Identification of a novel platelet-derived growth factor-like gene, fallotein, in the human reproductive tract

Role of platelet-derived growth factors in the testis

Normal development and function of the testis are controlled by endocrine and paracrine signaling pathways. Platelet-derived growth factors (PDGFs) are growth factors that mediate epithelial-mesenchymal interactions in various tissues during normal and abnormal processes such as embryo development, wound healing, tissue fibrosis, vascular disorders, and cancer. PDGFs and their receptors (PDGFRs) have emerged as key players in the regulation of embryonic and postnatal development of the male gonad. Cells that express PDGFs and PDGFRs are found in the testis of mammals, birds, and reptiles, and their distribution, regulation, and function vary across species. Testicular PDGFs and PDGFRs appear after the process of sex determination in animals that use either genetic sex determination or environmental sex determination. Sertoli cells are the main PDGF-producing cells during the entire period of prenatal and postnatal testis development. Fetal Leydig cells and their precursors, adult Leydig cells and their stem cell precursors, peritubular myoid cells, cells of the blood vessels, and gonocytes are the testicular cell types expressing PDGFRs. Genetically targeted deletions of PDGFs, PDGFRs, PDGFR target genes or pharmacological silencing of PDGF signaling produce profound damage on the target cells that, depending on the developmental period, are under direct or indirect control of PDGF. PDGF signaling may also serve diverse functions outside of the realm of testis development, including testicular tumors. In this review, we provide a framework of the current knowledge to clarify the useful information regarding how PDGFs function in individual cells of the testis.

Increased expression of platelet-derived growth factor C messenger ribonucleic acid in uterine leiomyomata

This study was intended to investigate the possible roles of the platelet-derived growth factor (PDGF) gene family's involvement in the pathogenesis of uterine leiomyomata. We examined the differential gene expressions of PDGF-A, -B, -C, -D, PDGF receptor alpha (PDGFR-alpha), and receptor beta (PDGFR-beta) between uterine leiomyomata and the adjacent normal myometrium. Expression of PDGF-C in leiomyomata was significantly higher (approximately 2.4-fold) than in the adjacent normal myometrium, whereas there were no significant differences in the expressions of PDGF-A, -B, -D, PDGFR-alpha, or PDGFR-beta between leiomyomata and the adjacent myometrial tissues.

Granulocyte-macrophage colony stimulating factor (GM-CSF) and co-culture can affect post-thaw development and apoptosis in cryopreserved embryos

PURPOSE

The objective of this study was to evaluate the effects of growth factor supplementation and Vero cell co-culture on apoptosis and development of frozen thawed one-cell mouse embryos.

METHODS

The following treatment regimens were assessed: (a) control medium (b) Vero cell co-culture and (c) growth factor supplemented medium. The individual growth factors tested were: GM-CSF, IGF-I, IGF-II, TNF-alpha, FGF-4, LIF, TGF-alpha, TGF-beta, IL-6, PDGF and EGF. Blastocyst development and differentiation were monitored. At termination of the experiments, overall blastomere number and apoptosis were assessed using the TUNEL assay.

RESULTS

No differences were observed in blastulation and hatching rates. ICM differentiation in thawed embryos was notably improved with either co-culture or growth factor supplementation. The only growth factor significantly modulating apoptosis in thawed embryos was granulocyte-macrophage colony stimulating factor (GM-CSF). GM-CSF enhanced continued cell survival and prevented apoptosis but did not influence overall cell number in developing blastocysts. Vero cell co-culture significantly increased cell number in blastocysts (124+/-42 vs 100+/-44 in control; P<0.05). Embryonic apoptosis was higher in the co-cultured embryos. The increased presence of apoptotic cells in blastocysts of high cell number may reflect the regulatory role of apoptosis in balancing ICM: TE ratios.

CONCLUSION

These data indicate that culture conditions can modulate post-thaw embryonic development and apoptosis.

Nuclear localisation of endogenous SUMO-1-modified PDGF-C in human thyroid tissue and cell lines

We investigated post-translational modification and subcellular localisation of endogenous platelet-derived growth factor-C (PDGF-C) in human thyroid papillary carcinomas (PTC), non-neoplastic thyroid tissues, and a selection of cultured cell lines. PDGF-C expressed nuclear localisation in 95% of all tested cell types in culture and in 10% of the thyrocytes from both PTC and non-neoplastic tissue. The cell lines expressed two forms of full-length PDGF-C, approximately 39 and approximately 55 kDa, in cell membrane and cytosol, while the approximately 55 kDa form dominated in the nucleus where it was partly chromatin-associated. The approximately 55 kDa form was post-translationally modified by SUMO-1. The putative PDGF-C SUMOylation site is the surface exposed (314)lysine part of a positively charged loop ((312)RPKTGVRGLHK(322)) with characteristics of a nuclear localisation signal. The tissue thyrocytes expressed a non-SUMOylated approximately 43 kDa and the 55 kDa PDGF-C. The SUMO-1 modified approximately 55 kDa PDGF-C expression was low in PTC where the approximately 43 kDa PDGF-C dominated. This is in contrast to non-neoplastic tissue and cultured cells where the SUMOylated approximately 55 kDa PDGF-C was strongly expressed. Our data provide novel evidence for nuclear localisation of PDGF-C, post-translational modification by SUMOylation and the expression of a novel form of PDGF-C in human papillary thyroid carcinomas.

