A rapid, two-step method for high-yield purification of recombinant rat acidic and basic fibroblast growth factors

A two-step process for capture and purification of human basic fibroblast growth factor from E. coli homogenate: Yield versus endotoxin clearance

A two-step purification process for human basic fibroblast growth factor (FGF-2) from clarified E. coli homogenate has been developed in which the impurity level after the second step is below the limit of quantification. Endotoxin content is cleared to 0.02 EU/μg FGF-2 and the overall yield is 67%. The performance of the cation exchanger Carboxymethyl-Sepharose Fast Flow (CM-SFF) was compared to the affinity resin Heparin-SFF regarding the impurity profile and product quality in the elution peak. The CM-SFF eluate was further purified using hydrophobic interaction resin Toyopearl-Hexyl-650C. The relative amounts of target product, host cell proteins (HCPs), dsDNA, endotoxin, monomer content, and high molecular weight impurities differed along the elution peak depending on the applied method. The bioactive monomer (>99%) was obtained with a yield of 48% for CM-SFF and 68% for Heparin-SFF. A half-load reduction in CM-SFF increased the yield up to 67% without deterioration of the impurity content. Assuming a dose of 400 μg FGF-2, endotoxin was reduced to 188 EU/dose, dsDNA <10 ng/dose, and HCP <2 ppm/dose using the cation exchanger. In the pooled eluate fractions, dsDNA was removed 4-fold (291 ng/mL) and endotoxin 14-fold (0.47 EU/μg FGF-2) more efficiently by CM-SFF than by affinity chromatography. In contrast, HCP clearance was 3-fold (13 ppm) more efficient with Heparin-SFF than CM-SFF. In contrast to process monitoring by UV_280nm or SDS-PAGE, this characterization is the basis for a Process Analytical Technology attempt when correlated with online monitored signals, as it enables knowledge-based pooling according to defined quality criteria.

The heparin/heparan sulfate sequence that interacts with cyclophilin B contains a 3-O-sulfated N-unsubstituted glucosamine residue

Many of the biological functions of heparan sulfate (HS) proteoglycans can be attributed to specialized structures within HS moieties, which are thought to modulate binding and function of various effector proteins. Cyclophilin B (CyPB), which was initially identified as a cyclosporin A-binding protein, triggers migration and integrin-mediated adhesion of peripheral blood T lymphocytes by a mechanism dependent on interaction with cell surface HS. Here we determined the structural features of HS that are responsible for the specific binding of CyPB. In addition to the involvement of 2-O,6-O, and N-sulfate groups, we also demonstrated that binding of CyPB was dependent on the presence of N-unsubstituted glucosamine residues (GlcNH2), which have been reported to be precursors for sulfation by 3-O-sulfotransferases-3 (3-OST-3). Interestingly, 3-OST-3B isoform was found to be the main 3-OST isoenzyme expressed in peripheral blood T lymphocytes and Jurkat T cells. Moreover, down-regulation of the expression of 3-OST-3 by RNA interference potently reduced CyPB binding and consequent activation of p44/42 mitogen-activated protein kinases. Altogether, our results strongly support the hypothesis that 3-O-sulfation of GlcNH2 residues could be a key modification that provides specialized HS structures for CyPB binding to responsive cells. Given that 3-O-sulfation of GlcNH2-containing HS by 3-OST-3 also provides binding sites for glycoprotein gD of herpes simplex virus type I, these findings suggest an intriguing structural linkage between the HS sequences involved in CyPB binding and viral infection.

Exogenous Fibroblast Growth Factors Maintain Viability, Promote Proliferation, and Suppress GADD45α and GAS6 Transcript Content of Prostate Cancer Cells Genetically Modified to Lack Endogenous FGF-2

Understanding processes regulating prostate cancer cell survival is critical to management of advanced disease. We used prostate cancer cell transfectants genetically modified to be deficient in either endogenous fibroblast growth factor (FGF-1) or endogenous FGF-2 to examine FGF maintenance of transfectant survival and proliferation and FGF-2-regulated expression of transfectant growth arrest DNA damage (GADD) and growth arrest sequences (GAS) family genes (known modulators of cell cycle progression and survival) and the AS3 gene (an androgen-modulated effector of prostate cell proliferation). When propagated in the absence of exogenous FGFs, FGF-2-deficient transfectants undergo exponential death, whereas FGF-1-deficient transfectants proliferate. Exogenous FGF-1, FGF-2, FGF-7, or FGF-8 promote survival and proliferation of FGF-2-deficient transfectants and enhance FGF-1-deficient transfectant proliferation. Transfectants express FGF receptor FGFR1, FGFR2(IIIb), FGFR2(IIIc), and FGFR3 transcripts, findings consistent with the effects of exogenous FGFs. FGF-2-deficient transfectants express high levels of AS3, GADD45α, GADD45γ, GAS8, and GAS11 transcripts and moderate levels of GADD153, GAS2, GAS3, and GAS6 transcripts and lack demonstrable GAS1 or GAS5 transcripts. FGF withdrawal-mediated death of FGF-2-deficient transfectants did not significantly affect cell AS3, GADD153, GADD45γ, GAS2, GAS3, GAS7, GAS8, or GAS11 transcript content, whereas GADD45α and GAS6 transcript content was elevated. These studies establish that endogenous FGF-2 dominantly regulates prostate cancer cell survival and proliferation and that exogenous FGFs may assume this function in the absence of endogenous FGF-2. Additionally, we provide the first evidence that FGFs regulate prostate GADD45α and GAS6 transcript content. The latter observations suggest that GADD45α and GAS6 proteins may be effectors of processes that regulate prostate cancer cell survival. Additional studies are required to examine this possibility in detail.

