Assembly and levels of P-TEFb depend on reversible phosphorylation of cyclinT1

The positive transcription elongation factor b (P-TEFb) is a critical co-activator for transcription of most cellular and viral genes, including those of HIV. While P-TEFb is regulated by 7SK snRNA in proliferating cells, it is absent in quiescent and terminally differentiated cells, which has remained unexplored. In these cells, we found that CycT1 not bound to CDK9 is rapidly degraded. Moreover, productive CycT1:CDK9 interactions require phosphorylation of two threonine residues (Thr143 and Thr149) in CycT1 by PKC. Conversely, PP1 dephosphorylates these sites. Thus, PKC inhibitors or removal of PKC by chronic activation results in P-TEFb disassembly and CycT1 degradation. This finding not only recapitulates P-TEFb depletion in resting CD4+ T cells but also in anergic T cells. Importantly, our studies reveal mechanisms of P-TEFb inactivation underlying T cell quiescence, anergy, and exhaustion as well as proviral latency and terminal differentiation of cells.

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Reversible phosphorylation of cyclin T1 promotes assembly and stability of P-TEFb

eLife ◽

10.7554/elife.68473 ◽

2021 ◽

Vol 10 ◽

Author(s):

Fang Huang ◽

Trang TT Nguyen ◽

Ignacia Echeverria ◽

Rakesh Ramachandran ◽

Daniele C. Cary ◽

...

Keyword(s):

T Cells ◽

Elongation Factor ◽

Proliferating Cells ◽

Cyclin T1 ◽

Positive Transcription Elongation Factor ◽

Differentiated Cells ◽

Cell Quiescence ◽

Viral Genes ◽

Chronic Activation ◽

Anergic T Cells

The positive transcription elongation factor b (P-TEFb) is a critical co-activator for transcription of most cellular and viral genes, including those of HIV. While P-TEFb is regulated by 7SK snRNA in proliferating cells, P-TEFb is absent due to diminished levels of CycT1 in quiescent and terminally differentiated cells, which has remained unexplored. In these cells, we found that CycT1 not bound to CDK9 is rapidly degraded. Moreover, productive CycT1:CDK9 interactions are increased by PKC mediated phosphorylation of CycT1 in human cells. Conversely, dephosphorylation of CycT1 by PP1 reverses this process. Thus, PKC inhibitors or removal of PKC by chronic activation results in P-TEFb disassembly and CycT1 degradation. This finding not only recapitulates P-TEFb depletion in resting CD4+ T cells but also in anergic T cells. Importantly, our studies reveal mechanisms of P-TEFb inactivation underlying T cell quiescence, anergy, and exhaustion as well as proviral latency and terminally differentiated cells.

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Histone Deacetylase Inhibitors (HDACis) That Release the Positive Transcription Elongation Factor b (P-TEFb) from Its Inhibitory Complex Also Activate HIV Transcription

Journal of Biological Chemistry ◽

10.1074/jbc.m113.464834 ◽

2013 ◽

Vol 288 (20) ◽

pp. 14400-14407 ◽

Cited By ~ 60

Author(s):

Koen Bartholomeeusen ◽

Koh Fujinaga ◽

Yanhui Xiang ◽

B. Matija Peterlin

Keyword(s):

T Cells ◽

Histone Deacetylase ◽

Cell Lines ◽

Histone Deacetylase Inhibitors ◽

Elongation Factor ◽

Factor B ◽

Transformed Cell ◽

Positive Transcription Elongation Factor ◽

Transcription Elongation Factor ◽

Transformed Cell Lines

Numerous studies have looked at the effects of histone deacetylase inhibitors (HDACis) on HIV reactivation in established transformed cell lines and primary CD4+ T cells. However, their findings remain confusing, and differences between effects of class I- and class II-specific HDACis persist. Because no clear picture emerged, we decided to determine how HDACis reactivate HIV in transformed cell lines and primary cells. We found that neither histone H3 nor tubulin acetylation correlated with HIV reactivation in Jurkat and HeLa cells. Rather, HDACis that could reactivate HIV in chromatin or on episomal plasmids also released free positive transcription elongation factor b (P-TEFb) from its inhibitory 7SK snRNP. In resting primary CD4+ T cells, where levels of P-TEFb are vanishingly low, the most potent HDACi, suberoylanilide hydroxyamic acid (SAHA), had minimal effects. In contrast, when these cells were treated with a PKC agonist, bryostatin 1, which increased levels of P-TEFb, then SAHA once again reactivated HIV. We conclude that HDACis, which can reactivate HIV, work via the release of free P-TEFb from the 7SK snRNP.

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