Crystal structure and enzymatic activity of an ADAMTS-13 mutant with the East Asian-specific P475S polymorphism

BACKGROUND

An East Asian-specific P475S polymorphism in the gene encoding ADAMTS-13 causes an approximately 16% reduction in plasma ADAMTS-13 activity.

OBJECTIVES

To demonstrate the impact of this dysfunctional polymorphism by characterizing the structure and activity of the P475S mutant protein.

METHODS

We determined the crystal structure of the P475S mutant of ADAMTS-13-DTCS (DTCS-P475S, residues 287-685) and compared it with the wild-type structure. We determined the enzymatic parameters of ADAMTS-13-MDTCS (residues 75-685) and MDTCS-P475S, and further examined the effects of denaturants and reaction temperature on their activity. We also examined the cleavage of shear-treated von Willebrand factor (VWF) by MDTCS-P475S.

RESULTS

MDTCS-P475S showed a reaction rate similar to that of wild-type MDTCS, but showed two-fold lower affinity for the peptidyl substrate, indicating that the Pro475-containing V-loop (residues 474-481) in the CA domain is a substrate-binding exosite. Structural analysis showed that the conformation of the V-loop was significantly different in DTCS-P475S and the wild type, where no obvious interactions of Ser475 with other residues were observed. This explains the higher susceptibility of the enzymatic activity of MDTCS-P475S to reaction environments such as denaturants and high temperature. MDTCS-P475S can moderately cleave shear-treated VWF.

CONCLUSIONS

We have provided structural evidence that the P475S polymorphism in ADAMTS-13 leads to increased local structural instability, resulting in lowered affinity for the substrate without changing the reaction rate. The moderate activity of ADAMTS-13-P475S for shear-treated VWF is sufficient to prevent thrombotic thrombocytopenic purpura (TTP) onset.

α-tubulin is rapidly phosphorylated in response to hyperosmotic stress in rice and Arabidopsis

By using high-resolution two-dimensional PAGE followed by phosphoprotein-specific staining and peptide mass fingerprint analysis along with other assays, we found that α-tubulin is phosphorylated in response to hyperosmotic stress in rice and Arabidopsis. The onset of the phosphorylation response was as early as 2 min after hyperosmotic stress treatment, and a major proportion of α-tubulin was phosphorylated after 60 min in root tissues. However, the phosphorylated form of α-tubulin was readily dephosphorylated upon stress removal. The phosphorylation site was identified as Thr349 by comprehensive mutagenesis of serine/threonine residues in a rice α-tubulin isoform followed by evaluation in cultured cell protoplasts. This residue is located at the surface for the interaction with β-tubulin in polymerized α-β tubulin dimers and has been proposed to be directly involved in this interaction. Thus, α-tubulin phosphorylation was considered to occur on free tubulin dimers in response to hyperosmotic stress. The incorporation of green fluorescent protein (GFP)-α-tubulin into cortical microtubules was completely inhibited in transgenic Arabidopsis when Thr349 was substituted with glutamate or aspartate. Using transgenic Arabidopsis plants expressing GFP-α-tubulin, we found that hyperosmotic stress causes extensive cortical microtubule depolymerization. Microtubule-destabilizing treatments such as propyzamide or oryzalin and temperature stresses resulted in α-tubulin phosphorylation, whereas hyperosmotic stress-induced α-tubulin phosphorylation was partially inhibited by taxol, which stabilizes microtubules. These results and the three-dimensional location of the phosphorylation site suggested that microtubules are depolymerized in response to hyperosmotic stress via α-tubulin phosphorylation. Together, the results of the present study reveal a novel mechanism that globally regulates the microtubule polymerization.

Estrogen receptor 1 gene as a tumor suppressor gene in hepatocellular carcinoma detected by triple-combination array analysis

