Platelet-derived Growth Factor Receptor Expression Research Articles

The Effects of Trapidil on Fibroblastic Activity, Schwann Cell Proliferation, and Platelet-derived Growth Factor Receptor Levels in the Experimental Sciatic Nerve Injury

Background Trapidil, an antianginal drug with inhibitory effects on platelet-derived growth factor (PDGF), has been shown to reduce reactive fibrosis in models of central nervous system injury. Therefore, we evaluated trapidil's effects on fibroblast activity, Schwann cell proliferation, and PDGF receptor levels in rats after transection and anastomosis of the sciatic nerve. We also evaluated the effect of Schwann cell proliferation on regeneration of anastomosed sciatic nerves. Methods Wistar rats were randomly divided into 3 groups. Group 1 (N=10) was used to determine normal peripheral nerve morphology (via light and electron microscopy) and PDGF receptor levels. Group 2 (N=20) underwent sciatic nerve anastomosis after nerve transection to examine the influence of the surgical procedure on PDGF receptor levels and the microscopic findings. Group 3 (20 rats) received a single intraperitoneal dose of trapidil (40 mg/kg) immediately after the surgical procedure to investigate its effects on fibroblast activity, Schwann cell proliferation, and PDGF levels. Results PDGF-A and PDGF-B receptor levels were lower in group 3, the trapidil-treated group, than group 2 on all posttransection days examined. Ultrastructural analysis revealed that group 3 also had lower levels of fibroblast activity and Schwann cell proliferation than group 2. However, the peripheral nerve ultrastructure and degree of axonal regeneration were similar between groups 2 and 3 at 14 days posttransection. Conclusions Trapidil treatment significantly decreased reactive fibrosis and PDGF receptor expression after peripheral nerve injury, and thus, may be useful therapeutically. These results also suggest that Schwann cells alone are not effective in promoting neurite formation.

A Phase II Study of Imatinib Mesylate and Capecitabine in Metastatic Breast Cancer: Southwest Oncology Group Study 0338

Background Imatinib mesylate is a potent inhibitor of the Bcr-Abl, c-Kit, and platelet-derived growth factor receptor (PDGFR) tyrosine kinases. On the basis of variable expression of c-Kit and PDGFR in breast cancer and of in vitro data supporting synergy between imatinib and capecitabine, the Southwest Oncology Group conducted a phase II trial of the combination in metastatic breast cancer. Patients and Methods Eligible patients had progressive, measurable metastatic breast cancer and received ≤ 2 previous chemotherapy regimens for metastatic disease. Previous 5-fluorouracil or capecitabine for metastatic disease was not allowed. Patients were accrued on a 2-stage design and received imatinib mesylate 400 mg by mouth daily and capecitabine at 1000 mg/m 2 by mouth twice daily for 14 days of a 21-day cycle. The primary endpoint was the confirmed response rate (RR). Tumors were evaluated for c-Kit, PDGFR-β, and hormone receptor expression. Results Nineteen fully evaluable patients were enrolled, with a confirmed RR of 11% (95% CI, 1%-33%). Eleven percent had unconfirmed partial responses, and 42% had stable disease. The trial did not accrue to the second stage. The estimated 6-month progression-free survival was 16% (95% CI, 0%-32%), and the median overall survival was 14 months (95% CI, 7-15 months). The combination was well tolerated. Of 8 available tumor samples, 2 stained for c-Kit, and all had stromal staining for PDGFR-β. Conclusion In unselected patients, the combination of imatinib mesylate and capecitabine was well tolerated but did not result in improved RRs compared to those reported with capecitabine alone.

