Emergence of the keratinocyte growth factor multigene family during the great ape radiation

Microarray and real-time RT-PCR analyses of differential human gene expression patterns induced by severe acute respiratory syndrome (SARS) coronavirus infection of Vero cells

Vero E6 African green monkey kidney cells are highly susceptible to infection with the newly emerging severe acute respiratory syndrome coronavirus (SARS-CoV), and they are permissive for rapid viral replication, with resultant cytopathic effects. We employed cDNA microarray analysis to characterize the cellular transcriptional responses of homologous human genes at 12 h post-infection. Seventy mRNA transcripts belonging to various functional classes exhibited significant alterations in gene expression. There was considerable induction of heat shock proteins that are crucial to the immune response mechanism. Modified levels of several transcripts involved in pro-inflammatory and anti-inflammatory processes exemplified the balance between opposing forces during SARS pathogenesis. Other genes displaying altered transcription included those associated with host translation, cellular metabolism, cell cycle, signal transduction, transcriptional regulation, protein trafficking, protein modulators, and cytoskeletal proteins. Alterations in the levels of several novel transcripts encoding hypothetical proteins and expressed sequence tags were also identified. In addition, transcription of apoptosis-related genes DENN and hIAP1 was upregulated in contrast to FAIM. Elevated Mx1 expression signified a strong host response to mediate antiviral resistance. Also expressed in infected cells was the C-terminal alternative splice variant of the p53 tumor suppressor gene encoding a modified truncated protein that can influence the activity of wild-type p53. We observed the interplay between various mechanisms to favor virus multiplication before full-blown apoptosis and the triggering of several pathways in host cells in an attempt to eliminate the pathogen. Microarray analysis identifies the critical host–pathogen interactions during SARS-CoV infection and provides new insights into the pathophysiology of SARS.

Keratinocyte growth factor/fibroblast growth factor 7, a homeostatic factor with therapeutic potential for epithelial protection and repair

Keratinocyte growth factor (KGF) is a paracrine-acting, epithelial mitogen produced by cells of mesenchymal origin. It is a member of the fibroblast growth factor (FGF) family, and acts exclusively through a subset of FGF receptor isoforms (FGFR2b) expressed predominantly by epithelial cells. The upregulation of KGF after epithelial injury suggested it had an important role in tissue repair. This hypothesis was reinforced by evidence that intestinal damage was worse and healing impaired in KGF null mice. Preclinical data from several animal models demonstrated that recombinant human KGF could enhance the regenerative capacity of epithelial tissues and protect them from a variety of toxic exposures. These beneficial effects are attributed to multiple mechanisms that collectively act to strengthen the integrity of the epithelial barrier, and include the stimulation of cell proliferation, migration, differentiation, survival, DNA repair, and induction of enzymes involved in the detoxification of reactive oxygen species. KGF is currently being evaluated in clinical trials to test its ability to ameliorate severe oral mucositis (OM) that results from cancer chemoradiotherapy. In a phase 3 trial involving patients who were treated with myeloablative chemoradiotherapy before autologous peripheral blood progenitor cell transplantation for hematologic malignancies, KGF significantly reduced both the incidence and duration of severe OM. Similar investigations are underway in patients being treated for solid tumors. On the basis of its success in ameliorating chemoradiotherapy-induced OM in humans and tissue damage in a variety of animal models, additional clinical applications of KGF are worthy of investigation.

Molecular and cellular biology of moderate-dose (1-10 Gy) radiation and potential mechanisms of radiation protection: report of a workshop at Bethesda, Maryland, December 17-18, 2001

Exposures to doses of radiation of 1-10 Gy, defined in this workshop as moderate-dose radiation, may occur during the course of radiation therapy or as the result of radiation accidents or nuclear/radiological terrorism alone or in conjunction with bioterrorism. The resulting radiation injuries would be due to a series of molecular, cellular, tissue and whole-animal processes. To address the status of research on these issues, a broad-based workshop was convened. The specific recommendations were: (1) RESEARCH: Identify the key molecular, cellular and tissue pathways that lead from the initial molecular lesions to immediate and delayed injury. The latter is a chronic progressive process for which postexposure treatment may be possible. (2) Technology: Develop high-throughput technology for studying gene, protein and other biochemical expression after radiation exposure, and cytogenetic markers of radiation exposure employing rapid and accurate techniques for analyzing multiple samples. (3) Treatment strategies: Identify additional biological targets and develop effective treatments for radiation injury. (4) Ensuring sufficient expertise: Recruit and train investigators from such fields as radiation biology, cancer biology, molecular biology, cellular biology and wound healing, and encourage collaboration on interdisciplinary research on the mechanisms and treatment of radiation injury. Communicate knowledge of the effects of radiation exposure to the general public and to investigators, policy makers and agencies involved in response to nuclear accidents/events and protection/treatment of the general public.

