Masao Miki

Sericin, a protein derived from silkworms, accelerates the proliferation of several mammalian cell lines including a hybridoma

Sericin, a constituent of the silkworm cocoon, was added to the culture of four mammalian cell lines: murine hybridoma 2E3-O,human hepatoblastoma HepG2, human epithelial HeLa and human embryonal kidney 293 cells. The proliferation of all cell lineswas accelerated in the presence of sericin. The hybridoma cellline was further studied. The 2E3-O cell line was so well adapted to serum-free medium that both the proliferation rate and maximum cell density in serum-free ASF103 medium were higher than in RPMI medium supplemented with all lots of FBS tested, and this proliferation was stimulated by the addition of sericin in a dose-dependent manner. Stimulation was observed at sericin concentrations from 0.01 to 0.1 %, although 1% sericin was severely harmful to the culture. In comparison with bovine serum albumin (BSA), a widely used supplement in serum-free medium, sericin had an equivalent effect on the proliferation of the hybridomas and sericin additively stimulated the proliferation with BSA. Although heat easily denatures and inactivates most proteins, the activity of sericin was not affected by autoclaving. In a similar manner to the silkworm-derived sericin, recombinant sericin synthesized in E. coli also stimulated the hybridoma proliferation, irrespective of whether it was autoclaved or filtered. Since BSA is obtained from bovine serum and the risk of infections such as bovine spongiform encephalopathy cannot be eradicated, sericin derived from insects could be a preferable culture medium supplement for stimulating the proliferation of mammalian cells.

Inducing proliferation of human amniotic epithelial (HAE) cells for cell therapy.

Probably because amnion is derived from the fetus and is exposed to the maternal immune system, human amniotic epithelial (HAE) cells do not express the HLA-A, -B, -C, or -DR antigens on their surfaces, suggesting that HAE cells do not induce rejection (immune reaction) after allotransplantation. And the amnion, like the placenta, is useless to the mother and child after birth. Therefore, HAE cells or tissues were expected to be suitable for allotransplantation. Because HAE cells produce large amounts of enzymes, amnion transplantation has been carried out in order to correct inborn errors of metabolism by supplementing lysosomal enzyme deficiencies. However, several problems remain before amnion allotransplantation can be accepted as effective. The HAE cell population is limited, because the maximum number of HAE cells obtainable from one donor is about 2 × 108 cells, and HAE cells proliferate poorly in in vitro culture. In this study, we aimed at increasing the HAE cell population in vitro. First, we investigated the effect of several cytokines on HAE cell proliferation and found that hepatocyte growth factor (HGF), epidermal growth factor (EGF), and transforming growth factor-β stimulated it, whereas IL-6 and LIF inhibited it. Second, we investigated the effects of amniotic fluid on HAE cell proliferation and observed that IL-6 in amniotic fluid inhibits it. Then, to inhibit the dying of cells, we attempted to inhibit apoptosis (one mode of cell death). Treatment with caspase III inhibitor increased the cell viability of HAE cells by 20%.

Improvement of islet culture with sericin.

Islet transplantation is a promising treatment for diabetes. Serum is a necessary supplement in islet cultures, but it has various disadvantages including the risk of contamination by several pathogens. Results of this study suggest that sericin is a useful alternative supplement. Sericin accelerated the proliferation of the rat insulinoma cell line RIN-5F and improved the serum-free culture of rat islets.

Switch Action of Troponin on Muscle Thin Filament as Revealed by Spin Labeling and Pulsed EPR

We have used pulsed electron-electron double resonance (PELDOR) spectroscopy to measure the distance between spin labels at Cys133 of the regulatory region of TnI (TnI133) and a native or genetically substituted cysteine of TnC (TnC44, TnC61, or TnC98). In the +Ca2+ state, the TnC44-TnI133-T distance was 42 Å, with a narrow distribution (half-width of 9 Å), suggesting that the regulatory region binds the N-lobe of TnC. Distances for TnC61-TnI133 and TnC98-TnI133 were also determined to be 38 Å (width of 12 Å) and 22 Å (width of 3.4 Å), respectively. These values were all consistent with recently published crystal structure (Vinogradova, M. V., Stone, D. B., Malanina, G. G., Karatzaferi, C., Cooke, R., Mendelson, R. A., and Fletterick, R. J. (2005) Proc. Natl Acad. Sci. U.S.A. 102, 5038–5043). Similar distances were obtained with the same spin pairs on a reconstituted thin filament in the +Ca2+ state. In the −Ca2+ state, the distances displayed broad distributions, suggesting that the regulatory region of TnI was physically released from the N-lobe of TnC and consequently fluctuated over a variety of distances on a large scale (20–80 Å). The interspin distance appeared longer on the filament than on troponin alone, consistent with the ability of the region to bind actin. These results support a concept that the regulatory region of TnI, as a molecular switch, binds to the exposed hydrophobic patch of TnC and traps the inhibitory region of TnI away from actin in Ca2+ activation of muscle.

