Role of MAP kinases p42erk-2/p44erk-1 in cementum-derived attachment-protein-mediated cell attachment

Isolation of protein-tyrosine phosphatase-like member-a variant from cementum

Cementum has been shown to contain unique polypeptides that participate in cell recruitment and differentiation during cementum formation. We report the isolation of a cDNA variant for protein-tyrosine phosphatase-like (proline instead of catalytic arginine) member-a (PTPLA) from cementum. A cementifying fibroma-derived λ-ZAP expression library was screened by panning with a monoclonal antibody to cementum attachment protein (CAP), and 1435 bp cDNA (gb AC093525.3) was isolated. This cDNA encodes a 140-amino-acid polypeptide, and its N-terminal 125 amino acids are identical to those of PTPLA. This isoform, designated as PTPLA-CAP, results from a read-through of the PTPLA exon 2 splice donor site, truncating after the second putative transmembrane domain. It contains 15 amino acids encoded within the intron between PTPLA exons 2 and 3, which replace the active site for PTPLA phosphatase activity. The recombinant protein, rhPTPLA-CAP, has Mr 19 kDa and cross-reacts with anti-CAP antibody. Anti-rhPTPLA-CAP antibody immunostained cementum cells, cementum, heart, and liver. Quantitative RT-PCR showed that PTPLA was expressed in all periodontal cells; however, PTPLA-CAP expression was limited to cementum cells. The rhPTPLA-CAP promoted gingival fibroblast attachment. We conclude that PTPLA-CAP is a splice variant of PTPLA, and that, in the periodontium, cementum and cementum cells express this variant.

Laminin-2 stimulates the proliferation of epithelial cells in a conjunctival epithelial cell line

Laminin-2 (LN-2, alpha2beta1gamma1) is a basement membrane-associated laminin isoform usually considered in the context of muscle and nerve tissues. To test the hypothesis that LN-2 can additionally modulate epithelial cell biology, an analysis of the role of LN-2 in cell adhesion, activation of signalling intermediates and proliferation was undertaken. A virally transformed human conjunctival epithelial cell line (HC0597) was utilized in this study. Adhesion assays using function-inhibiting antibodies demonstrated that alpha3beta1 integrin is essential for the rapid attachment of conjunctival epithelial cells to LN-2. Bromodeoxyuridine (BrdU) incorporation analyses revealed that, compared with LN-1 or LN-10, LN-2 significantly promotes epithelial proliferation. Phosphorylation of the signalling intermediates Erk1/2 and Akt-1 was observed within 15 min of cell adhesion to LN-2. Inhibiting alpha3beta1 integrin function decreased total cellular phosphotyrosine levels, specifically inhibited phosphorylation of Erk1/2 and Akt-1, and dampened the proliferation response of epithelial cells adherent to LN-2. Inhibition of Erk or Akt activation inhibited cell proliferation in a dose-dependent manner. However, the inhibition of Erk resulted in a stronger suppression of proliferation compared with Akt inhibition. From these results, it is concluded that human conjunctival epithelial cells adhere to immobilized LN-2 using alpha3beta1 integrin. alpha3beta1 integrin/LN-2 signalling, transduced primarily through an Erk pathway, enhances epithelial cell proliferation. These results demonstrate that LN-2 can impact on epithelial cell biology in addition to nerve and muscle, and provide information regarding the role of this isoform in ocular surface epithelial cells.

ERK, JNK, and p38 MAP kinases differentially regulate proliferation and migration of phenotypically distinct smooth muscle cell subtypes

Proliferation and migration of vascular smooth muscle cells (SMCs) are important processes involved in the pathogenesis of vascular disorders such as atherosclerosis and post-angioplasty restenosis. Here we demonstrate that proliferation and migration of specific SMC subtypes is mitogen-activated protein (MAP) kinase-dependent. WKY12-22 SMCs derived from the aortae of 12 day-old pup rats proliferate and migrate faster than WKY3M-22 SMCs derived from the aortae of adult rats. WKY12-22 and WKY3M-22 cells equally expressed the active forms of phospho (Thr(183)/Tyr(185))-c-Jun N-terminal kinase (JNK) and phospho (Tyr(182))-p38, whereas the activity of extracellular signal-regulated kinase (ERK) was greater in WKY12-22 cells compared with WKY3M-22 cells. Proliferation of both SMC subtypes was attenuated by PD98059, SP600125 and SB202190, inhibitors of ERK, JNK, and p38, respectively. However, inhibition of PD98059 had a more profound effect on WKY12-22 SMCs. Furthermore, migration of WKY12-22 and WKY3M-22 cells was inhibited by SP600125 and SB202190, however, PD98059 failed to influence migration of either SMC subtype. Hence, migration of both SMC subtypes is JNK- and p38-dependent, but not ERK-dependent. These findings demonstrate that SMC heterogeneity is mediated, at least in part, by the activity of specific MAP kinase subtypes.

