Erk1/2 inactivation promotes a rapid redistribution of COP1 and degradation of COP1 substrates

Abstract

Anthrax lethal toxin (LT) is a protease virulence factor produced by Bacillus anthracis that is required for its pathogenicity. LT treatment causes a rapid degradation of c-Jun protein that follows inactivation of the MEK1/2-Erk1/2 signaling pathway. Here we identify COP1 as the ubiquitin E3 ligase that is essential for LT-induced c-Jun degradation. COP1 knockdown using siRNA prevents degradation of c-Jun, ETV4, and ETV5 in cells treated with either LT or the MEK1/2 inhibitor, U0126. Immunofluorescence staining reveals that COP1 preferentially localizes to the nuclear envelope, but it is released from the nuclear envelope into the nucleoplasm following Erk1/2 inactivation. At baseline, COP1 attaches to the nuclear envelope via interaction with translocated promoter region (TPR), a component of the nuclear pore complex. Disruption of this COP1–TPR interaction, through Erk1/2 inactivation or TPR knockdown, leads to rapid COP1 release from the nuclear envelope into the nucleoplasm where it degrades COP1 substrates. COP1-mediated degradation of c-Jun protein, combined with LT-mediated blockade of the JNK1/2 signaling pathway, inhibits cellular proliferation. This effect on proliferation is reversed by COP1 knockdown and ectopic expression of an LT-resistant MKK7-4 fusion protein. Taken together, this study reveals that the nuclear envelope acts as a reservoir, maintaining COP1 poised for action. Upon Erk1/2 inactivation, COP1 is rapidly released from the nuclear envelope, promoting the degradation of its nuclear substrates, including c-Jun, a critical transcription factor that promotes cellular proliferation. This regulation allows mammalian cells to respond rapidly to changes in extracellular cues and mediates pathogenic mechanisms in disease states.

The Photomorphogenic Central Repressor COP1: Conservation and Functional Diversification during Evolution

“…In addition, human COP1 possesses intrinsic E3 ligase activity in its RING domain together with the coiled-coil domain in vitro ( Dornan et al., 2004 ), and targets tumorigenic factors for degradation in vivo ( Bianchi et al., 2003 , Migliorini et al., 2011 , Vitari et al., 2011 ). Human COP1 basically localizes in the nuclear envelope, and extracellular cues rapidly induce its nucleoplasm localization ( Ouyang et al., 2020 ). Human COP1 also undergoes nuclear export.…”

Erk1/2 Inactivation-Induced c-Jun Degradation Is Regulated by Protein Phosphatases, UBE2d3, and the C-Terminus of c-Jun

“…Our previous study showed that the ubiquitin E3 ligase, COP1, is sequestered and maintained in a poised status under steady-state conditions [ 5 ]. Erk1/2 inactivation following treatment with anthrax LT or the MKK1/2 inhibitor, U0126, induces rapid activation of COP1, leading to the degradation of its substrates, c-Jun, and ETV proteins [ 5 ]. The sequestration of COP1 is dependent on the Erk1/2-mediated phosphorylation of COP1-binding partners.…”

“…c-Jun is degraded by the ubiquitination-dependent proteasome pathway [ 3 ]. Studies from our laboratory have revealed that inactivation of the MKK1/2–Erk1/2 signaling pathway by chemical MKK1/2 inhibitors or anthrax lethal toxin (LT) reduces levels of the c-Jun protein rapidly by promoting its degradation via a COP1-dependent pathway [ 4 , 5 ].…”

“…At a steady state, COP1 is sequestered on the nuclear envelope, allowing the accumulation of transcription factors that are required for cellular proliferation. MKK1/2–Erk1/2 inactivation leads to a rapid release of COP1 from sequestration [ 5 ], thereby promoting the degradation of COP1-targeted transcription factors in the nucleus, leading to cell growth arrest [ 5 ]. Our previous study suggested that the sequestration of COP1 requires Erk1/2-mediated phosphorylation of its binding partners, such as translocated promoter region (TPR) [ 5 ].…”

“…MKK1/2–Erk1/2 inactivation leads to a rapid release of COP1 from sequestration [ 5 ], thereby promoting the degradation of COP1-targeted transcription factors in the nucleus, leading to cell growth arrest [ 5 ]. Our previous study suggested that the sequestration of COP1 requires Erk1/2-mediated phosphorylation of its binding partners, such as translocated promoter region (TPR) [ 5 ]. The phosphorylation status of these COP1-binding partners is co-regulated by protein kinases and protein phosphatases.…”