Overexpression of the fragile histidine triad (FHIT) gene in inflammatory bowel disease.

OBJECTIVE: FHIT gene encodes human diadenosine triphosphate hydrolase involved in the regulation of cell cycle and nucleotide metabolism and is a candidate tumor suppressor gene. AIM: To investigate expression of FHIT gene at the mRNA and protein levels in sporadic inflammatory bowel disease (IBD). MATERIALS AND METHODS: FHIT mRNA was quantified by the validated real-time PCR (QPCR) and FHIT protein was detected by immunohistochemistry (IHC) in mucosal biopsies of 139 ulcerative colitis (UC), 19 Crohn's disease (CD) and 37 control patients. RESULTS: Significant FHIT gene overexpression was found in 78% of active UC but not in CD. IHC showed comparable results to QPCR. CONCLUSION: The local up-regulation of FHIT gene and protein expression in active UC may represent an adequate response against inflammatory challenge of epithelial cell homeostasis and protect against DNA damage and cell cycle disturbances.

Decreased Toll-like receptor-5 (TLR-5) expression in the mucosa of ulcerative colitis patients.

OBJECTIVE: Although there is a convincing evidence supporting an important role for microorganisms in the pathogenesis of Inflammatory Bowel Disease (IBD) which comprises ulcerative colitis (UC) and Crohn's disease (CD), the specific mechanisms involved remain unclear. Toll-like receptors (TLR) recognize various molecules of microbiota including flagellin, the principal protein of motile comensal and pathogenic bacteria implicated in the pathogenesis of IBD. AIM: To investigate the expression of the TLR-5 receptors at the mRNA and protein levels in the mucosa of UC patients. MATERIALS AND METHODS: TLR-5 mRNA was quantified by the validated real-time PCR (QPCR) in mucosal biopsies of 99 UC patients and 34 control patients and TLR-5 protein was detected by immunohistochemistry (IHC) in 57 UC and 10 control patients. RESULTS: Significantly decreased TLR-5 gene expression at mRNA and protein level was found in the mucosa of patients with moderate and severe disease activity as compared to patients with low UC activity and control. TLR-5 immunoreactivity was found in the mucosa of UC patients and normal controls in the cytoplasm of enterocytes and at their basolateral domain. However, the intensity of the IHC reaction in specimens from UC patients was substantially lower than in control samples. CONCLUSION: The decreased expression of TLR-5 gene and protein in the mucosa of UC patients suggests that down-regulation of TLR-5 is probably caused by the increased number of ligand molecules in the proximity of epithelial cells in the inflamed tissue.

Copper staining method for extracting biologically active proteins from native gels.

An attempt was made to make protein bands visible on native gel using copper staining, since such a mild staining procedure would make the entire native gel electrophoresis process non-denaturing. Copper staining not only was able to detect various proteins on native gel with reasonable sensitivity, but also made extraction and recovery of active proteins possible from the gel using a gentle procedure.

CV706, a prostate cancer-specific adenovirus variant, in combination with radiotherapy produces synergistic antitumor efficacy without increasing toxicity.

Radiation is an effective means of treating localized prostate cancer. However, up to 40% of men with certain risk factors will develop biochemical failure 5 years after radiotherapy. CV706, a prostate cell-specific adenovirus variant, is currently in clinical trials for the treatment of recurrent organ-confined prostate cancer. We demonstrated previously that a single administration of CV706 at 5 x 10(8) particles/mm3 of tumor eliminated established tumors within 6 weeks in nude mouse xenografts (Rodriguez et al., Cancer Res. 57: 2559-2563, 1997). We now demonstrate that CV706-mediated cytotoxicity is synergistic with radiation. In vitro, addition of radiation to CV706 resulted in a synergistic increase of cytotoxicity toward the human prostate cancer cell line LNCaP and a significant increase of virus burst size, with no reduction in specificity of CV706-based cytopathogenicity for prostate cancer cells. In vivo, prostate-specific antigen (+) LNCaP xenografts of human prostate cancer were treated with CV706 (1 x 10(7) particles/mm3 of tumor), 10 Gy of single fraction local tumor radiation, or both. Tumor volumes of the group treated with CV706 or radiation was 97% or 120% of baseline 6 weeks after treatment. However, when the same dose of CV706 was followed 24 h later with the same dose of radiation, the tumor volume dropped to 4% of baseline at this time point and produced antitumor activity that was 6.7-fold greater than a predicted additive effect of CV706 and radiation. Histological analyses of tumors revealed that, compared with CV706 or radiation alone, combination treatment with two agents increased necrosis by 180% and 690%, apoptosis by 330% and 880%, and decreased blood vessel number by 1290% and 600%, respectively. Importantly, no increase in toxicity was observed after combined treatment when compared with CV706 or radiation alone. These data demonstrate that CV706 enhances the in vivo radioresponse of prostate tumors and support the clinical development of CV706 as a neoadjuvant agent with radiation for localized prostate cancer.

