The effect of vertical and horizontal head positioning in panoramic radiography on mesiodistal tooth angulations

The purposes of this study were to examine the effect of potentially common patient positioning errors in panoramic radiography on imaged mesiodistal tooth angulations and to compare these results with the imaged mesiodistal tooth angulations present at an idealized head position. A human skull served as the matrix into which a constructed typodont testing device was fixed according to anteroposterior and vertical cephalometric normals. The skull was then repeatedly imaged and repositioned five times at each of the following five head positions: ideal head position, 5 degrees right, 5 degrees left, 5 degrees up, and 5 degrees down. The images were scanned and digitized with custom software to determine the image mesiodistal tooth angulations. Results revealed that the majority of image angles from the five head positions were statistically significantly different than image angles from the idealized head position. Maxillary teeth were more sensitive to 5 degrees up/down head rotation, with 5 degrees up causing mesial projection and 5 degrees down causing distal projection of maxillary roots. Mandibular anterior teeth were more sensitive to 5 degrees right/left head rotation, with the projected mesiodistal angular difference between 5 degrees right and 5 degrees left rotation ranging from 4.0 degrees to 22.3 degrees. Maxillary teeth were relatively unaffected by 5 degrees right/left head rotation, and mandibular teeth were relatively unaffected by 5 degrees up/down head rotation. It was concluded that the clinical assessment of mesiodistal tooth angulation with panoramic radiography should be approached with extreme caution with an understanding of the inherent image distortions that can be further complicated by the potential for aberrant head positioning.

Vav is required for cyclin D2 induction and proliferation of mouse B lymphocytes activated via the antigen Receptor

B lymphocytes from mice null for the Rho-family guanine-nucleotide exchange factor, Vav, are defective in their ability to proliferate in response to BCR cross-linking, but are able to proliferate normally in response to LPS. In addition, they have a depletion of CD5(+) (B1) lymphocytes and defective IgG class switching. This phenotype is reminiscent of that observed in mice null for the cell cycle regulatory protein, cyclin D2. We demonstrate here that the inability of vav(-/-) B cells to proliferate in response to BCR ligation is due to an inability to induce cyclin D2. In addition, we show that the proliferative defect of these cells occurs after the cells have entered early G1 phase. Analyses of potential down-stream signaling intermediates revealed differential activation of the stress-activated MAP kinases in the absence of Vav, normal activation of the ERK, MAPK, and phosphatidylinositol 3-kinase pathways, and defective intracellular calcium mobilization. We further demonstrate that intracellular calcium homeostasis is required for cyclin D2 induction, implicating a possible link with the defective calcium response of vav(-/-) B cells and their inability to induce cyclin D2.

Direct relation between BCR-ABL tyrosine kinase activity and cyclin D2 expression in lymphoblasts

Leukemia cells bearing the Philadelphia (Ph) chromosome express a Bcr-Abl fusion protein with deregulated protein tyrosine kinase (PTK) activity, which plays a central role in the malignant transformation. Many different signal transduction pathways are activated by Bcr-Abl, but little is known about their downstream targets in specific cell lineages. We show here that Ph-positive cell lines as well as primary cells derived from chronic myeloid leukemia (CML) in lymphoid blast crisis or from acute lymphoblastic leukemia (ALL) consistently express high levels of cyclin D2, whereas expression of this protein is low or absent in comparable Ph-negative lines and Ph-positive myeloid lines. Inhibition of Bcr-Abl with STI571 resulted in down-regulation of cyclin D2 and reduction of the number of cells in S phase, although complete G1 arrest was not induced. The expression of cyclin D2 in Ph-positive lymphoblasts was mediated via the phosphatidyl-inositol-3 kinase pathway. Analogous results were seen in murine BaF/3 cells transfected with a BCR-ABL expression vector. In contrast to the human cell lines, murine Baf/BCR-ABL cells exposed to STI571 inhibitor were all arrested in G1. This arrest could be abrogated by exogenous expression of cyclin D2 from a transfected cDNA construct. We conclude that a direct connection exists between Bcr-Abl PTK activity and cell cycle progression in which cyclin D2 plays a critical role. However, cell cycle progression in human Ph-positive lymphoid cells is not entirely dependent on Bcr-Abl PTK, and additional genetic lesions must be present.

BCR signals target p27(Kip1) and cyclin D2 via the PI3-K signalling pathway to mediate cell cycle arrest and apoptosis of WEHI 231 B cells

Cross-linking of the B cell antigen receptor (BCR) on immature WEHI 231 B cells results in G1 cell cycle arrest and apoptosis. Here we investigated the molecular mechanisms that are necessary and sufficient for these changes to occur. We show that BCR stimulation of WEHI 231 cells results in down-regulation of cyclin D2 and up-regulation of p27(Kip1), which are associated with pocket protein hypophosphorylation and E2F inactivation. Ectopic expression of p27(Kip1) by TAT-fusion protein or retroviral transduction is sufficient to cause G1 cell cycle arrest, followed by apoptosis. In contrast, over-expression of cyclin D2 overcomes the cell cycle arrest and apoptosis induced by anti-IgM, indicating that down-regulation of cyclin D2 is necessary for the cell cycle arrest and apoptosis activated by BCR stimulation. Thus, cyclin D2 and p27(Kip1) have opposing roles in these pathways and our data also suggest that cyclin D2 functions upstream of p27(Kip1) and the pRB pathway and therefore plays an essential part in integrating the signals from BCR with the cell cycle machinery. We next investigated which signal transduction pathways triggered by the BCR regulate cell proliferation and apoptosis via cyclin D2 and p27(Kip1). Inhibition of PI3-K signalling by LY294002 down-regulated cyclin D2 and up-regulated p27(Kip1) expression at both protein and RNA levels, mimicking the effects of BCR-stimulation. Furthermore, ectopic expression of a constitutively active form of AKT blocked the cell cycle arrest and apoptosis triggered by anti-IgM and also abrogated down-regulation of cyclin D2 and up-regulation of p27(Kip1) expression induced by BCR-engagement. These results indicate that BCR activation targets p27(Kip1) and cyclin D2 to mediate cell cycle arrest and apoptosis and that down-regulation of PI3-K/AKT activity post BCR stimulation is necessary for these to occur.

