The advantageous chemical properties of the phosphate ester linkage were exploited early in evolution to generate the phosphate diester linkages that join neighbouring bases in RNA and DNA ...(Westheimer 1987 Science 235, 1173–1178). Following the fixation of the genetic code, another use for phosphate ester modification was found, namely reversible phosphorylation of the three hydroxyamino acids, serine, threonine and tyrosine, in proteins. During the course of evolution, phosphorylation emerged as one of the most prominent types of post-translational modification, because of its versatility and ready reversibility. Phosphoamino acids generated by protein phosphorylation act as new chemical entities that do not resemble any natural amino acid, and thereby provide a means of diversifying the chemical nature of protein surfaces. A protein-linked phosphate group can form hydrogen bonds or salt bridges either intra- or intermolecularly, creating stronger hydrogen bonds with arginine than either aspartate or glutamate. The unique size of the ionic shell and charge properties of covalently attached phosphate allow specific and inducible recognition of phosphoproteins by phosphospecific-binding domains in other proteins, thus promoting inducible protein–protein interaction. In this manner, phosphorylation serves as a switch that allows signal transduction networks to transmit signals in response to extracellular stimuli.
In the 30 years since its discovery, tyrosine phosphorylation has emerged as a fundamentally important mechanism of signal transduction and regulation in all eukaryotic cells, governing many ...processes, including cell proliferation, cell cycle progression, metabolic homeostasis, transcriptional activation, neural transmission, differentiation and development, and aging. Perturbations in tyrosine phosphorylation underlie many human diseases, and in particular cancer, and this has prompted the development of inhibitors of tyrosine kinases implicated in disease, a number of which have been approved for clinical use. The following is a brief personal reflection on some of the salient findings over the past 30 years that led to the development of tyrosine kinase inhibitors for disease therapy.
Crosstalk between different types of posttranslational modification is an emerging theme in eukaryotic biology. Particularly prominent are the multiple connections between phosphorylation and ...ubiquitination, which act either positively or negatively in both directions to regulate these processes.
Protein kinases regulate every aspect of cellular activity, whereas metabolic enzymes are responsible for energy production and catabolic and anabolic processes. Emerging evidence demonstrates that ...some metabolic enzymes, such as pyruvate kinase M2 (PKM2), phosphoglycerate kinase 1 (PGK1), ketohexokinase (KHK) isoform A (KHK-A), hexokinase (HK), and nucleoside diphosphate kinase 1 and 2 (NME1/2), that phosphorylate soluble metabolites can also function as protein kinases and phosphorylate a variety of protein substrates to regulate the Warburg effect, gene expression, cell cycle progression and proliferation, apoptosis, autophagy, exosome secretion, T cell activation, iron transport, ion channel opening, and many other fundamental cellular functions. The elevated protein kinase functions of these moonlighting metabolic enzymes in tumor development make them promising therapeutic targets for cancer.
In addition to their originally identified metabolic enzymatic activities, PKM2, PGK1, KHK-A, HK, and NDPK-A/B can act as protein kinases.
The protein kinase activity of metabolic enzymes phosphorylates a variety of protein substrates and regulates critical cellular activities.
Metabolic enzymes are often post-translationally modified, which changes their subcellular localization and allows them to phosphorylate protein substrates.
The protein kinase functions of metabolic enzymes make them promising therapeutic targets for cancer.
The evolutionally conserved DNA damage response (DDR) and cell cycle checkpoints preserve genome integrity. Central to these genome surveillance pathways is a protein kinase, Chk1. DNA damage induces ...activation of Chk1, which then transduces the checkpoint signal and facilitates cell cycle arrest and DNA damage repair. Significant progress has been made recently toward our understanding of Chk1 regulation and its implications in cancer etiology and therapy. Specifically, a model that involves both spatiotemporal and conformational changes of proteins has been proposed for Chk1 activation. Further, emerging evidence suggests that Chk1 does not appear to be a tumor suppressor; instead, it promotes tumor growth and may contribute to anticancer therapy resistance. Recent data from our laboratory suggest that activating, but not inhibiting, Chk1 in the absence of chemotherapy might represent an innovative approach to suppress tumor growth. These findings suggest unique regulation of Chk1 in cell biology and cancer etiology, pointing to novel strategies for targeting Chk1 in cancer therapy.