Structural and functional specificities of PDGF-C and PDGF-D, the novel members of the platelet-derived growth factors family

The platelet-derived growth factor (PDGF) family was for more than 25 years assumed to consist of only PDGF-A and -B. The discovery of the novel family members PDGF-C and PDGF-D triggered a search for novel activities and complementary fine tuning between the members of this family of growth factors. Since the expansion of the PDGF family, more than 60 publications on the novel PDGF-C and PDGF-D have been presented, highlighting similarities and differences to the classical PDGFs. In this paper we review the published data on the PDGF family covering structural (gene and protein) similarities and differences among all four family members, with special focus on PDGF-C and PDGF-D expression and functions. Little information on the protein structures of PDGF-C and -D is currently available, but the PDGF-C protein may be structurally more similar to VEGF-A than to PDGF-B. PDGF-C contributes to normal development of the heart, ear, central nervous system (CNS), and kidney, while PDGF-D is active in the development of the kidney, eye and brain. In adults, PDGF-C is active in the kidney and the central nervous system. PDGF-D also plays a role in the lung and in periodontal mineralization. PDGF-C is expressed in Ewing family sarcoma and PDGF-D is linked to lung, prostate and ovarian cancers. Both PDGF-C and -D play a role in progressive renal disease, glioblastoma/medulloblastoma and fibrosis in several organs.

Elevated expression of PDGF-C in coxsackievirus B3-induced chronic myocarditis

AIMS

Coxsackievirus B3 (CVB3) is a frequent cause of human chronic myocarditis and subsequent fibrosis, leading to dilated cardiomyopathy. The molecular processes underlying the development of fibrosis are poorly understood. Enhanced levels of platelet-derived growth factors (PDGFs), especially PDGF-C, have recently been linked with the development of different forms of fibrosis. Therefore, the expression of PDGF was analysed in hearts of CVB3-infected major histocompatability complex class II knockout mice. The latter were recently established as mouse model mimicking the chronic inflammation and fibrosis characteristic for this disease.

METHODS AND RESULTS

Expression of PDGF was analysed by reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemistry. Hearts of C57BL/6 mice served as controls because infection of these animals leads to acute cardiac inflammation, but the hearts heal without signs of chronic inflammation. In uninfected hearts, basal expression of PDGF, notably PDGF-C, was detectable throughout the heart. The chronic inflammatory process was associated with elevated and sustained expression of all tested PDGF isoforms. Immunostaining and in situ hybridization analysis localized enhanced PDGF levels to areas with highest virus load and inflammatory infiltrations, adjacent to fibrotic areas.

CONCLUSION

PDGF may participate in fibrosis development in CVB3-induced myocarditis. Therefore, PDGF signalling may be considered a target for therapeutic interference.

Platelet-derived growth factor D, tissue-specific expression in the eye, and a key role in control of lens epithelial cell proliferation

Platelet-derived growth factor D (PDGF-D), also known as Iris-expressed growth factor, is a member of the PDGF/vascular endothelial growth factor family. The expression of PDGF-D in the eye is tissue-specific. In the anterior segment, it is localized to iris and ciliary body, whereas in the retina, PDGF-D is restricted to the outer plexiform layer. PDGF-D is present in aqueous humor but is not detectable in mature lens or in mouse lens-derived alphaTN4-1 cells. However, it is expressed in rabbit lens-derived N/N1003A cells. N/N1003A cell-conditioned medium stimulates proliferation in rat lens explants, and this is blocked by immunodepletion of PDGF-D. Immunopurified PDGF-D also stimulates cell proliferation in rat lens explants and in NIH 3T3 cells. In organ culture of rat eye anterior segments, anti-PDGF-D strongly inhibits lens epithelial cell proliferation. This finding suggests a major in vivo role for PDGF-D in the mechanisms of coordinated growth of eye tissues. Intervention in the PDGF-D pathway in the eye, perhaps by antibody or blocking peptide, could be useful in the treatment of certain cataracts, including post-operative secondary cataract.

Novel PDGF family members: PDGF-C and PDGF-D

Platelet-derived growth factors (PDGFs) were discovered almost two decades ago. The classical PDGF polypeptide chains, PDGF-A and PDGF-B, are well studied and they regulate a number of physiological and pathophysiological processes in many types of mesenchymal cells via two receptor tyrosine kinases, PDGF receptors alpha and beta. Recently, two additional PDGF polypeptide chains were discovered, namely PDGF-C and PDGF-D. The discovery of two additional ligands for the two PDGF receptors suggests that PDGF-mediated signaling is more complex than previously anticipated.

