The absence of p53 during Human Cytomegalovirus infection leads to decreased UL53 expression, disrupting UL50 localization to the inner nuclear membrane, and thereby inhibiting capsid nuclear egress

Abstract

Our electron microscopy study found HCMV nuclear capsid egress was significantly reduced in p53 knockout cells (p53KOs), correlating with inhibited formation of infoldings of the inner nuclear membrane (IINMs). Molecular examination of these phenomena has found p53KOs expressed UL97 and phosphorylated lamins, however the lamina failed to remodel. The nuclear egress complex (NEC) protein UL50 was expressed in almost all cells. UL50 re-localized to the inner nuclear membrane (INM) in ~90% of wt cells, but only ~35% of p53KOs. UL53 expression was significantly reduced in p53KOs, and cells lacking UL50 nuclear staining, expressed no UL53. Re-introduction of p53 into p53KOs largely recovered UL53 positivity and UL50 nuclear re-localization. Nuclear rim located UL50/53 puncta, which co-localized with the major capsid protein, were largely absent in p53KOs. We believe these puncta were IINMs. In the absence of p53, UL53 expression was inhibited, disrupting formation of the NEC/IINMs, and reducing functional virion secretion.

WDR5 Facilitates Human Cytomegalovirus Replication by Promoting Capsid Nuclear Egress

“…When expressed individually, pUL50 mainly localized to the perinuclear rim and cytoplasm, while pUL53 principally localized in the nucleoplasm. Consistent with previous reports (21,53,54), when coexpressed, both pUL50 and pUL53 localized to the nuclear rim. In KD cells, colocalization of pUL50 and pUL53 formed discontinuous dashed-rim structures (Fig.…”

“…6A and B, white arrows). By 72 hpi, pUL53 gradually formed punctate structures that have been shown to coincide with IINMs (54). At 120 hpi, there were significantly more punctate pUL53 structures per pUL53-positive Ctl cell (12.2) or Rec cell (11.2) than per pUL53positive KD cell (5.7) (Fig.…”

“…IINMs are the primary site for nuclear egress of HCMV capsids (21,53), and viral proteins pUL50 and pUL53 are crucial for the proper formation of IINMs by contributing to the assembly of NEC. pUL50 interacts with pUL53 and forms a rim around the nucleus of the infected cell; thus, pUL53 can serve as a marker of NEC (17,22,54). To evaluate the effects of WDR5 knockdown on capsid nuclear egress, cells were costained with pUL53 and the HCMV major capsid protein (MCP).…”

Calpain-mediated cleavage of p53 in human cytomegalovirus-infected lung fibroblasts

“…In cells lacking p53, HCMV infection is compromised and HCMV DNA accumulation is delayed and decreased. 105 The cellular level of p53 is substantially increased in productive HCMV infection [40][41][42][43][44] ; however, cells still enter and traverse the cell cycle to a point at or near the G 1 /S boundary, 39 suggesting that at least some p53 functions are inactivated. 103 p53 is crucial for HCMV immediate early and early gene expression.…”

“…104 The absence of p53 during HCMV infection leads to decreased UL53 expression, disrupting UL50 localization to the inner nuclear membrane and in this way, inhibits nucleocapsid nuclear egress. 105 The cellular level of p53 is substantially increased in productive HCMV infection [40][41][42][43][44] ; however, cells still enter and traverse the cell cycle to a point at or near the G 1 /S boundary, 39 suggesting that at least some p53 functions are inactivated. The HCMV proteins IE1, 67 IE2, 63-65 UL44, 68 and UL84 63 can interact with p53, thereby altering p53-mediated transcription.…”