Jon Cogan

Genomic Androgen Receptor-Occupied Regions with Different Functions, Defined by Histone Acetylation, Coregulators and Transcriptional Capacity

Background The androgen receptor (AR) is a steroid-activated transcription factor that binds at specific DNA locations and plays a key role in the etiology of prostate cancer. While numerous studies have identified a clear connection between AR binding and expression of target genes for a limited number of loci, high-throughput elucidation of these sites allows for a deeper understanding of the complexities of this process. Methodology/Principal Findings We have mapped 189 AR occupied regions (ARORs) and 1,388 histone H3 acetylation (AcH3) loci to a 3% continuous stretch of human genomic DNA using chromatin immunoprecipitation (ChIP) microarray analysis. Of 62 highly reproducible ARORs, 32 (52%) were also marked by AcH3. While the number of ARORs detected in prostate cancer cells exceeded the number of nearby DHT-responsive genes, the AcH3 mark defined a subclass of ARORs much more highly associated with such genes – 12% of the genes flanking AcH3+ARORs were DHT-responsive, compared to only 1% of genes flanking AcH3−ARORs. Most ARORs contained enhancer activities as detected in luciferase reporter assays. Analysis of the AROR sequences, followed by site-directed ChIP, identified binding sites for AR transcriptional coregulators FoxA1, CEBPβ, NFI and GATA2, which had diverse effects on endogenous AR target gene expression levels in siRNA knockout experiments. Conclusions/Significance We suggest that only some ARORs function under the given physiological conditions, utilizing diverse mechanisms. This diversity points to differential regulation of gene expression by the same transcription factor related to the chromatin structure.

Lef1 Haploinsufficient Mice Display a Low Turnover and Low Bone Mass Phenotype in a Gender- and Age-Specific Manner

We investigated the role of Lef1, one of the four transcription factors that transmit Wnt signaling to the genome, in the regulation of bone mass. Microcomputed tomographic analysis of 13- and 17-week-old mice revealed significantly reduced trabecular bone mass in Lef1+/− females compared to littermate wild-type females. This was attributable to decreased osteoblast activity and bone formation as indicated by histomorphometric analysis of bone remodeling. In contrast to females, bone mass was unaffected by Lef1 haploinsufficiency in males. Similarly, females were substantially more responsive than males to haploinsufficiency in Gsk3β, a negative regulator of the Wnt pathway, displaying in this case a high bone mass phenotype. Lef1 haploinsufficiency also led to low bone mass in males lacking functional androgen receptor (AR) (tfm mutants). The protective skeletal effect of AR against Wnt-related low bone mass is not necessarily a result of direct interaction between the AR and Wnt signaling pathways, because Lef1+/− female mice had normal bone mass at the age of 34 weeks. Thus, our results indicate an age- and gender-dependent role for Lef1 in regulating bone formation and bone mass in vivo. The resistance to Lef1 haploinsufficiency in males with active AR and in old females could be due to the reduced bone turnover in these mice.

Krox20/EGR2 deficiency accelerates cell growth and differentiation in the monocytic lineage and decreases bone mass

Krox20/EGR2, one of the 4 early growth response genes, is a highly conserved transcription factor implicated in hindbrain development, peripheral nerve myelination, tumor suppression, and monocyte/macrophage cell fate determination. Here, we established a novel role for Krox20 in postnatal skeletal metabolism. Microcomputed tomographic analysis of 4- and 8-week-old mice revealed a low bone mass phenotype (LBM) in both the distal femur and the vertebra of Krox20(+/-) mice. This was attributable to accelerated bone resorption as demonstrated in vivo by increased osteoclast number and serum C-terminal telopeptides, a marker for collagen degradation. Krox20 haploinsufficiency did not reduce bone formation in vivo, nor did it compromise osteoblast differentiation in vitro. In contrast, growth and differentiation were significantly stimulated in preosteoclast cultures derived from Krox20(+/-) splenocytes, suggesting that the LBM is attributable to Krox20 haploinsufficiency in the monocytic lineage. Furthermore, Krox20 silencing in preosteoclasts increased cFms expression and response to macrophage colony-stimulating factor, leading to a cell-autonomous stimulation of cell-cycle progression. Our data indicate that the antimitogenic role of Krox20 in preosteoclasts is the predominant mechanism underlying the LBM phenotype of Krox20-deficient mice. Stimulation of Krox20 expression in preosteoclasts may present a viable therapeutic strategy for high-turnover osteoporosis.