Hepatocellular carcinoma (HCC) is one of the top five causes of cancer-related deaths worldwide. Recent developments in the treatment of HCC remain insufficient to cure unresectable disease or to prevent HCC. Consistent efforts are, therefore, needed to deepen understanding of pathogenesis of the disease. Genome-wide gene expression profile analyses can now detect various candidate genes that are modified by HCC. We have developed a new technique to identify tumor suppressor genes, triple-combination array analysis, which combines gene expression profiles, single nucleotide polymorphism and methylation arrays to identify genes with altered expression. Using HCC tissue samples, triple-combination array analysis was performed to identify a candidate tumor suppressor gene. Subsequently, samples from 48 HCC patients were subjected to quantitative polymerase chain reaction (qPCR) and methylation-specific PCR to further elucidate clinical relevance of the gene. Estrogen receptor 1 (ESR1) was detected as a candidate tumor suppressor gene. Of the 48 clinical samples, 40 (83.3%) showed ESR1 promoter hypermethylation. In 24 (50%) HCC samples, the expression levels of the ESR1 gene was decreased by >90%. The decreased expression was significantly related to high liver damage score, pathological invasion of the intrahepatic portal vein, the size of tumor (>3 cm in diameter) and hepatitis B virus infection. The present study represents another example that triple-combination array is a convenient technique for detecting genes with altered expression in disease. The ESR1 gene was identified as a candidate tumor suppressor gene in HCC and further validation is warranted.

RICE SALT SENSITIVE3 forms a ternary complex with JAZ and class-C bHLH factors and regulates jasmonate-induced gene expression and root cell elongation

Plasticity of root growth in response to environmental cues and stresses is a fundamental characteristic of land plants. However, the molecular basis underlying the regulation of root growth under stressful conditions is poorly understood. Here, we report that a rice nuclear factor, RICE SALT SENSITIVE3 (RSS3), regulates root cell elongation during adaptation to salinity. Loss of function of RSS3 only moderately inhibits cell elongation under normal conditions, but it provokes spontaneous root cell swelling, accompanied by severe root growth inhibition, under saline conditions. RSS3 is preferentially expressed in the root tip and forms a ternary complex with class-C basic helix-loop-helix (bHLH) transcription factors and JASMONATE ZIM-DOMAIN proteins, the latter of which are the key regulators of jasmonate (JA) signaling. The mutated protein arising from the rss3 allele fails to interact with bHLH factors, and the expression of a significant portion of JA-responsive genes is upregulated in rss3. These results, together with the known roles of JAs in root growth regulation, suggest that RSS3 modulates the expression of JA-responsive genes and plays a crucial role in a mechanism that sustains root cell elongation at appropriate rates under stressful conditions.

Cytokine responses in the Japanese pufferfish (Takifugu rubripes) head kidney cells induced with heat-killed probiotics isolated from the Mongolian dairy products

Cytokine responses in the Japanese pufferfish (Takifugu rubripes) head kidney (HK) cells to heat-killed lactic acid bacteria probiotics isolated from the Mongolian dairy products were investigated by transcriptomic examination. The HK cells were incubated with two heat-killed bacteria, namely Lactobacillus paracasei spp. paracasei (strain 06TCa22) and L. plantarum (strain 06CC2) and the responses of 16 cytokine genes at 0 (control), 1, 4, 8, 12, 24 and 48 h post-stimulation were assayed by multiplex RT-PCR analysis (GenomeLab Genetic Analysis System, GeXPS; Beckman Coulter, Inc.). The 16 genes included in the assay were pro-inflammatory cytokines (IL-1β, IL-6, IL-17A/F-3, TNF-α and TNF-N), cell-mediated immune regulators (IL-12p35, IL-12p40 and IL-18), antiviral (I-IFN-1 and IFN-γ) and other regulatory (IL-2, IL-7, IL-15, IL-21, IL-10 and TGF-β1) cytokines. Despite the differences in the transcriptional profiles, expression of all the cytokines tested here was significantly elevated by both the probiotic bacterial stimulants compared with the unstimulated control. Therefore, this in vitro study has demonstrated the modulation of cytokine defense mechanisms in the HK cells by the two heat-killed probiotics indicating their potentiality as novel immunostimulants to fish. However, strain-dependent varied expression of important cytokines (cell-mediated immune regulators, antiviral and anti-inflammatory cytokines) suggests better efficacy of L. paracasei spp. paracasei strain as fish immunostimulant. Further in vivo studies to elucidate the cytokine regulation networks will validate our present observations. A careful evaluation of ant-inflammatory properties may be undertaken using single strain to affirm the immunostimulatory capability. Moreover, application timings and frequency to assess the longevity of immunostimulant effects and to make the application cost-effective need to be evaluated before any practical use in aquaculture.

