A systematic analysis of nuclear heat-shock protein 90 identifies a metazoan-specific regulatory module

Molecular chaperones such as heat-shock proteins (HSPs) help in protein folding and complex assembly processes. Their role in cytosol has been very well elucidated. Chaperones are also present in the nucleus, a compartment where proteins enter after being fully folded in the cytosol, raising an important question about chaperones function in this compartment. We have performed a systematic analysis of nuclear heat- shock protein 90 to identify regulatory functions of this chaperone in the nucleus. Combining physical and genetic interactomes with a cancer co-expression screen allowed us to define 'core functional interactors' of nuclear HSP90 consisting of five proteins. Using transcriptional studies we identified Host Cell Factor C1 (HCFC1) as a metazoan-specific transcriptional regulator that depends on HSP90 for its stability in the nucleus. We found that HSP90 is required for optimal activity of HCFC1 in transcription. Thus our study provides the first global insight into the function of nuclear HSP90. Overall design: ChIP-Seq and RNA-Seq