E1a transactivation of human HSP70 gene promoter substitution mutants is independent of the composition of upstream and TATA elements

Structure of gene flanking regions and functional analysis of sequences upstream of the rat hsp70.1 stress gene

We present structural and comparative analysis of the flanking regions of the rat hsp70.1 stress gene. Several repetitive sequences, microsatellites and short interspersed repetitive elements (SINEs) were found, as well as a significant gap in the 3' UTR, as compared to the orthologous mouse gene. We also show that the complex microsatellite region composed of partially overlapping inverted repeat and long homopurine-homopyrimidine sequence, which is localized 1.8 kbp upstream of the transcription start site, is capable to adopt non-B DNA structures (an H-DNA and a cruciform structure) in vitro. Functional analysis performed with the use of various fragments of the 5'end flanking regions ligated to the chloramphenicol acetyltransferase (CAT) reporter gene revealed a crucial role of cooperation between heat shock element (HSE) regulatory sequences, while none of the three HSEs alone is able to drive efficient heat induced transcription of the reporter gene. We also found that the microsatellite region does not influence transcription by itself, however, it abolishes the effect of the adjacent putative silencing element. To our knowledge, this is a first extensive structural and functional analysis of the promoter region of the mammalian heat inducible hsp70i gene localized distally to the hsp70-related spermatid-specific gene in the major histocompatibility complex III.

Lack of modulation of MDR1 gene expression by dominant inhibition of cAMP-dependent protein kinase in doxorubicin-resistant MCF-7 breast cancer cells

The drug transporter P-glycoprotein (P-gp) appears to play an important role in the ability of tumor cells to evade killing by chemotherapeutic agents. Using pharmacological inhibitors of cAMP-dependent protein kinase (PKA), it has been suggested that, similar to rodent model systems, the human P-gp gene (MDR1) is also under PKA-dependent control and that PKA inhibition may prove useful in reducing drug resistance in human cancer cells. To test this hypothesis, we stably transformed doxorubicin (Adriamycin)-resistant human MCF-7 breast cancer cells (MCF-7(ADR)) with a vector that inhibits PKA activity by inducing over-expression of mutant type Ialpha PKA regulatory (RIalpha) subunits. Two transformants (MCF-7(ADR-A) and MCF-7(ADR-B)) were found to express mutant RIalpha subunits and to possess markedly reduced PKA activity; another transformant (MCF-7(ADR-9)) lacked mutant RIalpha subunit expression and exhibited no inhibition of PKA activity. In contrast with findings in Chinese hamster ovary and Y1 adrenal cells, P-gp levels and cellular sensitivity to drugs which are P-gp substrates were unchanged in the PKA-inhibited transformants, suggesting that P-gp expression and function are not under PKA-dependent control in MCF-7(ADR) cells. Growth and saturation densities of the cell lines were highly correlated with level of PKA catalytic activity, suggesting that PKA inhibition may prove useful in inhibiting growth of breast tumor cells, even upon establishment of resistance to doxorubicin. However, our results challenge current proposals that drug sensitivity in P-gp-expressing human tumor cells may be restored by blocking MDR1 gene expression through inhibition of PKA activity.

Transcriptional transactivation of parvovirus B19 promoters in nonpermissive human cells by adenovirus type 2

The pathogenic human parvovirus B19 contains a promoter at map unit 6 (B19p6) of the viral genome, expression from which is largely restricted to human cells in the erythroid lineage, whereas a putative promoter at map unit 44 (B19p44) is inactive during a natural viral infection. Although nonerythroid human cells, such as HeLa and KB, allow expression from the B19p6 promoter but not from the B19p44 promoter following DNA-mediated transfection, little expression from the B19p6 promoter occurs following recombinant virus infection (S. Ponnazhagan, X.-S. Wang, M.J. Woody, F. Luo, L.Y. Kang, M.L. Nallari, N.C. Munshi, S.Z. Zhou, and A. Srivastava, submitted for publication). However, significant expression from the B19p6 promoter as well as the B19p44 promoter could be detected in a human 293 cells line that expresses the adenovirus early gene products, suggesting that coinfection with adenovirus might mediate transcriptional transactivation of the B19 promoters in nonpermissive cells. Expression of the firefly luciferase reporter gene from the B19 promoters was evaluated either following plasmid transfection or following infection with the recombinant adeno-associated virus type 2 vectors. Both B19p6 and B19p44 promoters could be transactivated by coinfection with adenovirus in nonpermissive human cells, although the extent of transactivation of the B19p44 promoter was significantly lower than that of the B19p6 promoter. Expression of the adenovirus E1A proteins was necessary and sufficient for the observed transactivation of the B19 promoters. These studies further illustrate that the underlying molecular mechanisms of transactivation of parvovirus promoters in general by the adenovirus early proteins have similarities with those of the well-documented transactivation of the adeno-associated virus type 2 promoters.

Transcription stimulation of the adenovirus type 12 E1a gene in vitro by the 266-amino-acid E1A protein

We previously showed that the 13S but not the 12S mRNA product of the E1a gene of the highly oncogenic type 12 adenovirus (Ad12) stimulates the expression of its own gene. In this study, the mechanism for the autoregulation of the Ad12 E1a gene was investigated in vitro. The 266-amino-acid E1A protein of Ad12 was synthesized in yeast cells and purified as a 57-kDa polypeptide. The purified Ad12 E1A protein stimulated transcription from the proximal promoter of its own gene but had almost no effect on that from the distal promoter. A 35-bp upstream region including a TATA box for the proximal promoter seemed to be sufficient for transcription stimulation by the E1A protein. The Ad12 E1A protein formed a complex with a TATA box-binding protein (TBP), as does the E1A protein of nononcogenic Ad serotypes. Moreover, the E1A protein significantly reduced the binding of TBP to a TATA sequence, while it did not affect the DNA-binding activity of nuclear factor I, a stimulatory protein of the distal transcription of the Ad12 E1a gene. These results suggest that the 13S mRNA product of the Ad12 E1a gene regulates the transcription of its own gene by modulating the activity of TBP.

Promoter targeting by adenovirus E1a through interaction with different cellular DNA-binding domains

A puzzling property of the transcriptional activators encoded by several animal viruses is their ability to function promiscuously. The adenovirus E1a protein, for example, stimulates transcription of adenoviral genes as well as a wide variety of other viral and cellular genes. We show that E1a can interact with several classes of cellular DNA-binding domains and thereby be recruited to diverse promoters. Our results explain how a single protein can regulate transcription of multiple genes that lack a common promoter element.