Stimulation of mitochondrial DNA synthesis in HeLa cells by Herpes simplex virus

African green monkey kidney Vero cells require de novo protein synthesis for efficient herpes simplex virus 1-dependent apoptosis

During HSV-1 infection, IE gene expression triggers apoptosis, but subsequent synthesis of infected cell proteins blocks apoptotic death from ensuing. This "HSV-1-dependent" apoptosis was identified in HEp-2/HeLa cells infected with wild-type HSV-1 in the presence of an inhibitor of protein synthesis or a virus lacking ICP27 {HSV-1(vBSDelta27)}. Unlike HEp-2/HeLa cells, vBSDelta27-infected Vero cells fail to exhibit dramatic apoptotic morphologies at times prior to 24 hpi. Here, we examined the basis of these different apoptotic responses to HSV-1. We found that infected Vero cells take substantially longer than HEp-2/HeLa cells to display membrane blebbing, chromatin condensation, DNA laddering, and PARP cleavage. Vero, but not HEp-2/HeLa, cells required de novo protein synthesis to exhibit efficient HSV-1-dependent apoptosis, which included changes in mitochondrial membrane potential, and these factors were produced prior to 3 hpi. Vero cells infected with recombinant viruses devoid of the ICP27 and ICP4 proteins alone or both the ICP27 and ICP22 proteins were apoptotic. These results indicate a requirement for cellular or other viral protein synthesis in Vero cells and provide insight into cell type differences in HSV-1-dependent apoptosis.

Changes of mitochondrial DNA polymerase-gamma activity in synchronized mouse cell cultures

Following synchronization by a double hydroxyurea block, mouse cell cultures exhibited a period of accelerated precursor incorporation into mitochondrial DNA during the late nuclear S phase. Peak activity of mitochondrial DNA polymerase-gamma occurred concurrent to the interval of accelerated organelle DNA synthesis. Mixing experiments suggested that the variations in mitochondrial DNA polymerase activity during the cell cycle were not due to free inhibitors in the enzyme preparations examined.

Mitochondrial DNA synthesis in adenovirus type 2-infected HeLa cells

Mitochondrial DNA synthesis in adenovirus type 2-infected HeLa cells was measured at various times from 0 to 24 h postinfection. Although viral infection effectively turned off host chromosomal DNA synthesis, mitochondrial DNA synthesis was not inhibited. These findings indicate a dissociation between the regulation of host and mitochondrial DNA synthesis after infection with adenovirus type 2.