Human immunodeficiency virus type 1 protease microinjected into cultured human skin fibroblasts cleaves vimentin and affects cytoskeletal and nuclear architecture

Abstract

In human skin fibroblasts microinjected with purified human immunodeficiency virus type 1 protease (HIV-1 PR), stress fibers were lost and alterations in nuclear morphology and condensation of nuclear chromatin were observed. Thereafter, the vimentin intermediate filament (IF) network collapsed. No effect was seen on the microtubules. While complicated by loss of affected cells from the substratum, a minimum estimate of the proportion of cells demonstrating these effects is 50%. Observation of single cells demonstrated that these effects were largely irreversible and were steps leading to the death of the HIV-1 PR-injected cells. After microinjection of various dilutions of the HIV-1 PR, it was observed that the changes in nuclear morphology and chromatin condensation were detectable under conditions where little or no effect was observed on both stress fibers and the IF network. Proteins of cells labelled with [35S]methionine and microinjected with either HIV-1 PR or BSA were subjected to two-dimensional gel electrophoresis. The major differences in the gel patterns were a diminution in the amount of vimentin and the appearance of novel products comigrating with cleavage products obtained after treatment of vimentin with HIV-1 PR in vitro. Thus, the HIV-1 PR is capable not only of cleaving IF subunit proteins in vivo, but also can catalyze alterations in other cellular structures.