Generation of a novel apoptosis-resistant hepatoma cell line

The expansionable human hepatoma cell lines have potential for use in a bio-artificial liver (BAL) system for liver disease due to the shortage of donation. However, at present, bioartificial livers are incomplete and the functions need to be improved or at least maintained for a longer period. In the present study, the authors aimed to establish a novel hepatoma cell line for a longer-term or permanent artificial liver. For this purpose, bcl-2, an anti-apoptosis gene, was introduced into hepatoma HepG2 cells. Over-expression of Bcl-2 significantly inhibited apoptosis. After 15 d of serum-deprived culture, the viability of HepG2-Bcl2 was 51% while that of mock transfectant (HepG2-mock) was decreased to 14%. In the presence of hygromycin B, HepG2-mock were dead by day 6, while the HepG2-Bcl2 viability at day 9 was 65%. Over-expression of Bcl-2 prolonged the period of the stationary phase in the growth curve and did not affect the growth rate during the exponential phase. To test the liver function, albumin production was measured. After 10 d of culture, the albumin concentration in the culture supernatant of HepG2-Bcl2 was 30 ng ml(-1), while that of HepG2-mock was 23 ng ml(-1). The cytochrome P-450 activity per culture of 3-methyl-cholanthrene-treated HepG2-Bcl2 was double that of treated HepG2-mock. Introduction of Bcl-2 was effective for the generation of a novel hepatoma cell line for artificial livers.

A Three-Dimensional FRET Analysis to Construct an Atomic Model of the Actin-Tropomyosin-Troponin Core Domain Complex on a Muscle Thin Filament

It is essential to know the detailed structure of the thin filament to understand the regulation mechanism of striated muscle contraction. Fluorescence resonance energy transfer (FRET) was used to construct an atomic model of the actin-tropomyosin (Tm)-troponin (Tn) core domain complex. We generated single-cysteine mutants in the 167-195 region of Tm and in TnC, TnI, and the β-TnT 25-kDa fragment, and each was attached with an energy donor probe. An energy acceptor probe was located at actin Gln41, actin Cys374, or the actin nucleotide-binding site. From these donor-acceptor pairs, FRET efficiencies were determined with and without Ca(2+). Using the atomic coordinates for F-actin, Tm, and the Tn core domain, we searched all possible arrangements for Tm or the Tn core domain on F-actin to calculate the FRET efficiency for each donor-acceptor pair in each arrangement. By minimizing the squared sum of deviations for the calculated FRET efficiencies from the observed FRET efficiencies, we determined the location of Tm segment 167-195 and the Tn core domain on F-actin with and without Ca(2+). The bulk of the Tn core domain is located near actin subdomains 3 and 4. The central helix of TnC is nearly perpendicular to the F-actin axis, directing the N-terminal domain of TnC toward the actin outer domain. The C-terminal region in the I-T arm forms a four-helix-bundle structure with the Tm 175-185 region. After Ca(2+) release, the Tn core domain moves toward the actin outer domain and closer to the center of the F-actin axis.

Effect of the silk protein sericin on the production of adenovirus-based gene-therapy vectors.

Adenoviral vectors are extensively used as gene‐delivery vehicles in gene therapy. They are usually produced by HEK‐293 cell (human embryonic kidney‐293 cell) culture, which requires specially formulated serum‐free medium, the cost of which is considerable or by supplementation with FBS (fetal bovine serum). The risk of infectious diseases such as BSE (bovine spongiform encephalopathy) and endogenous retrovirus derived from cattle is a serious concern. The present study reports the use of sericin protein derived from silkworm (Bombyx mori) as an effective supplement instead of FBS. Without FBS, HEK‐293 cells significantly proliferated in the presence of 0.025–0.4% sericin, especially at 0.1%, but the effect was inferior to that of FBS. When a lower titre [MOI (multiplicity of infection) 0.03] of adenoviral vector pAxCAiLacZ was used as the inoculum, HEK‐293 cells in the presence of 0.1% sericin produced a nearly 3‐fold higher vector titre than culture in the presence of 5% (v/v) FBS. However, when a higher vector titre (MOI 3.7) was used as the inoculum, HEK‐293 cells in the presence of sericin produced a slightly higher vector titre than in the presence of FBS, which might suggest that HEK‐293 cells produce a maximum amount when a higher vector titre is used as the inoculum. These increases in vector production with sericin were confirmed by LacZ (β‐galactosidase reporter gene) activity assay. Supplementation with sericin decreased lactate dehydrogenase activity, an indicator of cell death, suggesting that sericin improved cell survival; hence, prolonging the culture period might be one of the reasons for increased vector production. On the basis of these results, sericin peptide seems to be a potent and effective alternative supplement for production of adenoviral vectors without such risks as BSE and retrovirus.

