C/EBP is an essential component of PDGFRA transcription in MG-63 cells

AKT1-CREB stimulation of PDGFRα expression is pivotal for PTEN deficient tumor development

As evidenced by the behavior of loss-of-function mutants of PTEN in the context of a gain-of-function mutation of AKT1, the PTEN-AKT1 signaling pathway plays a critical role in human cancers. In this study, we demonstrated that a deficiency in PTEN or activation of AKT1 potentiated the expression of platelet-derived growth factor receptor α (PDGFRα) based on studies on Pten-/- mouse embryonic fibroblasts, human cancer cell lines, the hepatic tissues of Pten conditional knockout mice, and human cancer tissues. Loss of PTEN enhanced PDGFRα expression via activation of the AKT1-CREB signaling cascade. CREB transactivated PDGFRα expression by direct binding of the promoter of the PDGFRα gene. Depletion of PDGFRα attenuated the tumorigenicity of Pten-null cells in nude mice. Moreover, the PI3K-AKT signaling pathway has been shown to positively correlate with PDGFRα expression in multiple cancers. Augmented PDGFRα was associated with poor survival of cancer patients. Lastly, combination treatment with the AKT inhibitor MK-2206 and the PDGFR inhibitor CP-673451 displayed synergistic anti-tumor effects. Therefore, activation of the AKT1-CREB-PDGFRα signaling pathway contributes to the tumor growth induced by PTEN deficiency and should be targeted for cancer treatment.

Novel guanidine compounds inhibit platelet-derived growth factor receptor alpha transcription and oligodendrocyte precursor cell proliferation

Oligodendrocyte precursor cells (OPCs), also known as NG2 cells or polydendrocytes, are distributed widely throughout the developing and mature central nervous system. They remain proliferative throughout life and are an important source of myelinating cells in normal and demyelinating brain as well as a source of glioma, the most common type of primary brain tumor with a poor prognosis. OPC proliferation is dependent on signaling mediated by platelet-derived growth factor (PDGF) AA binding to its alpha receptor (PDGFRα). Here, we describe a group of structurally related compounds characterized by the presence of a basic guanidine group appended to an aromatic core that is effective in specifically repressing the transcription of Pdgfra but not the related beta receptor (Pdgfrb) in OPCs. These compounds specifically and dramatically reduced proliferation of OPCs but not that of astrocytes and did not affect signal transduction by PDGFRα. These findings suggest that the compounds could be further developed for potential use in combinatorial treatment strategies for neoplasms with dysregulated PDGFRα function.

Phf14, a novel regulator of mesenchyme growth via platelet-derived growth factor (PDGF) receptor-α

The regulation of mesenchymal cell growth by signaling molecules plays an important role in maintaining tissue functions. Aberrant mesenchymal cell proliferation caused by disruption of this regulatory process leads to pathogenetic events such as fibrosis. In the current study we have identified a novel nuclear factor, Phf14, which controls the proliferation of mesenchymal cells by regulating PDGFRα expression. Phf14-null mice died just after birth due to respiratory failure. Histological analyses of the lungs of these mice showed interstitial hyperplasia with an increased number of PDGFRα(+) mesenchymal cells. PDGFRα expression was elevated in Phf14-null mesenchymal fibroblasts, resulting in increased proliferation. We demonstrated that Phf14 acts as a transcription factor that directly represses PDGFRα expression. Based on these results, we used an antibody against PDGFRα to successfully treat mouse lung fibrosis. This study shows that Phf14 acts as a negative regulator of PDGFRα expression in mesenchymal cells undergoing normal and abnormal proliferation, and is a potential target for new treatments of lung fibrosis.

Interaction of PDGFRA promoter haplotypes and maternal environmental exposures in the risk of spina bifida

BACKGROUND

Neural tube defects are multifactorial malformations involving both environmental exposures, such as maternal nutrition, and genetic factors. Aberrant expression of the platelet-derived growth factor alpha-receptor (PDGFRA) gene has been implicated in neural-tube-defect etiology in both mice and humans.

METHODS

We investigated possible interactions between the PDGFRA promoter haplotype of mother and child, as well as maternal glucose, myo-inositol, and zinc levels, in relation to spina bifida offspring. Distributions were determined of the PDGFRA promoter haplotypes H1 and H2 in a Dutch cohort, consisting of 88 spina bifida children with 56 of their mothers, and 74 control children with 72 of their mothers, as well as maternal plasma glucose, myo-inositol, and red blood cell zinc concentrations.

RESULTS

A significantly higher frequency of H1 was observed in children with spina bifida than in controls (30.1 vs. 20.3%; OR = 1.69, 95% CI 1.02-2.83). High maternal body mass index (BMI) and glucose were significant risk factors for both H1 and H2 children, whereas low myo-inositol and zinc were risk factors for H2 but not for H1 children. Stepwise multiple logistic regression analysis showed that high maternal glucose and low myo-inositol are the main risk factors for H2 spina bifida children, whereas for H1 spina bifida children, maternal BMI was the main risk factor. Interestingly, H1 mothers (median 165.5 cm) showed a significantly lower body height than H2 mothers (median 169.1 cm; p = 0.003).

CONCLUSIONS

These data suggest that the child's PDGFRA promoter haplotype is differentially sensitive for periconceptional exposure to glucose, myo-inositol, and zinc in the risk of spina bifida.