Paracrine action of keratinocyte growth factor (KGF) during ruminant mammogenesis

Keratinocyte growth factor (KGF) is a stroma-derived mitogen mediating epithelial-stromal interactions. We investigated the role of KGF during epithelial-stromal interactions accompanying ruminant mammogenesis. Target-specificity of KGF was demonstrated in that KGF-stimulated proliferation of bovine mammary epithelial, but not ovine mammary stromal cells. Consistent with a paracrine function, 4.6, 2.4, 1.5 and 0.9 kb mRNA transcripts were expressed by bovine stromal, but not epithelial cells. Within the ovine mammary gland, 2.4 and 1.5 kb KGF mRNAs were expressed in the fat pad while only the 2.4 kb transcript was transcribed in parenchyma. The abundance of KGF mRNA was greater in the extra-parenchymal fat pad than in the contralateral epithelium-free fat pad prior to puberty, and was less in parenchyma than in the intact or epithelium-free fat pads. Ovariectomy tended to increase KGF transcription while estrogen reduced expression. Of several tissues, mammary parenchyma expressed a 2.4 kb mRNA while adipose tissues expressed a 1.5 kb transcript. These results demonstrate local and systemic regulation of KGF transcription and support a paracrine role for KGF during ruminant mammogenesis.

Fibroblast growth factors

SUMMARY

Fibroblast growth factors (FGFs) make up a large family of polypeptide growth factors that are found in organisms ranging from nematodes to humans. In vertebrates, the 22 members of the FGF family range in molecular mass from 17 to 34 kDa and share 13-71% amino acid identity. Between vertebrate species, FGFs are highly conserved in both gene structure and amino-acid sequence. FGFs have a high affinity for heparan sulfate proteoglycans and require heparan sulfate to activate one of four cell-surface FGF receptors. During embryonic development, FGFs have diverse roles in regulating cell proliferation, migration and differentiation. In the adult organism, FGFs are homeostatic factors and function in tissue repair and response to injury. When inappropriately expressed, some FGFs can contribute to the pathogenesis of cancer. A subset of the FGF family, expressed in adult tissue, is important for neuronal signal transduction in the central and peripheral nervous systems.

Cloning of a cDNA encoding ovine keratinocyte growth factor

A cDNA encoding the ovine keratinocyte growth factor (KGF) has been cloned. A 622-bp cDNA, containing the entire protein coding region, was amplified from an ovine adenocarcinoma fibroblast cell line. The cDNA was found to share 95% nucleotide identity with dog KGF, 94% identity with human KGF, 90% identity with mouse KGF and 88% identity with rat KGF. The predicted ovine amino-acid sequence shares 98.5, 98, 96 and 94% identity, respectively, with the corresponding dog, human, mouse and rat proteins. The KGF gene is present as a single copy in the ovine genome.

Fluorescence in situ hybridization analysis of keratinocyte growth factor gene amplification and dispersion in evolution of great apes and humans

Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor family. Portions of the gene encoding KGF were amplified during primate evolution and are present in multiple nonprocessed copies in the human genome. Nucleotide analysis of a representative sampling of these KGF-like sequences indicated that they were at least 95% identical to corresponding regions of the KGF gene. To localize these sequences to specific chromosomal sites in human and higher primates, we used fluorescence in situ hybridization. In human, using a cosmid probe encoding KGF exon 1, we assigned the location of the KGF gene to chromosome 15q15-21.1. In addition, copies of KGF-like sequences hybridizing only with a cosmid probe encoding exons 2 and 3 were localized to dispersed sites on chromosome 2q21, 9p11, 9q12-13, 18p11, 18q11, 21q11, and 21q21.1. The distribution of KGF-like sequences suggests a role for alphoid DNA in their amplification and dispersion. In chimpanzee, KGF-like sequences were observed at five chromosomal sites, which were each homologous to sites in human, while in gorilla, a subset of four of these homologous sites was identified; in orangutan two sites were identified, while gibbon exhibited only a single site. The chromosomal localization of KGF sequences in human and great ape genomes indicates that amplification and dispersion occurred in multiple discrete steps, with initial KGF gene duplication and dispersion taking place in gibbon and involving loci corresponding to human chromosomes 15 and 21. These findings support the concept of a closer evolutionary relationship of human and chimpanzee and a possible selective pressure for such dispersion during the evolution of higher primates.

