Ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid induces apoptosis and cell cycle arrest in CNE-2Z nasopharyngeal carcinoma cells.

Ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F), a compound isolated from Pteris semipinnata L. (PsL), inhibits cell proliferation and induces cell apoptosis in several cancer lines. We found that 5F induced apoptosis and G2 phase cell cycle arrest in the CNE-2Z nasopharyngeal carcinoma (NPC) cells, accompanied by a decrease of NF-κB expression. 5F suppressed the viability of CNE-2Z cells in a time- and dose-dependent manner. 5F induced G2/M phase cell cycle arrest, but did not induce p21. Further analysis revealed that CNE-2Z cells harbored two p53 mutations. 5F treatment resulted in mitochondrial apoptosis, associated with increased Bax/Bcl-2 ratio, upregulation of cytochrome c in the cytosol, decreased NF-κB-p65 and increased IκB. Of note, 5F significantly sensitized CNE-2Z cells to cisplatin. 5F did not increase ROS, but reduced ROS production alone or in combination with cisplatin. Our data suggest that 5F is a potential anti-NPC drug for the development of single agent therapy and therapy in combination with cisplatin.

[Effect of Aloe emodin on invasion and metastasis of high metastatic breast cancer MDA-MB-231 cells].

OBJECTIVE: To investigate the effect of Aloe emodin (AE) on the invasive and metastatic abilities of human high metastatic breast cancer MDA-MB-231 cells. METHODS: MTT assay was used to evaluate the viability of MDA-MB-231 cells after treated with AE for 6 h and 24 h. The adhesive potential of MDA-MB-231 cells to FN and LN was tested by cell-matrix adhesion assay. The effect of AE on invasion of MDA-MB-231 cells was measured by Transwell chamber assay. Scratch wound healing assay was applied to determine the effect on migration of MDA-MB-231 cells. The effect of AE on MDA-MB-231 lung metastasis was determined on an experimental metastatic model. RESULTS: 80 micromol/L AE significantly inhibited the invasion, adhesion to FN, LN of MDA-MB-231 cells in vitro, the inhibitory rates were (52.98 +/- 5.46)%, (34.99 +/- 2.63)%, (28.73 +/- 7.00)%, respectively. After 24 h treatment, AE significantly inhibited the migration of MDA-MB-231 cells. The number and volume of lung metastatic nodules formed by MDA-MB-231 cells after 80 micromol/L AE 24 h treatment were decreased compared with control group. CONCLUSION: AE can suppress the metastasis of MDA-MB-231 cells. Their mechanisms may be related to the inhibition of the capabilities of invasion and migration of MDA-MB-231 cells.

Ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid induces apoptosis of human malignant cancer cells.

Ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F) is a chemical compound isolated from Pteris semipinnata L (PsL), a Chinese traditional herb. 5F has been known to exert antitumor activity in several kinds of human malignant cancer cells by leading cancer cell to apoptosis. 5F translocated Bax into the mitochondria, down-regulated Bcl-2, activated caspase-9 and caspase-3, released cytochrome c into the cytosol and translocated AIF from the mitochondria to the nucleus. The presentation of a wild-type p53 in the cancer cells facilitated cancer cells sensitive to the 5F treatment. 5F induces apoptosis of cancer cells by inhibiting NF-κB activation/induction, which leading to the decrease of Bcl-2 but the increase of Bax and Bak. MAPK kinases and Akt are also involved in process of 5F inducing cancer cell apoptosis. In lung cancer, 5F activated ERK1/2 and the inhibition of ERK1/2 suppressed 5F-mediated changes in apoptotic molecules. 5F activated Akt and suggested that Akt activation was anti-apoptotic rather than pro-apoptotic. However, in anaplastic thyroid carcinoma, JNK activation was related to cell death induced by 5F. ERK and p38 were also activated but as survival signals in response to 5F treatment to counteract the induction of cell death. Collectively, 5F is effective against several malignant cancers both in vivo and in vitro with minimal side effects. It induces apoptosis through the mitochondrialmediated pathway, in which regulation of Bcl-2 family proteins expression, the activation of MAPK and inactivation of NF-κB are critical. The good ability of 5F to inhibit cancer cells makes it in line with the successful development of other anti-tumor agents.

Ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid inhibits hepatocellular carcinoma in vitro and in vivo via stabilizing IkBα.

Ent-11-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F) isolated from Pteris Semipinnata L is known to inhibit certain tumor cells in vitro. The information on the in vivo effect of 5F is limited and its effect on hepatocellular carcinoma (HCC) is unknown. In this study, the anti-tumor effect of 5F was investigated in a diethylnitrosamine (DEN)-induced mouse HCC model. In addition to therapeutic effect, the potential side effect was monitored. A panel of cultured HCC cells was used to confirm the in vivo data and explore the responsible molecular pathway. The result showed that 5F significantly inhibited the DEN-induced HCC tumors by reducing the number of tumor foci and the volume of tumors. Furthermore, 5F induced the death of cultured HCC cells in dose- and time-dependent manners. The cell death was confirmed to be apoptotic by in vivo and in vitro TUNEL assays. 5F inhibited NF-kB by stabilizing its inhibitor IkBα, reducing the nuclear p65 and inhibiting NF-kB activity. Subsequently it affected the NF-kB downstream molecules with a decrease in anti-apoptotic Bcl-2 and increase in pro-apoptotic Bax and Bak. During the whole period of the experiment, mice receiving 5F appeared to be healthy, though they suffered from a mild degree of hair loss. 5F did not damage liver and renal functions. In conclusion, 5F is effective against HCC with minimal side effects. It induces apoptosis in HCC cells via inhibiting NF-kB, leading to the decrease of Bcl-2 but the increase of Bax and Bak.

Ent-11α-Hydroxy-15-oxo-kaur-16-en-19-oic-acid Inhibits Growth of Human Lung Cancer A549 Cells by Arresting Cell Cycle and Triggering Apoptosis.

OBJECTIVE: To examine the apoptotic effect of ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F), a compound isolated from Pteris semipinnata L (PsL), in human lung cancer A549 cells. METHODS: A549 cells were treated with 5F (0-80 µg/ml) for different time periods. Cytotoxicity was examined using a MTT method. Cell cycle was examined using propidium iodide staining. Apoptosis was examined using Hoechst 33258 staining, enzyme-linked immunosorbent assay (ELISA) and caspase-3 activity analysis. Expression of representative apoptosis-related proteins was evaluated by Western blot analysis. Reactive oxygen species (ROS) level was measured using standard protocols. Potential interaction of 5F with cisplatin was also examined. RESULTS: 5F inhibited the proliferation of A549 cells in a concentration- and time-dependent manner. 5F increased the accumulation of cells in sub-G1 phase and arrested the cells in the G2 phase. Exposure to 5F induced morphological changes and DNA fragmentation that are characteristic of apoptosis. The expression of p21 was increased. 5F exposure also increased Bax expression, release of cytochrome c and apoptosis inducing factor (AIF), and activation of caspase-3. 5F significantly sensitized the cells to cisplatin toxicity. Interestingly, treatment with 5F did not increase ROS, but reduced ROS production induced by cisplatin. CONCLUSION: 5F could inhibit the proliferation of A549 cells by arresting the cells in G2 phase and by inducing mitochondrial-mediated apoptosis.

[Effect of seven kinds of flavonoids on recombinant human protein tyrosine phosphatase].

OBJECTIVE: To observe the effects of seven kinds of flavonoids on recombinant human phosphatase of regenerating liver-3 activity. METHODS: The inhibitory effect of flavonoids was tested by DiFMUP assay. Calculation of IC50 values was performed according to the law of semi-effect-probit. RESULTS: Myricetin and gossypin could significantly inhibit recombinant PRL-3 activity in a concentration dependent manner with IC50 values of 55.54 and 68.86 micromol/L, respectively. Quercetin, luteolin and 7,8-Dihydroxyflavone had a weak inhibitory effect with IC50 values of 113.38, 151.56 and 249.49 micromol/L. respectively. While 3-hydroxyflavone and 6-hydroxyflavone had no significant effect on PRL-3 activity. Structure activity study indicated that C4 and C7 hydroxyls on the flavone skeleton were key functional groups to influencing PRL-3 inhibotory activity. The inhibitory effect of flavonoids on PRL-3 was increased with the number of hydroxyl group. CONCLUSION: Myricetin and gossypin were two strong inhibitors on recombinant human protein tyrosine phosphatase PRL-3.

