The Cellular lysine methyltransferase Set7/9-KMT7 binds HIV-1 TAR RNA, monomethylates the viral transactivator Tat, and enhances HIV transcription

Gladstone Institute of Virology and Immunology, University of California, San Francisco, San Francisco, CA 94158, USA.
Cell host & microbe (Impact Factor: 12.33). 03/2010; 7(3):234-44. DOI: 10.1016/j.chom.2010.02.005
Source: PubMed


The Tat protein of HIV-1 plays an essential role in HIV gene expression by promoting efficient elongation of viral transcripts. Posttranslational modifications of Tat fine-tune interactions of Tat with cellular cofactors and TAR RNA, a stem-loop structure at the 5' ends of viral transcripts. Here, we identify the lysine methyltransferase Set7/9 (KMT7) as a coactivator of HIV transcription. Set7/9-KMT7 associates with the HIV promoter in vivo and monomethylates lysine 51, a highly conserved residue located in the RNA-binding domain of Tat. Knockdown of Set7/9-KMT7 suppresses Tat transactivation of the HIV promoter, but does not affect the transcriptional activity of methylation-deficient Tat (K51A). Set7/9-KMT7 binds TAR RNA by itself and in complex with Tat and the positive transcription elongation factor P-TEFb. Our findings uncover a positive role for Set7/9-KMT7 and Tat methylation during early steps of the Tat transactivation cycle.

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    • "e l s e v i e r . c o m / l o c a t e / y a b i o [9] including tumor suppressor p53 [10], Tat protein of HIV [11], and estrogen receptor a [12] and it regulates transcriptional activity through alternate mechanisms [13]. SET7/9 was also reported as a novel coactivator of a transcription factor, the nuclear factor kappa-B that plays a key role in the regulation of proinflammatory genes [14]. "

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    • "At the end of the transcription cycle SIRT1 binds and deacetylates Tat at Lys50 which mediates the recycling of unacetylated Tat thought to be necessary for subsequent rounds of viral transcription (Pagans et al., 2005). Following deacetylation of Tat at the ARM region, monomethylation at Lys51 by Set7/9 bound to TAR enhances Tat-dependent HIV transcription by facilitating Tat interactions with TAR and recruitment of the host elongation factor P-TEFb to the RNA (Pagans et al., 2010). Subsequent demethylation of Lys51 by LSD1/CoREST allows for the re-acetylation of the ARM of Tat which triggers entry into the TAR-independent phase of proviral transcription elongation (Sakane et al., 2011). "
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    • "Thus these results altogether suggest that methylation when present at lysine 51 increases the binding efficiency of the peptide by modulating the kinetic as well as thermodynamic component of the binding. Our results also provide the thermodynmic and kinetic explanation for the enhancement of transactivation by monomethylation at K51 by cellular lysine methyltransferases Set7/9-KMT7 [41]. It shows that monomethylation at K51 results in stronger binding of Tat protein to TAR RNA element leading to transcriptional activation. "
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    ABSTRACT: Post-translational modification (PTM) of RNA binding proteins (RBPs) play a very important role in determining their binding to cognate RNAs and therefore regulate the downstream effects. Lysine can undergo various PTMs and thereby contribute to the regulation of different cellular processes. It can be reversibly acetylated and methylated using a pool of respective enzymes, to act as a switch for controlling the binding efficiency of RBPs. Here we have delineated the thermodynamic and kinetic effects of N-acetylation and N-monomethylation of lysine on interaction between HIV-1 TAR RNA and its cognate binder Tat peptide ( a model system). Our results indicate that acetylation of lysine 50 (K50), leads to eight- fold reduction in binding affinity, originating exclusively from entropy changes whereas, lysine 51 (K51) acetylation resulted only in three fold decrease with large enthalpy-entropy compensation. The measurement of kinetic parameters indicated major change (4.5 fold) in dissociation rate in case of K50 acetylation however, K51 acetylation showed similar effect on both association and dissociation rates. In contrast, lysine methylation did not affect the binding affinity of Tat peptide to TAR RNA at K50, nonetheless three fold enhancement in binding affinity was observed at K51 position. In spite of large enthalpy-entropy compensation, lysine methylation seems to have more pronounced position specific effect on the kinetic parameters. In case of K50 methylation, simultaneous increase was observed in the rate of association and dissociation leaving binding affinity unaffected. The increased binding affinity for methylated Tat at K51 stems from faster association rate with slightly slower dissociation rate.
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