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Histone deacetylase enzymes (HDACs) are emerging cancer drug targets. They regulate gene expression by removing acetyl groups from lysine residues in histone tails, resulting in chromatin condensation. The enzymatic activity of most class I HDACs requires recruitment into multi-subunit co-repressor complexes, which are in turn recruited to chromatin by repressive transcription factors. Here we report the structure of a complex between an HDAC and a co-repressor, namely, human HDAC3 with the deacetylase activation domain (DAD) from the human SMRT co-repressor (also known as NCOR2). The structure reveals two remarkable features. First, the SMRT-DAD undergoes a large structural rearrangement on forming the complex. Second, there is an essential inositol tetraphosphate molecule--D-myo-inositol-(l,4,5,6)-tetrakisphosphate (lns(l,4,5,6)[P.sub.4])--acting as an 'intermolecular glue' between the two proteins. Assembly of the complex is clearly dependent on the Ins(1,4,5,6)[P.sub.4], which may act as a regulator--potentially explaining why inositol phosphates and their kinases have been found to act as transcriptional regulators. This mechanism for the activation of HDAC3 appears to be conserved in class I HDACs from yeast to humans, and opens the way to novel therapeutic opportunities., The acetylation of lysine residues in the tails of histone proteins plays an important role in the regulation of gene expression in eukaryotic cells (1,2). The level of lysine acetylation [...]

Inositol polyphosphate 4-phosphatase-II (INPP4B) is a regulator of the phosphoinositide 3-kinase (PI3K) signaling pathway and is implicated as a tumor suppressor in epithelial carcinomas. INPP4B loss of heterozygosity (LOH) is detected in some human breast cancers; however, the expression of INPP4B protein in breast cancer subtypes and the normal breast is unknown. We report here that INPP4B is expressed in nonproliferative estrogen receptor (ER)-positive cells in the normal breast, and in ER-positive, but not negative, breast cancer cell lines. INPP4B knockdown in ER-positive breast cancer cells increased Akt activation, cell proliferation, and xenograft tumor growth. Conversely, reconstitution of INPP4B expression in ER-negative, INPP4B-null human breast cancer cells reduced Akt activation and anchorage-independent growth. INPP4B protein expression was frequently lost in primary human breast carcinomas, associated with high clinical grade and tumor size and loss of hormone receptors and was lost most commonly in aggressive basal-like breast carcinomas. INPP4B protein loss was also frequently observed in phosphatase and tensin homolog (PTEN)-null tumors. These studies provide evidence that INPP4B functions as a tumor suppressor by negatively regulating normal and malignant mammary epithelial cell proliferation through regulation of the PI3K/Akt signaling pathway, and that loss of INPP4B protein is a marker of aggressive basal-like breast carcinomas. phosphatidylinositol 3,4-bisphosphate doi/ 10.1073/pnas.1015245107

Vascular damage signals smooth muscle cells to proliferate, often exacerbating existing pathologies. Although the role of changes in 'global' [Ca.sup.2+] in vascular smooth muscle (VSM) cell dedifferentiation has been studied, the role of specific [Ca.sup.2+] signals in determining VSM phenotype remains relatively unexplored. Earlier work with cultured VSM cells suggests that inositol 1,4,5-trisphosphate receptor ([IP.sub.3]R) expression and sarcoplasmic reticulum (SR) [Ca.sup.2+] release may be linked to VSM cell proliferation in native tissue. Thus we hypothesized that SR [Ca.sup.2+] release through [IP.sub.3]Rs in the form of discrete transient signals is necessary for VSM cell proliferation. To investigate this hypothesis, we used mouse cerebral arteries to design an organ culture system that permitted examination of [Ca.sup.2+] dynamics in native tissue. Explanted arteries were cultured in normal medium with 10% FBS, and appearance of individual VSM cells migrating from explanted arteries (outgrowth cells) was tracked daily. Initial exposure to 10% FBS increased [Ca.sup.2+] waves in myocytes in the arteries that were blocked by the [IP.sub.3]R antagonist 2-aminoethoxydiphenylborate (2-APB). Inhibition of [IP.sub.3]R opening (via 100 [micro]M 2-APB, 10 [micro]M xestospongin C, or 25 [micro]M U-73122) dramatically reduced outgrowth cell number compared with untreated or ryanodine-treated (10 [micro]M) arteries. Consistent with this finding, 2-APB inhibited cell proliferation, as measured by reduced proliferating cell nuclear antigen immunostaining within 48 h of culture but did not inhibit cell migration. These results indicate that activation of [IP.sub.3]R [Ca.sup.2+] release is required for VSM cell proliferation in these arteries. calcium signaling; explant culture; calcium channels; sarcoplasmic reticulum

