title: Human cytomegalovirus stimulates monocyte-to-macrophage differentiation via the temporal regulation of caspase 3.
abstract: Monocytes are primary targets for human cytomegalovirus (HCMV) infection and are proposed to be responsible for hematogenous dissemination of the virus. Biologically, monocytes have a short life span of 48 h in the circulation, a period of time during which monocytes must make a cell fate decision on whether to undergo apoptosis or differentiate into a macrophage. We have previously shown that HCMV infection stimulates monocyte-to-macrophage differentiation; however, the mechanism(s) by which HCMV-infected monocytes simultaneously navigate the 48-h "viability gate" and undergo macrophagic differentiation has remained elusive. Studies have demonstrated that the level of caspase 3 and 8 activities in monocytes may mediate the delicate balance between apoptosis and macrophage colony-stimulating factor (M-CSF)-induced myeloid differentiation. Here, we show that HCMV infection, unlike M-CSF treatment, does not induce caspase 8 activity to promote myeloid differentiation. However, HCMV infection does induce a temporal activation of caspase 3, with only a low level of active caspase 3 being observed after the 48-h viability checkpoint. Consistent with the role of a time-dependent activation of caspase 3 in promoting myeloid differentiation, the inhibition of caspase 3 blocked HCMV-induced monocyte-to-macrophage differentiation. Temporal transcriptome and functional analyses identified heat shock protein 27 (HSP27) and Mcl-1, two known regulators of caspase 3 activation, as being upregulated prior to the 48-h viability gate following HCMV infection. Using small interfering RNAs (siRNAs), we demonstrate that HCMV targets the rapid induction of HSP27 and Mcl-1, which cooperatively function to precisely control caspase 3 activity in order to allow for HCMV-infected monocytes to successfully traverse the 48-h cell fate decision checkpoint and commence macrophage maturation. Overall, this study highlights a unique regulatory mechanism employed by HCMV to tightly modulate the caspase 3 activity needed to promote myeloid differentiation, a key process in the viral dissemination and persistence strategy.
authors: Department of Microbiology & Immunology, Center for Molecular and Tumor Virology, Louisiana State University Health Sciences Center, Shreveport, Louisiana, USA.
authors: Gary
authors: G
authors: Chan
authors: Maciej T
authors: MT
authors: Nogalski
authors: Andrew D
authors: AD
authors: Yurochko
mesh_terms: D053148:Caspase 3 / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D019070:Cell Lineage; D003587:Cytomegalovirus / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000166:cytology / Q000196:embryology; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000821:virology*; D009000:Monocytes / Q000166:cytology / Q000821:virology*; D020411:Oligonucleotide Array Sequence Analysis; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D034741:RNA, Small Interfering; D016173:Macrophage Colony-Stimulating Factor; D053148:Caspase 3; D053181:Caspase 8