Parkinson's disease-associated alpha-synuclein is more fibrillogenic than beta- and gamma-synuclein and cannot cross-seed its homologs.

Parkinson's disease (PD) is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies. Recently, two point mutations in alpha-synuclein were found to be associated with familial PD, but as of yet no mutations have been described in the homologous genes beta- and gamma-synuclein. alpha-Synuclein forms the major fibrillar component of Lewy bodies, but these do not stain for beta- or gamma-synuclein. This result is very surprising, given the extent of sequence conservation and the high similarity in expression and subcellular localization, in particular between alpha- and beta-synuclein. Here we compare in vitro fibrillogenesis of all three purified synucleins. We show that fresh solutions of alpha-, beta-, and gamma- synuclein show the same natively unfolded structure. While over time alpha-synuclein forms the previously described fibrils, no fibrils could be detected for beta- and gamma-synuclein under the same conditions. Most importantly, beta- and gamma-synuclein could not be cross-seeded with alpha-synuclein fibrils. However, under conditions that drastically accelerate aggregation, gamma-synuclein can form fibrils with a lag phase roughly three times longer than alpha-synuclein. These results indicate that beta- and gamma-synuclein are intrinsically less fibrillogenic than alpha-synuclein and cannot form mixed fibrils with alpha-synuclein, which may explain why they do not appear in the pathological hallmarks of PD, although they are closely related to alpha-synuclein and are also abundant in brain.

alpha-synuclein fibrillogenesis is nucleation-dependent. Implications for the pathogenesis of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies, the major components of which are filaments consisting of alpha-synuclein. Two recently identified point mutations in alpha-synuclein are the only known genetic causes of PD. alpha-Synuclein fibrils similar to the Lewy body filaments can be formed in vitro, and we have shown recently that both PD-linked mutations accelerate their formation. This study addresses the mechanism of alpha-synuclein aggregation: we show that (i) it is a nucleation-dependent process that can be seeded by aggregated alpha-synuclein functioning as nuclei, (ii) this fibril growth follows first-order kinetics with respect to alpha-synuclein concentration, and (iii) mutant alpha-synuclein can seed the aggregation of wild type alpha-synuclein, which leads us to predict that the Lewy bodies of familial PD patients with alpha-synuclein mutations will contain both, the mutant and the wild type protein. Finally (iv), we show that wild type and mutant forms of alpha-synuclein do not differ in their critical concentrations. These results suggest that differences in aggregation kinetics of alpha-synucleins cannot be explained by differences in solubility but are due to different nucleation rates. Consequently, alpha-synuclein nucleation may be the rate-limiting step for the formation of Lewy body alpha-synuclein fibrils in Parkinson's disease.

Both familial Parkinson's disease mutations accelerate alpha-synuclein aggregation.

Parkinson's disease (PD) is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies, the major component of which are filaments consisting of alpha-synuclein. Two recently identified point mutations in alpha-synuclein are the only known genetic causes of PD, but their pathogenic mechanism is not understood. Here we show that both wild type and mutant alpha-synuclein form insoluble fibrillar aggregates with antiparallel beta-sheet structure upon incubation at physiological temperature in vitro. Importantly, aggregate formation is accelerated by both PD-linked mutations. Under the experimental conditions, the lag time for the formation of precipitable aggregates is about 280 h for the wild type protein, 180 h for the A30P mutant, and only 100 h for the A53T mutant protein. These data suggest that the formation of alpha-synuclein aggregates could be a critical step in PD pathogenesis, which is accelerated by the PD-linked mutations.

Changes in conformation and stability upon SCF/sKit complex formation.

