Annually, 1.25 million individuals suffer burns in the United States and 6.5 million experience chronic skin ulcers, often from diabetes, pressure or venous stasis. Growth factors are essential mediators of wound repair, but their success as therapeutics in wound treatment has, so far, been limited. Therefore, there is a need to identify new wound-response regulatory factors, but few have appeared in recent years. Progranulin (also called granulin or epithelin precursor, acrogranin or PC-derived growth factor) is a growth factor involved in tumorigenesis and development. Peptides derived from progranulin have been isolated from inflammatory cells, which led to suggestions that progranulin gene products are involved in the wound response, but this remains undemonstrated. We report that in murine transcutaneous puncture wounds, progranulin mRNA is expressed in the inflammatory infiltrate and is highly induced in dermal fibroblasts and endothelia following injury. When applied to a cutaneous wound, progranulin increased the accumulation of neutrophils, macrophages, blood vessels and fibroblasts in the wound. It acts directly on isolated dermal fibroblasts and endothelial cells to promote division, migration and the formation of capillary-like tubule structures. Progranulin is, therefore, a probable wound-related growth factor.

Polynucleotide kinases catalyze phosphorylation of 5Ј-OH termini of nucleic acids. In a number of biochemical experiments over several decades, evidence for a mammalian polynucleotide kinase (PNK) 1 activities with an acidic pH optimum has mounted (reviewed in Refs. 1-8). We and others have purified such a PNK to near-homogeneity from bovine tissue, which lacks significant 5Ј-phosphorylation activity when assayed with RNA substrates (5, 6, 9). This activity, denoted SNQI-PNK, corresponded to a polypeptide of approximately 60 kDa in our experiments (6). Highly purified SNQI-PNK fractions contain a 3Ј-phosphatase activity (6), originally discovered in the PNK from bacteriophage T4 (10, 11) and also observed in PNKs from rat liver nuclei (2-5, 12). Furthermore, there are reports of mammalian PNK activities with a greater substrate specificity for RNA than DNA (8, 13, 14) 2 and of conservation of yeastlike tRNA ligation (with its requirement for a PNK activity) as a minor pathway in HeLa cells (15).Because of its widespread presence in mammalian cells, the acidic pH optimum PNK is likely to be a key enzyme in DNA metabolism, and its biochemical functions immediately suggest a role in the critical process of DNA repair. One of its enzymatic activities, DNA 3Ј-phosphatase, implies an ability to repair strand breaks terminated by 3Ј-phosphate, a type of DNA damage seen in cells treated with ionizing radiation or hydrogen peroxide (16). Removal of this 3Ј-end blocking lesion allows synthesis by DNA polymerase and joining of nicks by DNA ligase. DNA purified from irradiated thymocytes and irradiated thymus, but not DNA irradiated in vitro, contains strand breaks with 5Ј-OH termini (17, 18). The 5Ј-phosphorylation activity of the SNQI-PNK enzyme suggests a possible model in which 5Ј-OH termini are repaired prior to ligation. 5Ј-OH termini in DNA also occur in ischemia in rat brain (19), after cleavage by nucleases with the appropriate specificity such as DNase II (20), and as intermediates during topoisomerase cleavage (21,22). The highest concentration of 5Ј-DNA termini occurs during DNA replication, and Pohjanpelto and Hölttä (23) proposed that a small fraction of Okazaki fragments contain 5Ј-OH termini; this fraction decreases upon incubation of extracts with ATP at pH 6.0, which was inferred to reflect 5Ј-phosphorylation by a cellular PNK.Despite extensive biochemical studies, to date there are no molecular reagents such as antibodies or cDNAs available for mammalian PNKs, hampering further investigation. We present here the molecular cloning of the PNKP gene, the first gene for a mammalian PNK and the first gene for a DNA-specific kinase from any organism. Concomitantly, the PNKP gene also

Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34 ϩ progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-B (NF-B) activation impaired ATRAstimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cellspecific roles for NF-B in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-B signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.granulin; stem cell factor; colony-stimulating factor THE GRANULIN-EPITHELIN precursor progranulin (pgrn; see Ref. 4), which is also called proepithelin (47), PC-cell-derived growth factor (66), or acrogranin (1), is a multifunctional regulatory protein that promotes mitosis, survival, and migration in many cell types (43). It stimulates growth factor-related signaling pathways such as the phosphorylation of shc, p44/42 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, protein kinase B/AKT, and the p70 S6 kinase (24,35,65) and contributes to carcinogenesis in breast (51), ovarian (16,26), renal (18), hepatocellular (10), and prostate (44) cancers, gliomas (33), and multiple myelomas (63). Physiologically, pgrn is involved in wound repair (25,67) and is expressed during development (8) where it regulates cavitation in preimplantation embryos (17), blastocyst hatching (48), and malespecific differentiation of the neonatal hypothalamus (56,58).The granulin (GRN) gene is highly expressed in monocytederived cells, being the 17th and 30th most abundant transcript in human macrophage (9) and monocyte-derived dendritic cells (21), respectively. Peptides derived from pgrn, the granulin/ epit...

