Tandem PHD and bromodomains are often found in chromatin-associated proteins and have been shown to cooperate in gene silencing. Each domain can bind specifically modified histones: the mechanisms of cooperation between these domains are unknown. We show that the PHD domain of the KAP1 corepressor functions as an intramolecular E3 ligase for sumoylation of the adjacent bromodomain. The RING finger-like structure of the PHD domain is required for both Ubc9 binding and sumoylation and directs modification to specific lysine residues in the bromodomain. Sumoylation is required for KAP1-mediated gene silencing and functions by directly recruiting the SETDB1 histone methyltransferase and the CHD3/Mi2 component of the NuRD complex via SUMO-interacting motifs. Sumoylated KAP1 stimulates the histone methyltransferase activity of SETDB1. These data provide a mechanistic explanation for the cooperation of PHD and bromodomains in gene regulation and describe a function of the PHD domain as an intramolecular E3 SUMO ligase.

The DNA damage response requires a coordinated nucleocytoplasmic cascade of events, which ultimately converge on damaged DNA packaged in chromatin. Few connections between the proteins that remodel chromatin and the proteins that mediate this damage response have been shown. We have investigated the DNA damage-induced phosphorylation of the KRAB-ZFP-associated protein 1 (KAP1), the dedicated corepressor for Krüppel-associated box (KRAB) zinc finger protein (ZFP) proteins. We show that KAP1 is rapidly phosphorylated following DNA damage by members of the phosphatidylinositol-3 kinase-like family of kinases. This phosphorylation occurs at a single amino acid residue that is conserved from mice to humans and is located adjacent to the bromodomain, suggesting that it may regulate chromatin recognition by that module. Phosphorylated KAP1 rapidly localizes to sites of DNA strand breaks in the nucleus in response to ionizing radiation. This discovery provides a novel link between chromatinmediated transcriptional repression and the recognition/ repair of DNA, which must be accomplished by the cellular DNA damage response. (Cancer Res 2006; 66(24): 11594-9)

No abstract

The enantioselective synthesis of Nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines including the total synthesis of natural products and medicinal chemistry. In this manuscript, we describe the highly enantioselective palladium-catalyzed decarboxylative allylic alkylation of readily available lactams to form 3,3,-disubstituted pyrrolidinones, piperidinones, caprolactams, and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envision that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously employed in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures.

The repair of DNA damage in highly compact, transcriptionally silent heterochromatin requires that repair and chromatin packaging machineries be tightly coupled and regulated. KAP1 is a heterochromatin protein and co-repressor which binds to HP1 during gene silencing, but is also robustly phosphorylated by ATM at serine 824 in response to DNA damage. The interplay between HP1-KAP1 binding/ATM phosphorylation during DNA repair is not known. We show that HP1α and unmodified KAP1 are enriched in endogenous heterochromatic loci and at a silent transgene prior to damage. Following damage, γH2AX and pKAP1-s824 rapidly increase and persist at these loci. Cells which lack HP1 fail to form discreet pKAP1-s824 foci after damage but levels are higher and more persistent. KAP1 is phosphorylated at Serine 473 in response to DNA damage and its levels are also modulated by HP1. Unlike pKAP1-s824, pKAP1-s473 does not accumulate at damage foci but is diffusely localized in the nucleus. While HP1 association tempers KAP1 phosphorylation, this interaction also slows the resolution of γH2AX foci. Thus, HP1-dependent regulation of KAP1 influences DNA repair in heterochromatin.

The chamigrene subclass of sesquiterpenes, characterized by a spiro[5.5]undecane core, is an ever-growing family of natural products (Figure 1). 1 Well over one hundred members have been isolated thus far, and many of these compounds exhibit a diverse array of biological activity. 1c In particular, elatol (1), 2 one of the most widely studied chamigrenes, displays antibiofouling activity, 3a-b antibacterial activity (including human pathogenic bacteria), 3c-e antifungal activity, 3f and cytotoxicity against HeLa and Hep-2 human carcinoma cell lines. 3g Despite the interesting bioactivity and compact structure of these molecules, no general strategy for their preparation has been developed, and, to the best of our knowledge, no total synthesis of elatol has been reported in the thirty-three years since its original isolation. 4,5Structurally, elatol (1) consists of a densely functionalized A ring bearing three stereocenters, including an all-carbon quaternary stereocenter, which is vicinal to a second, non-stereogenic quaternary carbon. Within the B ring is also a fully substituted chlorinated olefin. We envisioned a strategy toward these challenging motifs based on methodological advances recently reported by our laboratories. Specifically, enantioselective decarboxylative allylation 6 could generate the all-carbon quaternary stereocenter, while ring-closing metathesis (RCM) 7 could be employed to concomitantly provide the tetrasubstituted olefin and the spirocyclic core of 1 (Scheme 1). Importantly, this approach serves as a general platform to access the chamigrene family.We envisioned 1 to ultimately arise from sequential reductive olefin transposition and diastereoselective reduction of α-bromoketone 10. In turn, compound 10 would be obtained from bromination of the enone resulting from 1,2-addition of a methyl anion to spirocycle 11. Intermediate 11 itself could be the product of RCM of α,ω-diene 12. Although generation of a fully substituted chlorinated olefin via RCM has not been previously reported, 8 we anticipated that the improved reactivity of catalyst 22 7 (vide infra) might be sufficient for this transformation. Access to 12 would be possible via enantioselective decarboxylative allylation of an appropriately substituted vinylogous ester derivative (i.e., 13), employing the Pd(0) complex of a phosphinooxazoline (PHOX) ligand. This would constitute a previously unexplored substrate class with this catalyst system. 9 Finally, enol carbonate 13 could be derived from commercially available dimedone (14).Our synthetic efforts began with the condensation of isobutyl alcohol and dimedone (14) to provide known vinylogous ester 15 (Scheme 2). 10 Direct alkylation of vinylogous ester 15 with 4-iodo-2-methyl-1-butene was sluggish; however, a two-step procedure involving conjugate addition to methyl vinyl ketone (MVK) followed by Wittig methylenation afforded olefin (±)-16 in good yield. Selective enolization of vinylogous ester (±)-16 and trapping with chloroformate 17 allowed access to enol carbonate 13 in 7...

α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursors: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.

The Snail transcription factor is a repressor and a master regulator of epithelial-mesenchymal transition (EMT) events in normal embryonic development and during tumor metastases.