Stem cell factor (SCF) is thought to be a member of the four-helical bundle cytokine superfamily, and exists in solution as a noncovalent homodimer. It is the ligand for Kit, a tyrosine kinase type III receptor. The interaction of SCF and Kit affects early hematopoietic progenitors, as well as gametocytes, melanocytes, and mast cells. Upon binding of SCF the Kit undergoes dimerization and transphosphorylation. Circular dichroism (CD), intrinsic fluorescence, and Fourier transform infrared (FTIR) spectroscopy were used for conformational analyses of free SCF, soluble Kit (sKit), and the complex. The sKit consisted of the extracellular domain of Kit, contained five Ig-like domains, and was prepared from the conditioned media of transfected Chinese hamster ovary cells. With these techniques, a reproducible conformational change was seen upon ligand/receptor binding. The far-UV CD and FTIR spectroscopy indicated a slight increase in the alpha-helical content. The near-UV CD and fluorescence spectra showed changes in the environments of the aromatic amino acids. The thermal denaturation of SCF was not affected by complex formation, while the melting temperature of sKit increased only a few degrees when binding SCF. This indicates that binding is temperature dependent, consistent with titration calorimetry results published previously which demonstrated that there is a large enthalpy of binding. The conformational changes which accompany SCF/sKit binding could play a role in the receptor dimerization and signal transduction which follow.

The majority of stem cell factor exists as monomer under physiological conditions. Implications for dimerization mediating biological activity.

Soluble Escherichia coli-derived recombinant human stem cell factor (rhSCF) forms a non-covalently associated dimer. We have determined a dimer association constant (Ka) of 2-4 x 10(8) M-1, using sedimentation equilibrium and size exclusion chromatography. SCF has been shown previously to be present at concentrations of approximately 3.3 ng/ml in human serum. Based on the dimerization Ka, greater than 90% of the circulating SCF would be in the monomeric form. When 125I-rhSCF was added to human serum and the serum analyzed by size exclusion chromatography, 72-49% of rhSCF was monomer when the total SCF concentration was in the range of 10-100 ng/ml, consistent with the Ka determination. Three SCF variants, SCF(F63C), SCF (V49L,F63L), and SCF(A165C), were recombinantly expressed in Escherichia coli, purified, and characterized. The dimer Ka values, biophysical properties, and biological activities of these variants were studied. Dimerization-defective variants SCF(F63C)S-CH2CONH2 and SCF(V49L,F63L) showed substantially reduced mitogenic activity, while the activity of the Cys165-Cys165 disulfide-linked SCF(A165C) dimer was 10-fold higher than that of wild type rhSCF. The results suggest a correlation between dimerization affinity and biological activity, consistent with a model in which SCF dimerization mediates dimerization of its receptor, Kit, and subsequent signal transduction.

Epitope mapping and immunoneutralization of recombinant human stem-cell factor.

The epitope regions of three anti-[stem-cell factor (SCF)]g have been mapped by characterization of immunoreactivities against truncated forms of SCF in immunoblots and against synthetic peptides in solution-phase competition ELISA. Two of the antibodies, mAb 7H6 and mAb 8H7A, were raised against Escherichia coli-derived human SCF-(1-164) while the third, polyclonal antibody (pAb) 1337, was raised against a peptide corresponding to residues 3-31 of human SCF. The epitopes of mAbs 7H6 and 8H7A have been mapped to residues 61-95 and 95-110, respectively. The epitope of pAb 1337 has been mapped to residues 21-31. The ability of the anti-SCF Ig to recognize E. coli-derived human SCF presented in various formats, i.e. partially denatured (fixed in standard ELISA or on a western blot) or native (in solution), was studied, mAb 7H6 recognized its epitope in partially denatured or native SCF with equally high affinity, while mAb 8H7A and pAb 1337 recognized their epitopes only when SCF was at least partially denatured, mAb 7H6 was found to neutralize in vitro SCF-mediated cell proliferation and SCF binding to its receptor, when present in equimolar concentrations relative to the ligand, suggesting that the epitope region is functionally significant. Evidence that the mAb 7H6 epitope is represented by discontinuous regions (residues within sequences 61-65 and 91-95 are critically involved) is presented. The observation that the mAb 7H6 epitope is discontinuous has implications for the structure of SCF.

A role for stem cell factor (SCF): c-kit interaction(s) in the intestinal tract response to Salmonella typhimurium infection.