Phosphorylation is a major regulator of protein interactions; however, the mechanisms by which regulation occurs are not well understood. Here we identify a salt-bridge competition or "theft" mechanism that enables a phospho-triggered swap of protein partners by Raf Kinase Inhibitory Protein (RKIP). RKIP transitions from inhibiting Raf-1 to inhibiting G-protein-coupled receptor kinase 2 upon phosphorylation, thereby bridging MAP kinase and G-Protein-Coupled Receptor signaling. NMR and crystallography indicate that a phosphoserine, but not a phosphomimetic, competes for a lysine from a preexisting salt bridge, initiating a partial unfolding event and promoting new protein interactions. Structural elements underlying the theft occurred early in evolution and are found in 10% of homo-oligomers and 30% of hetero-oligomers including Bax, Troponin C, and Early Endosome Antigen 1. In contrast to a direct recognition of phosphorylated residues by binding partners, the salt-bridge theft mechanism represents a facile strategy for promoting or disrupting protein interactions using solvent-accessible residues, and it can provide additional specificity at protein interfaces through local unfolding or conformational change.

Raf Kinase Inhibitory Protein (RKIP) maintains cellular robustness and prevents the progression of diseases such as cancer and heart disease by regulating key kinase cascades including MAP kinase and protein kinase A (PKA). Phosphorylation of RKIP at S153 by Protein Kinase C (PKC) triggers a switch from inhibition of Raf to inhibition of the G protein coupled receptor kinase 2 (GRK2), enhancing signaling by the β-adrenergic receptor (β-AR) that activates PKA. Here we report that PKA-phosphorylated RKIP promotes β-AR–activated PKA signaling. Using biochemical, genetic, and biophysical approaches, we show that PKA phosphorylates RKIP at S51, increasing S153 phosphorylation by PKC and thereby triggering feedback activation of PKA. The S51V mutation blocks the ability of RKIP to activate PKA in prostate cancer cells and to induce contraction in primary cardiac myocytes in response to the β-AR activator isoproterenol, illustrating the functional importance of this positive feedback circuit. As previously shown for other kinases, phosphorylation of RKIP at S51 by PKA is enhanced upon RKIP destabilization by the P74L mutation. These results suggest that PKA phosphorylation at S51 may lead to allosteric changes associated with a higher-energy RKIP state that potentiates phosphorylation of RKIP at other key sites. This allosteric regulatory mechanism may have therapeutic potential for regulating PKA signaling in disease states.

Raf Kinase Inhibitory Protein (RKIP), a 21 kDa protein and member of phosphatidylethanolamine binding protein (PEBP) family, regulates GPCR, MAPK, and NFκB pathways and is a metastasis suppressor. Although, kinases such as ERK2 and PKCα have been shown to phosphorylate RKIP, structural data on the protein kinase‐RKIP interaction are still lacking. Here we report that another kinase, PKA, phosphorylates RKIP at residue 51, triggering a feedback loop, and we determine the structural model of RKIP‐PKA catalytic subunit. Using different biophysical approaches including Nuclear Magnetic Resonance (NMR), Paramagnetic Relaxation Enhancements (PREs) and molecular modeling, we identify the binding interface between RKIP and PKA catalytic subunit. Chemical shift mapping and site directed mutagenesis studies revealed residues within RKIP that are critical to the catalysis and binding mediated by PKA catalytic subunit. As the first description of PKA binding to a full‐length physiological substrate, these results have wide applicability to the mechanism of PKA catalysis Grant Funding Source: Supported by NIH grant GM087630 to Marsha Rich Rosner, NIH grant GM100310 to Gianluigi Veglia

No abstract

Phosphorylation is a major regulator of protein interactions; however, the mechanisms by which regulation occurs are not well understood. Here we identify a salt‐bridge competition or “theft” mechanism that enables a phospho‐triggered swap of protein partners by Raf Kinase Inhibitory Protein (RKIP). RKIP transitions from inhibiting Raf‐1 to inhibiting G‐protein–coupled receptor kinase 2 upon phosphorylation, thereby bridging MAP kinase and G‐Protein–Coupled Receptor signaling. NMR and crystallography indicate that a phosphoserine, but not a phosphomimetic, competes for a lysine from a preexisting salt bridge, initiating a partial unfolding event and promoting new protein interactions. Structural elements underlying the theft occurred early in evolution and are found in 10% of homo‐oligomers and 30% of hetero‐oligomers including Bax, Troponin C, and Early Endosome Antigen 1. In contrast to a direct recognition of phosphorylated residues by binding partners, the salt‐bridge theft mechanism represents a facile strategy for promoting or disrupting peptide interactions using solvent‐accessible residues, and it can provide additional specificity at protein interfaces through local unfolding or conformational change.Support or Funding InformationGM087630 (to M.R.R.), GM55694 (to T.S.), Deutsche Forschungsgemeinschaft (FZ82: K.L., C.K., and H.S.; SFB688, TPA17: K.L.) and the Ministry for Innovation, Science and Research of the Federal State of North Rhine‐Westphalia (K.L.).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.