Modificación de la maquinaria de iniciación de la traducción por proteasas retrovirales

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular, Fecha de lectura 09-12-2004The initiation of banslation plays an important role in the regulation of gene expression in mammalian cells. The translation initiation factor elF4G, attached to elF4E and elF4A. constitutes the elF4F complex which is a key component to prornote the binding of ribosomes to mRNAs. elF4G has emerged as a key target for the regulation of translation in mammalian cells infected with different viruses. Thus, cleavage of elF4G by viral proteases from piwrnaviruses. as well as from human immunodeficiency virus type 1 (HIV-l), leads to inhibition of protein synthesis directed by capped cellular mRNAs. Notably, this cleavage of elF4G does not hamper translation directed by mRNAs containing an intemal ribosome entry site (IRES) strudure. In ihe present work, cleavage of both elF4GI and elF4GII has been examined with the proteases encoded within the genomes of several members of the family Retrovíndae, e.g., Moloney murine leukemia vinis (MoMLV), mouse mammary tumor virus, human T-cell leukemia virus íype 1, HIV-2, and simian immunodeficiency viws. All retmviral proteases examined were capable to cleave the initiation factor elF4GI both in intact cells and in cell-free systems, albeit with diíferent efñdencies. The pattern obtained from the hydrolysis of elF4GI with HIV-1 and HIV-2 proteases were very simllar to each other, but differed from that obtained wlth MoMLV protease. Both elF4GI and elF4GII were cleaved very efñdently by the MoMLV protease. Notably, elF4G11 was a poor substrate for HIV proteases. Proteolytic cleavage of elF4G by rettoviral proteases led to a profound inhibition of capdependent banslation, while protein synthesis driven by mRNAs contalning IRES elements remained unafíected or was even stimulated in transfected cells and in cell-free systems. Our present findings illusúating those retroviral proteases hydmlyze elF4G point to the idea that these viruses may follow a mechanism similar to that described for piwmavinises to regulate translation in ihe lnfected cells. RecenUy, the poly (A) binding protein (PABP), which plays an important mle in the iniüation of translation, has been shown to be a target for proteases from several piwrnaviruses and caliciviwses. In addition, our findings reveal by the first time that infection of cells with HIV-1 also leads to proteoiys's of PABP. Purified HIV-1 PR cleaves PABP both in transfected cells and in the test tube. The PABP hydrolysis by retroviral PR can be extended to other membars ofthe family Retrovindae such as HIV-2 and MMTV. These findings indicate that several retrovirusas share with plcomaviwses the capacity to proteolyze PABP