Tet-On Inducible Expression System Research Articles

Analysis of the Contribution of NF-κB in the Regulation of Chemotherapy-Induced Cell Senescence by Establishing a Tetracycline-Regulated Cell System.

Therapy-induced senescence (TIS or therapy-induced premature senescence) is a key cellular program triggered in the course of cancer radiotherapy and chemotherapy with genotoxic drugs, both in cancer cells and in normal cells, whose activation critically affects the outcome of cancer therapy. Drug-induced senescent cells undergo a permanent cell cycle arrest, acquire distinctive morphological and biochemical alterations, and an enhanced secretory ability, referred to as senescence-associated secretory phenotype (SASP). The transcription factor NF-κB acts as a master regulator of the SASP, driving the expression of senescence-associated secretome components.Here we describe protocols for the establishment of a tetracycline-regulated cell system for the investigation of the role of NF-κB in TIS. We also describe protocols routinely used in our laboratory, to investigate TIS in this Tet-On inducible expression system. Finally, we describe techniques for the validation of TIS induction.

Development of a Tet-On Inducible Expression System for the Anhydrobiotic Cell Line, Pv11.

Simple SummaryAnhydrobiosis is a unique ametabolic state that is characterized by extreme body water loss due to desiccation, generally over 95%. The sleeping chironomid, Polypedilum vanderplanki, is an anhydrobiotic insect inhabiting semi-arid regions in Africa. Pv11 is an anhydrobiotic insect cell line established from the P. vanderplanki larvae, and the cell line also displays the extreme desiccation tolerance. This unique feature could be useful for developing a dry preservation technique. However, effective expression systems for protein production have not been available due to a limited number of experimental tools in Pv11 cells. To solve this problem, we identified a minimal promoter from the genome sequence of P. vanderplanki because promoters designed for model organisms are not available in Pv11 cells, although minimal promoters are commonly used for molecular biology experiments and biotechnology fields. The identification of the minimal promoter allowed us to develop an effectively inducible expression system in Pv11 cells. By using the system, several proteins including a functional protein with complex structures were successfully expressed in the cells. The successful establishment of the inducible system on Pv11 cells could contribute to bio-industrial protein production.The Pv11 cell line established from an African chironomid, Polypedilum vanderplanki, is the only cell line tolerant to complete desiccation. In Pv11 cells, a constitutive expression system for Pv11 cells was previously exploited and several reporter genes were successfully expressed. Here we report the identification of an effective minimal promoter for Pv11 cells and its application to the Tet-On inducible expression system. First, using a luciferase reporter assay, we showed that a 202 bp deletion fragment derived from the constitutively active 121-promoter functions in Pv11 cells as an appropriate minimal promoter with the Tet-On inducible expression system. The AcGFP1 (Aequorea coerulescens green fluorescent protein) was also successfully expressed in Pv11 cells using the inducible system. In addition to these reporter genes, the avian myeloblastosis virus reverse transcriptase α subunit (AMV RTα), which is one of the most widely commercially available RNA-dependent DNA polymerases, was successfully expressed through the inducible expression system and its catalytic activity was verified. These results demonstrate the establishment of an inducible expression system in cells that can be preserved in the dry state and highlight a possible application to the production of large and complex proteins.

Kbtbd2 inhibits the cytotoxic activity of immortalized NK cells through down-regulating mTOR signaling in a mouse hepatocellular carcinoma model.