Anticancer efficacy of 5F in NNK-induced lung cancer development of A/J mice and human lung cancer cells.

The mechanism responsible for the apoptotic effect induced by ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F) is not fully understood and its in vivo effect has not been tested. In this study, the effect and mechanism of 5F was investigated in cigarette smoking carcinogen 4-methylnitrosamino-1-3-pyridyl-butanone (NNK)-induced mouse lung tumor model and in cultured lung cancer cells NCI-H23 and CRL-2066. 5F were given to mice after they were treated with NNK for 18 weeks. The effect of 5F on the lung tumor formation was examined, and its side effect was monitored. Cell proliferation and apoptosis were determined through expression of PCNA, Bcl-2, Bax, and TUNEL assay in in vivo animal model. 5F significantly inhibited the NNK-induced lung tumors by inducing apoptosis and suppressing cell proliferation in vivo with minimal side effects. Cell culture experiments showed that 5F translocated Bax into the mitochondria, downregulated Bcl-2, activated caspase-9 and caspase-3, released cytochrome c into the cytosol, and translocated AIF from the mitochondria to the nucleus, which leading to G2-M cell cycle arrest and cell apoptosis. 5F also activated ERK1/2 and the inhibition of ERK1/2 suppressed 5F-mediated changes in apoptotic molecules. In addition to ERK1/2, 5F activated Akt. The inhibition of Akt further facilitated the apoptosis induced, suggesting that Akt activation was anti-apoptotic rather than pro-apoptotic. Collectively, 5F is effective against lung cancer in vivo with minimal side effects. It induces apoptosis in lung cancer through the mitochondrial-mediated pathway, in which the activation of ERK is critical.

[Apoptosis effect and mechanism of 5F from Pteris semipinnata on HepG2 cells].

OBJECTIVE: To investigate the effect of Pteris semipinnata L. (PsL) extract Ent-11alpha-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F)-on HepG2 cells and explore its potential mechanism. METHODS: Cytotoxicity of 5F was studied in HepG2 cells treated with different doses of 5F (0 - 80 mg/L) for 24 h and cell viability was determined by MTT assay. To analyze apoptosis qualitatively, the Hoechst/PI assay was used. The level of Bax in mitochondria fraction of 5F-treated HepG2 cells was determined by western blotting. The levels of cyto-c and AIF in the cytosol were analyzed by western blotting. RESULTS: The cytotoxicity of 5F on HepG2 cells was elevated with the increasing of 5F concentrations, as evidenced by the cell viability assay. The apoptotic cells characterized by condensed neclei were observed after the exposure of HepG2 cells to 5F. The level of Bax in mitochondria fraction of 5F-treated HepG2 cells increased. The levels of cyto-c and AIF in the cytosol of 5F-treated HepG2 cells increased. CONCLUSION: 5F mediated apoptosis involves mitochondria-dependent pathway and 5F might have a therapeutic value against human cancer cell lines and especially on hepatocellular carcinoma (HCC) cells.

[Effects of mitoxantrone on the activity of human protein kinase CK2 holoenzyme].

BACKGROUND & OBJECTIVE: Protein kinase CK2, a highly conserved protein serine/threonine kinase that is ubiquitously distributed in eukaryotes, has a close relationship with human leukemia. Mitoxantrone is an effective drug used for acute leukemias. This study was to observe the effects of mitoxantrone on the activity of recombinant holoenzyme of human protein kinase CK2 and proliferation in human leukemia cell line HL-60. METHODS: The CK2 holoenzyme composed of alphao and beta subunits was recombined in vitro. Subsequently, CK2 was treated with mitoxantrone at various concentrations, followed by addition of reacting liquid containing [gamma-32P] ATP. CK2 activity was measured by detecting the radioactivity of 32P transferred onto the substrates of CK2. The effect of mitoxantrone on the proliferation of HL-60 cells was detected by the trypan blue dye exclusion assay; the changes in the cell cycle were analyzed by flow cytometry (FCM); apoptosis was analyzed by FCM and DNA agarose gel electrophoresis; effects of the drugs on the intrinsic CK2 activity were measured by a specific CK2 peptide substrate. RESULTS: Mitoxantrone strongly inhibited the holoenzyme activity of recombinant human protein kinase CK2 (IC50=0.66 micromol/L). The inhibition of CKZ by mitoxantrone was competitive with respect to ATP (Ki 0.25 micromol/L) and mostly non-competitive with respect to casein (Ki 0.66 micromol/L). Mitoxantrone exerted strong cytotoxicity to HL-60 cells. When treated with 0.1 micromol/L mitoxantrone for 12 h, the apoptotic rate of HL-60 cells was 9.3%. Mitoxantrone did not affect intracellular CK2 activity. CONCLUSIONS: Mitoxantrone is a strong inhibitor of recombinant human protein kinase CK2 in vitro. Apoptosis induced by mitoxantrone in HL-60 cells has no correlation to intracellular CK2 activity.

