Amino-terminal sequences of a novel heparin-binding protein from human, bovine, rat, and chick brain: high interspecies homology

Regulation of osteoblast-specific factor-1 (OSF-1) mRNA expression by dual promoters as revealed by RT-PCR

OSF-1 (osteoblast-specific factor-1), which is also referred to as p18, HBBM, HB-GAM, HBGF-8, HARP, HBNF, and pleiotrophin, is a 121-amino acid polypeptide that can induce neurite outgrowth in vitro and is highly expressed in several tissues during fetal development but exhibits expression restricted to brain and bone tissues in adults. We have reported the genomic structure of mouse OSF-1 gene, in which the open reading frame spans four exons and at least two additional 5'-UTR exons (upstream exon U2 and downstream exon U1) exist. From analysis of isolated cDNAs, two types of cDNAs were identified: one has a sequence for U1 and U2 and the other has a sequence for an intron (present between U1 and U2) and U1. This suggests that the OSF-1 gene utilizes two alternative promoters, a distal and a proximal promoter, designated promoters II and I, respectively, for the translation initiation site (ATG). Promoter II is thought to exist upstream of the intron, while promoter I is present in the intron. RT-PCR was employed to examine which OSF-1 promoters are used during development and in various cell lines. In adult mice (aged 2 months), usage of promoter I was predominant, and OSF-1 mRNAs were expressed in many organs including brain and bone. At one fetal stage (E-19), promoter I was active in the major organs including brain, liver, kidney, and intestine, while promoter II was active only in the brain. In the cell lines examined, usage of promoter I was frequent, while promoter II was active only in a few cell lines such as MC3T3-E1 (cultured for 7 days) and C3H10T1/2. These findings suggest that OSF-1 may play fundamental roles in differentiation, growth and maintenance of adult organs as well as in embryogenesis, and indicate that the expression of OSF-1 is regulated, at least in part, by the usage of different promoters in the mouse.

Immunocytochemical localization of the heparin-binding growth-associated molecule (HB-GAM) in the developing and adult rat cerebellar cortex

The heparin-binding, growth-associated molecule (HB-GAM) is a developmentally regulated protein that belongs to a new family of heparin-binding molecules, not related to the fibroblast growth factors (FGFs), with putative functions during cell growth and differentiation. In order to further study the functional role of HB-GAM we have used a polyclonal antiserum, raised against the purified protein to localize HB-GAM in the developing and adult rat cerebellar cortex. During postnatal development HB-GAM-like immunoreactivity (IR) was found to be present in all layers of the cerebellar cortex. IR was mainly associated with processes or extracellular structures but not with cell bodies. Throughout all the stages examined the molecular layer was clearly labeled, whereas staining in the internal granular layer was diffuse. IR in the external granular layer on postnatal day 1 and 8 was found to be associated with radially oriented fibres connecting the internal granular layer with the pial surface of the cerebellum. The intensity of this staining seemed to increase from day 1 to 8. Staining of corresponding areas with an antiserum against the glial fibrillary acidic protein (GFAP) suggested that the HB-GAM antiserum in the developing cerebellar cortex labels Bergmann glia fibres of Golgi epithelial cells. Because of the diffuse staining of the molecular layer in the adult rat it was not possible to distinguish whether radial fibres in the adult contained any HB-GAM IR. Golgi epithelial cells are considered as crucial for the migration of granular cells during the differentiation of the cerebellar cortex. We therefore speculate that the association of HB-GAM-like IR may be of functional relevance. The fact that molecules, such as tenascin, known to be involved in morphogenetic events show a similar spatiotemporal distribution pattern further underscores this hypothesis. HB-GAM, which possesses a classical signal sequence, might be release in the extracellular space and could mediate adhesion phenomena by binding to heparin-like molecules associated with the neuronal membrane. Therefore, it will be important to investigate whether specific antibodies against HB-GAM are able to interfere with normal cerebellar development in vitro and in vivo.

