SUMMARY EGFRvIII, a frequently occurring mutation in primary glioblastoma, results in a protein product that cannot bind ligand, but signals constitutively. Deducing how EGFRvIII causes transformation has been difficult because of autocrine and paracrine loops triggered by EGFRvIII alone or in heterodimers with wild-type EGFR. Here, we document co-expression of EGFR and EGFRvIII in primary human glioblastoma that drives transformation and tumorigenesis in a cell-intrinsic manner. We demonstrate enhancement of downstream STAT signaling triggered by EGFR-catalyzed phosphorylation of EGFRvIII, implicating EGFRvIII as a substrate for EGFR. Subsequent phosphorylation of STAT3 requires nuclear entry of EGFRvIII and formation of an EGFRvIII-STAT3 nuclear complex. Our findings clarify specific oncogenic signaling relationships between EGFR and EGFRvIII in glioblastoma.

Remodeling of the dermal extracellular matrix occurs during photoaging. Here, the effect of repetitive UVB irradiation on dermal hyaluronic acid (HA) was examined. C57/BL6 mice were chronically (182 days) irradiated with UVB, and consecutive skin biopsies were collected during the irradiation period and afterward (300 and 400 days of age). UVB caused marked loss of HA from the papillary dermis and down-regulation of HA synthase 1 (HAS1), HAS2, and HAS3 mRNA expression. In contrast, hyaluronidases (HYAL) 1, HYAL2, and HA receptor CD44 were unchanged. Furthermore, transforming growth factor ␤-1 (TGF-␤1) and TGF-␤1-receptor II expression were decreased in UVB-irradiated biopsies, and TGF-␤1 strongly induced HAS1 and HAS2 expression in cultured dermal fibroblasts. Therefore, TGF-␤1 might be one factor involved in UVB-induced down-regulation of HAS enzymes. In addition, total cell number and the percentage of proliferating fibroblasts in the papillary dermis of UVB-irradiated mice were decreased. Down-regulation of HAS2 by lentiviral overexpression of short hairpin RNA in vitro caused inhibition of HA synthesis, DNA synthesis, and migration of dermal fibroblasts. In conclusion, chronic UVB irradiation induces loss of HA from the dermis, thereby contributing to the quiescent phenotype of dermal fibroblasts. 1 Photoaging is the most common form of skin damage caused by chronic, repetitive sun exposure.2 The long-term exposure to solar UV irradiation induces damage to the dermal connective tissue and the extracellular matrix (ECM), which in turn leads to the aged appearance of photodamaged skin. Hallmark of this UV-induced ECM remodeling is the degradation of collagen and elastin through the UVB-induced activation of matrix metalloproteinases and decreased de novo synthesis of collagen. The mechanisms of UVB-induced matrix metalloproteinase activation 3 and inhibition of collagen synthesis have been studied in detail.2 In contrast the effect of UVB on hyaluronic acid (HA), another key component of the dermal ECM, is much less understood, and the underlying mechanisms are primarily unknown. HA is a linear polymer composed of repeating disaccharides (D-glucuronic acid-␤-1,3-N-acetylglucosamine-␤-1,4-) and assembled from the respective activated nucleotide sugars (UDPglucuronic acid, UDP-N-acetylglucosamine) at the inner plasma membrane by HA synthases (HAS). Three different HAS isoforms are known that reside in the plasma membrane and extrude the growing HA polymer into the extracellular space.4 HAS1 and HAS2 produce high molecular mass HA (2 to 4 ϫ 10 6 Da), whereas HAS3 synthesizes smaller HA (0.4 to 2.5 ϫ 10 5 Da). 5 The variation of the MW is the only modification of HA because O-or N-sulfations do not occur. HA is an agonist of CD44 and RHAMM (receptor of HA-mediated motility), which enables HA to initiate specific signaling events.6 This receptor signaling and the formation of pericellular HA coats supports proliferation and migration of a variety of cell types including skin fibroblasts. 7 In addition, antiapoptoti...