Abstract 476: The effect of combination of oncolytic herpes virus HF10 with bevacizumab in the treatment of human breast carcinoma xenograft

Background: Breast cancer is the most common cancer in females, and the second leading cause of cancer death in women. A more specific and effective multimodal therapy is thus urgently needed. Oncolytic HSVs are good candidates because of broad host range and tumor selectivity. HF10 is a spontaneous mutant strain of HSV-1 and its replication ability would be better than other oncolytic viruses which were genetically modified. Studies using oncolytic HSV have shown enhanced angiogenesis and increased micro-vascular density after the HSV-1 treatment. Anti-angiogenic adjuvant treatment is therefore expected to improve oncolytic HSV-1 treatment results. Bevacizumab, a monoclonal antibody against VEGFA, is generally accepted as a good treatment option because it inhibits angiogenesis and slows tumor growth. In our study, combination of HF10 and Bevacizumab is evaluated in the treatment of human breast carcinoma xenograft model. Here we present our preliminary data.

Method: The VEGFA gene transcription and protein expression was measured in human breast cancer cell line (MCF-7, T47D and MDA-MB-231) by RT-PCR, Western blot and ELISA. The MTT analysis was performed to evaluate the efficiency of combination therapy in vitro. The effect of various doses of Bevacizumab on viral replication was evaluated by PCR and tittering of the virus replicating. The in vivo study is designed to consist of 192 female BALB/c nude mice that will be inoculated with 10ˆ7 cells into the mammary fat pad. Control group (N=32) will receive no treatment. HF10 group will receive 10ˆ8 pfu of HF10 intratumorally. Bevacizumab group (N=32) will receive 5mg/kg Bevacizumab intra-peritoneally twice a week. Combination group (N=96) will receive both HF10 (10ˆ8 pfu) and Bevacizumab (5mg/kg). Tumor volume will be measured twice a week. Two days after the last dose of the treatment, tumors will be collected and analyzed histopathologically, including CD31 staining for microvascular density, TUNEL assay for apoptosis, and immunostaining for HSV antigen.

Results: Among the three candidate cell line, MDA-MB-231 has the highest level of VEGFA expression, while T47D has the lowest VEGFA expression. The in vitro cytotoxic effect of HF10 is both time and dose dependent. Combination therapy did not affect the viral replication in vitro. Our in vivo study is ongoing, and we expect the combination strategy would increase viral distribution, decrease angiogenesis, and enhance the antitumor effects.

Conclusion: It is considered that enhanced angiogenesis effect following viral treatment remains an obstacle for oncolytic viral therapy. We expect that Bevacizumab enhances the viral distribution by antagonizing vascular permeability and decreasing tumor interstitial pressure, and as a result, oncolytic effect is increased. The oncolytic viral therapy in combination with angiogenesis inhibitor can be a promising cancer treatment.

Citation Format: Gewen Tan, Hideki Kasuya, Tevfik T Sahin, Toshio Shikano, Suguru Yamada, Akiyuki Kanzaki, Kazuo Yamamura, Tsutomu Fujii, Hiroyuki Sugimoto, Shuji Nomoto, Yoko Nishikawa, Paeng Noriko, Shin Takeda, Akimasa Nakao, Yasuhiro Kodera, Maki Tanaka. The effect of combination of oncolytic herpes virus HF10 with bevacizumab in the treatment of human breast carcinoma xenograft. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 476. doi:10.1158/1538-7445.AM2013-476

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Abstract 1152: Identification of protein tyrosine kinase 7 gene in hepatocellular carcinoma using a novel triple-combination array analysis

Background. Hepatocellular carcinoma (HCC) is one of the top five causes of cancer-related deaths worldwide. Recent developments in the treatment of HCC still have failed to prevent HCC. Genome-wide gene-expression profile analyses can now detect many candidate genes that are modified by HCC. We have developed a new technique to identify suppressor genes of HCC: triple-combination array analysis, which combines gene expression profile, single nucleotide polymorphism array and methylation array.

Methods. Triple-combination array analysis was performed on one HCC sample from a 68-year-old female patient, and one candidate of tumor suppressor gene was selected. Subsequently, we analyzed the identified gene by quantitative real-time reverse-transcriptase polymerase chain reaction (PCR) and methylation-specific PCR in samples from 48 HCC patients and in nine cell lines.