[Improvement of synthesis of quercetin and genistein sulfates and identification by HPLC-MS].

OBJECTIVE: To improve synthesis of quercetin and genistein sulfates. METHODS: Quercetin and genistein were esterified with concentrated sulfuric acid for 3 hours in ice and esterfication was terminated by neutralization with 6N NaOH. Derivatives were identified by HPLC-APCI-MS. RESULTS: Quercetin and genistein derivatives were only one compound of monosulfate. CONCLUSION: The improvement of synthesis of quercetin and genistein sulfates is a convenient method for obtaining soluble derivatives of the flavonoids.

Inhibitory effect of aloe-emodin on metastasis potential in HO-8910PM cell line.

Aloe-emodin (AE) has been demonstrated to have antitumor activity in several tumor cells. However, no information is available on the effect of AE on metastasis in human carcinoma cells. This study was designed to investigate the inhibitory effect of AE on the metastasis potential of HO-8910PM cell line in vitro, and the role of AE in focal adhesion kinase (FAK) expression. Transwell chamber assay was performed to determine the effect of AE on the invasion and migration capacities of the cells. The effect of AE on the adhesion potential of HO-8910PM cells was determined by cell-Matrigel adhesion assay. We found that AE significantly inhibited invasion, migration, and adhesion capacities of HO-8910PM cells, and, furthermore, reduced the protein and mRNA expression of FAK. These findings suggest that the possible mechanistic explanation for the inhibitory effect of AE on metastasis potential in vitro is involved in FAK expression.

[Studies on quality standard of PsL 5F injections].

OBJECTIVE: To establish the quality standard of PsL injections containing mainly 5F (ent-11alpha-hydroxy-15-oxo-kaur-16-en-19-oic-acid). METHOD: The identification of PsL was performed by thin-layer chromatography, and the content was determined by HPLC. The column was Hypersil C18 (4.6 mm x 250 mm, 5 microm), the mobile phase was the mixture of methane-water-acitic acid (55:45: 0.045) with a flow rate of 1.0 mL x min(-1), the detective wavelength was 254 nm, and the column temperature was maintained at 35 degrees C. The pH value and K+ content of the three batchs injection were determined with pH meter and flame photometric meter, and the contents of tannin, protein, oxalic acid salt and heavy metals were detected by deferent methods. RESULT: The TLC method was suitable for the identification of PsL5F. The linearity for 5F was obtained over the range of 30-240 microg x mL(-1) (r = 0.999 8), the average recovery of 5F was 99.8%. The injections were of pH value range from 7.80 to 8.20, K+ contents less than 10 mmol x L(-1), and the contents of tannin, protein, oxalic acid salt and heavy metals were qualified with the Chinese pharmacopoeia, respectively. CONCLUSION: It's sensitive and reliable that can be used as quality control methods of PsL5F injections.

Sodium butyrate-induced death-associated protein kinase expression promote Raji cell morphological change and apoptosis by reducing FAK protein levels.