Purification and molecular cloning of a secreted, Frizzled-related antagonist of Wnt action

Frizzled polypeptides are integral membrane proteins that recently were shown to function as receptors for Wnt signaling molecules. Here, we report the identification of a novel, secreted 36-kDa protein that contains a region homologous to a putative Wnt-binding domain of Frizzleds. This protein, called Frizzled-related protein (FRP), was first identified as a heparin-binding polypeptide that copurified with hepatocyte growth factor/scatter factor in conditioned medium from a human embryonic lung fibroblast line. Degenerate oligonucleotides, based on the NH2-terminal sequence of the purified protein, were used to isolate corresponding cDNA clones. These encoded a 313-amino acid polypeptide, containing a cysteine-rich domain of approximately 110 residues that was 30-40% identical to the putative ligand-binding domain of Frizzled proteins. A 4.4-kb transcript of the FRP gene is present in many organs, both in the adult and during embryogenesis, and homologs of the gene are detectable in DNA from several vertebrate species. In biosynthetic studies, FRP was secreted but, like Wnts, tended to remain associated with cells. When coexpressed with several Wnt family members in early Xenopus embryos, FRP antagonized Wnt-dependent duplication of the embryonic dorsal axis. These results indicate that FRP may function as an inhibitor of Wnt action during development and in the adult.

Of worms and men: an evolutionary perspective on the fibroblast growth factor (FGF) and FGF receptor families

FGFs (fibroblast growth factors) play major roles in a number of developmental processes. Recent studies of several human disorders, and concurrent analysis of gene knock-out and properties of the corresponding recombinant proteins have shown that FGFs and their receptors are prominently involved in the development of the skeletal system in mammals. We have compared the sequences of the nine known mammalian FGFs, FGFs from other vertebrates, and three additional sequences that we extracted from existing databases: two human FGF sequences that we tentatively designated FGF10 and FGF11, and an FGF sequence from Caenorhabditis elegans. Similarly, we have compared the sequences of the four FGF receptor paralogs found in chordates with four non-chordate FGF receptors, including one recently identified in C. elegans. The comparison of FGF and FGF receptor sequences in vertebrates and nonvertebrates shows that the FGF and FGF receptor families have evolved through phases of gene duplications, one of which may have coincided with the emergence of vertebrates, in relation with their new system of body scaffold.

Keratinocyte growth factor is required for hair development but not for wound healing

Keratinocyte growth factor (KGF), also known as fibroblast growth factor 7 (FGF7), is synthesized by skin fibroblasts. However, its mitogenic activity is on skin keratinocytes, where it is the most potent growth factor identified thus far. To explore KGF's function in vivo, we used embryonic stem cell technology to generate mice lacking KGF. Over time, their fur developed a matted appearance, very similar to that of the rough mouse, whose recessive mutation maps at or near the KGF locus on mouse chromosome 2. In contrast to the recently reported transforming growth factor-alpha (TGF-alpha) and FGF5 knockouts, which showed defects in the follicle outer-root sheath and the hair growth cycle, respectively, the hair defect in the KGF knockout seemed to be restricted to the cells giving rise to the hair shaft. Thus, we have uncovered a third, and at least partially nonoverlapping, growth factor pathway involved in orchestrating hair follicle growth and/or differentiation. Surprisingly, the absence of KGF resulted in no abnormalities in epidermal growth or wound healing. This was true even when we engineered double knockout mice, null for both KGF and TGF-alpha, two factors that are increased dramatically in the normal wound-healing process. Whereas we found no evidence of compensatory changes at the mRNA level of wounded knockout mice, these data imply that the regulation of epidermal growth is complex and involves a number of growth stimulatory factors that go beyond what are thought to be the major paracrine and autocrine growth factors. We suggest that the redundancy in epidermal growth and wound healing is likely to stem from the vitality of these functions to the organism, a feature that is not a consideration for the hair follicle.