Attenuation of the phosphatidylinositol (PI) signal transduction pathway as a consequence of inhibition of inositol monophosphatase (IMPase) has been proposed as the mechanism for the efficacy of [Li.sup.+] in the treatment of bipolar disorder. Nevertheless, [Li.sup.+] also affects other aspects of PI signal transduction, and it is therefore not clear whether modulation of PI responses by [Li.sup.+] can be attributed solely to inhibition of IMPase. However, inhibitors of IMPase mimic the effects of [Li.sup.+] on some aspects of PI cell signalling, thus highlighting the potential of IMPase as a target for the treatment of bipolar disorder. The recent description of the three-dimensional structure of IMPase in conjunction with site-directed mutagenesis and kinetic studies has led to the elucidation of the enzyme mechanism. These structural and mechanistic data should prove useful in the development of novel inhibitors of IMPase that might ultimately prove useful clinically.

Inositol hexaphosphate (Ins(P.sub.6), phytic acid) is ubiquitous in the plant kingdom and is abundant in cereals and legumes. In much smaller amounts Ins(P.sub.6) and its lower phosphorylated forms (Ins(P.sub.1-5)) are contained in most mammalian cells, where they are important in regulating vital cellular functions. Both in vivo and in vitro experiments have suggested striking anticancer potential (preventive as well as therapeutic) for Ins(P.sub.6) with and without inositol. In addition to reduce cell proliferation, Ins(P.sub.6) increases differentiation of malignant cells often resulting in reversion to the normal phenotype. Ins(P.sub.6) is quickly absorbed from the rat stomach and upper intestine and distributed as inositol and Ins(P.sub.1). In vitro it is instantaneously taken up by malignant cells undergoing variable dephosphorylation to inositol and Ins(P.sub.1-5), pointing toward their role in mediating the action of Ins(P.sub.6). Because Ins(P.sub.6) is high in high-fiber diets, our studies also may explain, at least in part, the epidemiologic observation showing high-fiber diets are associated with a lower incidence of certain cancers. Although further studies are needed to elucidate the mechanism(s) of this action, inclusion of Ins(P.sub.6) in our strategies for cancer prevention and therapy is warranted. INDEXING KEY WORDS: chemoprevention; differentiation; Inositol hexaphosphate; phytic acid; signal transduction

These studies were conducted to determine if supplementation of a corn-soybean meal diet with 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) would increase the utilization of natural phytate phosphorus by broiler chickens. Two experiments were conducted to evaluate the effect of dietary 1,25-(OH)2D3 in the presence and absence of supplemental phytase and at several dietary levels of inorganic phosphorus supplementation. The criteria measured in these studies were weight gain, gain:feed ratio, bone ash, rickets due to phosphorus deficiency, plasma calcium and phosphorus and retention of calcium, phosphorus and phytate phosphorus. In the first experiment, the types and amounts of fecal inositol phosphates were determined by HPLC, and the total fecal phytate was determined by the classic FeCl3 precipitation technique. In the first experiment, the addition of 1,25-(OH)2D3) to the diet in the presence of dietary phytase resulted in greater 9-d weight and bone ash and lower incidence of rickets; the retention of total fecal phytate and phytate phosphorus was greater than in controls. The second experiment was a complete 2 x 2 x 2 factorial design (phosphorus levels x phytase x 1,25-(OH)2D3). The addition of 1,25-(OH)2D3) alone to the diet resulted in greater 9-d weight and bone ash, lower incidence of rickets, and greater retention of total calcium and phosphorus and phytate phosphorus. The highest retention of phytate phosphorus (79.4%) was obtained when both phytase and 1,25-(OH)2D3 were present in the diet. The possible mode of action and importance of these results in many areas of nutrition and environmental science are discussed. J. Nutr. 123: 567-577, 1993.