Progesterone, but not 17β-estradiol, up-regulates erythropoietin (EPO) production in human amniotic epithelial cells

Human amniotic epithelial (HAE) cells have great potential for successful use in cell therapy, since they do not cause acute rejection upon allotransplantation. However, to date, HAE cells have not well been studied. We previously reported that HAE cells produce erythropoietin (EPO), which is known to be a regulator of hematopoiesis, and that the induction mechanism of HAE cells is unknown, although EPO production from HAE cells is not increased by hypoxia which induces several cell types to produce EPO. In this study, we determined whether female sex hormones, including progesterone and 17beta-estradiol, affect the EPO production of HAE cells. Bioactive measurement of EPO activity in the culture supernatants of HAE-SV40 cells, which were immortalized by transfection with a simian virus 40 large T antigen, revealed that EPO bioactivity was significantly increased by treatment with progesterone, but not 17beta-estradiol. Treatment of HAE-SV40 cells with progesterone transiently increased the EPO mRNA level by fivefold, while there was no change in response to 17beta-estradiol. Furthermore, the progesterone receptor (PR)-B was detected in both HAE cells and HAE-SV40 cells by Western blotting. These results suggest that EPO synthesis in HAE-SV40 cells is stimulated by progesterone, but not by 17beta-estradiol, and thus it is highly likely that the EPO synthesis of HAE cells is also regulated by progesterone.

A Three-Dimensional FRET Analysis to Construct an Atomic Model of the Actin–Tropomyosin Complex on a Reconstituted Thin Filament

Fluorescence resonance energy transfer (FRET) was used to construct an atomic model of the actin-tropomyosin (Tm) complex on a reconstituted thin filament. We generated five single-cysteine mutants in the 146-174 region of rabbit skeletal muscle α-Tm. An energy donor probe was attached to a single-cysteine Tm residue, while an energy acceptor probe was located in actin Gln41, actin Cys374, or the actin nucleotide binding site. From these donor-acceptor pairs, FRET efficiencies were determined with and without Ca(2+). Using the atomic coordinates for F-actin and Tm, we searched all possible arrangements for Tm segment 146-174 on F-actin to calculate the FRET efficiency for each donor-acceptor pair in each arrangement. By minimizing the squared sum of deviations for the calculated FRET efficiencies from the observed FRET efficiencies, we determined the location of the Tm segment on the F-actin filament. Furthermore, we generated a set of five single-cysteine mutants in each of the four Tm regions 41-69, 83-111, 216-244, and 252-279. Using the same procedures, we determined each segments location on the F-actin filament. In the best-fit model, Tm runs along actin residues 217-236, which were reported to compose the Tm binding site. Electrostatic, hydrogen-bonding, and hydrophobic interactions are involved in actin and Tm binding. The C-terminal region of Tm was observed to contact actin more closely than did the N-terminal region. Tm contacts more residues on actin without Ca(2+) than with it. Ca(2+)-induced changes on the actin-Tm contact surface strongly affect the F-actin structure, which is important for muscle regulation.

Silk Protein Sericin Accelerates Proliferation of Various Mammalian Cells

Sericin protein derived from silkworm cocoon was added to the culture of various mammalian cell lines including human hepatoblastoma HepG2, human fibroblasts and so on. The proliferations of all cell lines tested were accelerated in the presence of sericin and its mitogenic activity was comparable to that of bovine serum albumin (BSA), one of the best supplements for the culture medium. Sericin derived from silkworm cocoons would be a preferable supplement for culture media because the risk of infection to human was not reported, while BSA is obtained from bovine serum and the risk of infection such as bovine spongiform encephalopathy cannot be avoided. Recombinant sericin peptides synthesized by E. coli (1) also stimulated the growth of hybridoma as well as sericin derived from silkworm did. These results indicate that sericin is a novel and suitable mitogenic supplement for mammalian cell culture.