Acute protection of ischemic heart by FGF-2: involvement of FGF-2 receptors and protein kinase C

We examined the effect of fibroblast growth factor (FGF)-2 on myocardial resistance to injury when administered after the onset of ischemia, in vivo and ex vivo, and the role of FGF-2 receptors and protein kinase C (PKC). FGF-2 was injected into the left ventricle of rats undergoing permanent surgical coronary occlusion leading to myocardial infarction (MI). After 24 h, FGF-2-treated hearts displayed significantly reduced injury, determined by histological staining and troponin T release, and improved developed pressure compared with untreated controls. An FGF-2 mutant with diminished affinity for the tyrosine kinase FGF-2 receptor 1 (FGFR1) was not cardioprotective. FGF-2-treated hearts retained improved function and decreased damage at 6 wk after MI. In the ex vivo heart, FGF-2 administration during reperfusion after 30-min ischemia improved functional recovery and increased relative levels of PKC subtypes alpha, epsilon, and zeta in the particulate fraction, in a chelerythrine-preventable mode; it also decreased loss of energy metabolites. We conclude that intramyocardial FGF-2 administration shortly after the onset of ischemia confers protection from acute and chronic cardiac dysfunction and damage; FGF-2 delivered during reperfusion protects from ischemia-reperfusion injury; and protection by FGF-2 requires intact binding to FGFR1 and is likely mediated by PKC.

Neither fibroblast growth factor-1 nor fibroblast growth factor-2 is an androgen receptor coactivator in androgen-resistant prostate cancer

We used rat prostate cancer cell stable transfectants that lacked either endogenous fibroblast growth factor (FGF)-1 secondary to constitutive expression of FGF-1 antisense RNA (aFa2-transfectants) or endogenous FGF-2 isoforms secondary to constitutive expression of FGF-2 antisense RNA (bFa9-transfectants) to examine the potential synergistic effects of mitogen and androgen as modulators of proliferation. During culture on 5% charcoal-stripped fetal bovine serum (CS-FBS), FGF-1 caused a 2- to 2.5-fold increase in the proliferation of aFa2-transfectants that lacked endogenous FGF-1 and retained full expression of FGF-2 isoforms. In marked constrast, bFa9-transfectants that lacked FGF-2 isoforms and retained full expression of FGF-1 died with exponential kinetics when cultured on either 5% CS-FBS or 5% FBS in the absence of FGF-2. However, FGF-2 promoted bFa9-transfectant survival and exponential proliferation during culture on either 5% CS-FBS or 5% FBS. The nonmetabolizable androgen R1881 did not affect proliferation of either the aFa2- transfectants, the bFa9-transfectants, or the parental prostate cancer cells used to generate these transfectants. Additionally, neither of the androgen receptor antagonists RU23908 or bicalutamide affected either FGF-1-mediated aFa2-transfectant proliferation or FGF-2-mediated bFa9-transfectant proliferation during culture on 5% CS-FBS. Notably, transient transfection analyses established R1881 concentration-dependent induction of chloramphenicol acetyltransferase activity in both aFa2-transfectants and bFa9-transfectants. Thus, the failure of either androgen or antiandrogen to affect either FGF-mediated or FGF-independent antisense-transfectant proliferation is not attributable to absence of functional androgen receptors. The results indicate that FGF effects in these androgen-resistant antisense transfectants do not involve either androgen-dependent or androgen-independent, mitogen-mediated androgen receptor activation. Our studies show that these rat prostate cancer cells are characterized by both retention of functional androgen receptors during development of androgen resistance and mitogen-mediated, autocrine or paracrine (or both) modulated proliferation. These are two prominent properties characteristic of advanced human prostate cancer.