Recombinant human platelet-derived growth factor: biology and clinical applications

The abilities of bone to remodel, fractures to repair, and bone grafts to incorporate are all fundamental reflections of the bone remodeling cycle. This process is characterized by the recruitment and differentiation of osteoblastic and osteoclastic cell populations, whose cellular activities are coordinated and regulated by an elaborate system of growth factors and cytokines. One of the crucial biological factors responsible for reparative osseous activity is platelet-derived growth factor (PDGF). The potent stimulatory effects of PDGF as a chemoattractant and mitogen for mesenchymal cells (including osteogenic cells), along with its ability to promote angiogenesis, have been demonstrated in a variety of preclinical models predicting maxillofacial, spine and appendicular skeletal, and soft-tissue applications. The biological profile of PDGF, including its ability to recruit osteoprogenitor cells, makes it particularly suited to address the skeletal defects that are seen with comorbid conditions such as osteoporosis, diabetes, and the effects of smoking. The clinical success and safety that have been demonstrated with use of recombinant human PDGF (rhPDGF) in the repair of periodontal defects have led to U.S. Food and Drug Administration (FDA) approval of rhPDGF for this indication. Ongoing pilot and pivotal trials in the United States and internationally will continue to clarify the promising role of PDGF in the treatment of challenging skeletal disorders.

Angiogenic factors FGF2 and PDGF-BB synergistically promote murine tumor neovascularization and metastasis

Tumors produce multiple growth factors, but little is known about the interplay between various angiogenic factors in promoting tumor angiogenesis, growth, and metastasis. Here we show that 2 angiogenic factors frequently upregulated in tumors, PDGF-BB and FGF2, synergistically promote tumor angiogenesis and pulmonary metastasis. Simultaneous overexpression of PDGF-BB and FGF2 in murine fibrosarcomas led to the formation of high-density primitive vascular plexuses, which were poorly coated with pericytes and VSMCs. Surprisingly, overexpression of PDGF-BB alone in tumor cells resulted in dissociation of VSMCs from tumor vessels and decreased recruitment of pericytes. In the absence of FGF2, capillary ECs lacked response to PDGF-BB. However, FGF2 triggers PDGFR-alpha and -beta expression at the transcriptional level in ECs, which acquire hyperresponsiveness to PDGF-BB. Similarly, PDGF-BB-treated VSMCs become responsive to FGF2 stimulation via upregulation of FGF receptor 1 (FGFR1) promoter activity. These findings demonstrate that PDGF-BB and FGF2 reciprocally increase their EC and mural cell responses, leading to disorganized neovascularization and metastasis. Our data suggest that intervention of this non-VEGF reciprocal interaction loop for the tumor vasculature could be an important therapeutic target for the treatment of cancer and metastasis.

IFNgamma regulates PDGF-receptor alpha expression in macrophages, THP-1 cells, and arterial smooth muscle cells

The recruitment of monocyte-derived macrophages (MDMs) and arterial smooth muscle cells (ASMCs) contributes to inflammation and development of intimal hyperplasia during atherosclerosis. Platelet-derived growth factor (PDGF) is a potent mitogen for SMC, signalling through PDGF-receptor subunits alpha (Ralpha) and beta (Rbeta). We have previously found that interferon gamma (IFNgamma) upregulates PDGF-Ralpha mRNA expression in human MDM (hMDM) which causes an increased migration towards PDGF. In the present study, we found that IFNgamma mediated an upregulation of PDGF-Ralpha mRNA also in THP-1 cells. The induction of PDGF-Ralpha in both hMDM and THP-1 cells was caused by STAT1 binding to the PDGF-Ralpha promoter. In human ASMCs, IFNgamma again stimulated a transient STAT1-binding to the PDGF-Ralpha promoter. However, this was not followed by an upregulation of PDGF-Ralpha mRNA. IFNgamma-stimulation resulted in augmented expression of PDGF-Ralpha protein in differentiated hMDM. Early hMDM only expressed an immature and not fully glycosylated form of the PDGF-Ralpha protein. In contrast, THP-1 cells did not synthesize PDGF-Ralpha protein, implying further posttranscriptional inhibition. Our results contribute to a better understanding of the complex regulation of PDGF-Ralpha expression and how proinflammatory factors may contribute to PDGF-related hyperplasia in vascular diseases.

A PDGFRA promoter polymorphism, which disrupts the binding of ZNF148, is associated with primitive neuroectodermal tumours and ependymomas

BACKGROUND

Platelet derived growth factor receptor alpha (PDGFRalpha) expression is typical for a variety of brain tumours, while in normal adult brain PDGFRalpha expression is limited to a small number of neural progenitor cells. The molecular mechanisms responsible for the PDGFRalpha expression in tumours are not known, but in the absence of amplification, changes in transcriptional regulation might be an important factor in this process.

METHODS AND RESULTS

We have investigated the link between single nucleotide polymorphisms (SNPs) within the PDGFRalpha gene promoter and the occurrence of brain tumours (medulloblastomas, supratentorial primitive neuroectodermal tumours (PNETs), ependymal tumours, astrocytomas, oligodendrogliomas, and mixed gliomas). These SNPs give rise to five different promoter haplotypes named H1 and H2alpha-delta. It is apparent from the haplotype frequency distribution that both PNET (10-fold) and ependymoma (6.5-fold) patient groups display a significant over-representation of the H2delta haplotype. The precise functional role in PDGFRalpha gene transcription for the H2delta haplotype is not known yet, but we can show that the H2delta haplotype specifically disrupts binding of the transcription factor ZNF148 as compared to the other promoter haplotypes.

CONCLUSIONS

The specific over-representation of the H2delta haplotype in both patients with PNETs and ependymomas suggests a functional role for the ZNF148/PDGFRalpha pathway in the pathogenesis of these tumours.