD with interphase PCD in staurosporine-treated KB cells. It would appear that staurosporine induces apoptosis regardless of the cell cycle phase and that mitosis and apoptosis are not necessarily mutually exclusive events.