Breast Cancer Metastasis Suppressor-1 Differentially Modulates Growth Factor Signaling

That metastatic tumor cells grow in selective non-native environments suggests an ability to differentially respond to local microenvironments. BRMS1, like other metastasis suppressors, halts ectopic growth (metastasis) without blocking orthotopic tumor formation. BRMS1-expressing tumor cells reach secondary sites but do not colonize distant tissues, compelling the hypothesis that BRMS1 selectively restricts the ability of tumor cells to respond to exogenous regulators in different tissues. Here we report that BRMS1 expression in metastatic human breast cancer cells leads to a selective reduction in epidermal growth factor receptor expression and downstream (AKT) signaling. Signaling through another receptor tyrosine kinase, hepatocyte growth factor receptor (c-Met), remains unaltered despite reduced levels of the signaling intermediate phosphatidylinositol (4,5)-bisphosphate. Interestingly, reduced downstream calcium signaling is observed following treatment with platelet-derived growth factor, consistent with decreased phosphatidylinositol (4,5)-bisphosphate. However, platelet-derived growth factor receptor expression is unaltered. Thus, BRMS1 differentially attenuates cellular responses to mitogenic signals, not only dependent upon the specific signal received, but at varying steps within the same signaling cascade. Specific modulation of signaling responses received from the microenvironment may ultimately dictate which environments are permissive/restrictive for tumor cell growth and provide insights into the biology underlying metastasis.

Platelet-derived growth factor isoform expression in carbon tetrachloride-induced chronic liver injury

Platelet-derived growth factor (PDGF) has an essential role in liver fibrogenesis, as PDGF-B and -D both act as potent mitogens on culture-activated hepatic stellate cells (HSCs). Induction of PDGF receptor type-β (PDGFRβ) in HSC is well documented in single-dose carbon tetrachloride (CCl4)-induced acute liver injury. Of the newly discovered isoforms PDGF-C and -D, only PDGF-D shows significant upregulation in bile duct ligation (BDL) models. We have now investigated the expression of PDGF isoforms and receptors in chronic liver injury in vivo after long-term CCl4 treatment and demonstrated that isolated hepatocytes have the requisite PDGF signaling pathways, both in the naive state and when isolated from CCl4-treated rats. In vivo, PDGF gene expression showed upregulation of all PDGF isoforms and receptors, with values peaking at 4 weeks and decreasing to near basal levels by 8 and 12 weeks. Interestingly, PDGF-C increased significantly when compared to BDL-models. PDGF-A, PDGF-C and PDGF receptor type-α (PDGFRα) correlated closely with inflammation and steatosis. Immunohistochemistry revealed expression of PDGF-B, -C and -D in areas corresponding to centrilobular necrosis, inflammation and fibrosis, whereas PDGF-A localized in regenerative hepatocytes. PDGFRβ was identified along the fibrotic septa, whereas PDGFRα showed positive staining in fibrotic septa and regenerative hepatocytes. Despite a significant decline of PDGF isoforms, hepatocyte regeneration peaked at 8 weeks. A marked difference in the degree of fibrosis was observed amongst the individual animals. In summary, PDGF expression in liver damage primarily parallels mesenchymal cell proliferation and extracellular matrix production, rather than hepatocyte regeneration. We conclude that PDGF levels in chronic liver injury peak at 4 weeks after onset of injury, and that the outcome of chronic toxic liver injury strongly depends on the individual capacity for tissue regeneration in the weeks following the peak of PDGF expression.

C-reactive protein and vein graft disease: evidence for a direct effect on smooth muscle cell phenotype via modulation of PDGF receptor-β