Cholera toxin (CT) has been shown to induce stem cell factor (SCF) production in mouse ligated intestinal loops. Further, SCF interaction(s) with its receptor (c-kit) was shown to be important for the intestinal tract secretory response after CT exposure. In this study, we have investigated whether SCF production is induced in the intestinal tract after exposure to Salmonella typhimurium and whether this production could be an important intestinal tract response to Salmonella infection. Using a mouse ligated intestinal loop model, increased levels of SCF mRNA were detected at 2-4 h post-Salmonella challenge. Intestinal fluid obtained from Salmonella-challenged loops contained high levels of SCF by ELISA. Human and murine intestinal epithelial cell lines were also shown to have increased levels of SCF mRNA after exposure to Salmonella. Inhibition of Salmonella invasion of epithelial cells was shown to be one potentially important role for SCF:c-kit interactions in host defense to Salmonella infection. Pretreatment of human or murine intestinal cell lines with SCF resulted in a cellular state that was resistant to Salmonella invasion. Finally, mice having mutations in the white spotting (W) locus, which encodes the SCF-receptor (c-kit), were significantly more susceptible to oral Salmonella challenge than their control littermates. Taken together, the above results suggest that an important intestinal tract response to Salmonella infection is an enhanced production of SCF and its subsequent interactions with c-kit.

Human stem cell factor dimer forms a complex with two molecules of the extracellular domain of its receptor, Kit.

Stem cell factor (SCF) is a cytokine that is active toward hematopoietic progenitor cells and other cell types, including germ cells, melanocytes, and mast cells, which express its receptor, the tyrosine kinase, Kit. SCF exists as noncovalently associated dimer at concentrations where it has been possible to study its quaternary structure; it stimulates dimerization and autophosphorylation of Kit at the cell surface. We have used recombinant versions of human SCF and human Kit extracellular domain (sKit) to study SCF-Kit interactions. By size exclusion chromatography, plus various physical chemical methods including light scattering, sedimentation equilibrium, and titration calorimetry, we demonstrate the formation of complexes containing a dimer of SCF (unglycosylated SCF1-165) plus two molecules of sKit. The concentrations of SCF and sKit in these studies were in the range of 0.35-16.2 microM. The data are analyzed and discussed in the context of several possible models for complex formation. In particular, the sedimentation data are not consistent with a model involving cooperative binding. The Kd estimate for SCF-sKit interaction, obtained by sedimentation equilibrium, is about 17 nm at 25 degrees C. With glycosylated SCF1-165, the Kd is considerably higher.

A role for stem cell factor and c-kit in the murine intestinal tract secretory response to cholera toxin.

The role of stem cell factor (SCF) and its receptor (c-kit) in the intestinal secretory response to cholera toxin (CT) was investigated using a ligated intestinal loop model in mice having mutations in the dominant white spotting (W) locus and the steel (Sl) locus. W/Wv mice, which express an aberrant form of the c-kit protein, failed to give an intestinal secretory response after luminal CT challenge. In contrast, W/Wv mice and their control littermates had equivalent intestinal secretory responses to Escherichia coli heat-stable enterotoxin (STa). Sl/Sld mice, which express only a soluble truncated form of SCF, also gave a significantly reduced intestinal secretory response to CT when compared to the secretory response of their littermate controls. The unresponsiveness of W/Wv mice to CT was restricted to the intestinal tract since these mice had foot pad swelling responses to CT challenge that were equivalent to their littermate controls. Restoration of mast cells in W/Wv mice by bone marrow transplantation of control littermate bone marrow did not reverse the CT-unresponsiveness of the intestinal tract. Histological evaluation of the gastrointestinal tract from W/Wv mice showed a normal distribution of enterochromaffin cells (ECC). CT challenge of either ligated intestinal loops from C57B1/6 mice or a mouse intestinal epithelial cell line (MODE-K) resulted in elevated levels of mRNA for SCF. MODE-K cells exposed to CT also had enhanced expression of c-kit. Finally, fluid obtained from CT-challenged ligated intestinal loops from C57B1/6 mice contained significant levels of SCF. Taken together, the above results suggest that CT-induced intestinal secretory responses are dependent upon SCF-c-kit interactions. These interactions appear to be induced as a consequence of CT stimulation of the intestinal tract and may also play a role in the development or functionality of the enteric nervous system.

Identification and characterization of a soluble c-kit receptor produced by human hematopoietic cell lines.

