ABSTRACT
The cleavage of target mRNA by ribozymes is being exploited as a means of gene silencing in nucleic-acid-based therapies. We previously established an HIV-1-dependent ribozyme-expression vector system, based on Cre-loxP technology with an LTR-gag-p17 promoter as a molecular switch for use in acute HIV-1 infection. The simultaneous expression of the Cre protein and loxP homologous recombination induced a high level of HIV-1-replication inhibition, but ribozyme expression was transient. In the current study, we overcame this limitation by inserting EBNA-1 and oriP genes from the Epstein-Barr virus (EBV) into the vector. When this plasmid was introduced into HeLa CD4(+) cells, we observed long-term expression of both the EGFP reporter gene and the ribozyme. Moreover, HIV-1 replication was inhibited in the long-term in transfected cells. These data suggest that the HIV-1-dependent ribozyme-expression vector containing EBNA-1/oriP sequences would be a useful tool in HIV-1 gene therapy applications.
ABSTRACT
We previously demonstrated the function of an HIV-1-dependent ribozyme expression vector, with which the site-specific excision of loxP sequences can be achieved by using the Cre-loxP system (ON/OFF) as a molecular switch in an acute HIV-1 infection. However, this expression system also revealed the lower, non-specific expression of the anti-H1V-1 ribozyme in the absence of tat. To circumvent this problem, we used the more efficient HIV-1-dependent Cre recombinase gene expression vector, encoding the LTR-gag-p17 (extending from the 5'-LTR to the middle of the gag gene (pLTR-gag-p17-Cre)). Comparatively, the pLTR-gag-p17-Cre induces a higher Cre-protein expression level in an HIV-1 infection-dependent manner than the minimal pLTR-Cre. Furthermore, we constructed the ploxP-Rz-U5 and pLTR-gag-p17-Cre plasmids and also combined them into a single vector, pLTR-gag-p17-Cre/loxP-Rz-U5, for a comparison of their anti-HIV-1 activities. The resultant simultaneous expression of the Cre protein and the homologous recombination of the two loxP sequences induced a high level of HIV-1 replication inhibition (95%). Significantly, a high steady-state of ribozyme expression was observed in the RT-PCR analysis. These data imply that targeting the HIV-1 genes with the pLTR-gag-p17-Cre/loxP-Rz-U5 vector, which mediates HIV-1-dependent ribozyme expression, would be a useful tool for HIV-1 gene therapy applications.
Subject(s)
Gene Products, gag/genetics , HIV Infections/genetics , HIV-1/genetics , Integrases/genetics , RNA, Catalytic/genetics , Viral Proteins/genetics , Virus Replication/genetics , Gene Expression/genetics , Genetic Therapy , Genetic Vectors , HIV Infections/therapy , HIV-1/growth & development , HeLa Cells , HumansABSTRACT
Antiviral strategies to inhibit HIV-1 replication have included the generation of gene products that provide the intracellular inhibition of an essential viral protein or RNA. When used in conjunction with the HIV-1 long terminal repeat (LTR), an inducible promoter dependent on the virus-encoded trans-activator (tat), relatively high background activity is still observed in the absence of tat (Caruso & Klatzmann, 1992; Dinges et al., 1995). In order to circumvent this problem, we used the Cre/loxP (ON/OFF) recombination system as a tool for our investigation. In the present study, we constructed a loxP-cassette vector with the ribozyme (Rz) expression portion under the control of the tRNAi(Met) promoter between two loxP sequences (plox-Rz-U5). We also constructed an HIV-1 LTR promoter-driven Cre recombinase gene (pLTR-Cre). These vectors were triple-transfected into HeLa CD4 cells with the HIV-1 pseudotype viral expression vector. Basal activity was not detectable before HIV-1 infection. The LTR-dependent Cre protein product in HIV-1 infected HeLa CD4 cells expressed the ribozyme by inducing loxP homologous recombination, which strongly inhibited the HIV-1 gene expression. These results demonstrate the potential of an anti-ribozyme with the Cre/loxP system for controlling HIV-1 infection via gene therapy.
Subject(s)
Attachment Sites, Microbiological/genetics , Gene Expression Regulation , HIV-1/genetics , HIV-1/physiology , Integrases/metabolism , RNA, Catalytic/metabolism , Viral Proteins/metabolism , Virus Replication , Gene Expression Regulation, Viral , Genetic Engineering , Genetic Therapy , Genetic Vectors/genetics , HeLa Cells , Humans , Integrases/genetics , Mutagenesis, Site-Directed , Promoter Regions, Genetic/genetics , RNA, Catalytic/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Transfer, Met/genetics , RNA, Viral/genetics , RNA, Viral/metabolism , Recombination, Genetic/genetics , Viral Proteins/geneticsABSTRACT
We used the HIV-1 5'LTR and the Cre/loxP system to develop an anti-gene expression system. The LTR promoter of HIV-1 has a specific activity that includes the intermediary region of gag, as shown in a previous report. We constructed the U5-region of HIV-1 as the target of the ribozyme expression vector (pCre/loxP-Rz), with the Cre/loxP system under the control of this LTR promoter. The function of this vector is to induce the HIV-1 dependent ribozyme-mediated inhibition in a dose-responsive manner. Furthermore, ribozyme mRNA expression was detected in the presence of pNL4-3 in HeLa-CD4+ cells. These studies are expected to yield novel applications of antiviral strategies for HIV-1.
