Interleukin-1 (IL-1) induces extracellular matrix degradation as a result of increased expression of matrix metalloproteinases (MMPs).Reversible phosphorylation of proteins on tyrosine residues is a pivotal, post-translational modification in many signal transduction pathways. The extent of these modifications is determined by the balance between the activities of proteintyrosine kinases and phosphatases (1, 2). Whereas proteintyrosine kinases are thought to regulate the amplitude of responses to extracellular signals, protein-tyrosine phosphatases (PTPs) 2 may determine the rate and duration of these responses (3). For IL-1 signaling in adherent cells, tyrosine phosphorylation of focal adhesion proteins such as the focal adhesion kinase is a critical, rate-limiting process (4). Tyrosine phosphorylated proteins, such as focal adhesion kinase, paxillin, and Src family kinases, which are enriched in focal adhesions (5), influence the assembly, maturation, and disassembly of these adhesive structures (6 -9) and also impact signaling through focal adhesions (10). The dynamic and reversible nature of tyrosine phosphorylation of focal adhesion proteins suggests an important role for protein-tyrosine kinases and PTPs in focal adhesion-dependent signaling (11). There are numerous PTPs in focal adhesions, and, in particular, SHP-2 is recruited to focal adhesions upon integrin engagement (12-14). In the absence of SHP-2, the number of focal adhesions and actin stress fibers increases, which is associated with diminished spreading and motility (15, 16). Expression of a dominant-negative SHP-2 enhances the formation of focal adhesions and stress fibers (17). The dynamics of focal adhesion assembly and IL-1-induced signaling pathways, including Ca 2ϩ release and ERK phosphorylation, are dependent on phosphorylation of Tyr 542 of 18,19), which can in turn affect the phosphatase activity of SHP-2 (20).We recently reported that another PTP, namely PTP␣, plays a prominent role in the regulation of focal adhesions during cell adhesion, spreading, and motility (21). PTP␣ is a receptor-like PTP that can activate Src family kinases (e.g. Src and Fyn) via dephosphorylation of an inhibitory C-terminal tyrosine residue (22)(23)(24)(25)(26)(27). We have also shown that through its interactions with Src, PTP␣ controls IL-1 induced phosphorylation of the inositol 1,4,5-phosphate receptor and consequently, Ca 2ϩ release (28). Further, PTP␣ regulates formation of focal adhesions in response to mechanical force, strengthens connections between integrins and the cytoskeleton, and modulates cytoskeletal reorganization in response to integrin ligation (26,27). In the absence of PTP␣, fibroblasts demonstrated reduced spreading, increased numbers of abnormal focal adhesions, decreased tyrosine phosphorylation of focal * This work was supported by grants from the Canadian Institutes of Health Research (MOP 84254; to C. A. M. and G. P. D.). This work was also supported in part by National Institutes of Health Grant HL090669 (to G. P. D.) and funds ...

IL-1β is a prominent proinflammatory cytokine that mediates degradation of extracellular matrix proteins through increased expression of matrix metalloproteinases, which involves a signaling pathway in adherent cells that is restricted by focal adhesions. Currently, the mechanism by which IL-1β affects cell adhesion to matrix proteins is not defined, and it is not known whether degraded matrix proteins affect IL-1β signaling. We examined adhesion-related IL-1β signaling in fibroblasts attaching to native or MMP3-degraded fibronectin. IL-1β increased cell attachment, resistance to shear force and the numbers of focal adhesions containing activated β(1) integrins. IL-1β-enhanced attachment required FAK, kindlins 1/2, and talin. MMP3-degraded fibronectin-inhibited IL-1β-enhanced cell adhesion and promoted spontaneous ERK activation that was independent of IL-1β treatment. We conclude that IL-1β enhances the adhesion of anchorage-dependent cells to MMP3-degraded fibronectin, which, in turn, is associated with deregulated cellular responses to IL-1β. These data point to a novel role of IL-1β as a proadhesive signaling molecule in inflammation that employs kindlins and talin to regulate adhesion.

