Fibroblast growth factors are translocated to the nucleus of human endothelial cells in a microtubule- and lysosome-independent pathway

Adenovirus-mediated delivery of bFGF small interfering RNA reduces STAT3 phosphorylation and induces the depolarization of mitochondria and apoptosis in glioma cells U251

Glioblastoma multiforme (GBM) carries a dismal prognosis primarily due to its aggressive proliferation in the brain regulated by complex molecular mechanisms. One promising molecular target in GBM is over-expressed basic fibroblast growth factor (bFGF), which has been correlated with growth, progression, and vascularity of human malignant gliomas. Previously, we reported significant antitumor effects of an adenovirus-vector carrying bFGF small interfering RNA (Ad-bFGF-siRNA) in glioma in vivo and in vitro. However, its mechanisms are unknown. Signal transducer and activator of transcription 3 (STAT3) is constitutively active in GBM and correlates positively with the glioma grades. In addition, as a specific transcription factor, STAT3 serves as the convergent point of various signaling pathways activated by multiple growth factors and/or cytokines. Therefore, we hypothesized that the proliferation inhibition and apoptosis induction by Ad-bFGF-siRNA may result from the interruption of STAT3 phosphorylation. In the current study, we found that in glioma cells U251, Ad-bFGF-siRNA impedes the activation of ERK1/2 and JAK2, but not Src, decreases IL-6 secretion, reduces STAT3 phosphorylation, decreases the levels of downstream molecules CyclinD1 and Bcl-xl, and ultimately results in the collapse of mitochondrial membrane potentials as well as the induction of mitochondrial-related apoptosis. Our results offer a potential mechanism for using Ad-bFGF-siRNA as a gene therapy for glioma. To our knowledge, it is the first time that the bFGF knockdown using adenovirus-mediated delivery of bFGF siRNA and its potential underlying mechanisms are reported. Therefore, this finding may open new avenues for developing novel treatments against GBM.

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.

Ligand dependent and independent internalization and nuclear translocation of fibroblast growth factor (FGF) receptor 1

Basic fibroblast growth factor (FGF-2) is one of the prototype members of a rapidly expanding family of polypeptides. FGF-2 acts on cells via a dual-receptor system consisting of high-affinity tyrosine kinase receptors (FGFR) and low-affinity receptors comprised of heparan sulfate proteoglycans. Following ligand binding and subsequent internalization, both FGF-2 and FGFR1 are translocated to the nucleus where they have activities distinct from those expressed at the cell surface. Despite the growing number of growth factors and receptors shown to translocate to the nucleus, little is known about the mechanisms of internalization and translocation and how these processes are regulated. In the studies reported in this paper, we examined the roles of clathrin-dependent and -independent endocytosis in the uptake of FGFR1 and one of its ligands, FGF-2. While the uptake of FGF-2 occurred at least partly by a caveolar-dependent mechanism, that of FGFR1 was independent of both caveolae and coated pits. Surprisingly, neither the uptake of FGF-2 nor FGFR1 required the activity of the receptor tyrosine kinase. In addition, we identified a cell cycle-dependent pathway of FGFR1 nuclear translocation that appears to be independent of ligand binding.

Nuclear and Nucleolar Localization of 18-kDa Fibroblast Growth Factor-2 Is Controlled by C-terminal Signals

Members of high (22-, 22.5-, 24-, and 34-kDa) and low (18-kDa) molecular mass forms of fibroblast growth factor-2 (FGF-2) regulate cell proliferation, differentiation, and migration. FGF-2s have been previously shown to accumulate in the nucleus and nucleolus. Although high molecular weight forms of FGF-2 contain at least one nuclear localization signal (NLS) in their N-terminal extension, the 18-kDa FGF-2 does not contain a standard NLS. To determine signals controlling the nuclear and subnuclear localization of the 18-kDa FGF-2, its full-length cDNA was fused to that of green fluorescent protein (GFP). The fusion protein was primarily localized to the nucleus of COS-7 and HeLa cells and accumulated in the nucleolus. The subcellular distribution was confirmed using wild type FGF-2 and FGF-2 tagged with a FLAG epitope. A 17-amino acid sequence containing two groups of basic amino acid residues separated by eight amino acid residues directed GFP and a GFP dimer into the nucleus. We systematically mutated the basic amino acid residues in this nonclassical NLS and determined the effect on nuclear and nucleolar accumulation of 18-kDa FGF-2. Lys(119) and Arg(129) are the key amino acid residues in both nuclear and nucleolar localization, whereas Lys(128) regulates only nucleolar localization of 18-kDa FGF-2. Together, these results demonstrate that the 18-kDa FGF-2 harbors a C-terminal nonclassical bipartite NLS, a portion of which also regulates its nucleolar localization.

Nuclear accumulation of basic fibroblast growth factor in human astrocytic tumors

BACKGROUND

The authors recently reported that nuclear accumulation of basic fibroblast growth factor (bFGF) demonstrated a significant correlation with recurrence of pituitary adenomas. The current study sought to determine whether nuclear bFGF accumulation was a predictor of survival in patients with astrocytic tumors.

METHODS

The authors examined 52 patients with primary astrocytic tumors. Immunohistochemical assays for bFGF, fibroblast growth factor receptor 1 (FGFR1), and proliferating cell nuclear antigen were performed. Immunoreactivity of bFGF in nuclei was recorded in terms of the bFGF nuclear index (NI), which was calculated as the percentage of tumor cells with nuclear immunoreactivity. Western blot analysis of bFGF in nuclear fractions was performed.

