Quantitative Proteomics of the CDK9 Interactome Reveals a Function of the HSP90-CDC37-P-TEFb Complex for BETi-Induced HIV‑1 Latency Reactivation

Brd4 has been intensively investigated as a promising
drug target
because of its implicated functions in oncogenesis, inflammation,
and HIV-1 transcription. The formation of the Brd4-P-TEFb (CDK9/Cyclin
T1) complex and its regulation of transcriptional elongation are critical
for HIV latency reactivation and expression of many oncogenes. To
further investigate the mechanism of the Brd4-P-TEFb complex in controlling
elongation, mass spectrometry-based quantitative proteomics of the
CDK9 interactome was performed. Upon treatment with the selective
BET bromodomain inhibitor JQ1, 352 proteins were successfully identified
with high confidence as CDK9-interacting proteins. Among them, increased
bindings of HSP90 and CDC37 to CDK9 were particularly striking, and
our data suggest that the HSP90-CDC37-P-TEFb complex is involved in
controlling the dynamic equilibrium of the P-TEFb complex during BETi-induced
reactivation of HIV-1 latency. Furthermore, the HSP90-CDC37-P-TEFb
complex directly regulates HIV-1 transcription and relies on recruitment
by heat shock factor 1 (HSF1) for binding to the HIV-1 promoter. These
results advance the understanding of HSP90-CDC37-P-TEFb in HIV-1 latency
reversal and enlighten the development of potential strategies to
eradicate HIV-1 using a combination of targeted drugs.