BCR-ABL and interleukin 3 promote haematopoietic cell proliferation and survival through modulation of cyclin D2 and p27Kip1 expression

Although it is evident that BCR-ABL can rescue cytokine-deprived hematopoietic progenitor cells from cell cycle arrest and apoptosis, the exact mechanism of action of BCR/ABL and interleukin (IL)-3 to promote proliferation and survival has not been established. Using the pro-B cell line BaF3 and a BaF3 cell line stably overexpressing BCR-ABL (BaF3-p210), we investigated the proliferative signals derived from BCR-ABL and IL-3. The results indicate that both IL-3 and BCR-ABL target the expression of cyclin Ds and down-regulation of p27(Kip1) to mediate pRB-related pocket protein phosphorylation, E2F activation, and thus S phase progression. These findings were further confirmed in a BaF3 cell line (TonB.210) where the BCR-ABL expression is inducible by doxycyclin and by using the drug STI571 to inactivate BCR-ABL activity in BaF3-p210. To establish the functional significance of cyclin D2 and p27(Kip1) expression in response to IL-3 and BCR-ABL expression, we studied the effects of ectopic expression of cyclin D2 and p27(Kip1) on cell proliferation and survival. Our results demonstrate that both cyclin D2 and p27(Kip1) have a role in BaF3 cell proliferation and survival, as ectopic expression of cyclin D2 is sufficient to abolish the cell cycle arrest and apoptosis induced by IL-3 withdrawal or by BCR-ABL inactivation, while overexpression of p27(Kip1) can cause cell cycle arrest and apoptosis in the BaF3 cells. Furthermore, our data also suggest that cyclin D2 functions upstream of p27(Kip1), cyclin E, and cyclin D3, and therefore, plays an essential part in integrating the signals from IL-3 and BCR-ABL with the pRB/E2F pathway.

BCR-ABL-Expressing Cells Transduced with the HSV-tk Gene Die by Apoptosis upon Treatment with Ganciclovir

The potential efficacy of prodrug activation of a transduced suicide gene in a cancer cell may be impaired or enhanced by oncoproteins produced by that cell. In the context of a gene therapy protocol for chronic myeloid leukemia (CML) we examined whether the Bcr-Abl fusion protein would have either of these effects. Thus, the mechanism of cell killing by transfer of herpes simplex virus thymidine kinase (HSV-tk) and subsequent ganciclovir (GCV) treatment was examined in pre-B (TonB210.1) cells and myeloid cells (32D) and in their BCR-ABL-expressing counterparts. HSV-tk-transduced cell lines, either in the presence or in the absence of BCR-ABL expression, became susceptible to GCV at concentrations which were nontoxic to the nontransduced cells. This susceptibility was represented by apoptotic cell death in all cases. Apoptosis was observed after 24 h of treatment with GCV in the tk-transduced parental cells and in the BCR-ABL-expressing TonB210.1 cells but only after a delay of more than 24 h in the 32Dp210 cells compared to 32D. Cell death in the BCR-ABL-expressing clones was preceded by S- and G2/M-phase cell cycle arrest. Activation of FAS/APO-1 and caspase-8 was observed in all the tk-transduced cell lines after GCV treatment. However, the caspase-8 inhibitor Z-IETD-FMK only partially abrogated tk/GCV-induced apoptosis. A possible role for inhibition of Bcl-2 or Bcl-x(L) expression in the apoptosis induced by GCV was observed in the tk-transduced TonB210.1 cells but not in the 32D or 32Dp210 cells. The data demonstrate that expression of the Bcr-Abl oncoprotein does not block the apoptosis induced by the HSV-tk/GCV system, suggesting that this suicide gene therapy strategy could be considered for the treatment of CML in blast crisis.

The influence of INK4 proteins on growth and self-renewal kinetics of hematopoietic progenitor cells

This study investigated the influence of expression of proteins of the INK4 family, particularly p16, on the growth and self-renewal kinetics of hematopoietic cells. First, retrovirus-mediated gene transfer (RMGT) was used to restore p16(INK4a) expression in the p16(INK4a)-deficient lymphoid and myeloid cell lines BV173 and K562, and it was confirmed that this inhibited their growth. Second, to sequester p16(INK4a) and related INK4 proteins, cyclin-dependent kinase 4 (CDK4) was retrovirally transduced into normal human CD34(+) bone marrow cells and then cultured in myeloid colony-forming cell (CFC) assays. The growth of CDK4-transduced colonies was more rapid; the cell-doubling time was reduced; and, upon replating, the colonies produced greater yields of secondary colonies than mock-untransduced controls. Third, colony formation was compared by marrow cells from p16(INK4a-/-) mice and wild-type mice. The results from p16(INK4a-/-) marrow were similar to those from CDK4-transduced human CFCs, in terms of growth rate and replating ability, and were partially reversed by RMGT of p16(INK4a). Lines of immature granulocytic cells were raised from 15 individual colonies grown from the marrow of p16(INK4a-/-) mice. These had a high colony-forming ability (15%) and replating efficiency (96.7%). The p16(INK4a-/-) cell lines readily became growth factor-independent upon cytokine deprivation. Taken together, these results demonstrate that loss of INK4 proteins, in particular p16(INK4a), increases the growth rate of myeloid colonies in vitro and, more importantly, confers an increased ability for clonal expansion on hematopoietic progenitor cells.

Factors that relate to treatment duration for patients with palatally impacted maxillary canines

The objectives of this study were to determine the relationship between the initial position of a palatally impacted maxillary canine (as seen on a panoramic radiograph) and the duration of orthodontic treatment and to determine whether a difference in treatment duration existed between patients with bilateral palatally impacted canines and patients with unilateral impaction. A total of 47 adolescent subjects were chosen (9 subjects with unilateral impactions and 18 subjects with bilateral impactions). All subjects had full fixed orthodontic appliances placed. The treatment duration of this group was compared with that of a control group with similar characteristics but without the impacted canine. The results showed that the average duration of treatment was 22.4 months for the control group, 25.8 months for the unilateral-impacted group, and 32.3 months for the bilateral-impacted canine group. The length of treatment for the impacted canine sample was related to the age of the patient at the start of treatment; younger patients required a longer treatment. The younger the patient, the more severely impacted the canine. The bilateral-impacted canine group had at least 1 canine that was more severely impacted than the impacted canine in the unilateral-impacted group. If the canine was impacted less than 14 mm from the occlusal plane, treatment duration averaged 23.8 months; if the canine was impacted more than 14 mm from the occlusal plane, treatment duration averaged 31.1 months.

Forkhead transcription factor FKHR-L1 modulates cytokine-dependent transcriptional regulation of p27(KIP1)

Interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor regulate the survival, proliferation, and differentiation of hematopoietic lineages. Phosphatidylinositol 3-kinase (PI3K) has been implicated in the regulation of these processes. Here we investigate the molecular mechanism by which PI3K regulates cytokine-mediated proliferation and survival in the murine pre-B-cell line Ba/F3. IL-3 was found to repress the expression of the cyclin-dependent kinase inhibitor p27(KIP1) through activation of PI3K, and this occurs at the level of transcription. This transcriptional regulation occurs through modulation of the forkhead transcription factor FKHR-L1, and IL-3 inhibited FKHR-L1 activity in a PI3K-dependent manner. We have generated Ba/F3 cell lines expressing a tamoxifen-inducible active FKHR-L1 mutant [FKHR-L1(A3):ER*]. Tamoxifen-mediated activation of FKHR-L1(A3):ER* resulted in a striking increase in p27(KIP1) promoter activity and mRNA and protein levels as well as induction of the apoptotic program. The level of p27(KIP1) appears to be critical in the regulation of cell survival since mere ectopic expression of p27(KIP1) was sufficient to induce Ba/F3 apoptosis. Moreover, cell survival was increased in cytokine-starved bone marrow-derived stem cells from p27(KIP1) null-mutant mice compared to that in cells from wild-type mice. Taken together, these observations indicate that inhibition of p27(KIP1) transcription through PI3K-induced FKHR-L1 phosphorylation provides a novel mechanism of regulating cytokine-mediated survival and proliferation.