Modulation of keratinocyte growth factor and its receptor in reepithelializing human skin

We investigated the expression and distribution of keratinocyte growth factor (KGF) (FGF-7) and its receptor (KGFR) during reepithelialization of human skin. KGF mRNA levels increased rapidly by 8-10-fold and remained elevated for several days. In contrast, KGFR transcript levels decreased early but were significantly elevated by 8-9 d. A KGF-immunoglobulin G fusion protein (KGF-HFc), which specifically and sensitively detects the KGFR, localized the receptor to differentiating keratinocytes of control epidermis, but revealed a striking decrease in receptor protein expression during the intermediate period of reepithelization. Suramin, which blocked KGF binding and stripped already bound KGF from its receptor, failed to unmask KGFRs in tissue sections from the intermediate phase of wound repair. The absence of KGFR protein despite increased KGFR transcript levels implies functional receptor downregulation in the presence of increased KGF. This temporal modulation of KGF and KGFRs provides strong evidence for the functional involvement of KGF in human skin reepithelialization.

Keratinocyte growth factor: an androgen-regulated mediator of stromal-epithelial interactions in the prostate

Members of the fibroblast growth factor (FGF) family are important growth-regulatory elements. Of the FGFs, keratinocyte growth factor (KGF) appears to have unique properties that implicate it as a paracrine factor in the prostate. Two KGF transcripts (approximately to 2.4 and 5.0 kb) encode a protein of approximately 22 kDa. In contrast to several other members of the FGF family, KGF has a signal peptide and is actively secreted. Cellular response to KGF is mediated by a specific receptor that is transcribed from an alternately spliced variant of the FGF type 2 receptor (FGFR-2). KGF transcripts have been detected in prostatic tissues and in stromal cells cultured from rat and human prostates as well as in a variety of stromal cells derived from other organs. Prostatic epithelial cells and numerous other types of epithelial cells are targets of KGF's mitogenic activity. Several factors involved in wound healing regulate the expression of KGF, but androgen regulation of KGF is of greatest relevance to the role of KGF in the prostate. Current efforts to localize and manipulate KGF activity in vivo should reveal the significance of KGF expression and function in the prostate and in other organs.

Cloning and characterization of the promoter region of the human keratinocyte growth factor gene

Keratinocyte growth factor (KGF), a member of the fibroblast growth factor family of related proteins, is expressed by stromal fibroblasts and acts on epithelial cells in a paracrine fashion. To understand the mechanisms responsible for regulating normal KGF expression and how these might be altered in disease, the 5'-flanking region of this gene was cloned. The presence of two KGF transcription initiation sites was suggested by ribonuclease protection assay and confirmed by primer extension analysis. Examination of the genomic DNA sequence revealed the presence of the putative promoter sequences TATTTA and CCAAT, located 31 and 50 base pairs upstream, respectively, from the first of the two mRNA start points, and putative initiator sequences surrounding each transcription start site. Transient transfection into murine NIH/3T3 fibroblasts demonstrated that the region required for basal level KGF promoter activity was located between bases -225 and +190. Inclusion of sequences between -1503 and -775 markedly reduced promoter activation, indicating the presence of negative regulatory element(s) in this region. A similar pattern of promoter activation was detected in human fibroblasts and in murine C2C12 myoblasts. In contrast, no chloramphenicol acetyltransferase activity was observed in macrophages and epithelial and lymphoid cells transfected with the same constructs. Northern blot analysis revealed a strong correlation between KGF RNA expression and promoter activation in all cells tested. Activation of the KGF promoter could be induced by the proinflammatory cytokines interleukin 1 and interleukin 6 and by the adenylate cyclase activator forskolin. Taken together, these results indicate the existence of cis-acting element(s) responsible for selective activation of the KGF promoter only in cells that express KGF mRNA and may provide a mechanistic basis for KGF gene expression during inflammation.

Fgf-8, activated by proviral insertion, cooperates with the Wnt-1 transgene in murine mammary tumorigenesis

We have used mouse mammary tumor virus (MMTV) infection of Wnt-1 transgenic mice to accelerate mammary tumorigenesis and to molecularly tag insertionally activated proto-oncogenes that cooperate oncogenically with Wnt-1 (G. M. Shackleford, C. A. MacArthur, H. C. Kwan, and H. E. Varmus, Proc. Natl. Acad. Sci. USA 90:740-744, 1993). Here we report the identification and characterization of a 31-kb genomic locus that contains clonal MMTV integrations in 8 of 80 mammary tumors from MMTV-infected Wnt-1 transgenic mice. Two genes were identified within this locus, one of which was transcriptionally activated by MMTV insertions. This activated gene is identical to androgen-induced growth factor (AIGF/Fgf-8) (A. Tanaka, K. Miyamoto, N. Minamino, M. Takeda, B. Sato, H. Matsuo, and K. Matsumoto, Proc. Natl. Acad. Sci. USA 89:8928-8932, 1992), the eighth member of the fibroblast growth factor (FGF) family. Transcriptional activation of Fgf-8 was found in all tumors with MMTV insertions in this locus. Fgf-8 mRNA was absent in normal mammary glands and was detected only in adult testis and ovary and in midgestational embryos. The sequences of Fgf-8 genomic and cDNA clones revealed five coding exons, in contrast to the three coding exons found in other FGF genes. cDNAs encoding three isoforms of the FGF-8 protein were isolated. The three corresponding mRNAs resulted from the alternative use of two 5' splice sites and two 3' splice sites for the second and third exons, respectively. These results implicate Fgf-8 as the third FGF gene found to cooperate with Wnt-1 in MMTV-induced murine mammary tumorigenesis, suggesting that FGFs and Wnts are strong collaborators in this process.

