Wound healing requires a coordinated interplay among cells, growth factors, and extracellular matrix proteins. Central to this process is the endogenous mesenchymal stem cell (MSC), which coordinates the repair response by recruiting other host cells and secreting growth factors and matrix proteins. MSCs are self-renewing multipotent stem cells that can differentiate into various lineages of mesenchymal origin such as bone, cartilage, tendon, and fat. In addition to multilineage differentiation capacity, MSCs regulate immune response and inflammation and possess powerful tissue protective and reparative mechanisms, making these cells attractive for treatment of different diseases. The beneficial effect of exogenous MSCs on wound healing was observed in a variety of animal models and in reported clinical cases. Specifically, they have been successfully used to treat chronic wounds and stimulate stalled healing processes. Recent studies revealed that human placental membranes are a rich source of MSCs for tissue regeneration and repair. This review provides a concise summary of current knowledge of biological properties of MSCs and describes the use of MSCs for wound healing. In particular, the scope of this review focuses on the role MSCs have in each phase of the wound-healing process. In addition, characterization of MSCs containing skin substitutes is described, demonstrating the presence of key growth factors and cytokines uniquely suited to aid in wound repair.

No abstract

Jaagsiekte sheep retrovirus (JSRV) can induce rapid, multifocal lung cancer, but JSRV is a simple retrovirus having no known oncogenes. Here we show that the envelope (env) gene of JSRV has the unusual property that it can induce transformation in rat fibroblasts, and thus is likely to be responsible for oncogenesis in animals. Retrovirus entry into cells is mediated by Env interaction with particular cell-surface receptors, and we have used phenotypic screening of radiation hybrid cell lines to identify the candidate lung cancer tumor suppressor HYAL2͞LUCA2 as the receptor for JSRV. HYAL2 was previously described as a lysosomal hyaluronidase, but we show that HYAL2 is actually a glycosylphosphatidylinositol (GPI)-anchored cell-surface protein. Furthermore, we could not detect hyaluronidase activity associated with or secreted by cells expressing HYAL2, whereas we could easily detect such activity from cells expressing the related serum hyaluronidase HYAL1. Although the function of HYAL2 is currently unknown, other GPI-anchored proteins are involved in signal transduction, and some mediate mitogenic responses, suggesting a potential role of HYAL2 in JSRV Env-mediated oncogenesis. Lung cancer induced by JSRV closely resembles human bronchiolo-alveolar carcinoma, a disease that is increasing in frequency and now accounts for Ϸ25% of all lung cancer. The finding that JSRV env is oncogenic and the identification of HYAL2 as the JSRV receptor provide tools for further investigation of the mechanism of JSRV oncogenesis and its relationship to human bronchiolo-alveolar carcinoma.J aagsiekte sheep retrovirus (JSRV) is the causative agent of a contagious lung cancer of sheep called ovine pulmonary carcinoma or sheep pulmonary adenomatosis (1). Tumors originate from type II secretory alveolar and nonciliated bronchiolar epithelial cells, and late stages of the disease are accompanied by the secretion of copious lung fluid containing the virus. Purified virus induces multifocal tumors in as little as 10 days (2), suggesting the role of a viral oncogene. However, JSRV is a simple retrovirus with typical gag, pol, and env genes and no known oncogenes. The viral structural (Gag) and enzymatic (Pol) proteins are unlikely to be responsible, because they interact primarily with viral components, but there is precedent for alteration of cellular functions by the envelope (Env) protein of retroviruses, which interacts with cellular components to mediate virus entry. For example, the deleted Env protein of the Friend spleen focus-forming virus causes erythroleukemia by binding to and activating the erythropoietin receptor (3). If the JSRV Env protein was indeed oncogenic, identification of the host cell receptor for JSRV would provide key insights into the oncogenic mechanism of this highly pathogenic retrovirus. Furthermore, the contagious nature of JSRV and its ability to survive exposure to proteases and surfactants present in lung fluid suggest that vectors based on JSRV might be useful for gene therapy targeted to the lung, pr...

Human mesenchymal stem cells (hMSCs) are rare progenitor cells present in adult bone marrow that have the capacity to differentiate into a variety of tissue types, including bone, cartilage, tendon, fat, and muscle. In addition to multilineage differentiation capacity, MSCs regulate immune and inflammatory responses, providing therapeutic potential for treating diseases characterized by the presence of an inflammatory component. The availability of bone marrow and the ability to isolate and expand hMSCs ex vivo make these cells an attractive candidate for drug development. The low immunogenicity of these cells suggests that hMSCs can be transplanted universally without matching between donors and recipients. MSCs universality, along with the ability to manufacture and store these cells long-term, present a unique opportunity to produce an "off-the-shelf" cellular drug ready for treatment of diseases in acute settings. Accumulated animal and human data support MSC therapeutic potential for inflammatory diseases. Several phase III clinical trials for treatment of acute Graft Versus Host Disease (GVHD) and Crohn's disease are currently in progress. The current understanding of cellular and molecular targets underlying the mechanisms of MSCs action in inflammatory settings as well as clinical experience with hMSCs is summarized in this review.