Ligation of the WC1 receptor induces gamma delta T cell growth arrest through fumonisin B1-sensitive increases in cellular ceramide

Ceramide is a powerful regulator of cell fate, inducing either apoptosis or growth arrest. We have previously shown that an Ab to the gammadelta T cell-specific orphan receptor, WC1, is able to induce growth arrest in proliferating IL-2-dependent gammadelta T cells. We now show that this WC1-mediated growth arrest is associated with an increase in cellular ceramide, in the absence of any measurable changes in acidic/neutral sphingomyelinase activity. Moreover, cell-permeable analogues of ceramide also mimicked WC1-induced growth arrest along with an associated decrease in pocket protein expression and phosphorylation status. An important role for ceramide in WC1-induced growth arrest was confirmed by demonstrating that the specific ceramide synthase inhibitor fumonisin B1 blocked WC1-induced growth arrest and the associated molecular effects on the pocket proteins. Finally, we observed constitutive expression of both antiapoptotic factors bcl-2 and bcl-X, the former having increased expression upon WC1 stimulation. It is therefore proposed that ligation of WC1 leads to an accumulation in cellular ceramide through activation of ceramide synthase. This in turn results in a decreased overall expression of the pocket proteins pRb and p107, their hypophosphorylation, and an eventual growth arrest of the gammadelta T cell. To our knowledge, these results demonstrate for the first time that cell surface receptor-mediated ceramide synthase activation can affect cell fate through increases in cellular ceramide and provide further evidence that the orphan receptor WC1 regulates gammadelta T cell biology through a novel signaling pathway.

Inhibition of the phosphoinositide 3-kinase pathway induces a senescence-like arrest mediated by p27Kip1

A senescence-like growth arrest is induced in mouse primary embryo fibroblasts by inhibitors of phosphoinositide 3-kinase (PI3K). We observed that senescence-like growth arrest is correlated with an increase in p27(Kip1) but that down-regulation of other cyclin-dependent kinase (CDK) inhibitors, including p15(INK4b), p16(INK4a), p19( INK4d), and p21(Cip1) as well as other negative cell cycle regulators such as p53 and p19(ARF), implies that this senescence-related growth arrest is independent of the activity of p53, p19(ARF), p16(INK4a), and p21(Cip1), which are associated with replicative senescence. The p27(Kip1) binds to the cyclin/CDK2 complexes and causes a decrease in CDK2 kinase activity. We demonstrated that ectopic expression of p27(Kip1) can induce permanent cell cycle arrest and a senescence-like phenotype in wild-type mouse embryo fibroblasts. We also obtained results suggesting that the kinase inhibitors LY294002 and Wortmannin arrest cell growth and induce a senescence-like phenotype, at least partially, through inhibition of PI3K and protein kinase B/Akt, activation of the forkhead protein AFX, and up-regulation of p27(Kip1)expression. In summary, these observations taken together suggest that p27(Kip1) is an important mediator of the permanent cell cycle arrest induced by PI3K inhibitors. Our data suggest that repression of CDK2 activity by p27(Kip1) is required for the PI3K-induced senescence, yet mouse embryo fibroblasts derived from p27(Kip1-/-) mice entered cell cycle arrest after treatment with LY294002. We show that this is due to a compensatory mechanism by which p130 functionally substitutes for the loss of p27(Kip1). This is the first description that p130 may have a role in inhibiting CDK activity during senescence.

Immunolocalization and adenoviral vector-mediated manganese superoxide dismutase gene transfer to experimental oral tumors

The anti-oxidant enzyme system protects cellular macromolecules against damage from reactive oxygen species. One component of this system, manganese superoxide dismutase (MnSOD), has also been shown to display tumor suppressor gene-like activity. The purpose of this study was to examine changes in MnSOD expression during hamster cheek pouch carcinogenesis, and the effects of MnSOD overexpression using an adenoviral vector. Tumor induction was carried out using 7,12-dimethylbenz[alpha]anthracene. Animals were killed at periodic intervals, and cheek pouch tissues were excised and examined for MnSOD expression by immunohistochemistry and digital image analysis. We observed a reduction in MnSOD expression as early as 2 weeks after the start of carcinogen application. Low MnSOD expression persisted until the end of the 23-week experimental period. Solid hamster cheek pouch carcinoma xenografts were then established in nude mice. An adenoviral vector encoding the human MnSOD gene was delivered to the xenografts by direct injection. We observed high, immediate expression of MnSOD in the xenografts that persisted for 10 days following cessation of viral construct delivery. Delivery of the MnSOD construct resulted in a maximal 50% reduction in tumor growth compared with untreated controls. Our results suggest that MnSOD may be a tumor suppressor gene in the hamster cheek pouch model system.

Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development

Progression into G(1) in B lymphocytes is regulated by cyclins D2 and D3, components of the cell cycle machinery currently believed to have overlapping and potentially redundant roles in cell cycle control. To study the specific role of cyclin D2 in B lymphocyte proliferation, we examined B cells from cyclin D2(-/-) mice and demonstrate a specific requirement for cyclin D2 in BCR- but not CD40- or lipopolysaccharide-induced proliferation. Furthermore, conventional B cell development proceeds normally in the mutant mice; however, the CD5 B cell compartment is dramatically reduced, suggesting that cyclin D2 is important in CD5 B cell development as well as antigen-dependent B cell clonal expansion.

Cyclin D3 compensates for loss of cyclin D2 in mouse B-lymphocytes activated via the antigen receptor and CD40

Cyclin D2 is the only D-type cyclin expressed in mature mouse B-lymphocytes, and its expression is associated with retinoblastoma protein (pRB) and pRB-related protein phosphorylation and induction of E2F activity, as B-cells enter the cell cycle following stimulation via surface IgM and/or CD40. Cyclin D-dependent kinase activity is required for cell proliferation, yet cyclin D2(-/-) mice have normal levels of mature B-lymphocytes. Here we show that B-lymphocytes from cyclin D2(-/-) mice can proliferate in response to anti-IgM and anti-CD40, but the time taken to enter S-phase is longer than for the corresponding cyclin D2(+/+) cells. This is due to the compensatory induction of cyclin D3, but not cyclin D1, which causes pRb phosphorylation on CDK4-specific sites. This is the first demonstration that loss of a D-type cyclin causes specific expression and functional compensation by another member of the family in vivo and provides a rationale for the presence of mature B-lymphocytes in cyclin D2(-/-) mice.