Molecular and pharmacologic targeting of angiogenesis factors--the example of pleiotrophin

Polypeptide growth factors contribute to the development and maintenance of normal tissues and are essential for the growth and metastasis of solid tumors. During tumor progression these factors function as autocrine stimulators of tumor cells and/or serve to recruit stromal tissue and blood supply to the expanding tumor. In particular, tumor-induced angiogenesis appears to be significant not only for local tumor growth but also for metastasis to distant organ sites. We purified several years ago the heparin-binding growth factor pleiotrophin (PTN) from the supernatants of human breast cancer cells and demonstrated that PTN can serve as an angiogenesis factor. We found the gene expressed in a number of human tumor cell lines as well as in human tumor tissues. Here we present different approaches to inhibit production and function of this growth factor. Finally we discuss how the experience from this growth factor can be applied to improve our understanding of the role of other factors thought to contribute to tumor angiogenesis.

Organisation and promoter activity of the retinoic-acid-induced-heparin-binding (RIHB) gene

The heparin-binding protein, RIHB, is encoded by a gene that is expressed temporarily during the early period of chicken embryogenesis. We have now isolated genomic clones of the chicken RIHB gene, determined its transcription initiation sites, characterized its promoter region and established the functional activity of the RIHB gene promoter. The 5' flanking region and the beginning of the first exon revealed a structural organisation characteristic of housekeeping and growth-control-related genes. It lacked canonical TATA or CAAT boxes but contained several GC boxes. The structure of the RIHB gene is compared with those of the human and mouse midgestation kidney (MK) genes. In the coding exons, the similarities between the three genes are striking. In contrast, the structure and location of the first non-coding exon is different. Analysis of the promoter activity suggests an indirect regulation of transcription by retinoic acid and demonstrates a high degree of complexity of the regulation of the RIHB gene.

Retinoic acid induced heparin-binding protein expression and localization during gastrulation, neurulation, and organogenesis

Retinoic acid induced heparin-binding protein (RIHB) is a highly basic, soluble polypeptide of the chick embryonic extracellular matrix. We have examined the expression and localization of RIHB during very early embryogenesis by in situ hybridization and immunohistochemistry. RIHB mRNA is very weakly detectable above background in the blastodiscs of unincubated eggs. The expression increases greatly over the first 24 hours of incubation, and is observed throughout the blastodisc in all three of the germ layers following gastrulation. As neurulation occurs, the expression becomes more restricted to certain areas, notably the ectoderm, the neural folds, and especially the notochord. After the neural tube has formed the expression in the tube itself decreases dramatically, whereas the expression in the head ectoderm and the notochord persists. After 72 hours of incubation expression remains relatively high throughout most of the embryo, with higher levels of expression in regions undergoing organogenesis and lower levels in organs which have already differentiated. RIHB protein is also weakly detectable in unincubated eggs as patches of immunoreactive material between the blastodisc and the vitelline. After 6 hours of incubation small regions of basement membrane are immunoreactive. RIHB is detected in this matrix, apparently before even fibronectin. The amount of RIHB protein increases dramatically over the first 24 hours of incubation. It is found in basement membrane separating the epiblast from the hypoblast, then later in that separating the ectoderm from the mesoderm. It is also detected surrounding individual cells, especially of the ectodermal layer. During neurulation RIHB is observed in the basement membrane surrounding the neural fold and the notochord, and in the lamina separating the ectodermal, mesodermal, and endodermal layers. Later in development, RIHB is detected in the basement membrane under the epidermis, throughout the developing limbs, and in the lamina of various developing organs, such as the eye, the pulmonary bud, the intestine, and the mesonephros. These results demonstrate that RIHB is highly expressed during the early embryonic period, by all three germ layers, and is an important and very early component of the embryonic extracellular matrix. Its very broad expression and localization argue for a more general role in development than its demonstrated weak neurotrophic activity.