RESULTS

The bFGF NI had a mean value of 35.1% and was < 30% (low NI) in 27 patients and >or= 30% (high NI) in 25 patients. In all cases, FGFR1 immunoreactivity was observed in the cytoplasm but not in the nucleus. Western blot analysis indicated that the nuclear fractions from tumor specimens with high NI contained high-molecular-weight bFGF. Univariate analyses showed that age, tumor histology, gender, and bFGF NI were significantly correlated with patient survival. Multivariate analyses demonstrated that NI had the greatest influence (P = 0.0073) on survival rate, compared with age (P = 0.0083) and gender (P = 0.0492). Compared with low NI, high NI was associated with a relative risk of 3.292.

CONCLUSIONS

The findings of the current study suggest that bFGF NI may be a useful predictor of survival in patients with astrocytic tumors.

Subcellular localization of basic fibroblast growth factor and fibroblast growth factor receptor 1 in pituitary adenomas

The aim of this study was to assess the subcellular localization of basic fibroblast growth factor (bFGF) and fibroblast growth factor receptor 1 (FGFR1) in pituitary adenomas. We studied 61 patients who had primary pituitary adenomas and underwent operation. The immunohistochemistry for bFGF, FGFR1, and MIB-1 was examined in paraffin-embedded tissues. The bFGF immunoreactivity in the nucleus was recorded as the bFGF nuclear index, which was calculated as the percentage of tumor cells with the bFGF immunoreactivity in the nuclei when more than 1000 tumor cells were examined. Recurrent adenomas were found in 7 patients during follow-up periods ranging from 8 to 134 months (mean, 57.2). The recurrent adenomas had significantly larger mean bFGF nuclear indices (74.8 +/- 28.8%) than the nonrecurrent adenomas (25.4 +/- 32.1%, P = 0.0003). The bFGF nuclear index also correlated significantly with the maximum tumor diameters and the invasiveness to the cavernous sinuses (Knosp grade) in the adenomas. The cytoplasmic FGFR1 immunoreactivity was inversely correlated (P < 0.02) with maximum tumor diameter. Neither cytoplasmic bFGF, cytoplasmic FGFR1, nor MIB-1 staining index showed any relationship with the recurrence of pituitary adenomas. These findings suggest that the nuclear accumulation of bFGF plays an important role in the progression of pituitary adenomas without its receptors.

Nuclear accumulation of basic fibroblast growth factor as a predictor for the recurrence of pituitary adenomas

Although pituitary adenomas often recur, a reliable predictor for their recurrences has not yet been established. The aim of this study is to assess the utility of the nuclear accumulation of basic fibroblast growth factor (bFGF) as a predictor for the recurrence of pituitary adenomas. We studied 64 patients who had primary pituitary adenomas and underwent operations. The immunohistochemistry for bFGF and MIB-1 was retrospectively examined in paraffin-embedded tissues. The bFGF immunoreactivity in the cytoplasm was assigned one of four grades and the bFGF immunoreactivity in the nucleus was recorded as the bFGF nuclear index (NI), which was calculated as a percentage of tumor cells with the bFGF immunoreactivity in the nuclei in more than 1000 tumor cells. Recurrent adenomas were found in 7 patients during follow-up periods ranging from 8 to 134 months (mean: 57.3). Kaplan-Meier analysis demonstrated that high bFGF NI (>30%) correlated with poor recurrence free rate (p < 0.02). We assessed the relative contribution of bFGF NI to recurrence free by using multivariate (Cox's proportional hazards model) analyses with variable factors. Multivariate analysis showed that only bFGF NI was a potential predictor of recurrence free, independent of all other variables. High bFGF NI (>30%) had a relative risk of 8.9, with a 95% confidence interval of 1.0-74.9 (p < 0.05). We suggest that the bFGF NI may be a potentially useful predictor for the recurrence of pituitary adenomas.

Adenovirus type 7 penton purification of soluble pentamers from Escherichia coli and development of an integrin-dependent gene delivery system

Adenoviral gene therapy vectors suffer from the disadvantages of toxicity and immunogenicity associated with the expression of adenoviral genes from the vector backbone. We report here an alternative strategy for gene delivery that utilizes a single component of the adenoviral type 7 capsid, the penton base (Ad7PB). The Ad7PB gene was sequenced and its amino-acid composition was deduced from its nucleotide sequence. The penton was expressed in Escherichia coli as a soluble C-terminal fusion with glutathione S-transferase (GST-Ad7PB) and was purified by single-step affinity chromatography. Both GST-Ad7PB and cleaved (GST-free) Ad7PB retained the ability to fold into pentamers as observed by electron microscopy. GST-Ad7PB was able to bind a synthetic peptide (FK20) derived from the Ad type 7 fiber and retard DNA through a polylysine chain present at the C-terminus of this linker peptide. GST-Ad7PB was an effective cell transfecting agent when assayed on 293 cells. Transfection was not dependent upon the presence of lysosomotropic agents indicating efficient endosome escape capability. Excess of an RGD-containing peptide derived from Ad7PB was able to inhibit transfection indicating specific integrin-mediated uptake of the GST-Ad7PB-FK20-DNA complexes. We propose that Ad7 pentons can be developed into integrin-specific gene delivery agents.