The segmental premature aging disease, Hutchinson-Gilford Progeria (HGPS) is caused by a truncated and farnesylated form of Lamin A. In a mouse model for HGPS, a similar Lamin A variant causes the proliferative arrest and death of post-natal but not embryonic fibroblasts. Arrest is due to an inability to produce a functional extracellular matrix (ECM), as growth on normal ECM rescues proliferation. The defects are associated with inhibition of canonical Wnt signaling, due to reduced nuclear localization and transcriptional activity of Lef1, but not Tcf4, in both mouse and human progeric cells. Defective Wnt signaling, affecting ECM synthesis, maybe critical to the etiology of HGPS as mice exhibit skeletal defects and apoptosis in major blood vessels proximal to the heart. These results establish a functional link between the nuclear envelope/lamina and the cell surface/ECM and may provide insights into the role of Wnt signaling and the ECM in aging.

Activation of STAT3 in cancers leads to gene expression promoting cell proliferation and resistance to apoptosis, as well as tumor angiogenesis, invasion, and migration. In the characterization of effects of ST3-H2A2, a selective inhibitor of the STAT3 N-terminal domain (ND), we observed that the compound induced apoptotic death in cancer cells associated with robust activation of proapoptotic genes. Using ChIP and tiling human promoter arrays, we found that activation of gene expression in response to ST3-H2A2 is accompanied by altered STAT3 chromatin binding. Using inhibitors of STAT3 phosphorylation and a dominant-negative STAT3 mutant, we found that the unphosphorylated form of STAT3 binds to regulatory regions of proapoptotic genes and prevents their expression in tumor cells but not normal cells. siRNA knockdown confirmed the effects of ST3-HA2A on gene expression and chromatin binding to be STAT3 dependent. The STAT3-binding region of the C/EBP-homologous protein (CHOP) promoter was found to be localized in DNaseI hypersensitive site of chromatin in cancer cells but not in nontransformed cells, suggesting that STAT3 binding and suppressive action can be chromatin structure dependent. These data demonstrate a suppressive role for the STAT3 ND in the regulation of proapoptotic gene expression in cancer cells, providing further support for targeting STAT3 ND for cancer therapy.H3K9me3 | peptide inhibitor | prostate cancer | transcription factor S TAT3, a member of the STAT family, is a key signaling protein that transduces extracellular signals to the nucleus and regulates transcription of genes (1). Following ligand stimulation, STAT3 is phosphorylated on Y705 tyrosine residue, dimerizes, and translocates to the nucleus to bind its cognate DNA-response elements, activating gene transcription (1). Constitutively activated STAT3 mediates deregulated growth, survival, and angiogenesis (2, 3). STAT3 is widely recognized as a potential drug target for cancer therapy, and various approaches, including targeting of upstream tyrosine kinases and direct inhibitors of STAT3 dimerization, have been advanced to inhibit STAT3 signaling in cancers (4). However, unphosphorylated STAT3 (U-STAT3) has also been shown to influence gene transcription, both in response to cytokines and in cancer cells, albeit by mechanisms that are distinct from those activated by phosphorylated STAT3 (5). We have developed a highly selective inhibitor of STAT3 ND, ST3-Hel2A-2 (ST3-H2A2), that binds to the N-terminal domain (ND) and inhibits STAT3 signaling (6). STAT3 ND is involved in the interactions of two STAT dimers on neighboring sites to form a more stable tetramer and the interactions with histone-modifier proteins to induce changes in chromatin structure (reviewed in ref. 7). These complex interactions may greatly affect STAT3-dependent transcriptional activity, suggesting that the STAT3 ND mediates important regulatory functions of STAT3 in normal cells (8) and in cancer (9). ST3-H2A2 induces death in breast cancer cells MDA-MB-231 an...

