No abstract

Histone deacetylases (HDACs) regulate the expression and activity of numerous proteins involved in both cancer initiation and cancer progression. By removal of acetyl groups from histones, HDACs create a non-permissive chromatin conformation that prevents the transcription of genes that encode proteins involved in tumorigenesis. In addition to histones, HDACs bind to and deacetylate a variety of other protein targets including transcription factors and other abundant cellular proteins implicated in control of cell growth, differentiation and apoptosis. This review provides a comprehensive examination of the transcriptional and post-translational mechanisms by which HDACs alter the expression and function of cancerassociated proteins and examines the general impact of HDAC activity in cancer.

The ataxia telangiectasia group D-complementing (ATDC) gene product, also known as TRIM29, is a member of the tripartite motif (TRIM) protein family. ATDC has been proposed to form homo-or heterodimers and to bind nucleic acids. In cell cultures, ATDC expression leads to rapid growth and resistance to ionizing radiation (IR), whereas silencing of ATDC expression decreases growth rates and increases sensitivity to IR. Although ATDC is overexpressed in many human cancers, the biological significance of ATDC overexpression remains obscure. We report here that ATDC increases cell proliferation via inhibition of p53 nuclear activities. ATDC represses the expression of p53-regulated genes, including p21 and NOXA. Mechanistically, ATDC binds p53, and this interaction is potentially fine-tuned by posttranslational acetylation of lysine 116 on ATDC. The association of p53 and ATDC results in p53 sequestration outside of the nucleus. Together, these results provide novel mechanistic insights into the function of ATDC and offer an explanation for how ATDC promotes cancer cell proliferation.Ataxia telangiectasia (AT) is an autosomal-recessive, complex, multisystem disorder (4, 33). One of the hallmarks for cells derived from AT patients is their unusual sensitivity to ionizing radiation (IR) and their failure to delay the cell cycle in S phase, termed radioresistant DNA synthesis. In addition, AT cells contain atypical cytoskeletal organization. An early attempt to complement the defect in an AT cell line (AT5BIVA) by transfection with a human cosmid library and selection by ␥IR resulted in the isolation of an AT cell line (1B3) that was partially resistant to IR (22). Subsequent isolation of the human DNA in the region of the integrated cosmid sequences in 1B3 cells resulted in the cloning of the ataxia telangiectasia group D-complementing (ATDC) gene (23).The ATDC gene is located at chromosome 11q23, where it is frequently associated with many different kinds of cancers. Analysis of the ATDC gene product revealed that it is a member of the tripartite motif (TRIM) protein family (also known as the RBCC family). This protein family is characterized by three zinc-binding domains, a RING, a B-box type 1, and a B-box type 2, followed by a coiled-coil region (5,29,42,43,47). Some TRIM proteins homo-multimerize through their coilcoil region, and the integrity of the TRIM motif is required for proper subcellular localization of TRIM proteins (43). Recently, it was discovered that one of the TRIM proteins is a component of the repressor binding site (RBS) binding complex found in EC and ES cells and functions in restricting retroviral replication (60).The ATDC protein has been shown to interact with a protein kinase C substrate and inhibitor, although the significance of this interaction is not exactly clear (6). Although early studies indicate that ATDC can complement the IR sensitivity of AT fibroblasts, later analysis reveals that ATDC does not affect radioresistant DNA synthesis and is most likely not mutated in any AT patient...

No abstract

Retinoic acid (RA) affects the response of many cells to growth factors, including the bone morphogenetic proteins (BMPs). The BMPs are members of the TGF-beta, family of growth factors, originally identified by their bone-inducing activities. Their widespread expression suggests many roles other than that in osteogenesis. Because RA modulates the cell's response to growth factors, this may be a means by which the retinoids exert some of their known teratogenic effects. One such cellular response may be apoptosis. While apoptosis is required for normal development, the location and timing of its induction must be carefully controlled. Recently, several TGF-beta family members have been implicated in the induction of apoptosis in certain cell types. We show here, using P19 embryonal carcinoma cells, that the combination of RA and BMP2 or BMP4 synergistically induces apoptosis in 40% of the population within 24 hr. In contrast, RA alone induces apoptosis in only 10-15% of the population and each of the BMPs alone minimally induces apoptosis. Apoptosis depends on the dose of both the RA and the BMP as well as on new protein synthesis. Further, the induction of apoptosis prevents the formation of fully differentiated neurons and glial cells and instead leads to primarily smooth muscle cell differentiation. These results suggest that some of the malformations caused by retinoids may be due to the induction of inappropriate apoptosis in cells exposed to BMPs.

Proper expression of the replication licensing factor Cdt1 is primarily regulated post-translationally by ubiquitylation and proteasome degradation. In a screen to identify novel non-histone targets of histone deacetylases (HDACs), we found Cdt1 as a binding partner for HDAC11. Cdt1 associates specifically and directly with HDAC11. We show that Cdt1 undergoes acetylation and is reversibly deacetylated by HDAC11. In vitro, Cdt1 can be acetylated at its N terminus by the lysine acetyltransferases KAT2B and KAT3B. Acetylation protects Cdt1 from ubiquitylation and subsequent proteasomal degradation. These results extend the list of non-histone acetylated proteins to include a critical DNA replication factor and provide an additional level of complexity to the regulation of Cdt1.

Bok/Mtd (Bcl-2-related ovarian killer/Matador) is considered a pro-apoptotic member of the Bcl-2 family. Although identified in 1997, little is known about its biological role. We have previously demonstrated that Bok mRNA is up-regulated following E2F1 overexpression. In the current work, we demonstrate that Bok RNA is low in quiescent cells and rises upon serum stimulation. To determine the mechanism underlying this regulation, we cloned and characterized the mouse Bok promoter. We find that the mouse promoter contains a conserved E2F binding site (؊43 to ؊49) and that a Bok promoter-driven luciferase reporter is activated by serum stimulation dependent on this site. Chromatin immunoprecipitation assays demonstrate that endogenous E2F1 and E2F3 associate with the Bok promoter in vivo. Surprisingly, we find that H1299 cells can stably express high levels of exogenous Bok protein. However, these cells are highly sensitive to chemotherapeutic drug treatment. Taken together these results demonstrate that Bok represents a cell cycle-regulated pro-apoptotic member of the Bcl-2 family, which may predispose growing cells to chemotherapeutic treatment.

No abstract