Cold shock Y-box protein-1 proteolysis autoregulates its transcriptional activities

Abstract

BackgroundThe Y-box protein-1 (YB-1) fulfills pleiotropic functions relating to gene transcription, mRNA processing, and translation. It remains elusive how YB-1 shuttling into the nuclear and cytoplasmic compartments is regulated and whether limited proteolysis by the 20S proteasome releases fragments with distinct function(s) and subcellular distribution(s).ResultsTo address these questions, mapping of domains responsible for subcellular targeting was performed. Three nuclear localization signals (NLS) were identified. NLS-1 (aa 149-156) and NLS-2 (aa 185-194) correspond to residues with unknown function(s), whereas NLS-3 (aa 276-292) matches with a designated multimerization domain. Nuclear export signal(s) were not identified. Endoproteolytic processing by the 20S proteasome before glycine 220 releases a carboxy-terminal fragment (CTF), which localized to the nucleus, indicating that NLS-3 is operative. Genotoxic stress induced proteolytic cleavage and nuclear translocation of the CTF. Co-expression of the CTF and full-length YB-1 resulted in an abrogated transcriptional activation of the MMP-2 promoter, indicating an autoregulatory inhibitory loop, whereas it fulfilled similar trans-repressive effects on the collagen type I promoter.ConclusionCompartmentalization of YB-1 protein derivatives is controlled by distinct NLS, one of which targets a proteolytic cleavage product to the nucleus. We propose a model for an autoregulatory negative feedback loop that halts unlimited transcriptional activation.

Secreted protein YB-1 and its prognostic significance

“…было показано, что YB-1 выделяется из клеток, в частности из мезангиальных, и моноцитов (находясь внутри микровезикул), в ответ на добавление индуктора воспаления -липополисахарида [16]. Белок сYB-1 связывался с рецептором Notch-3 на поверхно-сти клеток-мишеней [17] и активировал сигнальный путь, контролируемый рецептором Notch-3, в резуль-тате чего Notch-3 перемещался в ядра клеток-мишеней, где происходила активация генов, контролируемых Notch-3, а экспрессия гена Notch-3 возрастала [17,18]. Авторы этих работ выдвинули гипотезу, постулирую-щую: 1) ауторегуляцию количества YB-1: вслед за ак-тивацией экспрессии YB-1 такими стимуляторами, как PDGF-β, тромбин или интерферон-γ, YB-1 начи-нает регулировать свою собственную транскрипцию; 2) функционирование YB-1 в качестве компонента мРНП (мессенджерного рибонуклеинового комплек-са), определяющего синтез интерлейкина 2 при акти-вации Т-клеток; 3) участие YB-1 в осуществлении фе-нотипических эффектов TGF-β; 4) влияние YB-1 на передачу сигнала через рецептор Notch-3.…”

Nuclear shuttling of Y Box binding protein-1, its clinical relevance in cancer and as a therapeutic target

“…Literature suggests three nuclear localization signals in YB-1 i.e. NLS1 (aa149-55), and (van Roeyen et al, 2013). The NLS3 is bipartite in composition and both the parts are essential for functionality.…”

“…Phosphorylation of S102 in cold shock domain may induce conformational changes which mask the cytoplasmic retention sequence and/or exposes the NLS. Certain molecular mechanisms are known to date that explain the nuclear flipping of YB-1 (Lorsch, 2002;van Roeyen et al, 2013). However, S102 phosphorylation via proteins or kinases control nuclear translocation of YB-1 in cancer growth and survival signaling such as P13K/AKT, RSK, Ras/MAPK (Dalby et al, 1998;Lorsch, 2002;Sinnberg et al, 2012;Shen et al, 2011;Astanehe et al, 2012) and PKC signaling (Fujii et al, 2009) cascades.…”

“…The full length YB-1 phosphorylated at tyrosine 281 in NLS3 has been found to be localized in the nucleus while the unphosphorylated YB-1 localized in the cytoplasm. This indicates that the phosphorylation at T-281 renders complete YB-1 to be localized in nucleus under normal conditions (van Roeyen et al, 2013). At the time of stress or cell stimulation, nuclear flipping of shortened YB-1 having N-terminal portion of the proteins takes place through a highly regulated process (Bader and Vogt, 2005;van Roeyen et al, 2013).…”

“…This indicates that the phosphorylation at T-281 renders complete YB-1 to be localized in nucleus under normal conditions (van Roeyen et al, 2013). At the time of stress or cell stimulation, nuclear flipping of shortened YB-1 having N-terminal portion of the proteins takes place through a highly regulated process (Bader and Vogt, 2005;van Roeyen et al, 2013). Jürchott et al (2003) suggested that the both C-terminal and cold shock domain of YB-1 are involved in nuclear translocation.…”