Novel betacellulin derivatives. Separation of the differentiation activity from the mitogenic activity

Interstitial Outburst of Angiogenic Factors During Skeletal Muscle Regeneration After Acute Mechanical Trauma

Angiogenesis is a key event during tissue regeneration, but the intimate mechanisms controlling this process are still largely unclear. Therefore, the cellular and molecular interplay along normal tissue regeneration should be carefully unveiled. To this matter, we investigated by xMAP assay the dynamics of some angiogenic factors known to be involved in tissue repair, such as follistatin (FST), Placental Growth Factor-2 (PLGF-2), epidermal growth factor (EGF), betacellulin (BTC), and amphiregulin (AREG) using an animal model that mimics acute muscle contusion injuries. In situ immunofluorescence was used for the evaluation and tissue distribution of their cellular sources. Tissue levels of explored factors increased significantly during degeneration and inflammatory stage of regeneration, peaking first week postinjury. However, except for PLGF-2 and EGF, their levels remained significantly elevated after the inflammatory process started to fade. Serum levels were significantly increased only after 24 h for AREG and EGF. Though, for all factors except FST, the levels in injured samples did not correlate with serum or contralateral tissue levels, excluding the systemic influence. We found significant correlations between the levels of EGF and AREG, BTC, FST and FST and AREG in injured samples. Interstitial cells expressing these factors were highlighted by in situ immunolabeling and their number correlated with measured levels dynamics. Our study provides evidence of a dynamic level variation along the regeneration process and a potential interplay between selected angiogenic factors. They are synthesized, at least partially, by cell populations residing in skeletal muscle interstitium during regeneration after acute muscle trauma.

Oxylipin Signaling: A Distinct Role for the Jasmonic Acid Precursor cis-(+)-12-Oxo-Phytodienoic Acid (cis-OPDA)

Oxylipins are lipid-derived compounds, many of which act as signals in the plant response to biotic and abiotic stress. They include the phytohormone jasmonic acid (JA) and related jasmonate metabolites cis-(+)-12-oxo-phytodienoic acid (cis-OPDA), methyl jasmonate, and jasmonoyl-L-isoleucine (JA-Ile). Besides the defense response, jasmonates are involved in plant growth and development and regulate a range of processes including glandular trichome development, reproduction, root growth, and senescence. cis-OPDA is known to possess a signaling role distinct from JA-Ile. The non-enzymatically derived phytoprostanes are structurally similar to cis-OPDA and induce a common set of genes that are not responsive to JA in Arabidopsis thaliana. A novel role for cis-OPDA in seed germination regulation has recently been uncovered based on evidence from double mutants and feeding experiments showing that cis-OPDA interacts with abscisic acid (ABA), inhibits seed germination, and increases ABA INSENSITIVE5 (ABI5) protein abundance. Large amounts of cis-OPDA are esterified to galactolipids in A. thaliana and the resulting compounds, known as Arabidopsides, are thought to act as a rapidly available source of cis-OPDA.

Trimerization of murine TNF ligand family member LIGHT increases the cytotoxic activity against the FM3A mammary carcinoma cell line

LIGHT is a member of the tumor necrosis factor ligand superfamily, which plays important roles in inflammatory and immune responses. LIGHT forms a membrane-anchored homotrimeric complex on the cell surface and is often processed as a soluble protein. Recombinant soluble human LIGHT produced by mammalian cells or Escherichia coli is functional at nanomolar concentrations. However, there is little information about the biological activity of mouse LIGHT (mLIGHT) because of the difficulty in producing bioactive soluble mLIGHT. In this study, recombinant trimeric soluble mLIGHT, or Foldon-mLIGHT, was produced by fusing mLIGHT with the trimerization domain foldon from bacteriophage T4 fibritin. Foldon-mLIGHT was secreted from 293F cells as a 68-kDa trimeric protein. The recombinant protein potently inhibited the growth of the FM3A mouse mammary carcinoma cell line with an IC(50) of 77 pM; however, the monomer or dimer forms of mLIGHT produced by E. coli or mammalian cell systems showed weak or no inhibitory activity. These data clearly indicated that trimerization of soluble mLIGHT is essential for its biological activity.

A betacellulin mutant promotes differentiation of pancreatic acinar AR42J cells into insulin-producing cells with low affinity of binding to ErbB1

Betacellulin (BTC) is one of the members of the epidermal growth factor (EGF) ligand family of ErbB receptor tyrosine kinases. It is a differentiation factor as well as a potent mitogen. BTC promotes the differentiation of pancreatic acinar-derived AR42J cells into insulin-producing cells. It independently and preferentially binds to two type I tyrosine kinase receptors, the EGF receptor (ErbB1) and ErbB4. However, the physiochemical characteristics of BTC that are responsible for its preferential binding to these two receptors have not been fully defined. In this study, to investigate the essential amino acid residues of BTC for binding to the two receptors, we introduced point mutations into the EGF domain of BTC employing error-prone PCR. The receptor binding abilities of 190 mutants expressed in Escherichia coli were assessed by enzyme immunoassay. Replacement of the glutamic acid residue at position 88 with a lysine residue in BTC was found to produce a significant loss of affinity for binding to ErbB1, while the affinity of binding to ErbB4 was unchanged. In addition, the mutant of BTC-E/88/K showed less growth-promoting activity on BALB/c 3T3 cells compared with that of the wild-type BTC protein. Interestingly, the BTC mutant protein promoted differentiation of pancreatic acinar AR42J cells at a high frequency into insulin-producing cells compared with AR42J cells that were treated with wild-type BTC protein. These results indicate the possibility of designing BTC mutants, which have an activity of inducing differentiation only, without facilitating growth promotion.

