To determine if ultrastructural changes and increased mitochondrial ROS production affect cell proliferation and survival, population doubling time was determined during the exponential phase of cell growth. Genome-length replicon and Core-on cells showed a 41% and 11% increase in population doubling time, respectively, without a significant increase in cell death during the 72-hr period when cell number increase was monitored ( Figure 6A ). On the other hand, subgenomic replicon cells had a comparable population doubling time to that of Huh7 and Coreoff cells. To determine if cell cycle regulation is affected in HCV protein-expressing cells, in-cell westerns were carried out to determine total cyclin D1 levels. Consistent with increased population doubling time in genome-length replicon cells, cyclin D1 level was decreased ( Figure 6B ). There was also a trend in decreased cyclin D1 levels in Core-on cells.