Natural killer cell (NK cell)-based immunotherapy is a promising therapeutic strategy for hepatocellular carcinoma (HCC). However, the molecular mechanisms underlying the regulation of NK cell function in the tumor sites are not completely elucidated. In this study, we identified the enhanced expression of kelch repeat and BTB (POZ) domain containing 2(Kbtbd2) in intratumoral NK cells in a mouse HCC implantation model as a negative regulator of NK cells. To investigate this interaction, we used a Tet-on inducibleexpression system to control Kbtbd2 expression in an immortalized mouse NK cell line KIL C.2. With this approach, we found that overexpression of Kbtbd2 reduced KIL C.2 cell proliferation, decreased expression certain of Ly49 receptor family members, and substantially impaired cytotoxic activity of KIL C.2 cells in vitro. Moreover, phosphorylation of mTOR and its target 4E-binding protein 1 was reduced in Kbtbd2-expressing KIL C.2 cells, along with down-regulated phosphorylation of Erk1/2. Adoptively transferred Kbtbd2-expressing KIL C.2 cells exhibited weaker tumoricidal effect on hepatocellular carcinoma cells in the HCC implantation model, in comparison with transferred control KIL C.2 cells. Taken together, our investigation indicates that Kbtbd2 is an inhibitory molecule for the tumoricidal activity of KIL C.2 cells and perhaps intratumoral NK cells.

Abstract 1879: Transcriptional regulation of KAI1 by p73 in colorectal cancer metastasis

Abstract Background: p73 is a member of the p53 family transcription factors and known tumor suppressor. However, its transcriptional activity is complex owing to its multiple isoforms, and limited information is available regarding the transcriptional and functional regulation of the p73 gene in colorectal cancer. In this study, we examined the role of p73 in colorectal cancer. Methods: We established a TAp73 overexpressing cell line using the Tet-on inducible expression system and analyzed global RNA expression by RNA-sequencing (RNA-seq). We studied the effects of TAp73 expression on the migration, invasiveness, and EMT of colon cancer cells. We conducted experiments in animals with liver metastasis of colorectal cancer. To investigate the roles of p73 in colon cancer, we examined the samples from patients, who had undergone surgical resection for colorectal cancer between 2009 and 2013. mRNA expression of TAp73 and KAI1 was analyzed in 108 colorectal cancer specimen and adjacent non-cancerous tissues by real-time RT-PCR. Results: RNA-seq showed the association between TAp73 and KAI1 expression. Migration and invasiveness of colon cancer cells were reduced by TAp73 expression, but induced by KAI1 knockdown. TAp73 regulates KAI1 expression in colon cancer cell lines. TAp73-induced decrease in invasiveness and epithelial-mesenchymal transition (EMT) was abrogated by KAI1 knockdown in TAp73 overexpressing cells. Migration ability of TAp73 overexpressing cells was recovered by KAI1 knockdown. Hepatic metastases were significantly reduced in mice injected with TAp73 overexpressing cells and increased in those injected with TAp73 overexpressing cells with KAI1 knockdown. mRNA expression of TAp73 and KAI1 was higher in colorectal cancer tissues than in adjacent non-cancerous tissues. Significant correlation between TAp73 and KAI1 mRNA expression was detected in early stage primary colorectal cancer, but not in the advanced stage. Conclusions: This study suggests that p73 (TAp73) acts as a tumor suppressor in the progression of colorectal cancer and regulates the expression of KAI1, which is a key target of p73 in colorectal cancer liver metastases. Note: This abstract was not presented at the meeting. Citation Format: Woo Kyun Bae, Kyung Hyun Yoo, Keunsoo Kang, Lothar Hennighausen, Ik-Joo Chung. Transcriptional regulation of KAI1 by p73 in colorectal cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1879. doi:10.1158/1538-7445.AM2017-1879

Cellular Model of CEBPA N321D Captures Gene Expression Profile in the Transition to Pre-Leukaemic Status

