Emergency Spatiotemporal Shift: The Response of Protein Kinase D to Stress Signals in the Cardiovascular System

Abstract

Protein Kinase D isoforms (PKD 1-3) are key mediators of neurohormonal, oxidative, and metabolic stress signals. PKDs impact a wide variety of signaling pathways and cellular functions including actin dynamics, vesicle trafficking, cell motility, survival, contractility, energy substrate utilization, and gene transcription. PKD activity is also increasingly linked to cancer, immune regulation, pain modulation, memory, angiogenesis, and cardiovascular disease. This increasing complexity and diversity of PKD function, highlights the importance of tight spatiotemporal control of the kinase via protein-protein interactions, post-translational modifications or targeting via scaffolding proteins. In this review, we focus on the spatiotemporal regulation and effects of PKD signaling in response to neurohormonal, oxidant and metabolic signals that have implications for myocardial disease. Precise targeting of these mechanisms will be crucial in the design of PKD-based therapeutic strategies.

Keywords: GPCR; cardiovascular disease; heart failure; metabolism; oxidative stress; protein kinase D.

FIGURE 1

Microdomain Functions of Protein Kinase D (PKD). Spatial regulation of PKD activity allows for specificity of PKD function. PKD localizes to the membrane after Gα_q signaling initiates DAG production via phospholipase C. There PKD phosphorylation of Rem1 results in greater membrane insertion and activity of L-type Ca²⁺ channels (LTCC). PKD targeting to the myofilaments and its substrates, TnI and MyBPC, results in decreased myofilament Ca²⁺ sensitivity, increased cross bridge cycling rate, and increased contraction tension. Nuclear localization and exclusion sequences within PKD regulate nuclear localization potentially along with the chaperone protein Hsp20. PKD regulates growth through phosphorylation of HDAC5 and CREB. In non-cardiovascular cell types, PKD is linked to Golgi organization, membrane-vesicle fusion, and secretion. In the heart, vesicle trafficking is potentially linked to increased glucose uptake during pacing through GLUT4 membrane translocation. Of the actin remodeling effects described for PKD, only the Slingshot 1L (SSH1L)-cofilin signaling axis has been demonstrated in myocytes and linked to cell survival. PKD-IKKβ signaling has also been linked to cell survival and reactive oxygen species (ROS) clearance. Dashed arrows indicate pathways or functions not shown in cardiovascular cell types.

FIGURE 2

Oxidative stress regulation of PKD mediated anti-apoptotic signaling. PKD both regulates and is regulated by apoptotic signals. (A) In response to ischemia reperfusion injury, cardiac myocytes release of sphingosine 1 phosphate which acts through Gα_12/13-coupled receptors to activate RhoA. Rho A mediates PKC and PKD activation through activation of phospholipase C𝜀. PKD phosphorylation of the phosphatase slingshot 1 L (SSH1L) inhibits the ability of SSH1L to activate cofilin, preventing it from translocating with Bax to the mitochondria. (B) Generation of mitochondrial ROS results in DAG production through phospholipase D1 and PKD localization at the mitochondria. Once at the mitochondria, c-Abl and Src phosphorylation of PKD allows for PKCδ activation of PKD. Active PKD goes on to phosphorylate IκBα resulting in NFκB gene transcription of MnSOD, which allows for greater mitochondrial clearance of ROS. (C) Increased oxidative stress through H₂O₂ treatment causes PKD translocation to the nucleus and results in 14-3-3 interaction with two phosphorylated serine pairs in the linker region between the C1 domains of PKD. Apoptosis signal-regulating kinase 1 (ASK1) associates with the PH domain of PKD1, leading to ASK1 activation of c-Jun N-terminal kinase (JNK); and JNK-mediated apoptosis in endothelial cells.