Plasma C-reactive protein (CRP) concentration is a biomarker of systemic atherosclerosis and may also be associated with vein graft disease. It remains unclear whether CRP is also an important modulator of biological events in the vessel wall. We hypothesized that CRP influences vein graft healing by stimulating smooth muscle cells (SMCs) to undergo a phenotypic switch. Distribution of CRP was examined by immunohistochemistry in prebypass human saphenous veins (HSVs, n = 21) and failing vein grafts (n = 18, 25-4,400 days postoperatively). Quiescent HSV SMCs were stimulated with human CRP (5-50 microg/ml). SMC migration was assessed in modified Boyden chambers with platelet-derived growth factor (PDGF)-BB (5-10 ng/ml) as the chemoattractant. SMC viability and proliferation were assessed by trypan blue exclusion and reduction of Alamar Blue substrate, respectively. Expression of PDGF ligand and receptor (PDGFR) genes was examined at RNA and protein levels after 24-72 h of CRP exposure. CRP staining was present in 13 of 18 diseased vein grafts, where it localized to the deep media and adventitia, but it was minimally detectable in most prebypass veins. SMCs pretreated with CRP demonstrated a dose-dependent increase in migration to PDGF-BB (P = 0.02), which was inhibited by a PDGF-neutralizing antibody. SMCs treated with CRP showed a dose-dependent increase in PDGFRbeta expression and phosphorylation after 24-48 h. Exogenous CRP had no effect on SMC viability or proliferation. These data suggest that CRP is detectable within the wall of most diseased vein grafts, where it may exert local effects. Clinically relevant levels of CRP can stimulate SMC migration by a mechanism that may involve upregulation and activation of PDGFRbeta.

Imatinib mesylate in combination with docetaxel for the treatment of patients with advanced, platinum‐resistant ovarian cancer and primary peritoneal carcinomatosis

Ovarian tumors frequently express c-Kit and/or platelet-derived growth factor receptors (PDGFRs). Imatinib mesylate blocks the growth of ovarian cancer cells in vitro and may enhance the activity of chemotherapy. This study was conducted to determine the activity of imatinib in combination with docetaxel in patients with recurrent, platinum-resistant epithelial ovarian cancer (EOC). Eligible patients had recurrent, platinum-resistant, or refractory EOC that expressed PDGFRalpha or c-kit, as determined by immunohistochemistry. Imatinib mesylate at a dose of 600 mg orally once daily was administered continuously with docetaxel at a dose of 30 mg/m(2) given intravenously once weekly in Weeks 1 through 4 of every 6-week cycle. The primary endpoint was objective response rate (ORR) as assessed by the Response Evaluation Criteria in Solid Tumors (RECIST). Thirty-four patients were screened for PDGFRalpha and c-kit expression to enroll 23 patients between December 2003 and October 2005. Four patients had c-kit-positive/PDGFR-negative tumors, 11 patients had PDGFR-positive/c-kit-negative tumors, and 8 patients had c-kit-positive/PDGFR-positive tumors. The median patient age was 56 years (range, 33-76 years). Patients had received a median of 3 prior treatments. The ORR was 21.7% and included 1 complete and 4 partial responses. An additional 3 patients had stable disease for more than 4 months. Expression of PDGFR, c-kit, phosphatase and tensin homolog (PTEN), and phosphorylated protein kinase B (Akt) did not predict response to therapy. The most common adverse events encountered were fatigue (83%), nausea (74%), diarrhea (61%), anorexia (52%), and edema (65%), and the majority of those events were graded as grade 1 or 2. The combination imatinib and docetaxel was tolerated in patients with heavily pretreated EOC that expressed c-kit or PDGFRalpha. Few patients had sustained responses or stable disease.

Activation of peroxisome proliferator-activated receptor-γ by curcumin blocks the signaling pathways for PDGF and EGF in hepatic stellate cells