Results. Using this method, protein tyrosine kinase 7 (PTK7) was detected as a candidate of tumor suppressor gene. PTK7 gene is located on 6q21.2, and expression was reduced in HCC tissues at the high level of -2.5 compared with normal tissues. PTK7 locus did not show any deletion or amplification in the SNP array. The methylation value (0-1.0) in the tumor sample was 0.825 compared to 0.047 in normal tissues, indicating high methylation in tumor tissues in the methylation array. Of the 48 clinical samples, 30 (62.5%) showed PTK7 promoter hypermethylation. The PTK7 promoter hypermethylated cases were significantly low expressions status (P=0.035), and bad prognosis in both overall survival (P<0.01) and recurrence-free survival (P=0.018) compared to hypomethylated cases. On the other hand, the cases, of which the PTK7 expressions in tumor tissues decreased by more than 20% degrees compared to those in normal tissues, were significantly worse prognosis in overall survival (P=0.0136) than the other cases, but not in recurrence-free survival (P=0.3102).

Conclusions. We suggest that the PTK7 gene acts as a tumor suppressor gene in HCC. This present study indicates that triple-combination array is an available and convenient technique for detecting the genes with altered expression in disease.

Citation Format: Mitsuhiro Hishida, Shuji Nomoto, Yoshikuni Inokawa, Masamichi Hayashi, Suguru Yamada, Tsutomu Fujii, Hiroyuki Sugimoto, Shin Takeda, Yasuhiro Kodera. Identification of protein tyrosine kinase 7 gene in hepatocellular carcinoma using a novel triple-combination array analysis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1152. doi:10.1158/1538-7445.AM2013-1152

Abstract 3145: Investigation of a functional polymorphism in the epidermal growth factor gene for pathogenesis and prognosis of hepatocellular carcinoma in Japanese patients

[Introduction] A single nucleotide polymorphism (SNP) in the epidermal growth factor (EGF) gene (rs4444903) has been investigated as a predictor of hepatocellular carcinoma (HCC). Previous reports identified an A to G transition at position 61 in the 5’ untranslated region of the EGF gene and demonstrated that the G/G genotype was associated with an increased risk of developing HCC as compared to the A/G and A/A genotype. Racial differences with respect to the distribution of this SNP have been reported; however, no investigation has examined a Japanese population.

[Objectives] To examine the relationship between EGF SNP genotype and the development and prognosis of HCC in a Japanese population.[Methods] Restriction fragment-length polymorphism was used to determine EGF SNP genotype in two hundred and eight patients with HCC, who underwent resection in our department between 1994 and 2010. The level of EGF mRNA expression in cancerous tissues was measured by quantitative reverse transcription-PCR. EGF SNP was also analyzed in three hundred and four patients with either hepatitis, liver cirrhosis, or healthy controls. The correlation between EGF SNP genotype and prognosis was statistically analyzed in patients with HCC.

[Results] A/A, A/G, and G/G genotype were 5.3%, 42.8%, and 51.9% in the Japanese patients with HCC. Tumoral EGF mRNA expression in G/G patients was significantly higher than that in A/A patients (P=0.04). A/A, A/G, and G/G genotype were 8.2%, 35.9%, and 55.9% in patients without HCC. Analysis of the distribution of allelic frequencies revealed that the odds ratios of developing HCC were 1.86 (95% CI 0.88-4.12, P=0.23) in A/G patients and 1.44 (95% CI 0.70-3.17, P=0.33) in G/G patients compared with A/A patients. However, when the analysis was limited to patients with hepatitis C, the odds ratio were 3.37 (95% CI 1.20-12.06, P=0.02) in A/G patients, and 2.77 (95% CI 1.10-9.78, P=0.04) in G/G patients, compared with A/A patients. 3) No statistically significant differences were observed between EGF SNP genotype and disease-free and overall survival.

[Conclusions] The frequency of the EGF SNP genotype in a Japanese population was characterized by a very low distribution of A/A patients. The EGF 61*G allele was associated with greater EGF mRNA expression in HCC tissue. The EGF SNP genotype was also associated with risk for development of HCC in hepatitis C patients but not with prognosis.