Stem cell factor (SCF) triggers cell growth by binding to cell surface c-kit receptors. Soluble forms of several cytokine receptors have been described and may play a role in the modulation of cytokine activity in vivo. For these reasons, we investigated whether human hematopoietic cells produce soluble c-kit receptors. The human leukemia cell lines OCIM1 and MO7e display approximately 80,000 and approximately 35,000 high-affinity cell surface c-kit receptors, respectively. Soluble c-kit receptors were detected by enzyme immunoassay in OCIM1 and MO7e culture supernatants. We determined the molecular weight and binding affinity of soluble c-kit receptor produced by OCIM1 cells, soluble c-kit receptor purified from human serum, and recombinant soluble c-kit receptor expressed in CHO cells. The three soluble c-kit receptors each have a molecular weight of 98 kD. Quantitative binding experiments with 125I-SCF indicate that the soluble c-kit receptors obtained from human serum or OCIM1 cells have binding affinities for SCF of approximately 200 to 300 pmol/L, in contrast to the recombinant form, which has a binding affinity of approximately 1.5 nmol/L. All three forms of the soluble c-kit receptor were able to compete with c-kit receptors on OCIM1 cells for 125I-SCF binding. Thus human hematopoietic cells can produce a soluble form of the c-kit receptor that retains high-affinity SCF binding activity. We speculate that the soluble c-kit receptor may bind SCF and function as a receptor antagonist in vivo.

Soluble kit receptor in human serum.

c-kit encodes the transmembrane receptor tyrosine kinase (Kit) for the recently described ligand stem cell factor (SCF). We have developed an enzyme-linked immunosorbent assay for measuring soluble human Kit and we have used the assay to show high levels of soluble Kit in human serum. The distribution of soluble Kit levels was investigated among 112 normal human serum donors. The mean serum level (+/- SD) was found to be 324 +/- 105 ng/mL with the values falling between 163 ng/mL and 788 ng/mL. No correlation between soluble Kit levels and the sexes or ages of the donors was found. Partial purification using immunoaffinity chromatography allowed us to characterize the soluble Kit from pooled human serum. Antibodies generated to a 497-amino acid recombinant human soluble Kit corresponding to the N-terminal extracellular domain of the receptor recognized the serum-derived soluble Kit by immunoblotting. We found that the serum-derived soluble Kit is glycosylated, with mostly N-linked but also O-linked carbohydrate, and with terminal sialic acid residues. When compared with the recombinant human soluble Kit, the serum-derived material was similar both in size and glycosylation pattern. CNBr cleavage of the isolated serum-derived material followed by amino terminal sequencing confirmed the presence of five peptides expected for the extracellular portion of the Kit molecule. The immunoaffinity purified serum-derived soluble Kit inhibited binding of [125I]SCF to membrane-bound receptor in an in vitro assay. These results indicate that soluble Kit could modulate the activity and functions of SCF in vivo.

Determination of elemental carbon emission.

The studies on elemental carbon content in the atmospheric air, performed at the air monitoring station in Katowice (Poland), have revealed violations of allowable maximum average annual and diurnal concentrations. Elemental carbon is introduced into the atmosphere mainly as soot generated from combustion processes. This work presents the determination of elemental carbon in emission generated from coal combustion processes.

Soluble stem cell factor in human serum.

Stem cell factor (SCF) is a recently described factor active in the early stages of hematopoiesis. It can exist in membrane-bound form and in proteolytically released soluble form. The levels and nature of SCF in human serum are described. As determined by an enzyme-linked immunosorbent assay performed for 257 samples, SCF level in serum averaged 3.3 +/- 1.1 ng/mL. The serum SCF was partially purified by immunoaffinity chromatography and analyzed by glycosidase treatments in conjunction with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The results show that the SCF has N-linked and O-linked carbohydrate and corresponds to the soluble form, at or about 165 amino acids in length. The findings suggest functional importance for soluble SCF in humans.

Post-translational processing of membrane-associated recombinant human stem cell factor expressed in Chinese hamster ovary cells.

