The Activity-Dependent Regulation of Protein Kinase Stability by the Localization to P-Bodies

Abstract

The eukaryotic cytoplasm contains a variety of ribonucleoprotein (RNP) granules in addition to the better-understood membrane-bound organelles. These granules form in response to specific stress conditions and contain a number of signaling molecules important for the control of cell growth and survival. However, relatively little is known about the mechanisms responsible for, and the ultimate consequences of, this protein localization. Here, we show that the Hrr25/CK1d protein kinase is recruited to cytoplasmic processing bodies (P-bodies) in an evolutionarily conserved manner. This recruitment requires Hrr25 kinase activity and the Dcp2 decapping enzyme, a core constituent of these RNP granules. Interestingly, the data indicate that this localization sequesters active Hrr25 away from the remainder of the cytoplasm and thereby shields this enzyme from the degradation machinery during these periods of stress. Altogether, this work illustrates how the presence within an RNP granule can alter the ultimate fate of the localized protein.KEYWORDS ribonucleoprotein granules; processing bodies; protein kinase; protein stability; Dcp2 decapping enzyme; casein kinase 1 T HE eukaryotic cell is subdivided into distinct functional areas by the presence of a variety of organelles. The best understood of these are the membrane-bound structures, like the nucleus, endoplasmic reticulum, and mitochondria. These traditional compartments are relatively stable and essential for the proper compartmentalization of the different reactions occurring in the cytoplasm. However, the cell also contains a collection of nonmembraneous organelles that are more dynamic in nature and form in response to particular cellular and environmental stimuli. Perhaps the two best characterized of these are the centrosome and nucleolus, which act as a microtubule-organizing center and a subnuclear site of ribosome assembly, respectively (Greenan et al. 2010;Brangwynne 2011;Brangwynne et al. 2011). This latter class also includes a number of recently identified cytoplasmic ribonucleoprotein (RNP) granules like the processing body (P-body) and stress granule (Anderson and Kedersha 2009;Balagopal and Parker 2009;Thomas et al. 2011). These cytoplasmic structures have been conserved through evolution and have been linked to a variety of human diseases, including certain neurodegenerative disorders, cancers, and autoimmune conditions (Li et al. 2013;Anderson et al. 2015). Despite this importance to human health, relatively little is known about the manner in which these RNP granules influence biological processes in the cell.These cytoplasmic RNP granules typically assemble in response to environmental stress or particular developmental cues (Thomas et al. 2011). Granule formation occurs as a consequence of the regulated coalescence of specific sets of proteins and translationally repressed mRNAs at discrete sites in the cytoplasm (Anderson and Kedersha 2009;Balagopal and Parker 2009). The presence of these core proteins often depends upon specific RNA-...

The low complexity regions in the C-terminus are essential for the subcellular localisation of Leishmania casein kinase 1 but not for its activity

“…This localisation is characteristic of the CK1 family [27]. Although, the origins of these structures are unknown in Leishmania , human CK1δ and HRR25, its Saccharomyces cerevisiae ortholog are known to localise to P-bodies, which protect the kinase from degradation, especially during stress [11, 50]. P-bodies also store repressed mRNAs that mainly encode for regulatory processes [50].…”

“…In budding yeast, ScHrr25/CK1δ is localised to the bud neck, where it is essential for proper cytokinesis, and to endocytic sites, where it is required for their initiation and stabilisation [8] [9] [10]. Lastly, ScHrr25/CK1δ is recruited to cytoplasmic processing bodies (P-bodies), which protects the active kinase from the cytoplasmic degradation machinery during stress [11]. These few examples reflect the tight association of CK1 localisation to its functions, suggesting that investigating its localisation may increase our knowledge on this kinase and allow the identification of potential novel functions.…”

Structure of the Saccharomyces cerevisiae Hrr25:Mam1 monopolin subcomplex reveals a novel kinase regulator

“…The species distribution of this domain suggests that its main function is to cooperate with Mam1 in a monopolin‐specific role, likely in regulation and/or localization of Hrr25's kinase activity. A recent report has implicated this domain in its localization to P‐bodies, however, suggesting that the domain may also play a role in Hrr25 localization outside the context of monopolin (Zhang et al , ).…”

P-Body Localization of the Hrr25/Casein Kinase 1 Protein Kinase Is Required for the Completion of Meiosis

“…These findings have led researchers to propose that these RNP granules could have a role in the rewiring of cellular signaling networks under specific conditions of stress (25,30,31). Work from our laboratory has shown that the Hrr25 protein kinase is efficiently localized to P-bodies under all conditions tested in the yeast Saccharomyces cerevisiae (25,31). Hrr25 is an essential enzyme and is the yeast ortholog of the ␦/ isoforms of the mammalian CK1 protein kinase (32).…”

“…Hrr25/CK1 enzymes have been shown to have conserved roles in ribosome maturation, vesicle trafficking, DNA repair, clathrin-mediated endocytosis, and meiosis (33)(34)(35)(36)(37)(38)(39)(40)(41)(42). The association with P-body granules is also evolutionarily conserved, as the human CK1␦ enzyme was detected within P-body foci in HeLa cells (31). In yeast, this P-body localization has been shown to be important for the maintenance of the normal cellular levels of Hrr25 by shielding this protein from degradation by the proteasome (31).…”