Abstract
Heat shock transcription factor 1 (HSF1) functions as the master regulator of the heat shock response in eukaryotes. We have previously shown that, in addition to its role as a transcription factor, HSF1 stimulates the activity of the DNA-dependent protein kinase (DNA-PK). DNA-PK is composed of two components: a 460-kDa catalytic subunit and a 70- and 86-kDa heterodimeric regulatory component, also known as the Ku protein. We report here that HSF1 binds specifically to each of the two components of DNA-PK. Binding occurs in the absence of DNA. The complex with the Ku protein is stable and forms at a stoichiometry close to unity between the Ku protein heterodimer and the active HSF1 trimer. The binding is blocked by antibodies against HSF1. Our results show that HSF1 also binds directly, but more weakly, to the catalytic subunit of DNA-PK. Both interactions are dependent on a specific region within the HSF1 regulatory domain. This sequence is necessary but not sufficient for HSF1 stimulation of DNA-PK activity. The ability of HSF1 to interact with both components of DNA-PK provides a potential mechanism for the activation of DNA-PK in response to heat and other forms of stress.
Highlights
Prior to stress, heat shock transcription factor 1 (HSF1)1 is present in human and other metazoan cells in a latent, monomeric form [1,2,3,4]
Previous work showed that the transcription factor HSF1, which regulates the heat shock response in eukaryotes, is capable of stimulating the activity of purified DNA-PK in an in vitro reaction [26]
We have shown that HSF1 binds directly to each component of DNA-PK
Summary
Heat shock transcription factor 1 (HSF1) is present in human and other metazoan cells in a latent, monomeric form [1,2,3,4]. The trimeric form of HSF1 binds to heat shock elements in DNA and activates transcription of heat shock genes by RNA polymerase II. Molecule contains several elements that maintain HSF1 in its latent form [5, 9] or that regulate the activity of transcriptional activation domains in response to stress [15,16,17,18]. HSF1 activates preparations of the DNA-PK catalytic subunit containing little or no Ku protein, suggesting that there is a direct functional interaction between HSF1 and the catalytic subunit [26]. A truncated form of HSF1 containing only the DNA binding domain does not activate DNA-PK, suggesting that the interaction between these proteins is dependent on specific amino acid sequences within HSF1 [26]
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