AIM: To investigate the role of death-associated protein kinase (DAPK) on the apoptosis of Raji cells induced by sodium butyrate. METHODS: The apoptosis of Raji cells were induced by sodium butyrate for 2, 4, 6, 8, and 10 d. Simultaneity, the Raji cells were inhibited to adhere on culture flask by polyHEME. Cell viability was detected by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method and the cell apoptosis percentage was estimated by flow cytometry. DAPK and focal adhesion kinase (FAK) expression were measured by Western blotting. Coding sequence on the C-terminal of DAPK, which can suppress the function of DAPK, was transfected into the Raji cells to investigate whether the C-terminal of DAPK could inhibit the apoptosis of Raji cells induced by sodium butyrate. RESULTS: After being treated with sodium butyrate, the Raji cells expressed DAPK and displayed many protrusions to adhere onto the culture flask. The Raji cells were susceptible to apoptosis when they were inhibited adhesion by polyHEME. At that time, the cell viability decreased, the cell apoptosis percentage increased and the protein levels of total FAK were reduced. The Raji cells, which were transfected with the coding region on the C-terminal of DAPK, sustained apoptosis and the FAK protein level when treated with sodium butyrate. CONCLUSION: Sodium butyrate induced DAPK expression. It caused the Raji cells to display many protrusions all around the cells and adhere onto the culture flask. DAPK expression prompted apoptosis by reducing the FAK protein level in sodium butyrate-induced Raji cells.

[Advances in study on chemical constituents and pharmacological activities of plants of genus Pteris].

The main chemical constituents in plants of genus pteris include diterpenoids, diterpenoid glycosides, flavonoids, flavonoid glycosides, sesquiterpenoids and volatile oils, etc. Some of extracts show the following activities, such as antitumor, antifungi and antibacteria. Some of compounds have inhibitory effect on platelet aggregation and antiinflamatory action. The latest progress on chemical constituents and pharmacological activity were reviewed in the paper. Main problems and study directions in future of pteris were indicated.

[Study on the effect of resveratrol on metastasis-associated ability of ovarian carcinoma HO-8910PM cells in vitro].

OBJECTIVE: To investigate the inhibitory effect of resveratrol on the metastasis-associated ability of human highly metastatic ovarian carcinoma HO-8910PM cells in vitro. METHODS: MTf assay was used to examine the cytotoxicity of resveratrol in HO-8910PM cells; Transwell Chamber assay was performed to determine the effect on invasion and migratory capacity of the cells by resveratrol; Effect on adhesion potential of HO-8910PM cells was tested by cell-Matrigel adhesion assay. RESULTS: Resveratrol showed no cytotoxicity on HO-8910PM cells after 6 h treatment. Resveratrol significantly inhibited migration and adhesion capacity of HO-8910PM cells in vitro. Their inhibitory rates after treated with the chemical of 100 micromol/L for 6 h were (30. 1 +/- 10. 8) % ,(34. 27 +/- 1. 28)% , respectively. However, Resveratrol had no effect on invasion capacity of HO-8910PM cells. CONCLUSION: Resveratrol can inhibit the migration and adhesion of HO-8910PM cells in vitro. Resveratrol might be a potential drug to inhibit tumor metastasis.

[Determination of 5F in Pteris semipinnata L. from various origins by TLC-scanning].

OBJECTIVE: To determine the content of 5F in Pteris semipinnata L. from various origins. METHODS: 5F was determined by TLC-Scanning. RESULTS: The linear relationship was in range of 0. 504 - 2. 520 microg. The mean recovery was 96. 68% and RSD = 1.24% (n = 5). CONCLUSION: The method is available with a good reproducibility, and pretreatment is simple and easy to operate.

[Effect of three flavones on enzyme activity of recombinant human phosphoinositide 3-kinase p110beta catalytic subunit].

OBJECTIVE: To study the effect of three flavones-luteolin, apigenin and genistein on activity of recombinant human phosphoinositide 3-kinase (PI3-K) p110beta catalytic subunit. METHODS: Recombinant human P13-K p110beta catalytic subunit was expressed by gene engineering. PI3-K activity was assayed by incubation recombinant PI3-K p110beta with phosphatidylinostiol-4,5-bisphosphate and [gamma-32P] ATP; the 32P-radiolabeled lipids were extracted with cholroform and methanol, and assessed by scintillation counter. RESULTS: Luteolin and apigenin showed inhibition on the recombinant p110beta catalytic subunit with IC50 8. 65 micromol/L and 11.56 micromol/L, but genistein had no inhibition. CONCLUSION: Luteolin and apigenin are inhibitors of P13-K. The recombinant P13-K p1100 catalytic subunit may be used as a molecular target for simpler screening and development of more effective inhibitors of P13-K.