BackgroundC/EBPα plays a pivotal role in myeloid differentiation at the CMP to GMP transition point, where it interacts with other transcription factors (TFs) implicated in haematopoiesis. CEBPA mutations are common in acute myeloid leukaemia (AML), predominantly in patients with M1 and M2 French-American-British (FAB) morphological classifications, but relatively little is understood about the pre-leukaemic alterations caused by mutated CEBPA. Murine models have established N321D as a particularly potent CEBPA mutation which causes AML with high mortality (Togami et al, Experimental Hematology, 2015). We aimed to develop an inducible expression system for CEBPA N321D in a cellular model which replicates early haematopoietic progenitors, to study the effects of this mutation on gene expression profiles relevant for malignant haematopoiesis.MethodsWe constructed a Piggy-bac Tet-on inducible expression system which has a 2A peptide mechanism enabling simultaneous expression of both N321D and mCherry fluorescent protein from the same transcript (Fig. 1). We also constructed a control with inducible expression of mCherry. These two plasmids were then transfected into the mouse progenitor cell line Hoxb8-FL (Redecke et al, Nature Methods, 2013), which is conditionally immortalized and models multipotent myelo-lymphoid progenitors. Single cell clones were established and selected for analysis on the basis of cell growth and mCherry fluorescence on induction. RNA was collected post-induction and without induction at 24, 48 and 72 hours in two replicates each from the N321D clone and from the empty control vector. RNA-seq data was aligned to the mouse genome using STAR aligner, processed to generate high throughput sequencing counts, and finally differential expression analysis was performed between N321D and the control.ResultsDifferential expression analysis identified 172 downregulated and 60 upregulated genes after N321D induction. Further analysis of the 172 downregulated genes against online published datasets of gene expression (Gene Expression Commons, https://gexc.stanford.edu), revealed that 19 of these genes are normally upregulated at the CMP to GMP transition. These include genes such as Hck, Met, Hdac8 and Kdm7a which have been previously implicated in haematological malignancy and which may provide novel insights into the leukaemic process fostered by the CEBPA N321D mutation. To further validate our data, we performed unsupervised hierarchical clustering of previously published microarray data from a large collection of over 400 AML expression profiles (Verhaak et al, Haematologica, 2009) using the genes identified in our study, and found that patient samples who had predominantly FAB classifications M1 and M2 clustered together (Fig. 2A,B), as would be expected in CEBPA-mutated AML.ConclusionsOur inducible expression system has the potential to provide novel insights into altered gene expression caused by induction of mutated CEBPA. In particular, our cellular model replicates an early stage of haematopoiesis, and implicates genes which were not previously known to interact with CEBPA. The importance of these genes in CEBPA N321D-mediated re-configuration of the myeloid transcriptional regulatory network requires further analysis. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Reversible immortalization of sheep fetal fibroblast cells by tetracycline-inducible expression of human telomerase reverse transcriptase.

To achieve reversible immortalization of cells, we design a modified tetracycline-inducible expression (Tet-on) system to conditionally regulate the ectopic expression of human telomerase reverse transcriptase (hTERT) in primary cells. The hTERT gene, hygromycin-resistant gene and all essential elements for achieving tetracycline induction were combined into a single plasmid vector. Sheep fetal fibroblast cells were transfected with the vector and four putative immortalized cell clones were obtained via induction of hTERT expression by doxycycline. These immortalized cells maintained a normal karyotype and showed no transformed phenotype after 250days continuous culture. When hTERT expression was switched off by withdrawal of doxycycline, the immortalized cells reverted to a normal proliferative state and eventually senesced after limited divisions. This single-plasmid based Tet-on inducible hTERT expression system can be applied for reversible immortalization of animal cells.

MiR-497 decreases cisplatin resistance in ovarian cancer cells by targeting mTOR/P70S6K1.

The mechanism of cisplatin resistance in ovarian cancer is not clearly understood. In the present investigation, we found that the expression levels of miR-497 were reduced in chemotherapy-resistant ovarian cancer cells and tumor tissues due to hypermethylation of miR-497 promoter. Low miR-497 expression levels were associated with chemo-resistant phonotype of ovarian cancer. By analyzing the expression levels of miR-497, mTOR and p70S6K1 in a clinical gene-expression array dataset, we found that mTOR and p70S6K1, two proteins correlated to chemotherapy-resistance in multiple types of human cancers, were inversely correlated with miR-497 levels in ovarian cancer tissues. By using an orthotopic ovarian tumor model and a Tet-On inducible miR-497 expression system, our results demonstrated that overexpression of miR-497 sensitizes the resistant ovarian tumor to cisplatin treatment. Therefore, we suggest that miR-497 might be used as a therapeutic supplement to increase ovarian cancer treatment response to cisplatin.

