Analysis of cis‐regulatory elements in the 5′ untranslated region of murine leukemia virus controlling protein expression

Abstract

It has previously been reported by us that high-level expression of the Env protein of Fr-MLV clone A8 in brains is crucial for induction of spongiform neurodegeneration, and that the 0.3-kb fragment containing the R, U5, and the 5 leader sequence of A8 is responsible for neuropathogenicity. In the present study, the role of the 5 untranslated region in protein expression was investigated. Luciferase expression vectors containing the LTR (R-U3-U5) and 5 leader sequence of A8 and non-neuropathogenic 57 Fr-MLV, designated gl-A8 and gl-57, and their chimeric vectors, were constructed, and transfected into rat glial cells F10. Replacement of the region containing the 3 half of R, U5, and 5 leader sequence of gl-A8 with that of 57 showed a reduction in luciferase activities, and replacement of this region of gl-57 with that of A8 showed increased luciferase activity. These results show that the region containing the 3 half of R, U5, and 5 leader sequence of A8 more efficiently up-regulates protein expression than 57. In particular, the 3 half of 5 leader of A8 was most responsible for the up-regulation of protein expression. Of interest, after replacement of the fragments between A8 and 57, changes in the activities of vectors containing A8-U3 paralleled the amount of mRNA, but the activities of vectors containing 57-U3 did not. Furthermore, it is suggested that the region containing R, U5, and the 5 leader sequence influences transcriptional or post-transcriptional steps, depending on the upstream sequence containing enhancer elements and promoter.Key words cis-regulatory element, murine leukemia virus, retrovirus, 5 untranslated region.The 5 untranslated region of the proviral genome of retrovirus which contains the LTR (U3-R-U5) and 5 leader sequence is involved in a variety of functions that affect different steps in retrovirus replication (1). The U3 region found upstream of the transcription start site contains the majority of cis-acting control elements which regulate transcriptional initiation by cellular RNA polymerase II. The R region, present at both ends of viral RNA, mediates the 5 -3 jump of reverse transcriptase during synthesis of minus-strand DNA. In addition, the R region is

XMRV accelerates cellular proliferation, transformational activity, and invasiveness of prostate cancer cells by downregulating p27Kip1

“…XMRV being a gammaretrovirus does not encode accessory proteins (9) that are known to regulate host gene expression in complex retroviruses such as HIV (46). Given that XMRV integration has been documented near miRNA genes of host genome (15), our data supports the unique mechanisms utilized by gammaretroviruses to control host gene expressions (47–48). …”