GSK3-mediated BCL-3 phosphorylation modulates its degradation and its oncogenicity

The balance between acetylation and deacetylation controls Smad7 stability

Transforming growth factor beta (TGFbeta) regulates multiple cellular processes via activation of Smad signaling pathways. We have recently demonstrated that the inhibitory Smad7 interacts with the acetyl transferase p300 and that p300 acetylates Smad7 on two lysine residues. These lysine residues are critical for Smurf-mediated ubiquitination of Smad7, and acetylation protects Smad7 from TGFbeta-induced degradation. In this study we demonstrate that Smad7 interacts with specific histone deacetylases (HDACs) and that the same HDACs are able to deacetylate Smad7. The interaction with HDACs is dependent on the C-terminal MH2 domain of Smad7. In addition, HDAC1-mediated deacetylation of Smad7 decreases the stability of Smad7 by enhancing its ubiquitination. Thus, our results demonstrate that the degradation of Smad7 is regulated by the balance between acetylation, deacetylation and ubiquitination, indicating that this could be a general mechanism to regulate the stability of cellular proteins.

Phosphorylation of NF-kappaB and IkappaB proteins: implications in cancer and inflammation

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that has crucial roles in inflammation, immunity, cell proliferation and apoptosis. Activation of NF-kappaB mainly occurs via IkappaB kinase (IKK)-mediated phosphorylation of inhibitory molecules, including IkappaBalpha. Optimal induction of NF-kappaB target genes also requires phosphorylation of NF-kappaB proteins, such as p65, within their transactivation domain by a variety of kinases in response to distinct stimuli. Whether, and how, phosphorylation modulates the function of other NF-kappaB and IkappaB proteins, such as B-cell lymphoma 3, remains unclear. The identification and characterization of all the kinases known to phosphorylate NF-kappaB and IkappaB proteins are described here. Because deregulation of NF-kappaB and IkappaB phosphorylations is a hallmark of chronic inflammatory diseases and cancer, newly designed drugs targeting these constitutively activated signalling pathways represent promising therapeutic tools.