During hepatic fibrogenesis, reduction in the abundance of peroxisome proliferator-activated receptor-γ (PPARγ) is accompanied by activation of mitogenic signaling for platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) in hepatic stellate cells (HSCs), the major effector cells. We previously reported that curcumin, the yellow pigment in curry, interrupted PDGF and EGF signaling, stimulated PPARγ gene expression, and enhanced its activity, leading to inhibition of cell proliferation of activated HSC in vitro and in vivo. The aim of this study was to elucidate the underlying mechanisms. We hypothesized that the enhancement of PPARγ activity by curcumin might result in the interruption of PDGF and EGF signaling. Our experiments demonstrated that curcumin, with different treatment strategies, showed different efficiencies in the inhibition of PDGF- or EGF-stimulated HSC proliferation. Further experiments observed that curcumin dose dependently reduced gene expression of PDGF and EGF receptors (ie, PDGF-βR and EGFR), which required PPARγ activation. The activation of PPARγ by its agonist suppressed pdgf-βr and egfr expression in HSC. In addition, curcumin reduced the phosphorylation levels of PDGF-βR and EGFR, as well as their downstream signaling cascades, including ERK1/2 and JNK1/2. Moreover, activation of PPARγ induced gene expression of glutamate–cysteine ligase, the rate-limiting enzyme in de novo synthesis of the major intracellular antioxidant, glutathione. De novo synthesis of glutathione was required for curcumin to suppress pdgf-βr and egfr expression in activated HSCs. Our results collectively demonstrated that enhancement of PPARγ activity by curcumin interrupted PDGF and EGF signaling in activated HSCs by reducing the phosphorylation levels of PDGF-βR and EGFR, and by suppressing the receptor gene expression. These results provide novel insights into the mechanisms of curcumin in the inhibition of HSC activation and the suppression of hepatic fibrogenesis.

R Regulation of tumor angiogenesis and metastasis by FGF and PDGF signaling pathways

In a fast-growing malignant tissue, tumor blood vessels are exposed to multiple growth factors and cytokines. Although the role of individual factors and their signaling pathways in regulation of tumor neovascularization is relatively well-studied, little is known about complex interactions between these factors and their cooperative effects in promoting tumor angiogenesis and metastasis. Our recent studies show that quiescent vascular endothelial cells usually remaining silence to platelet-derived growth factor (PDGF)-BB stimulation acquire their hyperresponsiveness after stimulation with fibroblast growth factor (FGF)-2, which transcriptionally switches on PDGF receptor expression in the activated endothelial cells. Interestingly, PDGF-BB also transduces positive feedback signals to the FGF-2 signaling system by amplifying its receptor expression in vascular mural cells. These uncoordinated reciprocal interactions in the tumor environment lead to the formation of disorganized and primitive vasculatures that facilitate tumor growth and metastasis in mice. These findings provide an example of complex interaction between tumor angiogenic factors. Thus, therapeutic development of antiangiogenic agents for the treatment of cancer should be aimed to block multiple angiogenic signaling pathways and their interactive loops.

Mechanical load increases gene expression of Pdgf Receptor alpha and beta in Bladder smooth muscle cells

PURPOSE In previous experiments we have shown a proliferative effect of platelet derived growth factor (PDGF) on smooth muscle cells (SMC) of the bladder of the rat. Thereby the signalling pathway is lipid raft (cholesterol-enriched microdomains) dependent and can be manipulated reversibly by altering membrane cholesterol levels. This study we performed to prove the role of PDGF as a potential regulative mitogen of SMC of the human bladder. MATERIAL AND METHODS Specimens from detrusor and trigone were taken from patients in the course of an ureteral reimplant procedure. Primary SMC-cultures were created. The proliferative effect of growth factors was determined by BrdU incorporation. In select experiments SMC were treated with predefined pressure and stretch for 1 hour. Gene expression was measured by real-time PCR. RESULTS Under full serum conditions both SMC cultures showed different proliferation with a higher growth rate of the trigone. SMC of the trigone showed also a higher proliferation rate in response to the growth factor PDGF. After mechanical load both SMC showed a significant increase in gene expression of PDGF receptor (PDGFR) alpha and beta. PDGF itself was not expressed in this SMC. CONCLUSIONS Gene expression of PDGFR after short-term mechanical load of SMC of the bladder supports a regulatory role for PDGF in terms of pressure-induced hypertrophy of the human bladder. Since PDGF is not expressed in SMC, it may act on a paracrinic way with expression in the urothelium. Otherwise in vascular SMC PDGFR is known to be activated in response to stretch, in the absence of PDGF.

