Methylation of RAR-β2, RASSF1A, and CDKN2A Genes Induced by Nickel Subsulfide and Nickel-carcinogenesis in Rats

Objective To investigate the expression variation of RAR‐β2, RASSF1A, and CDKN2A gene in the process of nickel‐induced carcinogenesis. Methods Nickel subsulfide （Ni 3 S 2 ） at dose of 10 mg was given to Wistar rats by intramuscular injection. The mRNA expression of the three genes in induced tumors and their lung metastasis were examined by Real‐time PCR. The methylation status of the 5’ region of these genes were detected by Quantitative Real‐time methylation specific PCR. Results The mRNA expressions of the three genes both in muscle and lung tumor were decreased distinctly in comparison with normal tissue. But hypermethylation was found only in muscle tumor. Conclusion These findings suggest that loss of function or decrease of RAR‐β2, RASSF1A, and CDKN2A, as well as the hypermethylation of 5’ region of these genes, are related with nickel exposure.

Molecular Cloning and Expression of Squalene Epoxidase from a Medicinal Plant, Bupleurum chinense

Objective In plant, squalene epoxidase （SE） catalyzes the first oxygenation step in the biosynthetic pathway of triterpenoid and phytosterol, representing one of the rate-limiting enzymes in this pathway. Bupleurum chinense is an important medicinal herb with its major active constituents such as triterpenoid saponins and saikosaponins. In order to obtain the series of enzymatic genes involved in saikosaponin biosynthesis, a cDNA of SE, designated BcSEI, was cloned from B. chinense. Methods The BcSEI gene was cloned by homology-based PCR and 5＇/3＇ RACE methods from the adventitious roots of B. chinense. The physical and chemical parameters of BcSE1 protein were predicted by protparam. In order to discover hints in amino acid sequences on the dominant functions in the biosynthesis of saponin or phytosterol, sequences of SE from other plants were downloaded from NCBI for sequences alignment and phylogenetic analysis. BcSEI was cloned into a yeast mutant KLNI （MATa, ergl.＇：URA3, leu2, ura3, and trpl） to verify the enzyme activity of BcSE1. Additionally, the tissue-specific expression and methyl jasmonate （MeJA） inducibility of BcSEI were investigated using quantitative real-time PCR. Results The predicted protein of BcSE1 is highly similar to SEs from other plants sharing amino acid sequence identities of up to 88%. The BcSEI can functionally complement with yeast SE gene （ERGI） when expressed in the KLNI mutant （MATa, ergl：：URA3, leu2, ura3, and trpl）. Using as controls with ^-amyrin synthase （G-AS） which is presumed to catalyze the first committed step in saikosaponin biosynthesis and a cycloartenol synthase （CAS） relating to the phytosterol biosynthesis, the transcript of BcSE1 was significantly elevated by MeJA in adventitious roots of B. chinenseand the transcript of BcSElwas most abundant in the fruits and flowers of plants, followed by that in the leaves and roots, and least in stems. Conclusion It is the first time to illustrate the molecular information of SE in B. chinense and to clone the full-length SEgene in plants of genus Bupleurum L.