Growth factor targeted and conventional therapy of breast cancer

Sustained breast cancer growth and metastasis requires paracrine signals between the tumor cells and the normal surrounding host tissue. One crucial function of these signals is to recruit endothelial cells and thus new blood vessels for the nourishment of the expanding tumor mass. This proliferation and migration of endothelial cells in the vicinity of progressing tumors contrasts with the extremely low turn-over rate of endothelial cells in the healthy adult. A blockade of tumor-induced endothelial cell proliferation should inhibit tumor growth and potentially metastasis with only few adverse effects. Different therapeutic approaches that take advantage of this situation are discussed with respect to their interaction with conventional therapies of breast cancer.

The potential role of the heparin-binding growth factor pleiotrophin in breast cancer

We propose that the secreted protein pleiotrophin (PTN) is a major factor in the malignant progression of breast cancer. This hypothesis is based on the growth-stimulatory effects of PTN on cells in vitro and in vivo and on its high levels of expression in 60% of tumor samples from breast cancer patients. The stimulation of proliferation and tube formation of endothelial cells by PTN suggests that it can serve as an angiogenesis factor during tumor growth. We hypothesize that PTN has the potential to support growth of breast cancer at its primary site and to enhance the ability of tumor cells to metastasize. Furthermore, we suggest that specific endocrine signals interact to regulate the expression of PTN in vitro and in vivo. Finally, we propose that understanding the functions of PTN and its hormonal regulation can lead to the development of novel therapeutic strategies for breast cancer.

Structure of the gene coding for the human retinoic acid-inducible factor, MK

The retinoic acid-inducible MK gene shows a distinct developmental pattern of expression, which implies that it has potential growth regulation and differentiation functions, particularly in the brain. We report here the cloning of the human MK gene from a phage library constructed from placental tissue. The structure of this gene has been determined using Southern hybridization and DNA sequence analysis. An isolated fragment was cloned and found to contain sequences identical to those of a previously isolated human MK cDNA clone, MKHC4. The gene contains three introns within the MK coding region as well as additional sequence, which indicates the presence of an intron prior to the putative protein start site. As judged by sequence analysis of cDNA clones, primer extension studies, and Northern analysis, the most abundant human MK message corresponds to the major mRNA of the previously described mouse gene. Primer extension studies and cDNA sequence data suggest that minor messages may be transcribed from the human gene, but no evidence of additional messages has been found by Northern analysis. This is in contrast to the mouse MK gene, from which three mRNAs are transcribed. Nevertheless, the similarity in the overall genomic structure of the human and mouse genes is striking.

Expression of the HBNF (heparin-binding neurite-promoting factor) gene in the brain of fetal, neonatal and adult rat: an in situ hybridization study

HBNF (heparin-binding neurite-promoting factor) and MK (midkine) are members of a newly recognized family of proteins, the expression of which is developmentally regulated. These proteins are expressed highest during fetal development in many tissues but they seem to be rather restricted to the brain in adult animals. Gene expression for these proteins is inducible by retinoic acid in embryonal carcinoma cell lines. They induce neurite outgrowth in cultured neurons, and they are characterized by high sequence conservation between species. While the function(s) of these proteins are unknown, available evidence suggests possible roles in the development and the maintenance of neural tissues. This in situ hybridization study investigates the temporal and spatial expression pattern of the HBNF gene in the brain of developing rats. The HBNF gene is highly expressed in the neuroepithelium and the ependyma from fetal day 15 on. Although most ependymal structures express the gene strongly, a few restricted areas of the ependyma do not express HBNF (ventral part of the fourth ventricle, subcommissural organ). In the brain parenchyma, HBNF is expressed in the thalamo-hippocampal area from fetal day 15 and in the cerebral cortex from fetal day 16, with high expression occurring in the superficial layers of the cortex. The nature of the cells expressing the gene, while difficult to ascertain, is probably glial for the most part. However, certain neurons (in limited areas of the brain parenchyma) and most pial cells (in the meninges), also express the gene. HBNF gene expression decreases sharply a few days after birth. HBNF mRNA is also detectable at fetal days 15 and 16 in the face fetal mesenchyma. In the adult rat brain, the expression of the HBNF gene appears to be restricted to neurons of the hippocampus and of the olfactory bulb and to the superficial layers of the cortex. The structurally related MK gene, though not extensively studied here, shows an entirely different temporal and spatial expression pattern. MK gene is weakly expressed during ontogeny in most brain areas, and in the adult animal, MK mRNA is present only in the choroid plexus. The intense and widely distributed expression of the HBNF gene in several cell populations in the fetus, the progressive spatial and quantitative restriction of HBNF gene expression with brain differentiation, as well as the properties of the protein suggest important and diverse functions for HBNF in cellular interactions and cell differentiation in the developing brain, that must act temporally and spatially by ways distinct from its MK companion molecule.

