Mitochondrial Transcription Factor A and Its Downstream Targets Are Up-regulated in a Rat Hepatoma

Xiaocheng Dong,Kalpana Ghoshal,Sarmila Majumder,Satya P Yadav,Samson T Jacob

doi:10.1074/jbc.m206958200

Xiaocheng Dong, Kalpana Ghoshal + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m206958200

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Abstract

Mitochondrial transcription factor A is a key regulator involved in mitochondrial DNA transcription and replication. In a poorly differentiated rat hepatoma, Morris hepatoma 3924A, the mRNA and protein levels of this factor were elevated about 10- and 11-fold, respectively, relative to the host liver. The mRNA levels for the hepatoma cytochrome c oxidase I, II, and NADH dehydrogenase 5, 6, the downstream targets of Tfam, were augmented 10-, 8-, 5-, and 3-fold, respectively. Interestingly, Tfam was also found in the hepatoma nucleus. The mRNA levels for nuclear respiratory factor 1 and 2 (NRF-1 and -2), the proteins that are known to interact with specific regulatory elements on human TFAM promoter, were 5- and 3-fold higher, respectively, in the hepatoma relative to the host liver. Unlike the human promoter, the rat Tfam promoter did not form a specific complex with the NRF-1 in the liver or hepatoma nuclear extracts, which is consistent with the absence of an NRF-1 consensus sequence in the proximal rat promoter. A single specific complex formed between the rat promoter and the NRF-2 protein was comparable in the two extracts. The DNA binding activity of Sp1 in the hepatoma nuclear extract was 4-fold greater than that in the liver extract. In vivo genomic footprinting showed occupancy of NRF-2 and Sp1 consensus sites on the promoter of rat Tfam gene. Tfam was also up-regulated in other hepatoma cells. Together, these results show up-regulation of Tfam in some tumors, particularly the liver tumors. Further, the relatively high level of Sp1 binding to the promoter in the hepatoma could play a major role in the up-regulation of Tfam in these tumor cells.

Highlights

Tfam Gene Expression Is Up-regulated in the Rat Hepatoma—Since Morris hepatoma 3924A is a rapidly growing tumor, we examined the mRNA level of Tfam in the hepatoma and compared with that of the host liver
To confirm and extend this observation, we studied the role of Tfam in the mitochondrial function in this tumor
The data showed that the steady state level of Tfam transcripts was at least 10-fold higher in the hepatoma than in the liver (Fig. 1, D and E), implying that the Tfam gene is up-regulated at the transcriptional level or that its mRNA is relatively more stable in the hepatoma compared with the host liver

Summary

Introduction

The mRNA levels for nuclear respiratory factor 1 and 2 (NRF-1 and -2), the proteins that are known to interact with specific regulatory elements on human TFAM promoter, were 5- and 3-fold higher, respectively, in the hepatoma relative to the host liver. Northern blot analysis with mouse Tfam as a probe suggested a higher level (ϳ8-fold) of Tfam expression in the hepatoma relative to the host liver (Fig. 1A).

Results

Conclusion