Protease activation during HIV infection in a CD4-positive cell line

The mechanism of cytopathic effects associated with HIV infection in a continuous line of CD4-positive lymphocytes (CEM cells, clone 13) has been studied. Here we report the following observations: (1) HIV infection killed a variable but always significant number of cells without a strict relationship with the syncytia formation; (2) an important decrease in the proliferation rate occurred soon after infection; (3) a marked inhibition of protein synthesis took place within the first few hours of infection and clearly before the beginning of viral protein expression. In addition, when three-day-old cultures were incubated in serum-free medium, a larger degradation of proteins was observed in infected cells in comparison to controls. An increase in protein degradation activity was observed also in vitro with extracts obtained from HIV-infected cells and incubated in the presence of endogenous- or exogenous-labeled substrates. Extracts from cells infected with heat-inactivated HIV did not show a similar degradative activity. The possible induction or activation of latent proteases during the development of the HIV infection is discussed.