Different functions are required for initiation and maintenance of immortalization of rat embryo fibroblasts by SV40 large T antigen

We have used two different, but complementary assays to characterize functions of SV40 T antigen that are necessary for its ability to immortalize rat embryo fibroblasts. In accordance with previous work, we found that several functions were required. These include activities that map to the p53 binding domain and the amino terminal 176 amino acids which contain the J domain as well as the CR1 and CR2 domain required for binding and sequestering the RB family of pocket proteins. Moreover, we found that even though activities dependent only upon the amino terminus were sufficient for immortalization they were unable to maintain it. This suggests that immortalization by these amino terminal functions requires either additional events or immortalization of a subset of cells within the heterogeneous rat embryo fibroblast population. We further found that an activity dependent upon amino acids 17 - 27 which remove a portion of the CR1 domain and the predicted alpha-1 helix of the J domain was not necessary to maintain growth but was required for direct immortalization suggesting that at least one of the functions required initially was not required to maintain the immortal state. This represents the first demonstration that some of the functions required for maintenance of the immortal state differ from those required for initiation of immortalization.

Modulation of E2F activity in primary mouse B cells following stimulation via surface IgM and CD40 receptors

Since signals via CD40 and the B cell receptor are known to synergize to induce B cell activation, we have analyzed the pocket protein/E2F complexes in mouse B lymphocytes following stimulation by anti-IgM, anti-CD40, alone or together. We find that E2F4 and DP1 form the predominant E2F heterodimers in the G0 and G1 phases of the cell cycle, complexed with hypophosphorylated p130. During late G1 and S phase this complex is replaced by at least three different E2F complexes, one of which is an E2F complex containing p107 or pRB as well as two "free" E2F complexes consisting of E2F4/DP1 and E2F1-3/DP1. These effects were mirrored by the levels and phosphorylation status of the three pocket proteins. We also observed an increase in electrophoretic mobility of DP1 and E2F4 as B cells progressed from G0 into early G1, resulting from their dephosphorylation. This is known to correlate with a decrease in DNA binding capacity of these proteins and could also be important for derepression of genes negatively regulated through E2F sites in their promoters. These results therefore indicate that the pRB/E2F pathway integrates proliferative signals emanating from the sIgM and CD40 receptors.

Effects of antioxidant enzyme overexpression on the invasive phenotype of hamster cheek pouch carcinoma cells

To examine the role of reactive oxygen species on the invasive phenotype of cancer cells, we overexpressed manganese- and copper-zinc-containing superoxide dismutases (MnSOD, CuZnSOD) and catalase (Cat) in hamster cheek pouch carcinoma (HCPC-1) cells in vitro using adenoviral vector-mediated gene transfer. Hamster cheek pouch carcinoma cells were transduced with these adenoviral vector constructs alone, or in combination, at concentrations [i.e., multiplicity of infectivity (MOI)] of 100 MOI each. The Escherichia coli beta-galactosidase reporter construct was used as a control virus. Protein expression was examined by Western blot analysis and enzymatic activities were measured using spectrophotometry. To observe the effects of transgene overexpression on in vitro tumor cell invasion, we used the membrane invasion culture system, an accurate and reliable method for examining tumor cell invasion, in vitro. This assay measures the ability of tumor cells to invade a basement membrane matrix consisting of type IV collagen, laminin, and gelatin. MnSOD overexpression resulted in a 50% increase in HCPC-1 cell invasiveness (p < .001); co-overexpression of MnSOD with Cat partially inhibited this effect (p < .05). Moreover, co-overexpression of both SODs resulted in a significant increase in invasiveness compared with the parental HCPC-1 cells (p < .05). These changes could not be correlated with the 72 kDa collagenase IV or stromolysin activities using zymography, or the downregulation of the adhesion molecules E-cadherin or the alpha4 subunit of the alpha4beta1 integrin. These results suggest that hydrogen peroxide may play a role in the process of tumor cell invasion, but that the process does not rely on changes in matrix metalloproteinase activity in the cells, or the expression of cell adhesion molecules.

Modulation of E2F complexes during G0 to S phase transition in human primary B-lymphocytes

The pocket protein-E2F complexes are convergence points for cell cycle signaling. In the present report, we identified and monitored the pocket protein-E2F complexes in human primary B-lymphocytes after activation by phorbol 12-myristate 13-acetate. Consistent with previous data from human and mouse fibroblasts and T-lymphocytes, E2F4 and DP1 form the predominant E2F heterodimers both in G0 and G1 phases of the human B-lymphocyte cell cycle, whereas E2F1 and -3 are first detected in late G1, and their expression levels increase towards S phase. Intriguingly, the major E2F complex that we detected in quiescent human B-lymphocytes is consisted of pRB, E2F4, and DP1. Though the levels of DP1 and -2 increase when cells progress from G0 to S, the proportion of DP1 to DP2 remains relatively constant during the cell cycle. We also observed an increase in electrophoretic mobility of the predominant E2F components, DP1 and E2F4, as B-lymphocytes progressed from G0 into early G1. This increase in mobility was attributable to dephosphorylation, as lambda phosphatase treatment could convert the slower migrating forms into the corresponding faster mobility forms. We further demonstrated that this change in phosphorylation status correlates with a decrease in DNA binding activity. This modulation of DNA binding activity mediated through the dephosphorylation of DP1 and E2F4 could help to explain the lack of in vivo DNA footprinting in late G1 and S phases of gene promoters negatively regulated through E2F sites and suggests a novel mechanism for controlling E2F transcriptional activity during the transition from quiescence to proliferation.

Rapid dephosphorylation of p107 following UV irradiation

In response to UV irradiation, mouse NIH3T3 fibroblasts transiently arrest predominantly in the G1 phase of the cell cycle. Here, we investigate the role of the retinoblastoma-related pocket proteins in this biological process. We report here that UV induces an increase in p107/E2F complexes, shown previously to be repressors of E2F-dependent transcriptional activity. Several lines of evidence indicate that the increase of p107/E2F complexes following UV irradiation is a consequence of rapid dephosphorylation of p107. First, UV-mediated p107 dephosphorylation could be abolished by pretreatment of NIH3T3 fibroblasts with the serine/threonine phosphatase inhibitors calyculin A and okadaic acid. Second, alteration of protein phosphatase 2A holoenzyme composition by over-expression of specific B subunits interfered with UV-mediated dephosphorylation of p107. Consistent with this, p107 could be dephosphorylated in vitro with PP2A. Moreover, dephosphorylation of p107 was shown to be independent of the activity of p53 and p21, as it occurred also in UV-treated p53-null as well as p21-null mouse fibroblasts. We observed a close correlation between the UV dosages required for G1 cell cycle arrest and p107 dephosphorylation. Our data suggest a model in which UV radiation-induced cell cycle arrest depends, at least in part, on the induction of a PP2A-like phosphatase that acts on p107.

