Relationship between HOX2 homeobox gene expression and the human cytomegalovirus immediate early genes

The human embryonal carcinoma cell line NT2/D1 is known to be non-permissive for human cytomegalovirus (HCMV) but becomes permissive after being induced to differentiate by retinoic acid (RA). Because homeobox genes have been reported to be specifically activated in the RA-differentiated NT2/D1 cells, we investigated the possible correlation between expression of homeobox (HOX) 2 genes and expression of the immediate early (IE) genes of HCMV both in NT2/D1 cells and in HCMV permissive human embryonic lung (HEL) cells. HCMV infection did not induce activation of the HOX2A, HOX2E and HOX2I genes in undifferentiated NT2/D1 cells nor affect their activation in the RA-differentiated NT2/D1 cells. By in situ hybridization using a HOX2A RNA probe, HOX2A transcript-positive cells appeared as clusters in RA-differentiated NT2/D1 cells. Viral antigen-positive cells detected by immunofluorescence using an antibody specific for the IE-1 antigen of HCMV appeared as clusters among the population of cells in which the HOX2A transcript was detected. The HOX2A gene only was expressed in HEL cells, however none of the HOX2 genes was expressed in non-permissive HeLa, Raji or mouse embryonic cells. These results suggest that activation of the HOX2A may be necessary for the expression of IE genes. HCMV infection markedly increased the expression of the HOX2E gene in HEL cells in the presence, but not in the absence, of cycloheximide. Ultraviolet-inactivated HCMV also displayed this effect. On the other hand, HCMV infection suppressed expression of the HOX2A gene to some degree at the early and late phases of infection in HEL cells. Activation of the HOX2E gene by HCMV might possibly have a role in virus-induced abnormal embryogenesis.