Analysis of the Basis for Persistence of Herpes Simplex Virus Type 1 in Undifferentiated U937 Cells

Abstract

Replication of herpes simplex type 1 (HSV-1) is inhibited in the human monocyte-like cell line, U937, when the cells are in the undifferentiated state, but when the cells are stimulated to differentiate by treatment with the phorbol ester, phorbol 12-myristate 13-acetate virus is replicated. Because HSV-1 has been shown to persist in these cells and in their in vitro counterparts freshly isolated human blood monocytes, we initiated an analysis of viral persistence in undifferentiated U937 cells. No appreciable HSV-1 DNA replication was observed in undifferentiated U937 cells compared with differentiated U937 cells and with fully permissive Vero cells. However, using in situ hybridization, we established that a significant percent of the undifferentiated U937 cells contained viral DNA sequences. Interestingly, when analyzed by Southern blot hybridization, this DNA was found to have assumed a nonlinear configuration similar to that found in latently infected neurons. Analysis of viral proteins in undifferentiated U937 cells revealed a marked absence of proteins of all three kinetic classes. However, in transient transfection assays, the major viral transactivating protein ICP4, functioned normally, whereas ICP0, a promiscuous transactivator of both viral and cellular genes, was unable to transactivate viral promoters in undifferentiated U937 cells. Thus, a subtle dysfunction in the activity of ICP0 may account, at least in part, for the inability of undifferentiated U937 cells to support replication of HSV-1.

Herpes Simplex Virus Type 1-induced FasL Expression in Human Monocytic Cells and Its Implications for Cell Death, Viral Replication, and Immune Evasion

“…Previous studies showed that monocytes were resistant to HSV-1 infection, and only become susceptible to it upon differentiation towards macrophages (21)(22)(23). Another study showed that human peritoneal macrophages become partially permissive to viral infection upon treatment with thioglycollate, and are fully permissive after prior infection with Corynebacterium parvum (24).…”

“…These results are in agreement with those of Feng et al (25), who showed that the virus did not replicate in U937 cells, but was able to induce activation of NF-kB in them. The cell line, however, also becomes permissive to viral replication upon differentiation with phorbol myristate acetate, but not with dimethyl sulfoxide or all-trans retinoic acid (23). The cell line expresses the herpesvirus entry mediator (HVEM), a specific receptor for gD of the virion.…”

Nitric oxide production induced by herpes simplex virus type 1 does not alter the course of the infection in human monocytic cells.

“…The establishment of cytopathic effects (CPE) by HSV-1 on U937 cells treated with differentiation inducers has been already described (Tenney & Morahan, 1987, 1991Stewart et al, 1992). However, the molecular mechanisms underlying the shift in the permissiveness of U937 cells upon induction of differentiation remain undefined.…”

“…pez-Guerrero et al, 1989, 1990, dengue virus (Peiris & Porterfield, 1979), parvovirus (Lo! pezGuerrero et al, 1997), human immunodeficiency virus (HIV) (Hammer et al, 1986) and HSV (Tenney & Morahan, 1987, 1991Stewart et al, 1992). The infection of U937 cells by HSV-1 leads to persistence of the virus and undetectable levels of HSV-1 DNA replication.…”

“…The infection of U937 cells by HSV-1 leads to persistence of the virus and undetectable levels of HSV-1 DNA replication. A marked dysfunction in the activity of the viral immediate-early transactivating protein ICP0 is a possible contributory factor (Stewart et al, 1992). When U937 cells are treated with an inducer of differentiation such as phorbol 12-myristate 13-acetate (PMA), mezercin or vitamin D3, cells mature to a state permissive for HSV-1 replication, but the mechanisms underlying this process are still unknown.…”