Aminoglycosides Restore Full-length Type VII Collagen by Overcoming Premature Termination Codons: Therapeutic Implications for Dystrophic Epidermolysis Bullosa

Patients with recessive dystrophic epidermolysis bullosa (RDEB) have severe, incurable skin fragility, blistering, and multiple skin wounds due to mutations in the gene encoding type VII collagen (C7), the major component of anchoring fibrils mediating epidermal-dermal adherence. Nearly 10-25% of RDEB patients carry nonsense mutations leading to premature stop codons (PTCs) that result in truncated C7. In this study, we evaluated the feasibility of using aminoglycosides to suppress PTCs and induce C7 expression in two RDEB keratinocyte cell lines (Q251X/Q251X and R578X/R906) and two primary RDEB fibroblasts (R578X/R578X and R163X/R1683X). Incubation of these cells with aminoglycosides (geneticin, gentamicin, and paromomycin) resulted in the synthesis and secretion of a full-length C7 in a dose-dependent and sustained manner. Importantly, aminoglycoside-induced C7 reversed the abnormal RDEB cell phenotype and incorporated into the dermal-epidermal junction of skin equivalents. We further demonstrated the general utility of aminoglycoside-mediated readthrough in 293 cells transiently transfected with expression vectors encoding 22 different RDEB nonsense mutations. This is the first study demonstrating that aminoglycosides can induce PTC readthrough and restore functional C7 in RDEB caused by nonsense mutations. Therefore, aminoglycosides may have therapeutic potential for RDEB patients and other inherited skin diseases caused by nonsense mutations.

Opposing effects of glucocorticoids and Wnt signaling on Krox20 and mineral deposition in osteoblast cultures.

Krox20 is expressed in osteoblasts and chondrocytes, and is required for trabecular bone formation during embryogenesis. Here we show by RT‐qPCR and Western blot analysis that Krox20 is up‐regulated during late stages of osteoblast differentiation in culture. Glucocorticoids (GCs) rapidly inhibit the expression of Krox20 as well its co‐activator, HCF‐1, resulting in inhibition of the Osteocalcin Krox20‐binding Enhancer (OKE). GCs also inhibit expression of EGR1, EGR3, and EGR4. OKE activity, which is dependent on the presence of Runx2, was independent of the osteocalcin promoter Runx2 binding site. In contrast to GCs, activation of the Wnt, but not the BMP or the PTH signaling pathways, stimulated Krox20 expression as well as activity of the OKE. GC‐mediated suppression of Krox20 expression was compromised, albeit not completely, in the presence of DKK1, suggesting that the inhibition occurs in both Wnt‐dependent and Wnt‐independent manners. Furthermore, Wnt3A partially rescued Krox20 expression in GC‐arrested osteoblast cultures and this was accompanied by rescue of mineralization. These findings are consistent with a role for Krox20 in osteoblast function and suggest that this transcription factor may contribute to the opposing effects of GCs and Wnt signaling on bone formation. J. Cell. Biochem. 103: 1938–1951, 2007.

De Novo Anti-Type VII Collagen Antibodies in Patients with Recessive Dystrophic Epidermolysis Bullosa

The two main layers of human skin are held together by structures at the dermal-epidermal junction (DEJ) called anchoring fibrils (AFs). Without properly functioning AFs, the adherence between the epidermis and dermis is compromised. Clinically, this translates into skin fragility and skin bullae. AFs are composed of type VII collagen (C7) that has a central triple helical domain (TH) flanked by a 145-kDa non-collagenous amino-terminal domain (NC1) and a 30-kDa carboxyl-terminal domain (NC2) (Burgeson et al., 1993). AFs and C7 are perturbed in recessive dystrophic epidermolysis bullosa (RDEB), a disease characterized clinically by skin fragility, skin bullae, scarring, and nail loss (Fine et al., 2008). RDEB is caused by mutations in the COL7A1 gene encoding C7. Over 700 mutations have been identified in DEB patients (Wertheim -Tysarowska et al., 2012). According to a recent consensus report, RDEB is classified as RDEB, severe, generalized (RDEB-sev, gen), RDEB, generalized, other (RDEB-O) and RDEB inversa (RDEB-I) (Fine et al., 2008).

