Heat stress activates production of herpes simplex virus type 1 from quiescently infected neurally differentiated PC12 cells

We have previously described a novel in vitro model of a non-productive her pes simplex virus type 1 (HSV-1) infection in neurally differentiated (Nd)- PC12 cells that allows for inducible virus replication up on forskolin trea tment. In this study, we further characterized the quiescent state of infec tion and examined the ability of heat stress (HS) to induce virus from this non-productive state. These studies demonstrated that (i) the quiescent st ate is characterized by the absence of cell-associated virus, capsids, and viral antigens; (ii) MS (43 degrees C, 3 h) efficiently activated virus fro m quiescently infected Nd-PC12 (QIF-PC12) cells; (iii) the rate of virus pr oduction was significantly greater following MS than forskolin treatment, a nd the rates of both were dependent on MOI; (iv) forskolin and MS appeared to affect pathways of viral activation from a quiescent state as they did n ot enhance viral growth in Nd-PC12 cells; (v) viral alpha 4 gene and host H SP72 gene transcription were rapidly induced in QIF-PC12 as soon as 3 h pos t-HS initiation; (vi) induction of the viral alpha 27 gene followed that of representative beta and gamma genes, U(L)30 and U(L)18, respectively, and (vii) IIS induced asynchronous HSV-1 replication from QIF-PC12 cells with 1 :400 to 1:22 000 positive foci detected as rapid as 24 h post-induction whe n established at MOIs of 30 and 3, respectively. These findings provide evi dence that alpha 4 may be involved in the switch from quiescence to product ive infection. Furthermore, this model has the potential to advance our und erstanding of how MS initiates the HSV-1 productive cycle from a cryptic vi ral genome.