This report describes the structure of soluble human stem cell factor isolated from the conditioned medium of Chinese hamster ovary (CHO) cells transfected with stem cell factor (SCF) cDNA, which encodes a leader sequence plus 248 additional amino acids. The 248 amino acids include a hydrophobic transmembrane region at positions 190-212. The isolated material is glycosylated and three bands (apparent M(r) 28,000, M(r) 35,000, and M(r) 40,000) are evident by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. After complete deglycosylation, the molecular weight by SDS-polyacrylamide gel electrophoresis is 18,000-19,000. Structural analyses of the intact SCF, the deglycosylated SCF, and a deglycosylated C-terminal peptide were performed by laser desorption, fast atom bombardment, or electrospray mass spectrometry. Pulse-labeling of cells with 35S-labeled Met and Cys resulted in cell-associated glycosylated SCF of M(r) 33,000-45,000 which was converted to M(r) 33,000 by in vitro treatment with glycosidases. During a chase with unlabeled Met and Cys, labeled SCF of M(r) 28,000, M(r) 35,000, and M(r) 40,000 appeared in the medium; it was converted to M(r) 18,000-19,000 by glycosidase treatment. SCF at the surface of the transfected CHO cells could be demonstrated by immunofluorescence. The data obtained indicate that the recombinant human stem cell factor, as isolated, represents proteolytically processed forms containing amino acids 1-165, derived from the initially synthesized membrane-bound form of 248 amino acids. Further characterization indicated that the M(r) 28,000 form is glycosylated at Asn120, the M(r) 35,000 form at Asn120 and Asn65, and the M(r) 40,000 form at Asn120, Asn93, and Asn65. Each form also contains O-linked carbohydrate. The N-linked glycosylation, particularly that at Asn93 and at Asn65, adversely affects in vitro biological activity and receptor binding.

Purification and characterization of soluble forms of human and rat stem cell factor recombinantly expressed by Escherichia coli and by Chinese hamster ovary cells.

Stem cell factor (SCF) is a novel, early-acting hematopoietic factor. It was isolated from the medium of a rat cell line in a soluble, processed form (Zsebo et al., 1990, Cell 63, 195). The cloned human and rat genes encode the soluble form plus additional C-terminal amino acids including a hydrophobic transmembrane domain (Martin et al., 1990, Cell 63, 203). We have recombinantly expressed forms of human and rat SCF corresponding to the soluble, processed form in Escherichia coli and in Chinese hamster ovary (CHO) cells. After expression in E. coli, folding and oxidation of the SCF polypeptides are required. The SCFs expressed in CHO cells are secreted into the medium in active state and, like the natural SCF, are glycosylated. Purification of the recombinant SCFs is described. Biological and biochemical characterization includes activity toward responsive human and mouse cell lines, N-terminal amino acid sequences, disulfide bond linkages, and sites of glycosylation.

Glycosylated and unglycosylated recombinant-derived human stem cell factors are dimeric and have extensive regular secondary structure.

We have recently described the identification, isolation, and characterization of a factor, termed stem cell factor (SCF), which acts on primitive hematopoietic progenitors of the marrow. A soluble form of the factor was isolated from the conditioned medium of a rat cell line (Zsebo, K. M., Wypych, J., McNiece, I. K., Lu, H. S., Smith, K. A., Karkare, S. B., Sachdev, R. K., Yuschenkoff, V. N., Birkett, N. C., Williams, L. R., Satyagal, V. N., Tung, W., Bosselman, R. A., Mendiaz, E. A., and Langley, K. E. (1990) Cell 63, 195-201) and rat and human cDNAs have been cloned (Martin, F. H., Suggs, S. V., Langley, K. E., Lu, H. S., Ting, J., Okino, K. H., Morris, C. F., McNiece, I. K., Jacobsen, F. W., Mendiaz, E. A., Birkett, N. C., Smith, K. A., Johnson, M. J., Parker, V. P., Flores, J. C., Patel, A. C., Fisher, E. F., Erjavec, H. O., Herrera, C. J., Wypych, J., Sachdev, R. K., Pope, J. A., Leslie, I., Wen, D., Lin, C.-H., Cupples, R. L., and Zsebo, K. M. (1990) Cell 63, 203-211). The cDNAs encode amino acids C-terminal to those found in the isolated natural form, including a putative transmembrane domain. This paper describes the structural characterization of soluble forms of recombinant human SCF purified from Escherichia coli (unglycosylated) and from Chinese hamster ovary (CHO) cells (glycosylated). Fluorescence emission spectra indicate that the single Trp residue is present in a hydrophobic environment. Circular dichroism and infrared spectroscopy indicate considerable secondary structure, including both alpha-helix and beta-sheet. Molecular weight determinations by sedimentation equilibrium show that the molecules are dimeric (noncovalently associated), and gel filtration analyses are consistent with this conclusion. The CHO cell-derived SCF is about 30% carbohydrate by weight, with both N-linked and O-linked sugar. The presence or absence of the carbohydrate does not influence the results of the various structural analyses.