Gentamicin induces functional type VII collagen in recessive dystrophic epidermolysis bullosa patients

BACKGROUND. Recessive dystrophic epidermolysis bullosa (RDEB) is an incurable disease caused by mutations in the gene encoding type VII collagen, the major component of anchoring fibrils (AF). We previously demonstrated that gentamicin produced functional type VII collagen in RDEB cells harboring nonsense mutations. Herein, we determined whether topical or intradermal gentamicin administration induces type VII collagen and AFs in RDEB patients. METHODS. A double-blind, placebo-controlled pilot trial assessed safety and efficacy of topical and intradermal gentamicin in 5 RDEB patients with nonsense mutations. The topical arm tested 0.1% gentamicin ointment or placebo application 3 times daily at 2 open erosion sites for 2 weeks. The intradermal arm tested daily intradermal injection of gentamicin solution (8 mg) or placebo into 2 intact skin sites for 2 days in 4 of 5 patients. Primary outcomes were induction of type VII collagen and AFs at the test sites and safety assessment. A secondary outcome assessed wound closure of topically treated erosions. RESULTS. Both topical and intradermal gentamicin administration induced type VII collagen and AFs at the dermal-epidermal junction of treatment sites. Newly created type VII collagen varied from 20% to 165% of that expressed in normal human skin and persisted for 3 months. Topical gentamicin corrected dermal-epidermal separation, improved wound closure, and reduced blister formation. There were no untoward side effects from gentamicin treatments. Type VII collagen induction did not generate anti–type VII collagen autoantibodies in patients’ blood or skin. CONCLUSION. Topical and intradermal gentamicin suppresses nonsense mutations and induces type VII collagen and AFs in RDEB patients. Gentamicin therapy may provide a readily available treatment for RDEB patients with nonsense mutations. TRIAL REGISTRATION. ClinicalTrials.gov NCT02698735. FUNDING. Epidermolysis Bullosa Research Partnership, Epidermolysis Bullosa Medical Research Foundation, NIH, and VA Merit Award.

Inhibition of AR-mediated Transcription by Binding of Oct1 to a Motif enriched in AR-Occupied Regions

The androgen receptor (AR) plays roles in prostate development and cancer (PCa). In response to androgens, the AR binds to androgen‐response elements (AREs) to modulate gene transcription. The responses of such genes are dependent on the cellular milieu and on sequences around the AREs, which attract other transcription factors. Previously, bioinformatic analysis of 62 AR‐occupied regions (ARORs) in PCa cells revealed enrichment for both AREs and a TTGGCAAATA‐like motif. We undertook the present study to investigate the significance of the TTGGCAAATA‐like motif.

Gentamicin induces LAMB3 nonsense mutation readthrough and restores functional laminin 332 in junctional epidermolysis bullosa

Significance Premature termination codons (PTCs) generated by nonsense mutations produce abnormal, short, or diminished proteins. Eighty-three percent of patients with Herlitz junctional epidermolysis bullosa (H-JEB), an inherited, incurable skin disease, harbor nonsense mutation(s) in genes encoding a structural protein (laminin 332) responsible for skin adherence. Gentamicin, a common antibiotic, was shown to induce readthrough of PTCs in various disease models. Using in vitro assays and 3D skin models, we found that H-JEB cells harboring nonsense mutations exposed to gentamicin produce full-length structural protein, deposit it correctly between skin layers, and exhibit reversal of other H-JEB–associated cellular abnormalities. Our findings indicate that gentamicin may present an immediate therapy for this otherwise fatal disease and other skin disorders caused by nonsense mutations. Herlitz junctional epidermolysis bullosa (H-JEB) is an incurable, devastating, and mostly fatal inherited skin disease for which there is only supportive care. H-JEB is caused by loss-of-function mutations in LAMA3, LAMB3, or LAMC2, leading to complete loss of laminin 332, the major component of anchoring filaments, which mediate epidermal-dermal adherence. LAMB3 (laminin β3) mutations account for 80% of patients with H-JEB, and ∼95% of H-JEB–associated LAMB3 mutations are nonsense mutations leading to premature termination codons (PTCs). In this study, we evaluated the ability of gentamicin to induce PTC readthrough in H-JEB laminin β3-null keratinocytes transfected with expression vectors encoding eight different LAMB3 nonsense mutations. We found that gentamicin induced PTC readthrough in all eight nonsense mutations tested. We next used lentiviral vectors to generate stably transduced H-JEB cells with the R635X and C290X nonsense mutations. Incubation of these cell lines with various concentrations of gentamicin resulted in the synthesis and secretion of full-length laminin β3 in a dose-dependent and sustained manner. Importantly, the gentamicin-induced laminin β3 led to the restoration of laminin 332 assembly, secretion, and deposition within the dermal/epidermal junction, as well as proper polarization of α6β4 integrin in basal keratinocytes, as assessed by immunoblot analysis, immunofluorescent microscopy, and an in vitro 3D skin equivalent model. Finally, newly restored laminin 332 corrected the abnormal cellular phenotype of H-JEB cells by reversing abnormal cell morphology, poor growth potential, poor cell-substratum adhesion, and hypermotility. Therefore, gentamicin may offer a therapy for H-JEB and other inherited skin diseases caused by PTC mutations.