The natural product withaferin A (WFA) exhibits antitumor and antiangiogenesis activity in vivo, which results from this drug's potent growth inhibitory activities. Here, we show that WFA binds to the intermediate filament (IF) protein, vimentin, by covalently modifying its cysteine residue, which is present in the highly conserved alpha-helical coiled coil 2B domain. WFA induces vimentin filaments to aggregate in vitro, an activity manifested in vivo as punctate cytoplasmic aggregates that colocalize vimentin and F-actin. WFA's potent dominant-negative effect on F-actin requires vimentin expression and induces apoptosis. Finally, we show that WFA-induced inhibition of capillary growth in a mouse model of corneal neovascularization is compromised in vimentin-deficient mice. These findings identify WFA as a chemical genetic probe of IF functions, and illuminate a potential molecular target for withanolide-based therapeutics for treating angioproliferative and malignant diseases.

The medicinal plant Withania somnifera is widely researched for its anti-inflammatory, cardioactive and central nervous system effects. In Ayurveda , the major Traditional Indian medicine system, extracts from W. somnifera are distinctively employed for the treatment of arthritis and menstrual disorders. Because these conditions involve angiogenic processes we hypothesized that the W. somnifera extracts might contain angiogenesis inhibitors. We employed an endothelial cell-sprouting assay to monitor the purification of substances from W. somnifera root extracts and isolated as the active principle the previously known natural product withaferin A. We show that withaferin A inhibits human umbilical vein endothelial cell (HUVEC) sprouting in three-dimensional collagen-I matrix at doses which are relevant to NF-kappa B-inhibitory activity. Withaferin A inhibits cell proliferation in HUVECs (IC50 =12 nM) at doses that are significantly lower than those required for tumor cell lines through a process associated with inhibition of cyclin D1 expression. We propose that the inhibition of NF-kappa B by withaferin A in HUVECs occurs by interference with the ubiquitin-mediated proteasome pathway as suggested by the increased levels of poly-ubiquitinated proteins. Finally, withaferin A is shown to exert potent anti-angiogenic activity in vivo at doses that are 500-fold lower than those previously reported to exert anti-tumor activity in vivo. In conclusion, our findings identify a novel mode of action of withaferin A, which highlights the potential use of this natural product for cancer treatment or prevention.

The immunoproteasome, having been linked to neurodegenerative diseases and hematological cancers, has been shown to play an important role in MHC class I antigen presentation. However, its other pathophysiological functions are still not very well understood. This can be attributed mainly to a lack of appropriate molecular probes that can selectively modulate the immunoproteasome catalytic subunits. Herein, we report the development of molecular probes that selectively inhibit the major catalytic subunit, LMP2, of the immunoproteasome. We show that these compounds irreversibly modify the LMP2 subunit with high specificity. Importantly, LMP2-rich cancer cells compared to LMP2-deficient cancer cells are more sensitive to growth inhibition by the LMP2-specific inhibitor, implicating an important role of LMP2 in regulating cell growth of malignant tumors that highly express LMP2.

Matrix metalloproteinases (MMPs) drive normal tissue remodeling and are implicated in a wide range of pathologies. Although MMP activity is controlled at multiple levels, the primary regulation of MMP activity is transcriptional. The transcriptional promoter elements required for MMP gene expression in cultured cells have been defined, but this has not been extended to the in vivo situation. In this paper, we show that the DNA sequences between ؊522 and ؉19 of the rabbit gelatinase B gene (MMP-9) (as characterized in the transgenic mouse line 3445) constitute a minimal promoter that drives appropriate developmental and injury-induced reporter gene expression in transgenic mice. We further show that the expression and activity of three transcription factors (NF-B, AP-2, and Sp1) that control the activity of the gelatinase B promoter are selectively induced in the epithelium migrating to heal a wound. Although promoter activity parallels expression of the endogenous gene in cell cultures, we show by several criteria that cell cultures cannot model many aspects of promoter regulation in vivo. This study reveals that the transgenic mouse line 3445 might be a useful model for investigating the regulation of gelatinase B expression in vivo and for identifying and characterizing new drugs that can control gelatinase B gene transcription.