Discovering the first tyrosine kinase Hunter, Tony
Proceedings of the National Academy of Sciences - PNAS,
06/2015, Volume:
112, Issue:
26
Journal Article
Peer reviewed
Open access
In the middle of the 20th century, animal tumor viruses were heralded as possible models for understanding human cancer. By the mid-1970s, the molecular basis by which tumor viruses transform cells ...into a malignant state was beginning to emerge as the first viral genomic sequences were reported and the proteins encoded by their transforming genes were identified and characterized. This was a time of great excitement and rapid progress. In 1978, prompted by the discovery from Ray Erikson’s group that the Rous sarcoma virus (RSV) v-Src–transforming protein had an associated protein kinase activity specific for threonine, my group at the Salk Institute set out to determine whether the polyomavirus middle T-transforming protein had a similar kinase activity. Here, I describe the experiments that led to the identification of a kinase activity associated with middle T antigen and our serendipitous discovery that this activity was specific for tyrosine in vitro, and how this in turn led to the fortuitous observation that the v-Src–associated kinase activity was also specific for tyrosine. Our finding that v-Src increased the level of phosphotyrosine in cellular proteins in RSV-transformed cells confirmed that v-Src is a tyrosine kinase and transforms cells by phosphorylating proteins on tyrosine. My colleague Bart Sefton and I reported these findings in the March issue of PNAS in 1980. Remarkably, all of the experiments in this paper were accomplished in less than one month.
Proline-directed phosphorylation is a posttranslational modification that is instrumental in regulating signaling from the plasma membrane to the nucleus, and its dysregulation contributes to cancer ...development. Protein interacting with never in mitosis A1 （Pinl）, which is overexpressed in many types of cancer, isomerizes specific phosphorylat- ed Ser/Thr-Pro bonds in many substrate proteins, including glycolytic enzyme, protein kinases, protein phosphatases, methyltransferase, lipid kinase, ubiquitin E3 ligase, DNA endonuclease, RNA polymerase, and transcription activa- tors and regulators. This Pinl-mediated isomerization alters the structures and activities of these proteins, thereby regulating cell metabolism, cell mobility, cell cycle progression, cell proliferation, cell survival, apoptosis and tumor development.
Pinkl, a mitochondrial kinase, and Parkin, an E3 ubiquitin ligase, function in mitochondrial maintenance. Pinkl accumulates on depolarized mitochondria, where it recruits Parkin to mainly induce ...K63-1inked chain ubiquitina- tion of outer membrane proteins and eventually mitophagy. Parkin belongs to the RBR E3 ligase family. Recently, it has been proposed that the RBR domain transfers ubiquitin to targets via a cysteine~ubiquitin enzyme intermediate, in a manner similar to HECT domain E3 ligases. However, direct evidence for a ubiquitin transfer mechanism and its importance for Parkin＇s in vivo function is still missing. Here, we report that Parkin E3 activity relies on cysteine- mediated ubiquitin transfer during mitophagy. Mutating the putative catalytic cysteine to serine （Parkin C431S） traps ubiquitin, and surprisingly, also abrogates Parkin mitochondrial translocation, indicating that E3 activity is essential for Parkin translocation. We found that Parkin can bind to K63-1inked ubiquitin chains, and that targeting K63-mimicking ubiquitin chains to mitochondria restores Parkin C431S localization. We propose that Parkin trans- location is achieved through a novel catalytic activity coupled mechanism.
Protein kinases are important regulators of intracellular signal transduction pathways and play critical roles in diverse cellular functions. Once a protein kinase is activated, its activity is ...subsequently downregulated through a variety of mechanisms. Accumulating evidence indicates that the activation of protein kinases commonly initiates their downregulation via the ubiquitin/proteasome pathway. Failure to regulate protein kinase activity or expression levels can cause human diseases.
It is unclear how the Warburg effect that exemplifies enhanced glycolysis in the cytosol is coordinated with suppressed mitochondrial pyruvate metabolism. We demonstrate here that hypoxia, EGFR ...activation, and expression of K-Ras G12V and B-Raf V600E induce mitochondrial translocation of phosphoglycerate kinase 1 (PGK1); this is mediated by ERK-dependent PGK1 S203 phosphorylation and subsequent PIN1-mediated cis-trans isomerization. Mitochondrial PGK1 acts as a protein kinase to phosphorylate pyruvate dehydrogenase kinase 1 (PDHK1) at T338, which activates PDHK1 to phosphorylate and inhibit the pyruvate dehydrogenase (PDH) complex. This reduces mitochondrial pyruvate utilization, suppresses reactive oxygen species production, increases lactate production, and promotes brain tumorigenesis. Furthermore, PGK1 S203 and PDHK1 T338 phosphorylation levels correlate with PDH S293 inactivating phosphorylation levels and poor prognosis in glioblastoma patients. This work highlights that PGK1 acts as a protein kinase in coordinating glycolysis and the tricarboxylic acid (TCA) cycle, which is instrumental in cancer metabolism and tumorigenesis.
Display omitted
•ERK and PIN1 regulate mitochondrial translocation of PGK1•PGK1, acting as a protein kinase, phosphorylates and activates PDHK1•PGK1 suppresses ROS production and coordinates glycolysis and the TCA cycle•Mitochondrial PGK1 promotes tumor cell proliferation and brain tumorigenesis
PGK1 is a cytosolic glycolytic enzyme. Li et al. demonstrate that conditions such as hypoxia and oncogenic mutations that activate ERK signaling can induce mitochondrial translocation of PGK1. Mitochondrial PGK1, functioning as a protein kinase, phosphorylates and activates PDHK1 to suppress mitochondrial pyruvate metabolism and promotes the Warburg effect.
PDF