Transcription factor E2F controls the reversible gamma delta T cell growth arrest mediated through WC1

IL-2-stimulated expansion of T cells requires continued and sequential passage of the dividing cells through a major cell cycle check point in the G1 phase. We have previously shown that a gamma delta T cell-specific surface receptor, WC1, induces G0/G1 growth arrest, reversible with Con A, in proliferating IL-2-dependent gamma delta T cells. We now show that this reversible WC1-induced cell cycle arrest is correlated with induction of the cyclin kinase inhibitor p27kip1 and an associated down-regulation in cyclins A, D2, and D3 expression, along with dephosphorylation of pocket proteins p107, p130, and pRb. Together with diminished pocket protein phosphorylation, p107 expression levels are significantly down-regulated in response to WC1 stimulation. This coordinated sequence of signaling events is focused on E2F regulation so that, downstream of the pocket proteins, WC1 stimulation results in a diminished DNA binding activity for free E2F as a consequence of reduced E2F1 expression, whereas E2F4 expression is unaffected. Consistent with this interpretation, overexpression of E2F1 overcomes the growth-arresting effects induced by WC1 stimulation. Finally, in accordance with our previous observations at both the cellular and molecular level, subsequent mitogen stimulation can reverse all the above changes induced by WC1. These results, focused on E2F regulation, therefore provide a first insight into the effects of both positive (mitogen) and negative (anti-WC1) stimuli on cell cycle control in IL-2-dependent gamma delta T cells.

The p53 tumor suppressor inhibits transcription of the TATA-less mouse DP1 promoter

Cell cycle progression is subject to several regulatory controls, of which the p53 protein plays a major role in growth arrest, subsequent to the detection of cellular aberrations. It is well documented that p53 has the ability to inhibit transcription driven by several promoters, possibly via distinct mechanisms. In this report, we show that expression of the cell cycle regulatory transcription factor DP1 is strongly inhibited by p53, at the level of transcription and probably through the basal TATA-less promoter. This inhibitory activity has a relative specificity for the DP1 promoter compared with the functionally related E2F1 promoter or unrelated promoters such as those of the transcription factor ATFa or the thymidine kinase gene. Inhibition of DP1 transcription has implications in one of the several possible mechanisms through which p53 induces cell cycle arrest.

Modulation of E2F activity via signaling through surface IgM and CD40 receptors in WEHI-231 B lymphoma cells

Stimulation of the phenotypically immature B cell lymphoma WEHI-231 with anti-IgM induces G1 arrest followed by apoptotic cell death, which can be reversed by stimulation via the CD40 receptor. Here, we show that cells expressing bcl-xL (WEHI-bcl-xL) arrest at G0/G1 following culture with anti-IgM but do not undergo apoptosis. These arrested cells can be induced to reenter the cell cycle by ligation of CD40. We have therefore used these cells as a model to study the regulation of the transcription factor E2F, which is critically involved in transit through the cell cycle. We found that anti-IgM treatment induces the appearance of an inhibitory DNA binding complex containing the pRB-related pocket protein p130 together with E2F and a concomitant decrease in "free" E2F, consisting of E2F1 and its partner DP1; these effects were reversed following stimulation via CD40. These changes in free E2F levels were regulated by changes in E2F1 gene transcription, which is at least partly a result of control of E2F1 promoter activity through its E2F binding sites. Transient transfection experiments showed that either E2F1 or the viral oncoprotein E1A, which sequesters pocket proteins, including p130, overcame anti-IgM-induced cell cycle arrest in WEHI-bcl-xL. Taken together, these results indicate that in WEHI-231 sIgM ligation induces the accumulation of hypophosphorylated p130 with consequent inhibition of E2F1 gene transcription and cell cycle arrest. Conversely, ligation of CD40 causes hyperphosphorylation of p130, thereby releasing the repression of E2F1 and other E2F-regulated genes, enabling the cells to reenter the cycle. These results, therefore, provide novel insights into the mechanisms whereby antigen receptors on immature B cells deliver inhibitory signals (leading to negative selection of self-reactive B cells) and how these signals can be modulated by positive signals generated via CD40.

Adenovirus-mediated manganese superoxide dismutase gene transfer to hamster cheek pouch carcinoma cells

As a first step in evaluating the tumor suppressor activity of the manganese superoxide dismutase (MnSOD) gene on established tumors in vivo, we used adenovirus-mediated gene transfer as a means of delivering the MnSOD cDNA to hamster cheek pouch carcinoma (HCPC-1) cells in vitro. HCPC-1 cells were transduced with the adenovirus-MnSOD construct (AdMnSOD) at multiplicities of infectivity (MOI) of 0, 10, 25, 50, 100, 150, and 200 MOI or with the adenovirus-LacZ reporter gene construct (AdLacZ) at 100 MOI. Dose-dependent increases in MnSOD immunoreactivity were seen on Western blotting and indirect immunofluorescence microscopy with increasing AdMnSOD titers. Maximal immunoreactivity was observed at 100 MOI AdMnSOD with both techniques. Moreover, we observed a concomitant 6-7-fold increase in MnSOD activity compared with parental cell levels that also peaked at 100 MOI AdMnSOD. To determine the effect of transgene-expressed MnSOD on tumor cell behavior, we examined cell growth, plating efficiency, and anchorage-dependent growth in soft agar. Cell number measured on day 13 decreased approximately 50% with 100 MOI AdMnSOD (P < 0.05) compared with parental cells. Moreover, cell doubling time increased from 38 to 44 h with 100 MOI AdMnSOD. Plating efficiency and cell growth in soft agar decreased approximately two-thirds with 100 MOI AdMnSOD (P < 0.001). These assays of the transformed phenotype in vitro all appeared to show maximal effect with 100 MOI AdMnSOD. As tumor growth in vivo is most predictable by a combination of these in vitro data, our results suggest that if MnSOD can be effectively delivered to a tumor in vivo using the adenovirus paradigm, effective tumor growth suppression can be observed.

Radiographic findings, ridge resorption, and subjective complaints of complete denture patients

To evaluate the relationship between the complaints of complete denture wearers and alveolar bone resorption as well as the location of mental foramina, 96 patients were interviewed. All subjects had received new dentures at the University of Iowa between August 1985 and July 1990. Panoramic radiographs had been made for all the subjects before dentures were fabricated. The amount of estimated ridge resorption correlated significantly with the number of years females had been edentulous, but no correlation was found in males. The location of the mental foramen in relationship to the crest of residual ridge correlated negatively with the number of years both genders were edentulous. Subjective need for dental treatment, as expressed by "sore gums" or poor or fair chewing ability, were the most frequent complaints among the subjects. These complaints were more often recorded with the subjects who had lost more than 50% of their estimated original ridge height than with those with less than 50% resorption, but this difference was not significant.

CD40: a pivotal receptor in the determination of life/death decisions in B lymphocytes

CD40 is a 48 kDa glycoprotein predominantly expressed on B cells in both mouse and man, which interacts with a counterligand (CD40L), expressed on activated CD4+ T cells. CD40/CD40L interactions are now known to be essential for the initiation of antibody responses to T-dependent antigens. In this review we discuss the immunobiology of CD40, with a special emphasis on our own studies in the mouse. These have focused on signal transduction via CD40, the role of cytokines (both T cell-derived and B cell-derived) in CD40-mediated B cell activation, and the role of CD40 in protecting B cells from apoptotic cell death. The available data indicate clearly that this protein is a pivotal receptor on B cells, both for the delivery of activating signals and for promoting B cell survival.