Gliosis is a biological process that occurs during injury repair in the central nervous system and is characterized by the overexpression of the intermediate filaments (IFs) glial fibrillary acidic protein (GFAP) and vimentin. A common thread in manyThe overexpression of glial fibrillary acidic protein (GFAP) 2 with vimentin is a hallmark of reactive gliosis in the central nervous system (CNS) (1, 2). These intermediate filaments (IFs) are expressed by reactive astrocytes and macro-and microglia during traumatic and inflammatory injury and in a range of CNS degenerative diseases (2). In fact, an enigma of major retinal diseases, including age-related macular degeneration, glaucoma, diabetic retinopathy, and retinopathy of prematurity, is retinal gliosis, for which there is no available clinical treatment (3-5).Important fundamental insights on the structural and mechanical functions of IFs (6, 7) have now been validated in mouse lines deficient in type III IFs (2). These studies have illuminated that, whereas overexpression of vimentin and GFAP during CNS stress response and injury repair contributes to scar formation (8), their deficiency can be protective of tissue functions in certain contexts. For instance, pathogenic angiogenesis is impaired in vimentin-deficient (Vim KO) mice due to the decreased ability of newly formed blood vessels to cross the retinal inner limiting membrane in the model of hypoxia-induced retinal neovascularization (9). Interestingly, that study also identified in vimentin and GFAP double deficient (Vim GFAP dKO) mice, and to a lesser extent in Vim KO mice, that the retinal ganglion layer is highly sensitive to mechanical stress, which was not observed in GFAP KO mice. Pathological neovascularization was also reduced in Vim KO mice in the corneal alkali injury model (10) and delayed vascularization in skin injury model (11), which is attributed to defective vascular endothelial cell integrity (12), because vimentin is the sole type III IF expressed in endothelial cells (13). On the other hand, Vim GFAP dKO mice subjected to spinal cord or brain injury recover favorably with improvement of glial scars (14). In fact, the complete absence of type III IFs in Vim GFAP dKO mice helps promote axonal regeneration and regain ambulatory function after spinal cord injury (15). These Vim GFAP dKO

Background: Withaferin A (WFA) is a vimentin-targeting inhibitor that has potent anti-proliferative activity. Results: WFA protects against corneal fibrosis by down-regulating injury-induced vimentin to exert epithelial cell cycle arrest and inhibit myofibroblast expression, which is a mechanism closely mimicked in vimentin-deficient mice during injury healing. Conclusion: Vimentin is a novel fibrosis target. Significance: Ocular fibrotic conditions that overexpress vimentin could be treatable with WFA.

Small molecules designed to specifically activate or inactivate protein functions have been useful to study biological processes. PROTACS are small molecule chimera which comprise a ligand and a peptide recognition motif for an E3 ligase. These novel reagents exploit the ubiquitin-mediated proteasome degradation pathway to target the ligand-bound protein for intracellular degradation. Here, we report that an estrogen receptor (ER)-targeting PROTACS that causes degradation of ER is able to potently inhibit endothelial cell differentiation in a three-dimensional angiogenic sprouting assay. These findings support the use of ER-targeting PROTACS as probes of angiogenesis.

The natural product withaferin A (WFA) is a potent angiogenesis inhibitor and it targets the ubiquitin-proteasome pathway in vascular endothelial cells. We generated a biotinylated affinity analog WFA-LC 2 B for use as a probe to study angiogenesis. WFA-LC 2 B inhibits angiogenic sprouting in vitro and it causes levels of ubiquitinated proteins to increase in tumor necrosis factor-α-treated human umbilical vein endothelial cells, confirming the retention of WFA's biological activity. We show that WFA-LC 2 B forms protein adducts in endothelial cells which are competed by free WFA in vivo. This WFA-LC 2 B analog will be useful to isolate the biological target of WFA. KeywordsBiotinylated analog; Natural product; Binding protein; Ubiquitin; Angiogenesis inhibitor Withaferin A (WFA), an important prototype of the withanolide class of natural products ( Fig. 1), is a highly oxygenated steroidal lactone that is found in the medicinal plant Withania somnifera and its related solanaceas species. 1 The withanolides are known to exert very potent and diverse cytotoxic, anti-stress, cardioactive, central nervous system, and immunomodulatory activities. 2 Since the early discovery of WFA during the 1960s, the major interest has been on its anti-tumor cytotoxic activities. 3,4 However, the non-cytotoxic anti-inflammatory 5 and immunomodulatory mechanisms 6 of WFA have thus far remained rather poorly characterized. These latter disease-altering activities are highly pertinent to the practice of ayurveda, a traditional form of Indian medicine, which has borne out many effective formulations from W. somnifera, especially for the treatment of chronic human diseases such as arthritis and female bleeding disorders. 2 Angiogenesis, which is the growth of new blood vessels from preexisting vasculature, is a pathogenic manifestation in cancers, 7 and it is also widely recognized to be critically involved in the pathogenesis of arthritis, endometriosis, age-related macular degeneration, diabetic retinopathy, etc. 7 Since these non-malignant inflammatory diseases could also benefit from anti-angiogenic therapeutics, 8 that such extracts could possess heretofore unrecognized inhibitors of angiogenesis. In fact, we demonstrated that W. somnifera extracts containing non-cytotoxic levels of withanolides, and also WFA, the derived active principle of these extracts, exert potent anti-angiogenic activity in vivo at very low doses. 10 Furthermore, at low nanomolar concentrations, we showed that WFA directly targets endothelial cell proliferation and exerts cytostatic cell cycle G 1 arrest in human umbilical vein endothelial cells (HUVECs). Interestingly, noncytotoxic sub-to-low micromolar concentrations of WFA also inhibit in vitro vessel formation 10,11 in the three-dimensional endothelial cell sprouting assay (3D-ECSA). At such doses, WFA potently inhibits TNF-α-induced NF-κB-DNA-binding activity, a mechanism which is associated with stabilization of phosphorylated IκB-α in the cytoplasm. Our findings suggest that WFA does not in...