The gene expression profiling of human visceral adipose tissue and its secretory functions

In order to fully understand the physiological functions of adipose tissue, especially its secretory functions, and to provide a basis for the identification of novel obesity related genes, the gene expression profiling of human visceral adipose tissue was established by using cDNA array. 33P-labelled cDNA, derived from visceral adipose tissue total RNA, was hybridized to a cDNA array containing over 16,000 expressed sequence-tagged clones which represent human singleton genes. The expressed sequence tag (EST) was considered to be expressed in visceral adipose tissue when the ratio of signal to noise was greater than or equal to 2. The results were analyzed with bioinformatics. Totally, 8230 genes were found to be expressed in visceral adipose tissue with 5200 known genes and 3030 known ESTs. Most of 84 secretory proteins, 120 receptors, and 74 transcription factors expressed in adipose tissue were newly identified. Many appetite-regulating related peptides or receptors and some reproduction-related genes were first found to be expressed in adipose tissue. Eight autocrine/paracrine systems were described for the first time in the visceral adipose tissue. These results clearly demonstrate that the visceral adipose tissue has important secretory functions and there is a complex local autocrine/paracrine regulatory network. The present work suggests that the visceral adipose tissue is an important component of the neuroendocrine-immune network and plays an important role in regulating appetite not only via endocrine but also via autocrine/paracrine systems. The visceral adipose tissue might also play a role in regulating reproduction and sexual function.

The expression of SCDGF/PDGF-C/fallotein and SCDGF-B/PDGF-D in the rat central nervous system

We examined the expression patterns of the two homologous genes, spinal cord-derived growth factor (SCDGF)/platelet-derived growth factor (PDGF)-C/fallotein and SCDGF-B/PDGF-D in the rat central nervous system. In the spinal cord, SCDGF/PDGF-C/fallotein was expressed in the floor plate at embryonic day (E) 11 and also in the ventricular zone at E16 but not in adult. However, SCDGF-B/PDGF-D was prominently expressed in the adult motoneurons, although faint expression was observed in the ventral ventricular zone at E16. Also in the brain, the expression of SCDGF/PDGF-C/fallotein was more remarkable at E16 than at adult. It was highly expressed in the cortex, pontine area and choroid plexus at E16. Contrary to SCDGF/PDGF-C/fallotein, SCDGF-B/PDGF-D expression was notable in several nuclei at adult.

PDGF and the testis

Testicular development is controlled by a complex hierarchy of gene regulatory proteins, growth factors, cell adhesion molecules, signaling molecules and hormones that interact, often acting within short time windows, via reciprocal control relationships. The identification in the testis of platelet-derived growth factor (PDGF), a key regulator of connective tissue cells in embryogenesis and pathogenesis, has focused attention on the role of this growth factor in testicular pathophysiology. This review summarizes recent advances in the study of the actions of PDGF in the male gonad, and attempts to incorporate complex in vitro and in vivo experimental data into a model that might clarify the role played by PDGF in the mammalian testis.

Developmental roles of platelet-derived growth factors

Platelet-derived growth factor (PDGF) was originally identified in platelets and in serum as a mitogen for fibroblasts, smooth muscle cells (SMC) and glia cells in culture. PDGF has since expanded to a family of dimers of at least four gene products, whose biological actions are mediated through two receptor tyrosine kinases, PDGFRs. The present review summarizes and discusses the biological functions of PDGFs and PDGFRs in developmental processes, mainly as revealed through genetic analysis in mice. Such studies have demonstrated multiple critical roles of PDGFs and PDGFRs in embryonic and postnatal development. PDGFs seem to act upon specific populations of progenitor cells that give rise to several different cell types with distinct functions in a variety of developmental processes. Analogies are seen between the cell functions and the developmental processes controlled by PDGFs. This suggests that ancestral PDGF and PDGFR expression patterns and functions may have been iterated in related sets of morphogenetic processes in the course of evolution.

Molecular cloning of SCDGF-B, a novel growth factor homologous to SCDGF/PDGF-C/fallotein

Spinal cord-derived growth factor (SCDGF)/platelet-derived growth factor (PDGF)-C/fallotein has a unique two-domain structure, as it contains two regions homologousto CUB and PDGF/vascular endothelial growth factor (VEGF) domains. In this study, we isolateda novel gene homologous to SCDGF/PDGF-C/fallotein, and named SCDGF-B. The culture supernatant of CHO-K1 cells stably transfected with SCDGF-B showed mitogenic activity as SCDGF/PDGF-C/fallotein did. Although SCDGF-B and SCDGF/PDGF-C/fallotein might be the members of the PDGF/VEGF superfamily of growth factors, they were categorized into a new subfamily in addition to PDGF and VEGF subfamilies.