CONSTITUTIVE OVEREXPRESSION OF THE MAJOR INDUCIBLE 70 KDA HEAT-SHOCK-PROTEIN MEDIATES LARGE PLAQUE-FORMATION BY MEASLES-VIRUS

Induction of the cellular stress response elevates cytoplasmic levels of heat shock proteins (HSPs) belonging to multiple families. When inf ected with canine distemper virus or measles virus (MV), cells contain ing elevated HSPs support increased viral gene expression and cytopath ic effect. The present work tests the hypothesis that increases in the major inducible 70 kDa HSP (hsp72) are sufficient to mediate the effe ct of stress response induction on infection phenotype, Human astrocyt oma cells (U373) were stably transfected with the human hsp72 gene und er control of the p-actin promoter. Constitutive overexpression of hsp 72 was demonstrated in multiple clones by Western blot analysis of cyt oplasmic total protein. Southern blot analysis of cell DNA confirmed t he recovery of genetically distinct clones. Infection of these clonal populations with MV resulted in increased viral transcript production relative to infected control cell lines. Increased transcript producti on was associated with increased viral membrane glycoprotein expressio n and cytopathic effect (i.e., mean plaque area). Increases in cytopat hic effect were due to the emergence of a large plaque phenotype from a small plaque-purified inoculum, mimicking the effect of cellular str ess response induction upon viral infection phenotype. Large plaque ph enotypic variants reported in the literature are associated with enhan ced neurovirulence, a fact that highlights the potential significance of physiologic elevations in hsp72 (e.g., fever-induced) that accompan y in vivo viral infection.