Betacellulin-delta4, a novel differentiation factor for pancreatic beta-cells, ameliorates glucose intolerance in streptozotocin-treated rats

We previously described a novel alternatively spliced mRNA transcript of the betacellulin (BTC) gene. This splice isoform, termed BTC-delta4, lacks the C-loop of the epidermal growth factor motif and the transmembrane domain as a result of exon 4 'skipping'. In this study, we expressed BTC-delta4 recombinantly to explore its biological function. When BTC-delta4 was expressed in COS-7 cells, it was secreted largely into the culture medium, in contrast to BTC. Unlike BTC, highly purified recombinant BTC-delta4 produced in Escherichia coli failed to bind or induce tyrosine phosphorylation of either ErbB1 or ErbB4, nor did it antagonize the binding of BTC to these receptors. Consistent with this, BTC-delta4 failed to stimulate DNA synthesis in Balb/c 3T3 and INS-1 cells. However, BTC-delta4 induced differentiation of pancreatic beta-cells; BTC-delta4 converted AR42J cells to insulin-producing cells. When recombinant BTC-delta4 was administered to streptozotocin-treated neonatal rats, it reduced the plasma glucose concentration and improved glucose tolerance. Importantly, BTC-delta4 significantly increased the insulin content, the beta-cell mass, and the numbers of islet-like cell clusters and PDX-1-positive ductal cells. Thus, BTC-delta4 is a secreted protein that stimulates differentiation of beta-cells in vitro and in vivo in an apparent ErbB1- and ErbB4-independent manner. The mechanism by which BTC-delta4 exerts this action on beta-cells remains to be defined but presumably involves an, as yet, unidentified unique receptor.

ADAM10 Mediates Ectodomain Shedding of the Betacellulin Precursor Activated by p-Aminophenylmercuric Acetate and Extracellular Calcium Influx

Betacellulin belongs to the family of epidermal growth factor-like growth factors that are expressed as transmembrane precursors and undergo proteolytic ectodomain shedding to release a soluble mature growth factor. In this study, we investigated the ectodomain shedding of the betacellulin precursor (pro-BTC) in conditionally immortalized wild-type (WT) and ADAM-deficient cell lines. Sequential ectodomain cleavage of the predominant cell-surface 40-kDa form of pro-BTC generated a major (26-28 kDa) and two minor (20 and 15 kDa) soluble forms and a cellular remnant lacking the ectodomain (12 kDa). Pro-BTC shedding was activated by calcium ionophore (A23187) and by the metalloprotease activator p-aminophenylmercuric acetate (APMA), but not by phorbol esters. Culturing cells in calcium-free medium or with the protein kinase Cdelta inhibitor rottlerin, but not with broad-based protein kinase C inhibitors, blocked A23187-activated pro-BTC shedding. These same treatments were without effect for constitutive and APMA-induced cleavage events. All pro-BTC shedding was blocked by treatment with a broad-spectrum metalloprotease inhibitor (GM6001). In addition, constitutive and activated pro-BTC shedding was differentially blocked by TIMP-1 or TIMP-3, but was insensitive to treatment with TIMP-2. Pro-BTC shedding was functional in cells from ADAM17- and ADAM9-deficient mice and in cells overexpressing WT or catalytically inactive ADAM17. In contrast, overexpression of WT ADAM10 enhanced constitutive and activated shedding of pro-BTC, whereas overexpression of catalytically inactive ADAM10 reduced shedding. These results demonstrate, for the first time, activated pro-BTC shedding in response to extracellular calcium influx and APMA and provide evidence that ADAM10 mediates constitutive and activated pro-BTC shedding.

Isolation and identification of EG-VEGF/prokineticins as cognate ligands for two orphan G-protein-coupled receptors

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF, identical to prokineticin 1) is a novel peptide recently identified as a selective mitogen for endocrine gland endothelial cells. The present study demonstrates that EG-VEGF/prokineticin 1 and a peptide closely related to EG-VEGF, prokineticin 2, are cognate ligands of two orphan G-protein-coupled receptors designated ZAQ (=EG-VEGF/PK-R1) and I5E (=EG-VEGF/PK-R2). EG-VEGF/prokineticin 1 and prokineticin 2 induced a transient increase in intracellular calcium ion concentration ([Ca(2+)](i)) with nanomolar potency in Chinese hamster ovary (CHO) cells expressing EG-VEGF/PK-R1 and -R2 and bind to these cells with high affinity and with different receptor selectivity. EG-VEGF/prokineticins provoke rapid phosphorylation of p44/42 MAP kinase and DNA synthesis in the bovine adrenal capillary endothelial cells (BACE). The mRNAs of both EG-VEGF/PK-R1 and -R2 were expressed in BACE. The identification of the receptors for EG-VEGF/prokineticins may provide a novel molecular basis for the regulation of angiogenesis in endocrine glands.