The sirtuins promote Dishevelled-1 scaffolding of TIAM1, Rac activation and cell migration.

Rac1-GTPases serve as intermediary cellular switches, which conduct transient and constitutive signals from upstream cues, including those from Ras oncoproteins. Although the sirtuin1 (SIRT1) deacetylase is overexpressed in several human cancers and has recently been linked to cancer cell motility as a context-dependent regulator of multiple pathways, its role in Rac1 activation has not been reported. Similarly, SIRT2 has been demonstrated to be upregulated in some cancers; however, studies have also reported its role in tumor suppression. Here, we demonstrate that SIRT1 and SIRT2 positively regulate the levels of Rac1-GTP and the activity of T-cell lymphoma invasion and metastasis 1 (TIAM1), a Rac guanine nucleotide exchange factor (GEF). Transient inhibition of SIRT1 and SIRT2 resulted in increased acetylation of TIAM1, whereas chronic SIRT2 knockdown resulted in enhanced acetylation of TIAM1. SIRT1 regulates Dishevelled (DVL) protein levels in cancer cells, and DVL along with TIAM1 are known to augment Rac activation; however, SIRT1 or 2 has not been previously linked with TIAM1. We found that diminished sirtuin activity led to the disruption of the DVL1-TIAM1 interaction. We hence propose a model for Rac activation where SIRT1/2 positively modulates the DVL/TIAM1/Rac axis and promotes sustained pathway activation.

Children of chernobyl cleanup workers do not show elevated rates of mutations in minisatellite alleles.

The disaster at the Chernobyl Nuclear Power Plant in April 1986 was accompanied by the release of large amounts of radioisotopes, resulting in the contamination of extensive regions of the Ukraine, Byelorus and the Russian Federation. Cleanup workers (liquidators) and people living on land contaminated with radioactive materials were most exposed. To assess the genetic effects of exposure to ionizing radiation after the Chernobyl accident, we have measured the frequency of inherited mutant alleles at seven hypermutable minisatellite loci in 183 children born to Chernobyl cleanup workers (liquidators) and 163 children born to control families living in nonirradiated areas of the Ukraine. There was no significant difference in the frequency of inherited mutant alleles between the exposed and control groups. The exposed group was then divided into two subgroups according to the time at which the children were conceived with respect to the fathers' work at the power plant. Eighty-eight children were conceived either while their fathers were working at the facility or up to 2 months later (Subgroup 1). The other 95 children were conceived at least 4 months after their fathers had stopped working at the Chernobyl site (Subgroup 2). The frequencies of mutant alleles were higher for the majority of loci (i.e. 1.44 times higher for CEB1) in Subgroup 1 than in Subgroup 2. This result, if confirmed, would reconcile the apparently conflicting results obtained in the chronically exposed Byelorus population and the Hiroshima-Nagasaki A-bomb survivors.