Citation Format: Masaya Suenaga, Suguru Yamada, Tsutomu Fujii, Bryan C. Fuchs, Norio Okumura, Goro Nakayama, Shin Takeda, Kenneth K. Tanabe, Yasuhiro Kodera. Investigation of a functional polymorphism in the epidermal growth factor gene for pathogenesis and prognosis of hepatocellular carcinoma in Japanese patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3145. doi:10.1158/1538-7445.AM2013-3145

Flow cytometry as a diagnostic method for colorectal cancer

Intraoperative histopathological investigation plays an important role during surgery. Since the pathologist performs a diagnosis with a limited level of specimen, it may sometimes be difficult to reach a correct diagnosis. To improve the accuracy of the diagnosis, quantitative data from the whole specimen are helpful. It said that the detection capability for DNA aneuploidy (aneuploidy) is low for solid cancer compared with hematopoietic organ cancer. A new method that includes fresh tissue is introduced, the histogram from cancer tissue (cancer) and normal tissue (normal) is compared, new classification criteria are introduced, the Fast Fourier Transform (FFT) pattern (FFT pattern) obtained from FFT on the histogram is analyzed, and the area under the FFT pattern of the histogram (AUC) is compared. This method, named the "FFT-AUC method", which includes comparisons of AUC and the FFT pattern, shows good results.

New automatic cell isolation system for flow cytometry: cell isolation unit and staining reagent kit

Flow cytometry is well-known cell analysis method and useful to gain quantitative information from cells in blood, however, it is not widely used for solid tissues in clinical settings. This is partly because it takes a long time to prepare samples and the operation can be complicated. To resolve these problems, we developed a new automatic cell isolation system which consists of cell isolation unit and staining reagent kit specialized for flow cytometry. With this new system, cell isolation can be done more rapidly and easily. By using this method, we could determine optimum condition to disintegrate porcine colon tissue and stain cells stably in 6 minutes. This result indicates that our method can provide analysis data within 10 minutes. We also evaluated our method in colorectal cancer patients, and the result was promising. All the data suggests that this method can support and facilitate rapid diagnosis.

Clinical efficacy of adjuvant surgery following systemic treatments in patients with initially unresectable pancreatic cancer: Results of a project study for pancreatic surgery by the Japanese Society of Hepato-Biliary-Pancreatic Surgery

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Background: Medical oncologists or pancreatic surgeons have identified candidates for surgical resection in patients with initially unresectable pancreatic cancer who favorably responded to multimodal treatment. Additional surgical resection during multimodal treatment, is called “adjuvant surgery”. A multicenter survey was conducted to explore the clinical efficacy of adjuvant surgery for initially unresectable pancreatic cancer with a long-term favorable response to systemic treatments. Methods: Clinical data, including the primary endpoint of overall survival were retrospectively compared between 58 initially unresectable pancreatic cancer patients that underwent adjuvant surgery with a favorable response to non-surgical cancer treatments over 6 months after the initial treatment (adjuvant surgery group) and 101 patients who did not undergo adjuvant surgery (control group). Results: The median observation periods were 51 months (20-122) in the control group, and 54 months (26-125) in the adjuvant surgery group, respectively. The actuarial survival rate at 1, 3, and 5 years after initial treatment in adjuvant surgery group (95, 53, and 34%) was significantly better than that in control group (88, 18, and 10%, p<0.0001). The propensity score analysis to provide adjustment of significant differences in the clinical backgrounds between the two groups revealed that adjuvant surgery was a significant independent prognostic variable with an adjusted hazard ratio (95% confidential interval) of 0.569 (0.36-0.89). Subgroup analysis according to the time from initial treatment to surgical resection showed a significant favorable difference in the overall survival in patients who underwent adjuvant surgery over 240 days after the initial treatment. Conclusions: The adjuvant surgery can occupy an important position in the multimodal therapy for patients with initially unresectable pancreatic cancer. The overall survival rate from the initial treatment is extremely high, especially in patients who received systemic treatments for more than 240 days.

Morphological and topological transformation of membrane vesicles

Liposomes are micro-compartments made of lipid bilayer membranes withcharacteristics quite similar to those of biological membranes. To formartificial cell-like structures, we generated liposomes that containedsubunit proteins of cytoskeletons: tubulin or actin. Spherical liposomeswere transformed into bipolar or cell-like shapes by mechanical forcesgenerated by the polymerization of encapsulated subunits of microtubules.Disk- or dumbbell-shaped liposomes were developed by the polymerizationof encapsulated actin. Dynamic processes of morphological transformationsof liposomes were visualized by high intensity dark-field lightmicroscopy.Topological changes, such as fusion and division of membrane vesicles,play an essential role in cellular activities. To investigate themechanism of these processes, we visualized in real time the liposomesundergoing topological transformation. A variety of novel topologicaltransformations were found, including the opening-up of liposomes and thedirect expulsion of inner vesicles.

