The cellular protein hnRNP A2/B1 enhances HIV-1 transcription by unfolding LTR promoter G-quadruplexes.
G-quadruplexes are four-stranded conformations of nucleic acids that act as cellular epigenetic regulators. A dynamic G-quadruplex forming region in the HIV-1 LTR promoter represses HIV-1 transcription when in the folded conformation. This activity is enhanced by nucleolin, which induces and stabilizes the HIV-1 LTR G-quadruplexes. In this work by a combined pull-down/mass spectrometry approach, we consistently found hnRNP A2/B1 as an additional LTR-G-quadruplex interacting protein. Surface plasmon resonance confirmed G-quadruplex specificity over linear sequences and fluorescence resonance energy transfer analysis indicated that hnRNP A2/B1 is able to efficiently unfold the LTR G-quadruplexes. Evaluation of the thermal stability of the LTR G-quadruplexes in different-length oligonucleotides showed that the protein is fit to be most active in the LTR full-length environment. When hnRNP A2/B1 was silenced in cells, LTR activity decreased, indicating that the protein acts as a HIV-1 transcription activator. Our data highlight a tightly regulated control of transcription based on G-quadruplex folding/unfolding, which depends on interacting cellular proteins. These findings provide a deeper understanding of the viral transcription mechanism and may pave the way to the development of drugs effective against the integrated HIV-1, present both in actively and latently infected cells.
Department of Molecular Medicine, University of Padua, Padua, Italy.
Matteo
M
Scalabrin
Department of Molecular Medicine, University of Padua, Padua, Italy.
Ilaria
I
Frasson
Department of Molecular Medicine, University of Padua, Padua, Italy.
Emanuela
E
Ruggiero
Department of Molecular Medicine, University of Padua, Padua, Italy.
Rosalba
R
Perrone
Department of Molecular Medicine, University of Padua, Padua, Italy.
Elena
E
Tosoni
Department of Molecular Medicine, University of Padua, Padua, Italy.
Sara
S
Lago
Department of Molecular Medicine, University of Padua, Padua, Italy.
Martina
M
Tassinari
Department of Molecular Medicine, University of Padua, Padua, Italy.
Giorgio
G
Palù
Department of Molecular Medicine, University of Padua, Padua, Italy.
Sara N
SN
Richter
D054856:G-Quadruplexes; D015967:Gene Expression Regulation, Viral; D057809:HEK293 Cells; D015497:HIV-1 / Q000235:genetics*; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism*; D006801:Humans; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020079:Terminal Repeat Sequences; D015533:Transcriptional Activation
D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B