Deacetylation of the retinoblastoma tumour suppressor protein by SIRT1

Abstract

The activity of Rb (retinoblastoma protein) is regulated by phosphorylation and acetylation events. Active Rb is hypophosphorylated and acetylated on multiple residues. Inactivation of Rb involves concerted hyper-phosphorylation by cyclin-CDK (cyclin-dependent kinase) complexes combined with deacetylation of appropriate lysine residues within Rb. In the present study, using in vivo co-immunoprecipitation experiments, we identified mammalian SIRT1 (sirtuin 1) as a binding partner for Rb and its family members p107 and p130. Formation of Rb-SIRT1 complexes required the pocket domain of Rb. p300 catalysed the acetylation of Rb, and SIRT1 was a potent deacetylase for Rb. The ability of SIRT1 to catalyse the deacetylation of Rb was dependent on NAD and was inhibited by the SIRT1 inhibitor nicotinamide. Deacetylated lysine residues within Rb formed a domain similar to the SIRT1-targeted domain of the p53 tumour suppressor protein. Cultures of arrested cells, via contact inhibition or DNA damage, exhibited decreased Rb phosphorylation and increased Rb acetylation. Overexpression of SIRT1 in either confluent or etoposide-treated cells resulted in a significant reduction in Rb acetylation, which was restored with nicotinamide. Gene knockdown of SIRT1 by siRNA (short interfering RNA) produced an accumulation of acetylated Rb. This increase was augmented further when siRNA against SIRT1 was used in conjunction with nicotinamide. In conclusion, our results demonstrate that SIRT1 is an in vitro and in vivo deacetylase for the Rb tumour suppressor protein.

Diversity within the pRb pathway: is there a code of conduct?

“…SIRT1 (sirtuin 1) can interact with and deacetylate pRb (Wong and Weber, 2007). SIRT1 is the human homologue of yeast silent information regulator 2; it is a class III HDAC subunit and its activity is regulated by the cofactor NAD þ .…”

“…SIRT1 deacetylates a number of residues on histone proteins and more recently has been shown to deacetylate a wide range of non-histone proteins, including p53, p73, androgen receptor and Foxo proteins (Fang and Nicholl, 2011). SIRT1 interacts with pRb and the related pocket proteins, p107 and p130 (Wong and Weber, 2007). A marked reduction in pRb acetylation was observed when SIRT1 was introduced into cells at increasing levels, and omission of NAD þ failed to reduce pRb acetylation (Wong and Weber, 2007), suggesting that SIRT1 can act as an 'eraser' to remove the acetylation signals present on pRb.…”

“…SIRT1 interacts with pRb and the related pocket proteins, p107 and p130 (Wong and Weber, 2007). A marked reduction in pRb acetylation was observed when SIRT1 was introduced into cells at increasing levels, and omission of NAD þ failed to reduce pRb acetylation (Wong and Weber, 2007), suggesting that SIRT1 can act as an 'eraser' to remove the acetylation signals present on pRb.…”

SIRT1 suppresses breast cancer growth through downregulation of the Bcl-2 protein

“…SIRT1 acts as a deacetylase not only on histone but also by deacetylating cell cycle regulators such as p53 (3), p73 (4) and Rb (5). With regard to the growth of cancer cells, it has been reported that SIRT1 regulates cell proliferation, survival, and death, and plays a pivotal role in tumorigenesis and longevity.…”

Expression of DBC1 is associated with nuclear grade and HER2 expression in breast cancer

“…Recent reports have revealed that SIRT1 may be involved in both tumorigenesis and anti-tumorigenesis. The expression of SIRT1 has been shown to be increased in human prostate (11), gastric (2), colon (12), ovarian (13) and breast cancer (3,4,14), and SIRT1 was found to promote cellular survival by Expression of DBC1 is associated with nuclear grade and HER2 expression in breast cancer HARUKO deacetylating key cell cycle molecules and apoptosis regulatory proteins (15,16). SIRT1 inactivates p53 by deacetylation and then allows cells to proliferate in the presence of damaged DNA and subsequently promotes tumor progression (15).…”