[Entry mechanism of morbillivirus family]

The genus Morbillivirus includes measles virus, canine distemper virus and rinderpest virus. These are highly contagious and exhibit high mortality. These viruses have the attachment glycoprotein, hemagglutinin (H), at the virus surface, which bind to signaling lymphocyte activation molecule (SLAM) and Nectin 4 as receptors for the entry. However, the molecular mechanism for this entry has been limitedly understood. Here we summarize the current topics, (1) newly identified receptor, Nectin 4, (2) crystal structures of H-receptor complexes and (3) detail biochemical studies of the H-F communication for the entry. These provide insight on the mechanism of morbillivirus entry event and furthermore drug developments.

Combination of the tumor angiogenesis inhibitor bevacizumab and intratumoral oncolytic herpes virus injections as a treatment strategy for human gastric cancers

BACKGROUND/AIMS

Advanced gastric cancer is difficult to treat due to the frequency of liver metastases and peritoneal dissemination. A combination of two new strategies, including the anti-angiogenesis inhibitor bevacizumab and an oncolytic herpes virus is a promising treatment for advanced cancer.

METHODOLOGY

The effects of bevacizumab on oncolytic herpes virus replication and viral cytotoxicity were examined at varying bevacizumab concentrations and viral titers. In addition, the ability of these two new promising anticancer agents to inhibit tumor growth was studied. Histological examinations of CD31 and LacZ were used to assess angiogenesis and virus distribution within the tumor, respectively.

RESULTS

Bevacizumab did not affect viral replication or viral cytotoxicity in vitro. The combination of bevacizumab and the oncolytic herpes virus hrR3 significantly reduced tumor growth in vivo in an experimental gastric cancer model. Bevacizumab inhibited angiogenesis caused by local injection of hrR3 and induced virus spread. Bevacizumab increased the distribution of the intratumorally injected oncolytic herpes virus within the tumor.

CONCLUSIONS

Combination therapy consisting of bevacizumab and an oncolytic herpes virus is a promising new treatment strategy for gastric cancer.

[A case of lymph node recurrence of endocrine cell carcinoma of stomach effectively treated with carboplatin and etoposide]

We report a patient with lymph node recurrent endocrine cell carcinoma of the stomach who responded remarkably to carboplatin and etoposide chemotherapy. A 67-year-old woman underwent total gastrectomy under the diagnosis of poorly differentiated gastric carcinoma with esophagus and lymph node invasion. Adjuvant chemotherapy was not conducted because of the delay of postoperative recovery despite III b staging. Recurrence in thoracic paratracheal lymph node was diagnosed 6 months after surgery by follow-up CT scan. Carboplatin and etoposide were administrated for 4 months(6 courses of treatment), and complete response was obtained after 3 courses of treatment. The absence of recurrence was confirmed for 6 months after treatment. Although grade 4 neutropenia, grade 3 nausea and grade 2 vomiting were observed in first course of treatment, supportive therapy with G-CSF and aprepitant were useful for the continuity of treatment. Carboplatin and etoposide therapy may be one of the better candidates for stomach endocrine cell carcinoma in terms of its effects and tolerability, compared with a chemotherapy regimen combined with cisplatin.

Molecular characterization of the rice protein RSS1 required for meristematic activity under stressful conditions

Post embryonic growth of plants depends on cell division activity in the shoot and root meristems, in conjunction with subsequent cell differentiation. Under environmental stress conditions, where plant growth is moderately impaired, the meristematic activity is maintained by mechanisms as yet unknown. We previously showed that the rice protein RSS1, whose stability is regulated depending on the cell cycle phases, is a key factor for the maintenance of meristematic activity under stressful conditions. RSS1 interacts with a catalytic subunit of protein phosphatase 1 (PP1), but other molecular characteristics are largely unknown. Here we show that RSS1 interacts with all the PP1 expressed in the shoot apex of rice. This interaction requires one of the conserved regions of RSS1, which is important for RSS1 function. Interestingly, the recombinant RSS1 protein is highly resistant to heat with respect to its anti-coagulability and binding activity to PP1. The features of RSS1 are reminiscent of those of inhibitor-2 of animals, although it is likely that the mode of function of RSS1 is different from that of inhibitor-2. Noticeably, RSS1 binds to PP1 under extremely high ionic strength conditions in vitro. Therefore, RSS1 possibly functions by forming a stable complex with PP1.