Cementum and periodontal wound healing and regeneration

The extracellular matrix (ECM) of cementum resembles other mineralized tissues in composition; however, its physiology is unique, and it contains molecules that have not been detected in other tissues. Cementum components influence the activities of periodontal cells, and they manifest selectivity toward some periodontal cell types over others. In light of emerging evidence that the ECM determines how cells respond to environmental stimuli, we hypothesize that the local environment of the cementum matrix plays a pivotal role in maintaining the homeostasis of cementum under healthy conditions. The structural integrity and biochemical composition of the cementum matrix are severely compromised in periodontal disease, and the provisional matrix generated during periodontal healing is different from that of cementum. We propose that, for new cementum and attachment formation during periodontal regeneration, the local environment must be conducive for the recruitment and function of cementum-forming cells, and that the wound matrix is favorable for repair rather than regeneration. How cementum components may regulate and participate in cementum regeneration, possible new regenerative therapies using these principles, and models of cementoblastic cells are discussed.

Evidence for a role of mitogen-activated protein kinases in proliferating and differentiating odontogenic epithelia of inflammatory and developmental cysts

OBJECTIVE

The activation of intracellular signaling cascades involving serine/threonine kinases ERK1/2 has been variably reported either to stimulate or inhibit epithelial cell differentiation in response to extracellular signals. The purpose of our study was to determine the distribution of the signaling molecule ERK1 and its activated form pERK1/2 in the epithelial components of developmental and inflammatory odontogenic cysts in relation to parameters of differentiation and proliferation.

STUDY DESIGN

Thirty samples of dental follicles, dentigerous cysts, and radicular cysts were immunostained with antibodies to ERK1, pERK1/2, and proliferating cell nuclear antigen (a marker for proliferation). The tissues were subclassified according to the pattern of histomorphological differentiation (ie, squamous differentiation) and the proliferation rate of their epithelial components. The significance of differences in the proportion of ERK1- and pERK1/2-expressing cells among the tissue groups was determined by chi-square analysis or Fisher's exact test.

RESULTS

ERK1 and pERK1/2 were found to be expressed in a significantly higher proportion of cells with differentiated and highly proliferating epithelial components, as compared with those of nondifferentiated, quiescent epithelial rests. The epithelium of radicular cysts exhibited the highest proportion of pERK1/2-positive cells. In both dentigerous and radicular cyst samples, pERK1/2 expression was significantly higher in the inflamed tissues.

CONCLUSIONS

These data demonstrate that ERK1 and its active form pERK1/2 are associated with differentiating and actively proliferating epithelia of odontogenic cysts, and are consistent with pERK1/2 involvement in the activation of odontogenic epithelia in response to inflammation.

Heparan sulfate interacting protein (HIP/L29) negatively regulates growth responses to basic fibroblast growth factor in gingival fibroblasts

Basic fibroblast growth factor (bFGF) modulates gingival growth, and its release from heparan sulfate (HS) in the extracellular matrix (ECM) governs local tissue bioavailability. We identified a heparin/HS interacting protein (HIP/L29) that recognizes specific HS sequences. We hypothesize that HIP/L29, by modulating the interactions of bFGF with HS chains on proteoglycans, could regulate bFGF bioavailability. To investigate interactions between bFGF and HIP/L29, we isolated and cultured fibroblasts from normal gingiva and overgrown gingiva from patients on cyclosporine (CSA). bFGF significantly stimulated gingival fibroblast proliferation with or without heparin. Recombinant human HIP/L29 dramatically decreased bFGF-induced proliferation, but did not alter responses to insulin-like growth factor-1 (IGF-1). Analysis of mitogen-activated protein kinase (MAPK) phosphorylation patterns showed that bFGF stimulation of p44 (Erk-1), but not p42 (Erk-2), also was inhibited by HIP/L29 in a dose-dependent manner. Together, these results support our hypothesis that HIP/L29 modulates the bioavailability and action of bFGF.

Role of D1 and E cyclins in cell cycle progression of human fibroblasts adhering to cementum attachment protein

Cementum attachment protein (CAP) is a collagenous protein present in the matrix of tooth cementum that mediates preferential attachment of some mesenchymal cell types, and CAP binding capacity is related to mineralizing tissue-forming capacity in culture. We have examined if adhesion to surfaces containing CAP as the only attachment protein permits human fibroblasts to escape G1 arrest and synthesize DNA, and if adhesion to CAP modulates the levels of cyclins D1 and E. Human gingival fibroblasts (HGFs) were serum-starved, trypsinized, and added to plates coated with CAP or bovine serum albumin (BSA). Cells were then exposed to either 10% fetal bovine serum (FBS) or to cementum-derived growth factor (CGF), an insulin-like growth factor I (IGF-I)-like molecule sequestered in tooth cementum, plus epidermal growth factor (EGF). DNA synthesis was measured as [3H]thymidine uptake, and cyclin D1 and E levels were determined by Western analysis. Cyclin E-dependent kinase (Cdk) activity was assessed in terms of H1 kinase activity in immunoprecipitates of cyclin E. Cells adhering to CAP synthesized DNA, whereas on BSA they remained unattached and did not synthesize DNA. Protein levels of cyclin D1 were higher in cells adhering to CAP in the absence and presence of growth factors. Cyclin E levels were not affected by adhesion alone, but they increased in the presence of growth factors. Cyclin E-associated kinase activity was higher in cells adherent on CAP, and it increased further in the presence of growth factors. Our results indicate that adhesion to CAP increases cyclin D1 levels and cyclin E-associated Cdk activity, and that these increases contribute to cell cycle progression. We previously observed that the signaling reactions induced during adhesion are characteristic of the CAP; together these observations indicate that specific matrix components present in the local environment can contribute to recruitment and differentiation of specific cell types for normal homeostasis and wound healing.