Androgen regulation of prostate cancer cell FGF-1, FGF-2, and FGF-8: preferential down-regulation of FGF-2 transcripts

Using quantitative RT-PCR, we found that T1 rat prostate cancer cell relative FGF-1 transcript content was about 180-fold greater than that of FGF-2. This difference in transcript content was not representative of T1 cell relative FGF-1 and FGF-2 protein content which showed, at most, only a 4- to 5-fold greater FGF-1 content. Testosterone caused time-dependent down-regulation of prostate cancer cell FGF-2 transcript content without influencing either FGF-1 or FGF-8 transcript content or T1 cell proliferation. Moreover, testosterone-mediated down-regulation of prostate cancer cell FGF-2 transcripts did not result in a statistically significant change in 21.5 or 17.0 kD FGF-2 isoform content. By contrast, an approximately 20% statistically significant decrement in 19.5 kD FGF-2 isoform content was demonstrable following 24 h testosterone treatment. However, following 72 h testosterone treatment, T1 cell 19.5 kD FGF-2 isoform content was not statistically significantly different from that of control. It is probable that the modest and variable decrement in 19.5 kD isoform content is not physiologically significant and is attributable to artifact resulting from difficulty quantifying this minor component of the FGF-2 isoforms. Transient transfection analysis showed that androgen caused concentration-dependent increases in MMTV-LTR regulated expression of chloramphenicol acetyl transferase activity. Consequently, the failure of androgen to affect either T1 cell FGF-1 and FGF-8 transcript content or T1 cell proliferation could not be attributed to defective androgen receptor function. Moreover, the absence of a close relationship between T1 cell FGF-2 transcript and FGF-2 protein content implies that FGF-2 transcript content is not the dominant determinant of prostate cancer cell FGF-2 protein content. Testosterone-mediated down-regulation of prostate-cancer-cell gene expression may have significance for clinical management of human disease that is treated by androgen ablation. The possibility that such ablation may enhance aggressiveness of "androgen-independent" cells by selective upregulation of gene expression merits further consideration.

Single step purification of biologically active recombinant rat basic fibroblast growth factor by immobilized metal affinity chromatography

The construction and use of a plasmid which allows the expression and single step purification of recombinant rat basic fibroblast growth factor (bFGF) is described. A cDNA encoding rat bFGF was subcloned into the expression plasmid pQE-9 (Qiagen) in such a way that the bFGF which is produced from the resulting construct contains 6 histidine residues near the amino terminus. The resulting plasmid, pQE-9-bFGF, was expressed in the E. coli strain M15[pREP4] and the 6 x His-bFGF was purified to homogeneity from the soluble fraction of the bacterial cell lysate in a single step by affinity chromatography on a nickel chelate resin. About 5 mg of 6 x His-bFGF was obtained from the soluble fraction from one liter of bacterial cell culture. Testing of the 6 x His-bFGF in a PC12 cell differentiation assay showed that its activity was comparable to the activities for native bFGF and recombinant bFGF purified by multistep methods.

Isolation and localization of basic fibroblast growth factor-immunoreactive substance in the epiphyseal growth plate

Previous research in our laboratory has shown basic fibroblast growth factor (bFGF) to be a permissive mitogen for isolated avian growth plate chondrocytes. The present study was conducted to determine whether bFGF is present in avian growth plate and, if present, to determine its localization within the tissue. Immunohistochemical studies revealed that bFGF is present in the resting proliferative and hypertrophic calcifying zones of the growth plate but is absent from the prehypertrophic zone. Basic FGF appears to be associated with the extracellular matrix of the proliferative zone, but it is predominantly intracellular in the hypertrophic and mineralizing zone chondrocytes. Partial purification of cartilage-derived bFGF was performed on crude extracts of cartilage using heparin-Sepharose affinity chromatography. The presence of bFGF in the heparin-Sepharose column fractions was confirmed by immunoblotting and radioimmunoassay. Furthermore, western blot analysis of the extracts showed multiple protein bands having bFGF immunoreactivity, in the molecular weight range 14.4-18 kD. The data support the hypothesis that bFGF has a dual role in the growth plate. In the proliferative zone it acts as a chondrocyte mitogen, whereas when released from terminal hypertrophic chondrocytes, bFGF may serve as a chemotactic signal for metaphyseal blood vessel proliferation.

Purification and characterization of the 210-amino acid recombinant basic fibroblast growth factor form (FGF-2)

Four forms of basic fibroblast-growth factor (bFGF or FGF-2) using one AUG (155 amino acids) and three upstream CUG (210, 201 and 196 amino acids) start codons, were synthesized through an alternative use of initiation codons. The 210-amino acid form of FGF-2 (210FGF-2) was expressed in a plasmid vector under the control of a bacteriophage T7 RNA polymerase promoter system in Escherichia coli. Characterization of the purified protein was performed by electrospray mass spectrometry and Edman degradation. The recombinant 210FGF-2 produced in E. coli had a mitogenic activity similar to the 146-amino acid form extracted from tissues.