A site-specific genetic modification for induction of pluripotency and subsequent isolation of derived lung alveolar epithelial type II cells.

Human induced pluripotent stem cells (hiPSCs) have great therapeutic potential in repairing defective lung alveoli. However, genetic abnormalities caused by vector integrations and low efficiency in generating hiPSCs, as well as difficulty in obtaining transplantable hiPSC-derived cell types are still major obstacles. Here we report a novel strategy using a single nonviral site-specific targeting vector with a combination of Tet-On inducible gene expression system, Cre/lox P switching gene expression system, and alveolar epithelial type II cell (ATIIC)-specific Neomycin(R) transgene expression system. With this strategy, a single copy of all of the required transgenes can be specifically knocked into a site immediately downstream of β-2-microglobulin (B2M) gene locus at a high frequency, without causing B2M dysfunction. Thus, the expression of reprogramming factors, Oct4, Sox2, cMyc, and Klf4, can be precisely regulated for efficient reprogramming of somatic cells into random integration-free or genetic mutation-free hiPSCs. The exogenous reprogramming factor transgenes can be subsequently removed after reprogramming by transient expression of Cre recombinase, and the resulting random integration-free and exogenous reprogramming factor-free hiPSCs can be selectively differentiated into a homogenous population of ATIICs. In addition, we show that these hiPSC-derived ATIICs exhibit ultrastructural characteristics and biological functions of normal ATIICs. When transplanted into bleomycin-challenged mice lungs, hiPSC-derived ATIICs efficiently remain and re-epithelialize injured alveoli to restore pulmonary function, preventing lung fibrosis and increasing survival without tumorigenic side effect. This strategy allows for the first time efficient generation of patient-specific ATIICs for possible future clinical applications.

A dimerization defect caused by a glycine substitution at position 420 by serine in tissue‐nonspecific alkaline phosphatase associated with perinatal hypophosphatasia

Mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene cause hypophosphatasia (HPP), an inborn error of metabolism characterized by defects in bone and teeth mineralization accompanying subnormal levels of serum alkaline phosphatase activity. Missense mutations at position 420 of TNSALP (standard nomenclature), which convert glycine to serine [TNSALP (G420S)] or alanine [TNSALP (G420A)], have been reported in perinatal and childhood HPP, respectively. When expressed in COS-1 cells, both TNSALP mutants were indistinguishable from wild-type TNSALP [TNSALP (W)] as evidenced by immunofluorescence and western blotting. Nevertheless, the two TNSALP mutants did not show substantial alkaline phosphatase activity. In agreement with transiently transfected cells, TNSALP (G420S) expressed in a Tet-On inducible expression system lacked its alkaline phosphatase activity, although this mutant was anchored to the cell surface lipid bilayers by glycosylphosphatidylinositol as an 80 kDa mature form bearing complex-type oligosaccharides like TNSALP (W). Importantly, TNSALP (G420S) was found to largely fail to assemble into the homodimer in contrast to TNSALP (W). Taken together, these results demonstrate that the glycine residue at position 420 is crucial for the subunit interaction of TNSALP and hence its catalytic function without affecting trafficking of monomeric TNSALP. We conclude that the dimerization defect is the molecular basis for perinatal HPP associated with the genotype G420S/G420S.

Overexpression of 5-Lipoxygenase Increases the Neuronal Vulnerability of PC12 Cells to Aβ<sub>42</sub>