Platelet-derived growth factor receptor expression and amplification in choroid plexus carcinomas

Platelet-derived growth factor (PDGF) receptor signaling has been implicated in the development of glial tumors, but not yet been examined in choroid plexus carcinomas, pediatric tumors with dismal prognosis for which novel treatment options would be desirable. Therefore, protein expression of PDGF receptors α and β as well as amplification status of the respective genes, PDGFRA and PDGFRB, were examined in a series of 22 patients harboring choroid plexus carcinoma using immunohistochemistry and chromogenic in situ hybridization (CISH). The majority of choroid plexus carcinomas expressed PDGF receptors with 6 cases (27%) displaying high staining scores for PDGF receptor α and 13 cases (59%) showing high staining scores for PDGF receptor β. Correspondingly, copy-number gains of PDGFRA were observed in 8 cases out of 12 cases available for CISH and 1 case displayed amplification (six or more signals per nucleus). The proportion of choroid plexus carcinomas with amplification of PDGFRB was even higher (5/12 cases). PDGFRB amplification status and PDGF receptor β protein expression scores were significantly correlated (P=0.01, Spearman). Expression status of PDGF receptor α or PDGF receptor β was not significantly associated with progression-free survival. To conclude, expression and amplification of PDGF receptors, particularly PDGF receptor β, are frequent in choroid plexus carcinomas, providing a first rationale for the development of treatments targeting PDGF receptor signaling in these rare malignant pediatric tumors.

Interleukin-4 and Interleukin-13 Enhance Human Bronchial Smooth Muscle Cell Proliferation

Background: T_H2 inflammation and bronchial smooth muscle cell (BSMC) hyperplasia are characteristic features of asthma, but whether these phenomena are linked remains unknown. This study aims to define the effect of the T_H2 cytokines IL-4 and IL-13 on human BSMC proliferation when administered alone or in combination with the fibroblast growth factor 2 (FGF2) growth factor. In addition, the effects of the proinflammatory mediators TNFα and IL-1β and the involvement of members of the well-known family of platelet-derived growth factor (PDGF) mitogens were tested. Methods: BSMC proliferation was measured by crystal violet staining and PDGF and PDGF receptor (PDGFR) expression were determined by RT-PCR, immunocytochemistry, ELISA, flow cytometry and dot plot analysis. Results: Neither IL-4 nor IL-13 alone induced BSMC proliferation, despite both being potent inducers of PDGF-CC. However, following a pretreatment with FGF2, which increased PDGFR α chain expression, both IL-4 and IL-13 increased FGF2-induced BSMC proliferation in a time- and concentration-dependent manner. TNFα and IL-1β did not affect basal or FGF2-induced BSMC proliferation, but both proinflammatory mediators enhanced the proliferative synergism between FGF2 and the T_H2 cytokines. Conclusions: IL-4 and IL-13 potently induce FGF2-primed BSMC proliferation via an autocrine loop involving PDGFRα and PDGF-CC, and this proliferative synergism is amplified by proinflammatory cytokines.

Platelet-Derived Growth Factor Receptor Inhibition and Chemotherapy for Castration-Resistant Prostate Cancer with Bone Metastases