[Inhibitory effect of cantharidin on invasion and metastasis of highly metastatic ovarian carcinoma cell line HO-8910PM].

BACKGROUND & OBJECTIVE: Cantharidin, a natural toxin, has specific antitumor actions. Many researches confirmed that nuclear factor-kappaB (NF-kappaB) closely relates with invasion and metastasis of tumor. This study was designed to investigate inhibitory effect of cantharidin on metastasis-related ability of human highly metastatic ovarian carcinoma cell line HO-8910PM, and its mechanism. METHODS: MTT assay was used to examine cytotoxicity of cantharidin on HO-8910PM cells. Effect of cantharidin on adhesion potential of HO-8910PM cells was tested by cell-Matrigel adhesion assay. Transwell chamber assay was performed to determine its effect on invasion and migration capacities of HO-8910PM cells. Protein levels of NF-kappaB P65 subunit and vascular endothelial growth factor (VEGF) were assessed by Western blot. RESULTS: After 6-h treatment of 20 micromol/L of cantharidin, inhibitory rate of HO-8910PM cells was (8.4+/-2.2)%, inhibitory rates of invasion, migration, and adhesion capacities of HO-8910PM cells were (38.8+/-1.7)%, (40.3+/-5.6)%, and (55.1+/-6.7)%, respectively; protein levels of NF-kappaB P65 subunit and VEGF were down-regulated. CONCLUSIONS: Cantharidin can inhibit migration, invasion, and adhesion of HO-8910PM cells. Its possible mechanism may be involved in down-regulations of NF-kappaB P65 subunit and VEGF.

Cell death induced by Pteris semipinnata L. is associated with p53 and oxidant stress in gastric cancer cells.

In this study, we demonstrated that Ent-11alpha-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F) had stronger cytotoxicity against MKN-45, a gastric cancer cell line bearing wild-type p53 than MKN-28, another gastric cancer cell line containing missense mutation in p53. The rapid increase of ROS level was involved in the mechanism of cytotoxicity. Classical features of apoptosis induced by 5F were observed in MKN-45 cells only or more significant in MKN-45 cells than MKN-28 cells. Translocation of Bax from cytosol to mitochondria, reduction of delta psi m and DNA fragmentation were induced by 5F in the p53-dependent manner. We conclude that the expression of Bax and its downstream molecules requires the presentation of a wild-type p53 in the cells treated by 5F.

[Screening ubiquitin/ribosomal protein S27a by yeast two-hybridization system].

BACKGROUND & OBJECTIVE: Protein kinase CK2, a kind of ubiquitous eukaryotic messenger-independent protein serine/threonine kinase, plays a vital role in cell differentiation and proliferation, signal transduction and procession. Activity of CK2 in hematopoietic cells is 2-8 folds higher than that in relevant normal tissues, moreover changes of CK2 activity are correlated to tumor growth. In order to investigate the mechanism of its effect on hematopoietic cells, we used yeast two-hybridization screening the proteins interacting with protein kinase CK2alpha' subunit from HL-60 cells cDNA library. METHODS: The target CK2alpha' cDNA was obtained by amplifying recombinant plasmid pTHCK2A', containing human protein kinase CK2alpha' subunit cDNA, through polymerase chain reaction (PCR). Pst I/Nde I-digested PCR products were directionally cloned into DNA-BD vector pGBKT7, which had also been digested by Pst I/Nde I. The recombinant plasmid was named yeast two-hybridization BD bait plasmid, and confirmed by DNA sequencing, and auto-activated experiments. Total RNA of HL-60 cells was extracted, CLONTECH switching mechanism at 5' end of RNA transcript method was used to construct a cDNA library in yeast cells. Library plasmid was named AD plasmid. BD plasmid and AD plasmid were co-transformed into competent yeast AH109. Yeast two-hybridization was used to screen positive clones. RESULTS: Six proteins, interacting with human protein kinase CK2alpha' subunit, were screened. DNA sequencing and homology comparison showed that one of the proteins was highly homologous with ubiquitin/ribosomal protein S27a (99.8%). CONCLUSION: Using yeast two-hybridization system could screen out ubiquitin/ribosomal protein S27a, which may interact with human protein kinase CK2alpha' subunit, from HL-60 cells.