Immediate early protein 1 (human cytomegalovirus) (IE1)

Immediate early protein 1 (IE1) is a major regulatory protein encoded by the UL123 gene from human cytomegalovirus (HCMV), also known as human herpesvirus 5. It is one of the first proteins expressed upon infection and plays an essential role in initiating lytic replication and reactivation from latency. Functionally, IE1 acts as a transcriptional activator for both viral and cellular genes by modifying chromatin structure. It disrupts nuclear domain structures associated with intrinsic immunity—specifically PML-ND10 bodies—by interfering with post-translational modifications such as sumoylation on key cellular proteins like PML and SP100. IE1 also antagonizes multiple arms of the innate antiviral response: it inhibits type I interferon signaling through sequestration/inhibition of STAT2; represses IL6/STAT3-driven responses; sequesters ISGF3 complexes away from their targets; alters cell cycle control via interactions that override RB-mediated repression. These activities collectively promote efficient HCMV replication while evading host defenses. Clinically, peptides derived from IE1 serve as dominant epitopes recognized by CD8+ T cells during natural infection or after transplantation—a property exploited both diagnostically (as biomarkers) and therapeutically (in adoptive T-cell transfer). The presence or magnitude of an anti–IE1 T-cell response correlates strongly with protection against CMV disease following bone marrow transplantation. There are currently no approved drugs that directly target IE1 itself; rather, it serves primarily as an immunological marker or vaccine/immunotherapy target candidate due to its critical role in HCMV biology.[2][3][4][8]

Other names

Immediate-early protein 1IE72IE1p72UL123 (gene name)55 kDa immediate-early protein 1[3]