The molecular pathogenesis of pleomorphic xanthoastrocytoma (PXA), a rare astrocytic brain tumor with a relatively favorable prognosis, is still poorly understood. We characterized 50 PXAs by comparative genomic hybridization (CGH) and found the most common imbalance to be loss on chromosome 9 in 50% of tumors. Other recurrent losses affected chromosomes 17 (10%), 8, 18, 22 (4% each). Recurrent gains were identified on chromosomes X (16%), 7, 9q, 20 (8% each), 4, 5, 19 (4% each). Two tumors demonstrated amplifications mapping to 2p23-p25, 4p15, 12q13, 12q21, 21q21 and 21q22. Analysis of 10 PXAs with available high molecular weight DNA by high-resolution array-based CGH indicated homozygous 9p21.3 deletions involving the CDKN2A/ p14 ARF /CDKN2B loci in six tumors (60%). Interphase fluorescence in situ hybridization to tissue sections confirmed the presence of tumor cells with homozygous 9p21.3 deletions. Mutational analysis of candidate genes on 9q, PTCH and TSC1, revealed no mutations in PXAs with 9q loss and no evidence of TSC1 promoter methylation. However, PXAs consistently showed low TSC1 transcript levels. Taken together, our study identifies loss of chromosome 9 as the most common chromosomal imbalance in PXAs and suggests important roles for homozygous CDKN2A/p14 ARF /CDKN2B deletion as well as low TSC1 mRNA expression in these tumors.

Background: Skin aging involves UVB-induced degeneration of the dermal extracellular matrix. Results: Estrogen induces epidermal growth factor expression in keratinocytes thereby stimulating hyaluronan synthase 3 and versican expression in dermal fibroblasts of UVB-irradiated skin. Conclusion: Paracrine release of epidermal growth factor in response to estrogen maintains hyaluronan and versican-rich extracellular matrix. Significance: Estrogen prevents specific aging responses in the hyaluronan matrix of photoaged skin.

Medulloblastoma is the most common malignant brain tumor in children. A subset of medulloblastoma originates from granule cell precursors (GCPs) of the developing cerebellum and demonstrates aberrant hedgehog signaling, typically due to inactivating mutations in the receptor PTCH1, a pathomechanism recapitulated in Ptch1+/− mice. As nitric oxide may regulate GCP proliferation and differentiation, we crossed Ptch1+/− mice with mice lacking inducible nitric oxide synthase (Nos2) to investigate a possible influence on tumorigenesis. We observed a two-fold higher medulloblastoma rate in Ptch1+/− Nos2−/− mice compared to Ptch1+/− Nos2+/+ mice. To identify the molecular mechanisms underlying this finding, we performed gene expression profiling of medulloblastomas from both genotypes, as well as normal cerebellar tissue samples of different developmental stages and genotypes. Downregulation of hedgehog target genes was observed in postnatal cerebellum from Ptch1+/+ Nos2−/− mice but not from Ptch1+/− Nos2−/− mice. The most consistent effect of Nos2 deficiency was downregulation of growth-associated protein 43 (Gap43). Functional studies in neuronal progenitor cells demonstrated nitric oxide dependence of Gap43 expression and impaired migration upon Gap43 knock-down. Both effects were confirmed in situ by immunofluorescence analyses on tissue sections of the developing cerebellum. Finally, the number of proliferating GCPs at the cerebellar periphery was decreased in Ptch1+/+ Nos2−/− mice but increased in Ptch1+/− Nos2−/ − mice relative to Ptch1+/− Nos2+/+ mice. Taken together, these results indicate that Nos2 deficiency promotes medulloblastoma development in Ptch1+/− mice through retention of proliferating GCPs in the external granular layer due to reduced Gap43 expression. This study illustrates a new role of nitric oxide signaling in cerebellar development and demonstrates that the localization of pre-neoplastic cells during morphogenesis is crucial for their malignant progression.

Chronic UVB-exposure and declined estradiol production after menopause represent important factors leading to extrinsic and intrinsic aging, respectively. Remodeling of the extracellular matrix (ECM) plays a crucial role in both responses. Whether the dermal ECM is able to recover after cessation of UVB-irradiation in dependence of estradiol is not known, however of relevance when regarding possible treatment options. Therefore, the endogenous sex hormone production was depleted by ovariectomy in female mice. Half of the mice received estradiol substitution. Mice were UVB-irradiated for 20 weeks and afterwards kept for 10 weeks without irradiation. The collagen-, hyaluronan- and proteoglycan- (versican, biglycan, lumican) matrix, collagen cleavage products and functional skin parameters were analyzed. The intrinsic aging process was characterized by increased collagen fragmentation and accumulation of biglycan. Chronic UVB-irradiation additionally augmented the lumican, versican and hyaluronan content of the dermis. In the absence of further UVB-irradiation the degradation of collagen and accumulation of biglycan in the extrinsically aged group was perpetuated in an excessive matter. Whereas estradiol increased the proteoglycan content, it reversed the effects of the perpetuated extrinsic response on collagen degradation. Suspension of the intrinsic pathway might therefore be sufficient to antagonize UVB-evoked long-term damage to the dermal ECM.

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