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...