5-Lipoxygenase (5-LOX), which is believed to be a major source of oxidative stress, participates in somatostatin-receptor transmembrane signaling in the central nervous system. We used the Tet-On inducible expression system in PC12 cells to obtain cell lines with reproducible, stable 5-LOX expression levels to study its function. Cell apoptosis rates induced by Aβ(42) were determined using an apo-BrdDU kit. Lipid peroxide, antioxidant enzyme, and caspase-3 activities were evaluated with respective commercial kits. The expression of 5-LOX, bcl-2, and bax were detected by immunoblotting. A subclone of PC18 with Tet-On inducible expression of 5-LOX was selected from PC12 transfectants. Expression of 5-LOX had no significant inhibitory effect on the cell viability of the PC18 clone. In contrast, compared with the control group, the cell viability of clone PC18 was significantly reduced after the induction of 5-LOX during Aβ exposure. The differences in cell viability before and after the induction of 5-LOX during Aβ insult were significantly offset by AA861. Overexpression of 5-LOX only slightly improved the activities of superoxide dismutase (SOD). The levels of intracellular peroxides, SOD and caspase-3 activity, and Bax expression were significantly upregulated, and the levels of glutathione peroxidase and catalase were downregulated correspondingly in clone PC18 during Aβ exposure. These results indicate that constitutive expression of 5-LOX is not detrimental per se, but overexpression of 5-LOX may become problematic during Aβ exposure.

Inducible Mis- and Over-Expression of PKCIW Regulates the Expression of AMH and P450arom in Chicken Embryo Fibroblast

Sex in birds is determined genetically as in mammals and a Z-linked gene DMRT1 is required for testis development. But it remains possible that the W chromosome contains a similarly critical factor for female development. The W-linked gene PKCIW was put forward as the seductive candidate for avian sex determination and/or sex differentiation. Mis-expression and over-expression of PKCIW were performed respectively in male and female chicken embryo fibroblast with tet-on inducible expression system in this study. The results of RT-PCR showed that with the PKCIW recombinant vector introducing, PKCIW mRNA expression was significantly improved in female chicken embryo fibroblast and was close to that of the female controls and in male chicken embryo fibroblast, in which normally there was no expression. Both misand over-expression of PKCIW led to up-regulated expression of P450arom and down-regulated expression of AMH, while large increase of P450arom in female and large decrease of AMH in male appeared. With misand over-expression of PKCIW, there was no significant change of FOXL2, SOX9, DMRT1 and ATP5A1W mRNA expression. These results showed the possible regulatory effect of PKCIW on AMH and P450arom in transcription level.

A Proteomic approach for protein‐profiling the oncogenicrasinduced transformation (H‐, K‐, and N‐Ras) in NIH/3T3 mouse embryonic fibroblasts

Point mutations in three kinds of Ras protein (H-, K-, and N-Ras) that specifically occur in codons 12, 13, and 61 facilitate virtually all of the malignant phenotype of the cancer cells, including cellular proliferation, transformation, invasion, and metastasis. In order to elucidate an understanding into the oncogenic ras networks by H-, K-, and N-Ras/G12V, we have established various oncogenic ras expressing NIH/3T3 mouse embryonic fibroblast clones using the tetracycline-induction system, which are expressing Ras/G12V proteins under the tight control of expression by an antibiotics, doxycycline. Here we provide a catalog of proteome profiles in total cell lysates derived from three oncogenic ras expressing NIH/3T3 cells and a good in vitro model system for dissecting the protein networks due to these oncogenic Ras proteins. In this biological context, we compared total proteome changes by the combined methods of 2-DE, quantitative image analysis, and MALDI-TOF MS analysis using the unique Tet-on inducible expression system. There were a large number of common targets for oncogenic ras, which were identified in all three cell lines and consisted of 204 proteins (61 in the pH range of 4-7, 63 in 4.5-5.5, and 80 in 5.5-6.7). Differentially regulated expression was further confirmed for some subsets of candidates by Western blot analysis using specific antibodies. Taken together, we implemented a 2-DE-based proteomics approach to the systematical analysis of the dysregulations in the cellular proteome of NIH/3T3 cells transformed by three kinds of oncogenic ras. Our results obtained and presented here show that the comparative analysis of proteome from oncogenic ras expressing cells has yielded interpretable data to elucidate the differential protein expression directly and/or indirectly, and contributed to evaluate the possibilities for physiological, and therapeutic targets. Further studies are in progress to elucidate the implications of these findings in the regulation of Ras induced transformation.

Tetracycline-regulated expression enables purification and functional analysis of recombinant connexin channels from mammalian cells.