To further assess preclinical and early clinical evidence that imatinib mesylate, a platelet-derived growth factor receptor (PDGFR) inhibitor, modulates taxane activity in prostate cancer and bone metastases, a randomized study was conducted. Men with progressive castration-resistant prostate cancer with bone metastases (n = 144) were planned for equal randomization to i.v. 30 mg/m(2) docetaxel on days 1, 8, 15, and 22 every 42 days with 600 mg imatinib daily or placebo, for an improvement in median progression-free survival from 4.5 to 7.5 months (two-sided alpha = 0.05 and beta = 0.20). Secondary end points included differential toxicity and bone turnover markers, tumor phosphorylated PDGFR (p-PDGFR) expression, and modulation of p-PDGFR in peripheral blood leukocytes. Accrual was halted early because of adverse gastrointestinal events. Among 116 evaluable men (57 docetaxel + imatinib; 59 docetaxel + placebo), respective median times to progression were 4.2 months (95% confidence interval, 3.1-7.5) and 4.2 months (95% confidence interval, 3.0-6.8; P = 0.58, log-rank test). Excess grade 3 toxicities (n = 23) in the docetaxel + imatinib group were principally fatigue and gastrointestinal. Tumor p-PDGFR expression was observed in 12 of 14 (86%) evaluable bone specimens. In peripheral blood leukocytes, p-PDGFR reduction was more likely in docetaxel + imatinib-treated patients compared with docetaxel + placebo (P < 0.0001), as were reductions in urine N-telopeptides (P = 0.004) but not serum bone-specific alkaline phosphatase (P = 0.099). These clinical and translational results question the value of PDGFR inhibition with taxane chemotherapy in prostate cancer bone metastases and are at variance with the preclinical studies. This discordance requires explanation.

Role of Brazilian native medicinal plants on VEGF and PDGF receptors expression by glioblastoma cell line GL-15

12532 Background: Malignant gliomas are typically angiogenic and express greater amounts of angiogenic factors. Vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) are prominent glioblastoma-associated multifunctional cytokines that stimulate migration, invasion and angiogenesis. Their receptor inhibiton is considered an important target for anitumoral therapy. Flavonoids obtained from Dimorphandra mollis and Croton betulaster, native medicinal plants from Bahia-Brazil, have been described as proliferation inhibitors of a human glioblastoma derived cell line and reduce VEGF production by GL-15. In this study, VEGF and PDGF receptors expression by GL-15 cultures treated with bevacizumab and flavonoids were evaluated. Methods: GL-15 cultures were treated or not with pendulitin and rutin flavonoids (100μM) and bevacizumab (1μg/mL). After 24 hours VEGF and PDGF receptors were analyzed by flow cytometry using monoclonal antibodies labeled with FITC. Results: Flow cytometry showed that the GL-15 cells expressed PDGFR alfa (10%), PDGFR beta (52%), VEGFR 1 (26%) and VEGFR 2 (95%). It was observed that the pendulitin and rutin flavonoids treated cells showed a reduction on PDGFR alfa expression (2 and 1,6 % respectively) but the other receptors expression was similar to the non-treated or DMSO treated controls. Conclusions: GL-15 human glioblastoma derived cell line expresses receptors to the angiogenic cytokines studied. VEGFR 2 expression was predominant and bevacizumab didn’t alter the receptors production. Flavonoids extracted from D. mollis and C. betulaster seem to have an inhibitory action on the PDGRF alfa expression but not on the others receptors. No significant financial relationships to disclose.

Phase II trial of high dose imatinib in recurrent glioblastoma multiforme (GBM) with platelet derived growth factor receptor (PDGFR) expression

2056 Background: GBM are the most common primary brain tumors in adults. Despite available treatment they carry a poor prognosis with recurrences in most patients (pts) after initial therapy. PDGF signaling has been postulated to play a role in GBM transformation. We have demonstrated that PDGFRβ is expressed in tumor cells in 50% and in peritumoral endothelial cells in 65% of GBM (Barrios et al, abstract 11518, Proc ASCO 2006). Imatinib, an inhibitor of PDGFRa/β kinase activity could have therapeutic activity in these cases. Methods: We evaluated Imatinib in pts with recurrent GBM (previous radiation and chemotherapy) selected by PDGFR expression. Analysis of PDGFRa/β was performed by standard IHC. Positivity was considered in case of any qualitative expression. Pts were treated with 800 mg/day of Imatinib until tumor progression. All were on steroids and taking enzyme inducing antiepileptic drugs. Response was determined by MRI with spectroscopy and perfusion every 8 weeks according to RECIST criteria. Results: Twenty pts were enrolled (18 GBM, 2 AA). Median age: 51 (21–74), 7 were females. ECOG-PS at inclusion: 0 (3), 1 (10), 2 (7). All pts had expression of PDGFRa and 55% expressed PDGFRβ. Response data are available for all 20 pts. Main adverse events (all grade 1–2) were: edema (55%), nausea (50%), diarrhea and fatigue (35% each). We did not observe any PR but 13 pts (65%) showed disease stabilization. Median progression-free survival was 7.8 months with 60.8% of pts alive at 6 months; 6 months PFS was 52.2%. Conclusions: Imatinib was well tolerated in this group of poor prognosis highly pre-treated GBM pts demonstrating disease stabilization in a significant proportion of cases. These results, in a limited sample, compare favorably with historical data in similar populations. Selection of pts according to the specific molecular expression of their tumor may lead to better therapeutic results. No significant financial relationships to disclose.

