Collagenase-3 (MMP-13) is a novel matrix metalloproteinase, the expression of which has so far only been documented in human breast carcinomas and osteoarthritic cartilage. In this study we have examined the expression of MMP-13 during human fetal development. Northern blot hybridizations revealed abundant expression of MMP-13 mRNAs in total RNA from fetal cartilage and calvaria at gestational age of 15 weeks. By in situ hybridization MMP-13 transcripts were detected in chondrocytes of hypertrophic cartilage in vertebrae of the spinal column and in the dorsal end of ribs undergoing ossification, as well as in osteoblasts and periosteal cells below the inner periosteal region of ossified ribs. In contrast, no expression of MMP-13 could be detected in osteoclasts. Furthermore, expression of MMP-13 mRNA was detected in osteoblasts and fibroblasts primarily on the inner side of calvarial bone of the skull at 16 weeks of gestation. Expression of MMP-13 mRNA by primary human fetal chondrocytes in culture was enhanced by transforming growth factor-β (TGF-β) and inhibited by bone morphogenetic protein-2 (BMP-2). No expression of MMP-13 mRNA could be noted in other fetal tissues, including the skin, lungs, neural tissue, muscle, and liver. These results suggest that MMP-13 plays an important role in the extracellular matrix remodeling during fetal bone development both via endochondral and intramembranous ossification. Dev. Dyn. 208:387–395, 1997.

Four integrins, namely α₁β₁, α₂β₁, α₁₀β₁, and α₁₁β₁, form a special subclass of cell adhesion receptors. They are all collagen receptors, and they recognize their ligands with an inserted domain (I domain) in their α subunit. We have produced the human integrin α₁₀I domain as a recombinant protein to reveal its ligand binding specificity. In general, α₁₀I did recognize collagen types I–VI and laminin-1 in a Mg²⁺-dependent manner, whereas its binding to tenascin was only slightly better than to albumin. When α₁₀I was tested together with the α₁I and α₂I domains, all three I domains seemed to have their own collagen binding preferences. The integrin α₂I domain bound much better to fibrillar collagens (I–III) than to basement membrane type IV collagen or to beaded filament-forming type VI collagen. Integrin α₁I had the opposite binding pattern. The integrin α₁₀I domain was similar to the α₁I domain in that it bound very well to collagen types IV and VI. Based on the previously published atomic structures of the α₁I and α₂I domains, we modeled the structure of the α₁₀I domain. The comparison of the three I domains revealed similarities and differences that could potentially explain their functional differences. Mutations were introduced into the αI domains, and their binding to types I, IV, and VI collagen was tested. In the α₂I domain, Asp-219 is one of the amino acids previously suggested to interact directly with type I collagen. The corresponding amino acid in both the α₁I and α₁₀I domains is oppositely charged (Arg-218). The mutation D219R in the α₂I domain changed the ligand binding pattern to resemble that of the α₁I and α₁₀I domains and, vice versa, the R218D mutation in the α₁I and α₁₀I domains created an α₂I domain-like ligand binding pattern. Thus, all three collagen receptors appear to differ in their ability to recognize distinct collagen subtypes. The relatively small structural differences on their collagen binding surfaces may explain the functional specifics.

Echovirus 1 (EV1) is a human pathogen which belongs to the Picornaviridae family of RNA viruses. We have analyzed the early events of infection after EV1 binding to its receptor α2β1 integrin and elucidated the route by which EV1 gains access to the host cell. EV1 binding onto the cell surface and subsequent entry resulted in conformational changes of the viral capsid as demonstrated by sucrose gradient sedimentation analysis. After 15 min to 2 h postinfection (p.i.) EV1 capsid proteins were seen in vesicular structures that were negative for markers of the clathrin-dependent endocytic pathway. In contrast, immunofluorescence confocal microscopy showed that EV1, α2β1 integrin, and caveolin-1 were internalized together in vesicular structures to the perinuclear area. Electron microscopy showed the presence of EV1 particles inside caveolae. Furthermore, infective EV1 could be isolated with anti-caveolin-1 beads 15 min p.i., confirming a close association with caveolin-1. Finally, the expression of dominant negative caveolin in cells markedly inhibited EV1 infection, indicating the importance of caveolae for the viral replication cycle of EV1.

Read the full review for this F1000Prime recommended article: Integrin alpha 2 beta 1 promotes activation of protein phosphatase 2A and dephosphorylation of Akt and glycogen synthase kinase 3 beta.

The incidence of cutaneous squamous cell carcinoma (cSCC) is increasing globally. We have studied the expression of complement system components in cSCC. Expression profiling of cSCC cell lines (n=8) and normal human epidermal keratinocytes (n=5) with Affymetrix and quantitative real-time PCR (qPCR) revealed upregulation of complement factor H (CFH) and factor H-like protein-1 (FHL-1) in cSCC cell lines. The expression of CFH and FHL-1 mRNAs was also significantly higher in cSCC tumors (n=6) than in normal skin (n=11). Analysis of CFH and FHL-1 expression in vivo in invasive cSCCs (n=65), in situ cSCCs (n=38), and premalignant lesions (actinic keratoses, n=37) by immunohistochemistry showed that they were specifically expressed by tumor cells in cSCCs and the staining intensity was stronger in cSCCs than in in situ cSCCs and actinic keratoses. The expression of CFH by cSCC cells was upregulated by IFN-γ and the basal CFH and FHL-1 expression was dependent on extracellular signal–regulated kinase (ERK)1/2 and p38 signaling. Knockdown of CFH and FHL-1 expression inhibited proliferation and migration of cSCC cells and inhibited basal ERK1/2 activation. These results provide evidence for a role of CFH and FHL-1 in cSCC progression and identify them as progression markers and potential therapeutic targets in SCCs of skin.