Intercellular coupling mediated by gap junction channels composed of connexin protein underlies numerous physiological processes, such as cellular differentiation, tissue synchronization and metabolic homoeostasis. The distinct molecular permeability of junctional channels composed of different connexin isoforms allows cellular control of coupling via regulation of isoform expression. However, the permeability properties of most connexin isoforms have not been well characterized due to the difficulty of manipulating and measuring the diffusible concentrations of cytoplasmic messenger molecules and metabolites, and to a lack of control over channel isoform composition, in vivo. Here we present a method to express and purify active connexin hemichannels of a single isoform or a consistent ratio of two isoforms from cultured cells using the Tet-On inducible expression system and one-step anti-haemagglutinin immunoaffinity purification. The procedure yields 10-20 microg of pure connexin protein from 2.5x10(8) HeLa cells. The purified channels are shown to be useful for in vitro permeability analysis using well established techniques. This method has substantial advantages over existing methods for heterologous connexin expression, such as the ease of co-expression of two isoforms at a constant ratio, consistently high expression levels over many passages, and the ability to study channel properties in situ as well as in purified form. Furthermore, the generic cloning site of the new pBI-GT vector and the commercial availability of anti-haemagglutinin (clone HA-7)-agarose make this affinity tagging and purification procedure easily applicable to other proteins.

Regulation of steroidogenesis and steroidogenic acute regulatory protein in R2C cells by DAX-1 (dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene-1).

In the present study, steroidogenesis in two different Leydig tumor cell lines was compared. One, the MA-10 mouse tumor cell line, produces steroids and the steroidogenic acute regulatory (StAR) protein only when stimulated by trophic hormones and cAMP analogs. The other, the R2C rat tumor cell line, produces steroids and the StAR protein constitutively without stimulation. We observed that high levels of DAX-1 (dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene-1), a repressor of steroidogenesis and StAR gene expression, were present in MA-10 cells but not in R2C cells. Based upon this observation, we hypothesized that the absence of DAX-1 might result in constitutive steroidogenesis in R2C cells. To test this hypothesis, DAX-1 was overexpressed in the R2C cells using the Tet-on inducible gene expression system and resulted in a 45% decrease in steroid production, a 35% decrease in StAR protein, and a 39% decrease in cytochrome P450 side chain cleavage expression. Further, using retroviral infection with DAX-1, StAR expression and steroidogenesis were decreased 50-60% and 60% in R2C cells, respectively. These results corroborate previous findings that DAX-1 negatively regulates steroid synthesis through the inhibition of StAR expression and indicate that the absence of DAX-1 in R2C cells is, at least in part, responsible for the constitutive steroidogenesis and StAR expression observed.

BRD7, a novel bromodomain gene, inhibits G1-S progression by transcriptionally regulating some important molecules involved in ras/MEK/ERK and Rb/E2F pathways.

Bromodomain is a 110 amino acid domain. It is evolutionally conserved and is found in proteins strongly implicated in signal-dependent transcriptional regulation. BRD7 is a novel bromodomain gene and it is downexpressed in nasopharyngeal carcinoma (NPC) biopsies and cell lines; its function is poorly understood. In the present study, tet-on inducible expression system was used to investigate the role of BRD7 in cell growth and cell cycle progression. We found that ectopic expression of BRD7 in NPC cells inhibited cell growth and cell cycle progression from G1 to S. We further performed cell cycle cDNA array to screen potential transcriptional targets of BRD7 in cell cycle. Thirteen important signaling molecules, mainly implicated in ras/MEK/ERK and Rb/E2F pathways, were differentially expressed by induction of BRD7. Moreover, we observed that BRD7 could regulate the promoter activity of E2F3, one of its targets. Taken together, the present study indicated that BRD7 inhibited G1-S progression by transcriptionally regulating some important molecules involved in ras/MEK/ERK and Rb/E2F pathways and suggested that BRD7 may present a promising candidate of NPC trade mark associated tumor suppressor gene.