Expression of endothelial PDGF receptors α and β in breast cancer: Up-regulation of endothelial PDGF receptor β

The PDGF pathway is essential in tumor angiogenesis. Although the expression of the PDGF receptors has been excessively studied on breast cancer cells, few studies exist on PDGFR expression on the tumor endothelial cells. In the present study, it is investigated whether endothelial PDGF receptors' expression is altered in breast cancer. Endothelial PDGFRalpha and beta expression was initially studied under the influence of tumor conditioned medium derived from a breast cancer cell line. Following tissue culture experiments the endothelial expression of both receptors was studied on formalin-fixed paraffin-embedded tissue sections of normal breast and breast cancer specimens. The tissue culture experiment revealed a possible up-regulation of endothelial PDGFRbeta by breast cancer environment. Immunohistochemistry verified the result since 69.7% of the breast cancer sections were positive for PDGFRbeta compared to 43.3% of normal breast sections (p<0.05). No statistical difference was revealed by studying PDGFRalpha expression. In conclusion, our findings support the thesis of possible anti-PDGFRbeta anti-angiogenic therapy, in cases of endothelial PDGFRbeta-expressing breast cancer.

Estrogen-TNF interactions and vascular inflammation

cardiovascular disease (CVD), especially coronary heart disease (CHD), is by far the leading cause of death in women ([29][1], [40][2]). As the prevalence of these diseases increases after menopause, much effort has been devoted to determining whether endogenous estrogen confers a protective effect

Osteoblast-conditioned medium promotes proliferation and sensitizes breast cancer cells to imatinib treatment

Inhibition of platelet-derived growth factor receptor (PDGFR) signaling restricts the growth of human breast cancer in the bone of nude mice. We hypothesized that osteoblast-secreted substances may alter the response capacity of breast cancer cells to the PDGFRs tyrosine kinase inhibitor imatinib mesylate. We found that osteoblast-conditioned medium (OCM) increases the proliferation rate of the estrogen receptor negative (ER-) MDA-MB-231 and of the ER+ MCF-7 human breast cancer cell lines and the growth-promoting effect on ER+ cells is independent from estrogen. OCM significantly improved the dose- and the time-dependent sensitivity of the tumor cells to the anti-proliferative effect of imatinib. We also found that MDA-MB-231 and MCF-7 cells express the two PDGFRs subtypes, PDGFR-alpha and PDGFR-beta, and OCM treatment increases the expression of the PDGFRs. Furthermore, imatinib inhibited the phosphorylation rate of its target tyrosine kinase receptors. We conclude that bone microenvironment, through osteoblast-secreted substances may cause estrogen-independent proliferation of breast cancer cells by a mechanism mediated by the induction of PDGFRs expression. The enhanced sensitivity of OCM-treated breast cancer cells to imatinib would justify investigation on the efficacy of imatinib in bone breast cancer metastasis.

