Cyclin-Dependent Kinase 18 Controls Trafficking of Aquaporin-2 and Its Abundance through Ubiquitin Ligase STUB1, Which Functions as an AKAP

Abstract

Arginine-vasopressin (AVP) facilitates water reabsorption in renal collecting duct principal cells through regulation of the water channel aquaporin-2 (AQP2). The hormone binds to vasopressin V2 receptors (V2R) on the surface of the cells and stimulates cAMP synthesis. The cAMP activates protein kinase A (PKA), which initiates signaling that causes an accumulation of AQP2 in the plasma membrane of the cells facilitating water reabsorption from primary urine and fine-tuning of body water homeostasis. AVP-mediated PKA activation also causes an increase in the AQP2 protein abundance through a mechanism that involves dephosphorylation of AQP2 at serine 261 and a decrease in its poly-ubiquitination. However, the signaling downstream of PKA that controls the localization and abundance of AQP2 is incompletely understood. We carried out an siRNA screen targeting 719 kinase-related genes, representing the majority of the kinases of the human genome and analyzed the effect of the knockdown on AQP2 by high-content imaging and biochemical approaches. The screening identified 13 hits whose knockdown inhibited the AQP2 accumulation in the plasma membrane. Amongst the candidates was the so far hardly characterized cyclin-dependent kinase 18 (CDK18). Our further analysis revealed a hitherto unrecognized signalosome comprising CDK18, an E3 ubiquitin ligase, STUB1 (CHIP), PKA and AQP2 that controls the localization and abundance of AQP2. CDK18 controls AQP2 through phosphorylation at serine 261 and STUB1-mediated ubiquitination. STUB1 functions as an A-kinase anchoring protein (AKAP) tethering PKA to the protein complex and bridging AQP2 and CDK18. The modulation of the protein complex may lead to novel concepts for the treatment of disorders which are caused or are associated with dysregulated AQP2 and for which a satisfactory treatment is not available, e.g., hyponatremia, liver cirrhosis, diabetes insipidus, ADPKD or heart failure.

Phosphoproteomic identification of vasopressin‐regulated protein kinases in collecting duct cells

“…Cdk18 expression in collecting duct has recently been confirmed by Dema et al (2020) who proposed a role in regulation of AQP2 degradation. We found that Cdk8 is very abundant in nuclear fractions in both mpkCCD (Schenk et al, 2012) and native IMCD cells (Pickering et al, 2016) and speculate that it could be involved in regulation of transcriptional events in collecting duct cells as well.…”

Exogenous melatonin alleviates PEG-induced short-term water deficiency in maize by increasing hydraulic conductance

“…Studies in animals have shown that exposure to MEL can induce an increase in intracellular cyclic adenosine monophosphate levels [51]. Upon cyclic adenosine monophosphate elevation, it will cause a decrease of phosphorylation and poly-ubiquitination and hence facilitates the trafficking aquaporin bearing vesicles to the plasma membrane [52]. In addition, more evidence showed that there is significant crosstalk between MEL and other plant hormones, including: cytokinin, salicylic acid, jasmonic acid, gibberellins, abscisic acid and ethylene [2,[50][51][52][53][54][55].…”

“…Upon cyclic adenosine monophosphate elevation, it will cause a decrease of phosphorylation and poly-ubiquitination and hence facilitates the trafficking aquaporin bearing vesicles to the plasma membrane [52]. In addition, more evidence showed that there is significant crosstalk between MEL and other plant hormones, including: cytokinin, salicylic acid, jasmonic acid, gibberellins, abscisic acid and ethylene [2,[50][51][52][53][54][55]. Although no direct evidence has been shown up to date that MEL could regulate aquaporin activity by affecting plant hormones or signaling molecules, considering the extensive interaction between MEL and plant hormones, the possibility that MEL regulates aquaporin activity through plant hormones or signaling molecules cannot be ignored.…”

Phosphoproteomic Identification of Vasopressin-Regulated Protein Kinases in Collecting Duct Cells

“…If PKA does this in collecting duct cells, Cdk18 activation would provide a likely explanation for the many phosphorylation sites with proline in position +1 that increase in response to vasopressin ( Figure 6). Cdk18 expression in collecting duct has recently been confirmed by Dema et al (62) who proposed a role in regulation of AQP2 degradation. We found that Cdk18 is very abundant in nuclear fractions in both mpkCCD (63) and native IMCD cells (64) and speculate that it could be involved in regulation of transcriptional events in collecting duct cells as well.…”