Naturally occurring BLV- LTR variants show differential binding with transcriptional regulator E2F-4

Naturally occurring BLV- LTR variants show differential binding with transcriptional regulator E2F-4.

Sabrina M. Rodríguez1, Cecilia Varone2, Eduardo Cánepa2, Karina Trono1.
srodriguez@cnia.inta.gov.ar
1Instituto de Virología. CICVyA. INTA-Castelar. Castelar. Buenos Aires. Argentina
2Catedra de Biología Molecular. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Buenos Aires. Argentina

The proviral Long Terminal Repeats (LTR) of retroviruses constitute a critical element involved in the regulation of viral and cellular gene expression. It is well known for some viruses within the Retroviridae family that minimal changes in this region can influence tropism, virulence and pathogenicity.
The aim of this work was to elucidate if there is any association between the binding capacity of the Bovine Leukemia Virus (BLV) LTR region with cellular transcription factors and the pathogenic evolution of natural infection.
The complete 5´LTR sequence amplified from mononuclear cells and tumour tissues of 40 naturally infected cattle was analyzed.
Sequence analysis revealed the presence of two LTR variants associated with the different BLV pathogenic phenotypes: aleukemic (AL), persistent lymphocitosis (PL) and lymphosarcoma (LS).
Analysis by EMSA showed a clearly weaker specific binding pattern when a LS-derived sequence was used as probe. Together with this finding, we also demonstrated by gel shift and supershift assays that the cellular transcription factor E2F-4 specifically interacts with a putative E2F binding motif within the U5 region of BLV 5`LTR unveiled by “in sillico” analysis.
The results of this work demonstrates for the first time the presence of differential binding capacity of BLV natural derived variants to cellular nuclear proteins, together with physical characterization of an E2F-4 binding site in the U5 region of BLV-LTR that shows preferential binding to AL/PL derived sequences.
These findings can contribute to the knowledge of LTR-driven regulation of viral and cellular gene expression.