Cloning, nucleotide sequence, and chromosome localization of the human pleiotrophin gene

Pleiotrophin (PTN), midkine (MK), and retinoic acid-induced heparin-binding (RI-HB) protein are members of a recently discovered family of developmentally regulated cytokines. We report here the cloning, sequencing, chromosomal localization, and structural organization of the genomic version of the human PTN gene and its comparison to the mouse MK gene. The PTN gene was found to be arranged in five exons and four introns, in a fashion similar to that of the mouse MK gene. Exon 1, as for MK, does not appear to encode amino acid sequence. As in the case of the MK gene, exon 2 encodes the hydrophobic leader sequence of PTN, which constitutes the beginning of gene translation. The signal peptide cleavage site of both genes lies toward the 3' end of exon 2. Exons 3 and 4 of PTN were most closely related to exons 3 and 4 of the MK gene; in particular, six of the ten cysteine residues were coded for in exon 3 and the remaining 4 in exon 4. The intron-exon splice junctions of both genes occurred through the same residues. The two genes were found to be less closely related in the fifth exon which encodes the highly basic C-terminal domains, the translation termination codon, and the polyadenylation signal of both cDNAs. We also report approximately 2000 bp of the 5' untranslated sequence of the PTN gene and the site of initiation of transcription in human placenta. PTN was localized to human chromosome 7q33-34 by fluorescence in situ hybridization. These data confirm the existence of a new gene family of developmentally regulated cytokines.

Genomic organization of the mouse OSF-1 gene

The mouse OSF-1 protein (also known as pleiotrophin, HB-GAM, HBGF-8, or HBNF) gene was isolated from a mouse genomic library and sequenced. OSF-1 is a 15-kD secreted protein specifically expressed in bone and brain, and is believed to play a role in brain development and osteogenesis. The mouse OSF-1 gene consists of at least 5 exons and 4 introns and spans > 32 kb. Computer analysis of approximately 4 kb of 5'-flanking sequence of the OSF-1 gene revealed two candidate promoter regions. One candidate promoter contains a thyroid hormone/retinoic acid-responsive element and the other contains two glucocorticoid-responsive elements. DNA sequence analysis of novel OSF-1 cDNA clones indicates that two promoters can be utilized in MC3T3-E1 osteoblastic cells. The overall organization of the mouse OSF-1 gene is similar and the locations of the three exon-intron junctions within the coding region are identical to the mouse gene encoding the differentiation-related factor midkine (MK). Based on this similarity and on the high degree of nucleotide sequence homology (approximately 55%) of mouse OSF-1 and mouse MK, we conclude that OSF-1 and MK are generated from a common ancestral gene and are members of a family of structurally and probably functionally related proteins.

Growth factors in the uterus: steroidal regulation and biological actions

Rapid progress has been made within the last 5-6 years in characterizing polypeptide growth factors in uterine tissues and fluids. There is convincing evidence that their synthesis and/or secretion is regulated by steroid hormones. The possibility that these growth factors play a central role in growth and development of the uterus or placenta is suggested by the presence of their receptors on uterine or placental cells and their stimulatory effects on these cells in vitro. Since growth factors interact synergistically and also have non-mitogenic functions, the presence of a variety of these factors in the uterus suggests that they probably regulate various aspects of uterine function through complex autocrine and paracine pathways. However, experimental models need to be designed that will permit a more detailed analysis of the actual role of these factors in utero. Fruitful approaches may be to administer neutralizing antibodies or blocking peptides so as to antagonize uterine growth factor action, or to develop appropriate transgenic animals. These and other lines of study should help us to understand the role of growth factors in development of the immature uterus, growth of the placenta or gravid uterus, repair and angiogenesis of the endometrium, and uterine pathology.