Physical and functional interactions between p53 and cell cycle co-operating transcription factors, E2F1 and DP1

One way in which wild-type p53 is able to regulate cell cycle progression is thought to be via the induction of its downstream target gene Waf1/CIP1, thus indirectly regulating the transcriptional activity of E2F. The E2F transcription factors are known to be key effectors of the cell cycle. We report here that there is a physical and functional interaction between p53 and two of the components of the E2F transcription factors, E2F1 and DP1. The expression of wild-type p53 can inhibit the transcriptional activity of E2F, and the expression of both E2F1 and DP1 can also downregulate p53-dependent transcription. The transcriptional activity of p53 is known to be inhibited by the direct binding of mdm2, but we demonstrate here that both E2F1 and DP1 can inhibit p53 transcriptional activity independently of mdm2. Detailed studies of protein-protein interactions have provided evidence that E2F1 and its co-operating factor DP1 can complex with p53 both in vitro and in vivo.

Functional conservation of the cell cycle-regulating transcription factor DRTF1/E2F and its pathway of control in Drosophila melanogaster

The cellular transcription factor DRTF1/E2F is implicated in the control of early cell cycle progression due to its interaction with important regulators of cellular proliferation, such as pocket proteins (for example, the retinoblastoma tumour suppressor gene product), cyclins and cyclin-dependent kinase subunits. In mammalian cells DRTF1/E2F is a heterodimeric DNA binding activity which arises when a DP protein interacts with an E2F protein. Here, we report an analysis of DRTF1/E2F in Drosophila cells, and show that many features of the pathway which regulate its transcriptional activity are conserved in mammalian cells, such as the interaction with pocket proteins, binding to cyclin A and cdk2, and its modulation by viral oncoproteins. We show that a Drosophila DP protein which can interact co-operatively with E2F proteins is a physiological DNA binding component of Drosophila DRTF1/E2F. An analysis of the expression patterns of a Drosophila DP and E2F protein indicated that DmDP is developmentally regulated and in later embryonic stages preferentially expressed in proliferating cells. In contrast, the expression of DmE2F-1 in late stage embryos occurs in a restricted group of neural cells, whereas in early embryos it is widely expressed, but in a segmentally restricted fashion. Some aspects of the mechanisms which integrate early cell cycle progression with the transcription apparatus are thus conserved between Drosophila and mammalian cells. The distinct expression patterns of DmDP and DmE2F-1 suggest that the formation of DP/E2F heterodimers, and hence DRTF1/E2F, is subject to complex regulatory cues.

Cell-cycle regulation of human B-myb transcription

We demonstrate here that activity of the human B-myb promoter is regulated during the cell cycle by the E2 transcription factor (E2F). Comparison of the human B-myb promoter sequence with that of its murine counterpart revealed an evolutionally conserved sequence that contains an E2F-binding site. In transiently transfected murine NIH3T3 and human HaCaT cells, luciferase (Luc) reporter activity directed by the human B-myb promoter was found to increase significantly in late G1/S phase of the cell cycle. Mutation of the promoter E2F site resulted in significantly greater Luc activity in NIH3T3 and HaCaT cells made quiescent by serum deprivation, indicating that E2F repressed transcription of this gene during G0. Analysis of E2F DNA-binding activity in G0 HaCaT cells revealed a distinct complex that apparently contained neither the retinoblastoma gene protein, pRb, nor the related p107 protein. De-repression of transcription in S phase was accompanied by the disappearance of this G0 E2F complex and the appearance of a distinct complex containing p107. In addition, complexes containing pRb were detected at both stages of the cell cycle.

Comparison of two-dimensional orthoradially reformatted computed tomography and panoramic radiography for dental implant treatment planning

The widespread use of dental implants in partially and completely edentulous patients has brought about a need to preoperatively depict and quantify accurate bone height and contour. A number of conventional intraoral and extraoral radiographic techniques have been used, including the relatively new modality of two-dimensional orthoradially reformatted computed tomography. Despite rapid advances in imaging technology, many clinicians continue to rely on techniques such as panoramic radiography that produce images that distort the jaws nonuniformly. This study compared bone height measurements of jaws made with these two imaging modalities. Nineteen sites in 10 patients were imaged with both techniques and mean bone height was determined for each imaging technique and site. Significant differences were found between mean bone heights measured with the two imaging modalities (p < 0.0005). Situations in which the use of dental implants would be particularly advantageous demonstrated the largest discrepancies, that is, when bone height measurements were less than 15 mm.

Proto-oncogenic properties of the DP family of proteins

The cellular transcription factor DRTF1/E2F is implicated in the control of cellular proliferation due to its interaction with key regulators of cell cycle progression, such as the retinoblastoma tumour suppressor gene product, cyclins and cyclin-dependent kinases. DRTF1/E2F is a heterodimeric DNA binding activity which arises when a member of two distinct families of proteins, DP and E2F, interact as DP/E2F heterodimers, for example, DP-1 and E2F-1. In DRTF1/E2F the activity of DP-1 is under cell cycle control, possibly by phosphorylation, and in many types of cells it is a frequent, if not general DNA binding component of DRTF1/E2F. The expression of other DP proteins, such as DP-2, is tissue-restricted. Here, we show that DP-1 and DP-2 are integrated with another growth regulating pathway which involves signal transduction emanating from activated Ras protein. Thus, activated Ha-ras can co-operate with DP-1 or DP-2 in the transformation of rat embryo fibroblasts, establishing for the first time that DP proteins are endowed with proto-oncogenic activity. Moreover, an analysis of a dominant-negative and mutant DP-1 proteins suggests that the primary target through which DP-1 mediates its oncogenic activity is unlikely to be due to the regulation of E2F site-transcription, suggesting an E2F-independent effector function for DP-1. These results therefore establish DP genes as proto-oncogenes and thus argue that deregulating the normal control of DP protein activity will be important in promoting aberrant cellular proliferation.

DP and E2F proteins: coordinating transcription with cell cycle progression

Transcriptional control during the G1/S transition is important in regulating cell cycle progression. The transcription factor DRTF1/E2F is believed to play a crucial role in this process by integrating the activity of the machinery that drives the cell cycle with the transcription apparatus. Being the point of convergence for growth-promoting and growth-inhibitory signals, it is a pivotal cellular target for molecules which subvert normal cell cycle control, such as oncoviral proteins. Recent studies have indicated that members of two distinct families of proteins, DP and E2F, interact combinatorially as DP/E2F heterodimers in DRTF1/E2F. The activities of both DP and E2F proteins are under cell cycle control, being influenced by the level of phosphorylation imparted through the cell cycle regulated activity of cyclin-dependent kinases. Both DP and E2F proteins are endowed with proto-oncogenic activity and, conversely, have been implicated in regulating apoptosis. Current evidence suggests therefore that the activity of DRTF1/E2F is instrumental in regulating progression through the cell cycle.