Progesterone-dependent expression of keratinocyte growth factor mRNA in stromal cells of the primate endometrium: keratinocyte growth factor as a progestomedin

In vitro studies have shown that keratinocyte growth factor (KGF, also known as FGF-7) is secreted by fibroblasts and is mitogenic specifically for epithelial cells. Therefore, KGF may be an important paracrine mediator of epithelial cell proliferation in vivo. Because stromal cells are thought to influence glandular proliferation in the primate endometrium, we investigated the hormonal regulation and cellular localization of KGF mRNA expression in the rhesus monkey uterus. Tissues were obtained both from naturally cycling monkeys in the follicular and luteal phases of the cycle, and from spayed monkeys that were either untreated or treated with estradiol (E2) alone, E2 followed by progesterone (P), E2 plus P, or E2 plus P plus an antiprogestin (RU 486). Northern blot analysis of total RNA with 32P-labeled probes revealed that the level of KGF mRNA in the endometrium was 70-100-fold greater in the luteal phase or after P treatment than in untreated, E2-treated, or follicular phase animals. Northern analysis also showed that KGF mRNA was present in the myometrium but was unaffected by hormonal state. RU 486 treatment prevented the P-induced elevation of endometrial KGF mRNA. P-dependent elevation of endometrial KGF expression was confirmed by measurement of KGF protein in tissue extracts using a two-site enzyme-linked immunosorbent assay. In situ hybridization with nonradioactive digoxigenin-labeled cDNA probes revealed that the KGF mRNA signal, which was present only in stromal and smooth muscle cells, was substantially increased by P primarily in the stromal cells located in the basalis region. Smooth muscle cells in the myometrium and the walls of the spiral arteries also expressed KGF mRNA, but the degree of this expression did not differ with hormonal state. P treatment led to increased proliferation in the glandular epithelium of the basalis region and to extensive growth of the spiral arteries. We conclude that the P-dependent increase in endometrial KGF resulted from a dual action of P: (a) a P-dependent induction of KGF expression in stromal cells, especially those in the basalis (zones III and IV), and (b) a P-dependent increase in the number of KGF-positive vascular smooth muscle cells caused by the proliferation of the spiral arteries. KGF is one of the first examples in primates of a P-induced, stromally derived growth factor that might function as a progestomedin.

Neural BC1 RNA as an evolutionary marker: guinea pig remains a rodent

The traditional morphologically grounded placement of South American guinea pig-like rodents (Caviomorpha) within one of the two rodent suborders, Hystricognathi, has been disputed by recent analysis of protein and nucleic acid sequence data. The Caviomorpha and possibly all Hystricognathi would be considered a separate order, distinct from the other rodent suborder, Sciurognathi, and thus of the order Rodentia, and would be placed closer phylogenetically to other mammals [Graur, D., Hide, W. A. & Li, W.-H. (1991) Nature (London) 351, 649-652]. To address the discrepancy between morphological comparisons and sequence analyses, we have applied an alternative form of molecular analysis. We demonstrate that BC1 RNA, a neural-specific small cytoplasmic RNA that is the product of a retropositionally generated gene (a gene derived by reverse transcription of RNA followed by insertion of the DNA copy into the genome), is present in Sciurognathi and guinea pig but not in other mammalian orders including Lagomorpha, Artiodactyla, and Primates. The species-confined, tissue-specific expression of a retroposed sequence therefore supports the morphological evidence for monophyly of Rodentia inclusive of guinea pig and demonstrates the usefulness of such molecular genetic markers. Furthermore, the conservation and tissue-specific expression of the BC1 RNA gene in the two divergent rodent suborders suggests that this macromolecule has been exapted into a functional role (i.e., coopted into a variant or novel function) in the rodent nervous system.