Focal adhesion kinase (FAK) is critical in adhesion-dependent signaling, but its role in osteogenesis is ill defined. We deleted in fibroblasts and osteoblasts in mice bred with those expressing Cre-recombinase driven by 3.6-kb α1(I)-collagen promoter. Compared with wild-type (WT), conditional FAK-knockout (CFKO) mice were shorter (2-fold; < 0.0001) and had crooked, shorter tails (50%; < 0.0001). Microcomputed tomography analysis showed reduced bone volume (4-fold in tails; < 0.0001; 2-fold in mandibles; < 0.0001), whereas bone surface area/bone volume increased (3-fold in tails; < 0.0001; 2.5-fold in mandibles; < 0.001). Collagen density and fiber alignment in periodontal ligament were reduced by 4-fold ( < 0.0001) and 30% ( < 0.05), respectively, in CFKO mice. In cultured CFKO osteoblasts, mineralization at d 7 and mineralizing colony-forming units at d 21 were 30% ( < 0.0001) and >3-fold less than WT, respectively. Disruptions of FAK function in osteoblasts by conditional knockout, siRNA-knockdown, or FAK inhibitor reduced mRNA and protein expression of Runx2 (>30%), Osterix (>25%), and collagen-1 (2-fold). Collagen synthesis was abrogated in WT osteoblasts with Runx2 knockdown and in -null fibroblasts transfected with an FAK kinase domain mutant or a kinase-impaired mutant (Y397F). These data indicate that FAK regulates osteogenesis through transcription factors that regulate collagen synthesis.-Rajshankar, D., Wang, Y., McCulloch, C. A. Osteogenesis requires FAK-dependent collagen synthesis by fibroblasts and osteoblasts.

Periodontal ligament width is precisely maintained throughout the lifetime of adult mammals but the biological mechanisms that inhibit ingrowth of bone into this soft connective tissue are unknown. As bone morphogenic proteins strongly stimulate osteogenesis and can induce ectopic bone formation in vivo, we tested the hypothesis that topical application of this powerful osteogenic agent will overwhelm the osteogenic inhibitory mechanisms of periodontal ligament cells and induce ankylosis. Wounds through the alveolar bone and periodontal ligament were created in 45 male Wistar rats. Defects were filled with either a collagen implant or collagen plus bone morphogenic protein (BMP-7), or were left unfilled (controls). Three animals per time period were killed on days 2, 5, 10, 21 and 60 after surgery for each wound type. Cellular proliferation and clonal growth in periodontal tissues were assessed by 3H-thymidine labeling 1 h before death, followed by radioautography. Cellular differentiation of soft and mineralizing connective tissue cell populations was determined by immunohistochemical staining of alpha-smooth muscle actin, osteopontin and bone sialoprotein. In regenerating periodontium, BMP-7 induced abundant bone formation by 21 days (2.5-fold greater than controls or collagen implant only; P<0.001), but by day 60 the volume of the newly formed bone had returned to baseline levels and was similar for all groups. Independent of the type of treatment, periodontal ligament width was unchanged throughout the experimental period (P>0.05). Animals treated with BMP-7 implants showed greatly increased cellular proliferation in the periodontal ligament adjacent to the wound site and in the regenerating alveolar bone at days 5 and 10 after wounding compared to the other treatment groups (P<0.005). Animals in the BMP-7 group exhibited similar spatial and temporal staining patterns for alpha-smooth muscle actin, osteopontin and bone sialoprotein as controls. Collectively, these data show that BMP-7 promoted the proliferation of precursor cells in the periodontal ligament but did not induce osteogenic differentiation in this compartment. Consequently a powerful osteogenic stimulus like BMP-7 cannot significantly perturb the mechanisms that regulate periodontal ligament width and maintain periodontal homeostasis.