Molecular characterization of Xenopus laevis DP proteins

It is widely believed that in mammalian cells the cellular transcription factor (DRTF1/E2F integrates cell-cycle events with the transcription apparatus by interacting with important regulators of the cell cycle, such as the retinoblastoma gene product (pRb) and related proteins, cyclins, and cyclin-dependent kinases. Here, we have defined DRTF1/E2F in Xenopus laevis that, like its mammalian counterpart, specifically binds to the E2F site, is regulated during development, and interacts with pRb and related proteins. We have isolated cDNAs that encode the functional homologue of mammalian DP-1, X1 DP-1, together with a close relative, X1 DP-2. X1 DP-1, which is highly conserved with murine DP-1, is a major DNA binding component of X1 DRTF1/E2F. Both DP-1 and DP-2 synergistically interact with members of the E2F family of proteins, E2F-1, E2F-2, and E2F-3, to generate DNA binding complexes that specifically recognize the E2F site and functionally interact with E2F-1 in E2F site-dependent transcriptional activation of cellular genes. DP-1 and DP-2 encode maternally stored transcripts that are expressed during early development. In the adult however, the expression of DP-1 and DP-2 is tissue restricted. This study therefore defines a new family of transcription factors, the DP proteins, members of which can interact combinatorially with E2F proteins to generate an array of DNA binding complexes that integrate cell-cycle progression with the transcription apparatus through the E2F binding site. The tissue-specific expression of DP family members suggests that the combination of DP/E2F heterodimers that constitute DRTF1/E2F is influenced by the phenotype of the cell.

DP-1: a cell cycle-regulated and phosphorylated component of transcription factor DRTF1/E2F which is functionally important for recognition by pRb and the adenovirus E4 orf 6/7 protein

The cellular transcription factor DRTF1/E2F integrates cell cycle events with the transcription apparatus through its cyclical interactions with important regulators of cellular proliferation. Two sequence-specific DNA binding proteins, DP-1 and E2F-1, are components of DRTF1/E2F which synergistically interact in a DP-1/E2F-1 heterodimer. Here, we show that DP-1 is a very frequent, possibly universal, component of DRTF1/E2F in 3T3 cells since it is present in all forms of the DNA binding activity that occur during cell cycle progression. Furthermore, the DP-1 polypeptide, which is phosphorylated, undergoes a phosphorylation-dependent mobility shift during the cell cycle suggesting that its level of phosphorylation is regulated during cell cycle progression. A C-terminal region in DP-1 can interact with pRb which, in the context of the DP-1/E2F-1 heterodimer, contributes to the efficiency of pRb binding. The DP-1/E2F-1 heterodimer specifically interacts with the adenovirus type 5 E4 orf 6/7 protein, to produce a DNA binding activity which binds co-operatively to, and transcriptionally activates through, two appropriately positioned E2F sites in a manner which resembles the regulation of DRTF1/E2F by E4 orf 6/7 during adenovirus infection. We conclude that DP-1 is a frequent and cell cycle-regulated component of DRTF1/E2F, and that in the DP-1/E2F-1 heterodimer it is functionally important for recognition by pRb and the E4 orf 6/7 protein.

HPV16 E7 oncoprotein deregulates B-myb expression: correlation with targeting of p107/E2F complexes

HPV16 is a human tumour virus encoding two principal oncoproteins, E6 and E7. Expression of E7 can induce DNA synthesis in quiescent cells and this property coincides with its ability to bind to the cell proteins pRb and p107. As these cell proteins are regulators of the transcription factor E2F, we have investigated whether the interaction with E7 could result in induction of cell cycle regulated genes. We show that B-myb, whose induction at the G1/S boundary is regulated by release from E2F mediated transcriptional repression, is a target for transcriptional activation by E7 and is the first E7 responsive cell gene to be identified. E7 transactivation leads to both inappropriate transcription of B-myb during G1 and constitutive over-expression in cycling cells. B-Myb plays an essential role in cell cycle progression, and activation by E7 is likely to contribute to the mitogenic activity of the viral oncoprotein. Regulation of the B-myb promoter in NIH3T3 cells correlates with binding of distinct p107-containing complexes at the E2F binding site, and analysis of E7 mutants confirms that B-myb transcription in these cells is regulated through interactions with p107 rather than pRb. These results provide the first example of a potentially specific role for p107 in the regulation of the cell cycle.

An E2F-binding site mediates cell-cycle regulated repression of mouse B-myb transcription

Transcription of the B-myb gene is regulated at the G1/S boundary of the cell cycle. To begin to examine the mechanism controlling expression of this gene during the cell-cycle, a mouse B-myb 5' flanking sequence was isolated from a cosmid library and shown to promote efficiently the transcription of a luciferase reporter gene when transfected into NIH3T3 fibroblasts. It was further shown that in transfected cells released from G0 by readdition of serum, luciferase activity directed by the B-myb promoter was induced substantially as cells entered S phase, thus paralleling the regulation of endogenous B-myb. Analysis of the B-myb promoter identified a region that appeared to have no intrinsic promoter activity yet which acted to regulate transcription negatively in G0. Mutagenesis of an E2F consensus binding site within this region was sufficient to relieve transcription repression in G0, resulting in a promoter with constitutively high activity. Specific G0 and S phase E2F complexes binding to this B-myb element were detected in NIH3T3 cell extracts by mobility shift assays. These studies demonstrate for the first time a direct role for E2F in regulation of cell cycle gene expression by repression of transcription in G0/early G1.

Transcription regulation by murine B-myb is distinct from that by c-myb

The transcription regulatory properties of murine B-myb protein were compared to those of c-myb. Whereas c-Myb trans-activated an SV40 early promoter containing multiple copies of an upstream c-Myb DNA-binding site (MBS-1), and similarly the human c-myc promoter, B-Myb was unable to do so. Full-length B-Myb translated in vitro did not bind MBS-1; however, truncation of the B-Myb C-terminus or fusion of the B-Myb DNA-binding domain to the c-Myb C-terminus showed that it was inherently competent to interact with this motif. Further evidence from co-transfection experiments, demonstrating that B-Myb inhibited trans-activation by c-Myb, suggested that failure of B-Myb to trans-activate these promoters did not simply occur through lack of binding to MBS-1. Moreover, using GAL4/B-Myb fusions, it was found that an acidic region of B-Myb, which by comparison to c-Myb was expected to contain a transcription activation domain, actually had no inherent trans-activation activity and indeed appeared to trans-inhibit c-Myb. In contrast to the above findings, both B-Myb and c-Myb were able to weakly trans-activate the DNA polymerase alpha promoter. Results obtained here demonstrate that the activities of B-Myb and c-Myb are clearly distinct and suggest that these related proteins may have different functions in regulation of target gene expression.