In this study, we focus on different modes of regulation of STRA13, a human ortholog of the mouse basic helix-loop-helix transcriptional factor, previously identified by us as a new von Hippel-Lindau tumor suppressor gene (VHL) target. The gene was overexpressed in VHL-deficient cell lines and tumors, specifically clear cell renal carcinomas and hemangioblastomas. Introduction of wild type VHL transgene into clear cell renal carcinoma restored low level expression of STRA13. Overexpression was also detected in many common malignancies with an intact VHL gene, suggesting the existence of another, VHL-independent pathway of STRA13 regulation. Similar to many other von HippelLindau tumor-suppressor protein (pVHL) targets, the expression of STRA13 on the mRNA level was hypoxiasensitive, indicating oxygen-dependent regulation of the gene, presumably through the pVHL/hypoxia-inducible factor 1 (HIF-1) pathway. The yeast two-hybrid screening revealed interaction of the STRA13 protein with the human ubiquitin-conjugating enzyme (UBC9) protein, the specificity of which was confirmed in mammalian cells. By adding the proteasome inhibitor acetylleucinyl-leucinyl-norleucinal, we demonstrated that the 26 S proteasome pathway regulates the stability of pSTRA13. Co-expression of STRA13 and UBC9 led to an increase of the pSTRA13 ubiquitination and subsequent degradation. These data established that UBC9/STRA13 association in cells is of physiological importance, presenting direct proof of UBC9 involvement in the ubiquitindependent degradation of pSTRA13. Hypoxia treatment of mammalian cells transiently expressing STRA13 protein showed that stability of pSTRA13 is not affected by hypoxia or VHL. Thus, STRA13, a new pVHL target, is regulated in cells on multiple levels. We propose that STRA13 may play a critical role in carcinogenesis, since it is a potent transcriptional regulator, abundant in a variety of common tumors.Functional inactivation of the von Hippel-Lindau tumor-suppressor protein (pVHL) 1 causes a hereditary cancer syndrome characterized by the predisposition to develop tumors of kidney, central nervous system, retina, pancreas, and adrenal gland. Recent studies highlighted pVHL as a key regulator of cellular responses to oxygen deprivation. pVHL regulates activity of the hypoxia-inducible factor 1 (HIF-1), consisting of an HIF-1␣/HIF-1␤ heterodimer. Under normoxic conditions, the ␣ subunit interacts with the pVHL-elongin B-elongin C complex and is rapidly degraded (1). Hypoxia or pVHL deficiency stabilizes HIF-1␣, which results in activation of a set of genes including vascular endothelial growth factor (VEGF) (2, 3), glucose transporter GLUT-1 (3), glycolytic enzymes (reviewed in Ref. 4), transforming growth factor-␣ (5), and transforming growth factor-␤1 (6). We have recently expanded the list of hypoxia-sensitive pVHL targets. Using the RNA differential display technique, we identified and characterized two novel hypoxia-responsive VHL targets, carbonic anhydrases 9 and 12 (7). Here we describe a third gene down...

No abstract

Introduction c-Kit, also known as stem cell factor receptor or steel factor receptor, is a type 3 receptor tyrosine kinase (RTK) belonging to the platelet-derived growth factor receptor subfamily. The c-kit gene maps to the white spotting locus (W) in the mouse. 1,2 The absence of functional c-Kit or its ligand, stem cell factor (SCF), causes perinatal lethality. Mutations resulting in reduced expression or function of either c-Kit or SCF result in macrocytic anemia, aberrations in pigmentation, decreased fertility, mast cell deficiency, reduction in gastrointestinal motility, and impairment of learning functions in the hippocampal region of the brain. [3][4][5][6] Thus, c-Kit plays an important role in hematopoiesis, melanogenesis, and germ cell development and in the function of the gastrointestinal tract and the brain.Diverse cellular responses associated with c-Kit include differentiation, proliferation, growth, survival, adhesion, and chemotaxis. These pleiotropic functions are mediated through the activation of multiple signal transduction pathways. 7 These include Src family kinases, [8][9][10][11][12][13] Janus kinases, and signal transducer and activator of transcription (JAK/STAT) family members, [14][15][16][17][18][19][20] phosphatidylinositol 3 kinase (PI3K), [21][22][23][24][25][26][27][28][29][30] the Ras/Raf/Map kinase cascade, 10,[30][31][32][33][34][35][36][37][38] and phospholipase C. 26,28,32 Because many of these proteins are the products of proto-oncogenes, alterations in regulation of these pathways could result in cellular transformation.In the past decade, several gain-of-function c-Kit mutations have been identified. Many of these mutations are clustered in either the c-Kit juxtamembrane region or the second catalytic domain. [39][40][41][42] Factor-dependent cell lines expressing activated c-Kit mutants survive and proliferate in the absence of exogenous growth factors. [43][44][45] Gain-of-function mutations in c-Kit have been implicated in human disease. Mutations in the juxtamembrane region are found in many human gastrointestinal stromal tumors. 46 Many patients with mastocytosis have a point mutation in codon 816 encoding a residue in the second catalytic domain of c-Kit. [47][48][49] Some patients with germ cell tumors also have this mutation. 50 Equivalent mutations have been identified in mast cell leukemia lines derived from rats and humans and in a murine mastocytoma cell line. Substitution of aspartic acid 814 in murine c-Kit (the equivalent of amino acid 816 in human c-Kit) with valine (D814V) or tyrosine (D814Y) results in constitutive increases in kinase activity and in alterations in substrate preference of this RTK. 39,44,45,51,52 Cell lines expressing D816V human c-Kit or D814V murine c-Kit are tumorigenic in mice. [43][44][45] Previous studies have demonstrated that D816V c-Kit is constitutively phosphorylated on tyrosine residues and that degradation of Shp1 is enhanced in cells expressing this mutant. 39,44,45,51,52 From For personal use only. on May 9, 2018. by gue...

No abstract