Molecular cloning of RI-HB, a heparin binding protein regulated by retinoic acid

RI-HB is an extracellular heparin binding protein regulated by retinoic acid and essentially expressed during embryogenesis. This study reports the cloning and sequencing of the cDNA that encodes RI-HB. The sequence of RI-HB contains 121 amino acid residues and is very rich in basic amino acids and cysteines. This sequence was compared to those of HBGAM and MK protein, two other heparin binding proteins exhibiting growth and/or neurotrophic activities. Northern blot analysis indicates that RI-HB mRNA is strongly expressed during early chicken embryogenesis and that it is induced by retinoic acid treatment of chicken fibroblasts and myotubes in culture.

A new heparin binding protein regulated by retinoic acid from chick embryo

A 19 KDa heparin binding protein was previously purified from chicken embryos. Essentially localized within basement membranes in early embryonic tissues, this protein is very rich in basic and cystein residues. Its N-terminal fragment is similar to corresponding fragment of two other proteins expressed during embryogenesis and postnatal period. Its synthesis and secretion are induced by retinoic acid in chicken myoblasts and fibroblasts. This new retinoic acid induced heparin binding protein (RI-HB) does stimulate neurite outgrowth and proliferation on PC12 cells. These results suggest that retinoic acid could regulate some aspect of differentiation and development by inducing the synthesis of a new family of growth and neurotrophic factors.

Isolation from bovine brain and structural characterization of HBNF, a heparin-binding neurotrophic factor

A heparin-binding protein with neurotrophic activity for perinatal rat neurons, termed HBNF, was purified to homogeneity from bovine brain utilizing pH 4.5 extraction, ammonium sulfate precipitation, cation exchange and heparin-Sepharose affinity chromatographies, and reverse phase HPLC. In the presence of protease inhibitors during extraction, a protein with an apparent molecular weight of 18 kDa was obtained in a yield of approximately 0.5 mg/kg brain tissue. The amino acid sequence of the first 114 residues of HBNF was determined and found to highly homologous to the cDNA-derived amino acid sequence of human HBNF, a 136-residue protein. Bovine and human HBNFs have identical molecular weights as judged by SDS gel electrophoresis and very similar amino acid compositions. This and overall sequence conservation suggest that bovine HBNF is also a 136 amino acid protein with a calculated molecular weight of approximately 15.5 kDa. The apparent discrepancy between calculated and observed molecular weights of bovine HBNF (and of human HBNF of which the complete sequence is known) is most likely a result of the highly basic nature of HBNF. If protease inhibitors were omitted during tissue extraction, two additional proteins with lower apparent molecular weights and identical N-terminal sequences were isolated, with the smallest forms being the major product. Amino acid analysis showed that the smaller forms correspond to C-terminally truncated HBNFs with calculated molecular weights of 13.6 and 12.4 kDa, lacking approximately 14 and 22 residues. Comparison of the HBNF protein sequence with sequences stored in the Protein Identification Resource/Genbank databases reveals high homology to the translation product of the MK-1 gene, which is retinoic acid-inducible in embryonic carcinoma cells and developmentally expressed during gestation in mice.