Inositol is an important component of the human diet. A research study found premature infants with respiratory distress syndrome who receive supplementary inositol are more likely to survive without problems with lung and bronchial development. Studies in laboratory animals have found that inositol may prevent hair loss, accumulation of fat in the liver and fat metabolism disorders. Adults ingest an average of one gram of inositol a day in plant and animal products. It is present in high concentrations in breast milk, and the body can synthesize it from glucose (sugar). Inositol exists in several different forms in mammals, and phosphoinositides in cell membranes are important in many different physiological and biochemical processes. Dietary supplementation with inositol may be beneficial to diabetics, kidney disease patients or infants with respiratory distress syndrome.

Inositol monophosphatase, whose therapeutic activity resembles that of lithium, is used to treat manic-depressive illness. Lithium negatively regulates inositol monophosphatase from transforming to membrane inositol phospholipid precursors. The two magnesium ions of the monophosphatase enzyme are essential for enzyme activity.

Inositol hexaphosphate (I[P.sub.6]) is a naturally occurring polyphosphorylated carbohydrate, present in substantial amounts in almost all plant and mammalian cells, with a strong anticancer activity against numerous tumors. In vitro, I[P.sub.6] affects signal transduction pathways, leading to inhibition of cell growth and transformation, reduced invasive behavior, enhanced apoptosis, and slowed angiogenesis. Uncontrolled proliferation is a hallmark of malignant cells, and I[P.sub.6] can reduce the cell proliferation rate and cause [G.sub.0]/[G.sub.1] cell cycle arrest of many cell lines, both human and rodent. Our studies using estrogen receptor-positive MCF-7 and estrogen receptor-negative MDA MB-231 human breast cancer cells show that I[P.sub.6] causes [G.sub.0]/[G.sub.1] cell cycle arrest associated with inhibition of Akt and Erk1/2 and upregulation of PKC-[delta] and cyclin-dependent kinase inhibitor p[27.sup.Kip1] As a result, phosphorylation of retinoblastoma protein was decreased, and cells were [G.sub.0]/[G.sub.1] arrested. I[P.sub.6] was selective and synergistic with standard chemotherapeutics. One important characteristic of malignancy is the ability of tumor cells to metastasize and infiltrate normal tissue. A significant reduction in the number of lung metastatic colonies by I[P.sub.6] was observed in a mouse metastatic tumor model using FSA-1 cells. In vitro, I[P.sub.6] inhibits key steps of metastasis through effects on adhesion, migration, invasion, and inhibition of metrix metalloproteinases. Tumors depend on the formation of new blood vessels to support their growth and metastasis. I[P.sub.6] inhibited the growth and differentiation of endothelial cells and inhibited the secretion of vascular endothelial growth factor from malignant cells. Apoptosis is a hallmark of action of many anticancer drugs. I[P.sub.6] induces apoptosis involving cleavage of caspase 3, caspase 9, and poly(ADP-ribose) polymerase (an apoptotic substrate) in a time- and dose-dependent manner. Being a safe, selective, and potent antiproliferative and proapoptotic agent, I[P.sub.6] should be considered in our alternative or complementary strategies for cancer prevention and therapy.

The current treatment of breast carcinomas recognizes the importance of combination therapy in order to increase efficacy and decrease side effects of conventional chemotherapy. Inositol hexaphosphate (IP6), a naturally occurring [...]