Retinoic Acid Inducibility of the Human PDGF-A Gene Is Mediated by 5′-Distal DNA Motifs That Overlap With Basal Enhancer and Vitamin D Response Elements

Retinoic acid (RA) upregulates expression of PDGF ligands and receptors in neonatal rat lung fibroblasts, a process likely to promote maturation of the lung alveolus and possibly microstructures of other organs. A mutational analysis of the gene encoding the PDGF-A ligand has identified a complex retinoic acid response element (RARE) located far upstream of the transcription start site, in a 5'-distal enhanceosome region previously shown to harbor basal and vitamin D-inducible enhancer activity. Maximal RA responsiveness (fourfold) was conferred by nucleotide sequence located between -7064 and -6787, with a variety of deletion and point mutations revealing the importance of at least three nuclear receptor half-sites within the enhancer region (-6851 to -6824), as well as nucleotides located further upstream. Recombinant human retinoic acid receptor/retinoid-X receptor heterodimers bound with high affinity and sequence specificity to multiple regions within the RARE, as demonstrated by electrophoretic mobility shift and DNase I footprinting assays. The addition of RARE activity to previously described functions of the 5'-distal enhanceosome underscores the importance of this region as a key integration point for regulatory control of PDGF-A expression.

Expression and localization of PDGF-B, PDGF-D, and PDGF receptor in the kidney of angiotensin II-infused rat

Lipid accumulation in the kidney is a marker of tissue damage and may play a role in the development of renal injury. We have previously shown that long-term administration of angiotensin II in rats causes increased expression of transforming growth factor-β1, coupled with an accumulation of lipids in the tubular and vascular wall cells in the kidney. In this study, we examine the regulation of expression of platelet-derived growth factor (PDGF) and its receptor system and their co-localization with lipid deposits in the kidneys of angiotensin II-infused rats. Real-time RT-PCR showed that expression of PDGF-B, PDGF-D, and PDGF receptor-β (PDGFR-β) mRNA was increased by angiotensin II infusion, and in situ hybridization showed the co-localization of these mRNAs. Tubular cells that had increased PDGF-B mRNA expression were positive for lipid deposition and also for cellular proliferation, which was indicated by the presence of proliferating cell nuclear antigen. By contrast, in the kidneys of angiotensin II-infused rats, apoptosis occurred in tubular cells that contained deposits of iron but not lipids. The deposition of lipids and upregulation of PDGF-B, PDGF-D, and PDGFR-β induced by administration of angiotensin II were all suppressed by the selective angiotensin II type 1 (AT1) receptor antagonist losartan, but not by the nonspecific vasodilator hydralazine. The findings that lipid accumulation, upregulation of PDGF-B, PDGF-D, and PDGFR-β, and cellular proliferation were topologically associated and regulated in an AT1 receptor-dependent manner in the kidney of angiotensin II-infused rats suggests that these phenomena are related.

Epigallocatechin-3-gallate inhibits the PDGF-induced VEGF expression in human vascular smooth muscle cells via blocking PDGF receptor and Erk-1/2

Platelet-derived growth factor (PDGF) has been known to induce vascular endothelial growth factor (VEGF) expression in human vascular smooth muscle cells (hVSMCs). We previously reported that Erk-1/2 and AP-1 pathways are crucial in the PDGF-induced VEGF expression in hVSMCs . In this study, we investigated the effect of epigallocatechin-3-gallate (EGCG), the major green tea catechin, on the PDGF-induced VEGF expression in hVSMCs and the underlying mechanisms. EGCG were found to inhibit dose-dependently the VEGF expression and activation of PDGF receptor, Erk-1/2 and AP-1 induced by PDGF. In addition, cell free studies demonstrated that EGCG could directly inhibit the Erk-1/2 activity. Conditioned media from the hVSMCs treated with PDGF could remarkably stimulate the in vitro growth of human umbilical vein endothelial cells (HUVECs) but the media from the EGCG-pretreated hVSMCs lost its stimulatory activity for HUVEC proliferation. These results suggest that EGCG may exert the anti-angiogenic effect by inhibiting the PDGF-induced VEGF expression at multiple signaling levels.