HBNF and MK, members of a novel gene family of heparin-binding proteins with potential roles in embryogenesis and brain function

HBNF (heparin-binding neurite-promoting factor) is a heparin-binding protein which is found primarily in the brain and stimulates neurite outgrowth in cultured perinatal neurons. It was also reported to be mitogenic for fibroblasts and endothelial cells but this activity is still controversial. The sequence of HBNF is highly conserved in diverse species suggesting important function. Expression of the HBNF gene in brain tissue appears to be developmentally regulated, increasing during gestation to highest levels around the time of birth. The HBNF gene shows high sequence homology to another gene, MK (midkine). Like HBNF, the MK gene is developmentally regulated, however, high expression occurs in most fetal tissues during mid-gestation. The biological properties of the MK protein are remarkably similar to those of HBNF. The available evidence suggests that HBNF and MK are members of a new family of genes with potential roles in fetal development and in brain function or maintenance.

Cloning, characterization and developmental regulation of two members of a novel human gene family of neurite outgrowth-promoting proteins

This report describes the cloning, expression and characterization of two members of a novel human gene family of proteins, HBNF and MK, which exhibit neurite outgrowth-promoting activity. The HBNF cDNA gene codes for a 168-residue protein which is a precursor for a previously described brain-derived heparin-binding protein of 136 amino acids. The second human gene identified in this study, called MK, codes for a 143-residue protein (including a 22-amino acid signal sequence) which is 46% homologous with HBNF. Complementary DNA constructs coding for the mature HBNF and MK proteins were expressed in bacteria and purified by heparin affinity chromatography. These recombinant proteins exhibited neurite-outgrowth promoting activity, but lacked mitogenic activity. The HBNF gene is expressed in the brain of adult mice and rats, but only minimal expression of MK was observed in this tissue. Different patterns of developmental expression were observed in the embryonic mouse, with MK expression peaking in the brain between days E12 and E14 and diminishing to minimal levels in the adult, while expression of HBNF mRNA was observed to gradually increase during embryogenesis, reaching a maximal level at birth and maintaining this level into adulthood. Expression of these genes was also observed in the human embryonal carcinoma cell line, NT2/D1. Retinoic acid induced the expression of HBNF and MK 6- and 11-fold, respectively, in this cell line. Our studies indicate that HBNF and MK are members of a new family of highly conserved, developmentally regulated genes that may play a role in nervous tissue development and/or maintenance.

A method for the unambiguous identification of tryptophan in automated protein sequence analysis

Some widely used standard protocols for the separation of phenylthiohydantoin amino acid derivatives by reverse-phase gradient HPLC do not provide separation of the phenylthiohydantoin derivative of tryptophan (PTH-Trp) from diphenylurea (DPU), a by-product generated during Edman degradation of proteins in variable amounts. Furthermore, PTH-Trp is usually recovered in low yield under typical experimental conditions used with automated sequencing equipment. These factors may compromise the unambiguous assignment of tryptophan residues in automated protein sequence analysis, especially when sequencing is performed at high sensitivity. We devised a reverse-phase HPLC method which allows the separation of DPU and PTH-Trp and therefore the correct assignment of PTH-Trp. The method is based on a modification of the HPLC gradient used to elute and separate all PTH amino acids of interest. With Applied Biosystems Model 477A protein sequencers with on-line PTH amino acid identification, the correct assignment of tryptophan was consistent and reproducible even when sequencing at very high sensitivity (5 pmol).

Heparin-binding neurotrophic factor (HBNF) and MK, members of a new family of homologous, developmentally regulated proteins

A partial rat cDNA clone coding for a novel neurotrophic factor HBNF was isolated. Nucleotide sequence determination, in combination with the known N-terminal sequence of rat HBNF, allowed deduction of the amino acid sequence of the first 102 residues of mature rat HBNF. HBNF shares high structural homology (55%) with the MK protein (Tomomura et al., J. Biol. Chem. 265, 10765, 1990). Complete alignment of 9 cysteine residues suggests further that the two proteins have similar 3-dimensional structures. HBNF was reported to stimulate neurite outgrowth in neurons and to be expressed in a developmentally regulated manner in the rat brain. MK mRNA was found in retinoid acid-induced teratocarcinoma cells and during early development of the mouse embryo, but no biological activity for MK is yet known. These data suggest that HBNF and MK are members of a novel family of structurally and probably functionally related proteins.