Kaiso, a p120 catenin-binding protein, is expressed in the cytoplasmic and nuclear compartments of cells; however, the biological consequences and clinical implications of a shift between these compartments have yet to be established. Herein, we report an enrichment of nuclear Kaiso expression in cells of primary and metastatic prostate tumors relative to the normal prostate epithelium. Nuclear expression of Kaiso correlates with Gleason score (P < 0.001) and tumor grade (P < 0.001). There is higher nuclear expression of Kaiso in primary tumor/normal matched samples and in primary tumors from African American men (P < 0.0001). We further found that epidermal growth factor (EGF) receptor up-regulates Kaiso at the RNA and protein levels in prostate cancer cell lines, but more interestingly causes a shift of cytoplasmic Kaiso to the nucleus that is reversed by the EGF receptor-specific kinase inhibitor, PD153035. In both DU-145 and PC-3 prostate cancer cell lines, Kaiso inhibition (short hairpin RNA-Kaiso) decreased cell migration and invasion even in the presence of EGF. Further, Kaiso directly binds to the E-cadherin promoter, and inhibition of Kaiso in PC-3 cells results in increased E-cadherin expression, as well as re-establishment of cell-cell contacts. In addition, Kaiso-depleted cells show more epithelial morphology and a reversal of the mesenchymal markers N-cadherin and fibronectin. Our findings establish a defined oncogenic role of Kaiso in promoting the progression of prostate cancer.

The ubiquitin-proteasome system plays a critical role in controlling the level, activity and location of various cellular proteins. Significant progress has been made in investigating the molecular mechanisms of ubiquitination, particularly in understanding the structure of the ubiquitination machinery and identifying ubiquitin protein ligases, the primary specificity-determining enzymes. Therefore, it is now possible to target specific molecules involved in ubiquitination and proteasomal degradation to regulate many cellular processes such as signal transduction, proliferation and apoptosis. In particular, alterations in ubiquitination are observed in most, if not all, cancer cells. This is manifested by destabilization of tumor suppressors, such as p53, and overexpression of oncogenes such as c-Myc and c-Jun. In addition to the development and clinical validation of proteasome inhibitor, bortezomib, in myeloma therapy, recent studies have demonstrated that it is possible to develop inhibitors for specific ubiquitination and deubiquitination enzymes. With the help of structural studies, rational design and chemical synthesis, it is conceivable that we will be able to use 'druggable' inhibitors of the ubiquitin system to evaluate their effects in animal tumor models in the not-so-distant future. (Cancer Sci 2009; 100: 24-28) Ubiquitin system U biquitination is catalyzed by the sequential action of E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme) and E3 (ubiquitin protein ligase), which leads to the conjugation of ubiquitin to the ε-amino group of a lysine residue in target proteins (Fig. 1).(1) Under certain circumstances, ubiquitin can also be conjugated to the N-terminal or even non-lysine residues of proteins.(2,3) Interestingly, the formation of the polyubiquitin chain on certain proteins requires an additional factor (E4), (4) whereas monoubiquitination of protein that contains a ubiquitin-binding domain may occur in the absence of E3. (5) Additionally, there is a family of small ubiquitin-like modifiers (Ubl), including SUMO, Nedd8, FAT10 and ISG15. They can be conjugated to lysine residues of specific target proteins through mechanisms parallel to but distinct from that of ubiquitin. (6) While SUMO can be conjugated to a variety of substrate proteins, other Ubl appear to have a limited number of targets. Besides affecting many cellular activities directly, these modifications also regulate ubiquitination at multiple levels. (7,8) Intriguingly, RING protein Hdm2 can function as ligase for both ubiquitin and Nedd8.(9) RING protein Topors can act as an E3 for both ubiquitin and SUMO. (10) Although it is generally believed that there is only one E1 (UBE1) in human cells, recent studies have shown that both UBE1L2 and Uba6 can activate ubiquitin.(11-13) Because they only transfer ubiquitin to particular E2s, it is likely that UBE1L2 and Uba6 may regulate a subset of ubiquitinations or modulate ubiquitination at specific organs. There are more than 40 putative E2s in mammalian cells, and each...