Characterization and cell cycle-regulated expression of mouse B-myb

We have isolated a full-length mouse B-myb cDNA clone and used this to examine cell cycle-regulated expression of this gene. Mouse B-Myb was predicted to comprise 704 amino acids and to be 84% homologous with human B-Myb. There were three regions of extensive amino acid homology which may indicate functional domains: the first corresponded to the c-Myb DNA-binding domain, while the second had no counterpart in c-Myb but was instead homologous to a short segment of the related A-myb protein. The third region of homology is partially conserved in both c-Myb and A-Myb and may correspond to the c-Myb negative regulatory domain. Stimulation of quiescent 3T3 fibroblasts with serum was found to result in induction of B-myb expression in late G1 and to lead to high levels of gene transcripts that persisted through S phase. Similarly, maximum B-myb mRNA levels were reached in G2/M synchronized cells prior to entry into S phase. These results are consistent with a role in G1/S transition as has been suggested for c-myb.

Regional 31P magnetic resonance spectroscopy of exercising human masseter muscle

Changes in fibre structure and function associated with exercise have been quantified ultrastructurally and biochemically in selected limb muscles, but the biochemical events associated with contraction are rarely studied in the human jaw muscles. Here, 31P NMR spectroscopy, or MRS, was used to examine the multipennate masseter in six adult men at rest and while performing isometric clenching exercises. NMR spectra were acquired from three locations within the muscle with a 2 x 3 cm, single-turn, copper receiver coil. The spectra, corrected for partial saturation effects, were quantified on the basis of relative peak area and position. The inorganic phosphate (Pi) to creatine phosphate (PCr) ratio (Pi/PCr), which has been shown to be indirectly related to the phosphate potential and hence the metabolic activity, as well as pH, were calculated for each site and exercise. The mean resting Pi/PCr ratio was greater for the deep part of the muscle than for the superficial and intermediate parts; these differences were significant to p less than 0.01. The mean pH was similar in all parts of the muscle at rest. During exercise, a significant increase in mean Pi/PCr was found in the superficial and intermediate parts of the muscle; both these differences were significant to p less than 0.05. An accompanying decrease in mean pH was observed in all parts of the muscle during exercise. In the superficial part, this decrease was significant to the p less than 0.05 level, and in the deep part, to the p less than 0.001 level. No significant differences were found for these measures between left and right molar clenching.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of tendon-plane orientation within human masseter muscle from reconstructed magnetic resonance images

The human masseter is a powerful multipennate jaw elevator with complex internal architecture. The three-dimensional disposition of tendon planes within the muscle is thought to be an important determinant of function. We selected five adult subjects and used cephalometric radiography, magnetic resonance imaging and graphical, three-dimensional reconstruction to describe the organization of these planes within the muscle. Putative tendon planes were fitted to the surfaces of the three-dimensional reconstructions, and these were related to the mid-sagittal plane in the coronal and transverse views. To confirm whether putative planes disclosed by magnetic resonance represented true anatomical entities, a fresh human cadaver head was imaged and the magnetic resonance slices were compared with cryosections obtained in the same planes. Tendon-plane angulation appeared to be related to ramal length and lower face height measured cephalometrically. In the transverse view, the tendon planes appeared roughly to follow the angulations of the zygomatic arch and the lateral face of the mandibular ramus. These findings suggest that the angulation of tendon planes, and possibly pennation angles, are different depending on the viewing angle. Rather than reporting pennation angle as a single angle, alpha, which has been the convention, it may be more appropriate to express it as a three-dimensional angle relative to the normal of a particular tendon plane. The inference is that muscle fibres inserting on either side of a central tendon may need to develop different tensile forces if translation is to occur directly along the tendon axis.

Imaging orofacial tissues by magnetic resonance

Magnetic resonance imaging was used to study the human orofacial complex. Two imaging methods, a fixed head coil and a surface coil, were used. Images from a database of 31 subjects revealed details of many structures including the masseter, temporal, medial and lateral pterygoid muscles, the teeth, articular condyles, and facial bones. A dentigerous cyst and a maxillary sinus "polyp" were also identified. Our study demonstrates the utility of this imaging modality in the identification and localization of soft tissue lesions. The strengths and weaknesses of the technique and its clinical potential are discussed.

Risk factors and 10-year breast cancer survival in northern Alberta

1,121 women in northern Alberta diagnosed as having breast cancer between 1971-74 were followed for 10 years. Risk factors for breast cancer were studied with respect to their possible influence on survival by comparing survival curves, using both Logrank and Cox's regression model, and controlling for intercurrent death, stage and axillary node status. A complex interaction was found between age and menopausal status and survival rates. Premenopausal women aged 45-55 had a better survival rate than postmenopausal women of the same age. However, one subgroup of premenopausal women aged 35-39 had a significantly worse prognosis than those aged 40-44 as did a group of post menopausal women aged 70-74. No cause was found other than the effect of age. There was a significant trend to worsening survival with heavier weight at time of diagnosis and with breast feeding. Parity of five or more and family history of breast cancer were less consistently associated with worse survival. Oral contraceptive use was only associated with worsened prognosis significantly when stage was controlled for; there was no overall effect. Age at menarche and age at first birth did not influence prognosis. Theories to explain the findings are discussed.

Patterns of basement membrane deposition in benign, premalignant, and malignant endometrium

Immunocytochemical staining for laminin, an intrinsic basement membrane component, was used to show and quantify the distribution of basement membranes in endometrium. In normal endometrium, glands which are not mechanically disrupted have almost entirely continuous basement membranes, even in the menstrual phase. This is also seen in benign cystic hyperplasia. In atypical hyperplasia a small proportion of glands show small breaks in basement membrane staining in the absence of invasion. The number of breaks increases with more severe cytological changes, and this abnormality may persist even when a second biopsy specimen shows an apparent return to normal morphology. Invasive tumours show a strikingly different pattern of basement membrane staining, even when very well differentiated.

Membranolytic effects of monosodium urate monohydrate: influence of grinding

The effect of grinding on the membranolytic interaction between monosodium urate monohydrate (MSUM) crystals and intact erythrocyte membranes was studied. Crystals were ground for between 1-72 h, and percent hemolysis and zeta potentials determined. A cationic amphiphilic probe (CAT12) was incorporated into the erythrocyte membrane and incubated with MSUM. Increasing grinding times caused a decrease in both the crystallinity and zeta potential of the samples, a decrease in percent hemolysis values and a change in the distribution of free and bound spin label populations. The probe redistribution is thought to be due to an electrostatic interaction between negatively charged MSUM and the CAT12 probe.

A spin label study of the membranolytic effects of crystalline monosodium urate monohydrate

The nature of the membranolytic interaction between monosodium urate monohydrate (MSUM) crystals and phospholipid membranes was studied using electron spin resonance. Two spin probe molecules were incorporated into intact human erythrocytes and incubated with MSUM crystals. The apparent increased fluidity of 5-doxyl stearic acid incorporated erythrocytes after a 2 h incubation with MSUM was probably due to an electrostatically induced redistribution of probe from the outer more rigid layer to the fluid inner leaflet via a flip-flop mechanism. It was suggested that the MSUM induced redistribution of cationic amphiphilic probe population in the whole erythrocyte was also due to an electrostatic interaction between negatively charged MSUM crystals and positively charged probe. Possible mechanisms of MSUM induced membranolysis are discussed.