[Solitary median maxillary central incisor syndrome]. / Het solitaire mediane maxillaire centrale incisief-syndroom.

Solitary Median Maxillary Central Incisor syndrome is a rare condition (prevalence 1:50,000), with the characteristic dental feature of a solitary central incisor in the maxilla, positioned exactly in the midline. This single incisor is symmetrical and can be present in the deciduous as well as in the permanent dentition. The syndrome can occur as a mild form of the broad holoprosencephaly-spectrum, but can also be associated with other characteristics. The etiology is still largely unknown, but the syndrome is probably based especially on genetic causes. Early recognition of the syndrome is of great importance for establishing the diagnosis, for additional investigation, for possible treatment of associated anomalies and for the correct advice concerning the risk of inheritance of severe congenital birth defects, related to holoprosencephaly. Dentists and orthodontists can play an important role in this regard and should therefore be able to recognise the clinical features of this condition and know how to refer a patient for further diagnostic counselling.

Characterization of the EMS1 gene and its product, human Cortactin.

We have identified a novel gene, EMS1, that is consistently amplified and overexpressed in human carcinomas with an amplification of the chromosome 11q13 region. Comparisons of the EMS1 sequences with those present in the GenBank databases revealed a high identity with chicken cortactin. Southern and western blot analyses confirm the high sequence conservation during evolution. An antiserum specific for human cortactin, showed in gene transfer experiments that both human p80 and p85 isoforms are encoded by the EMS1 cDNA. Further comparisons demonstrated an high sequence and structural homology with HS1 that is implicated in signal transduction in lymphoid cells only. Expression of EMS1/cortactin mRNA was restricted to tumor cell lines derived from non-lymphoid origin. Cortactin contains (i) a filamentous actin binding tandem repeat domain, (ii) a proline-rich SH3-binding and (iii) a SH3 domain that is common in proteins involved in signal transduction. Our data suggest that human EMS1/cortactin has a function in signal transmission between cell-matrix contact sites and the cytoskeleton and, as such, its overexpression due to 11q13 amplification might effect adhesive properties of human carcinomas.

The redistribution of cortactin into cell-matrix contact sites in human carcinoma cells with 11q13 amplification is associated with both overexpression and post-translational modification.

The EMS1 gene, located at the chromosome 11q13 region, is the human homologue of p80/p85 cortactin, a chicken pp60(src) tyrosine kinase substrate. In cells derived from breast carcinomas and squamous carcinomas of the head and neck, DNA amplification of this region results in overexpression of cortactin. Overexpression is accompanied by a partial redistribution of cortactin from the cytoplasm into cell-matrix contact sites. To investigate whether overexpression only is sufficient for this redistribution, we performed biochemical analysis of human cortactin derived from carcinoma cell lines with either normal levels (UMSCC8) or with excessive levels of cortactin due to chromosome 11q13 amplification (UMSCC2). Pulse-chase experiments performed with UMSCC2 cells revealed that p85 originated from p80 by post-translational modifications. However, the conversion of p80 into p85 was hardly observed in UMSCC8 cells, indicating a different processing of the two isoforms in cells with a normal expression level of cortactin. Western blot analysis showed that treatment of UMSCC2 cells with cycloheximide, serum, epidermal growth factor, or vanadate resulted in the disappearance of the p80 form and conversion into p85. Conversion of p80 into p85 was accompanied by a redistribution of cortactin from cytoplasm to cell-matrix contact sites. In UMSCC8 cells, these treatments had no effect on the p80/p85 ratio, and cortactin remained in the cytoplasm. Conversion into p85 therefore is correlated with a relocalization of cortactin to the cell periphery. In addition, p85 from epidermal growth factor- or vanadate-treated UMSCC2 cells showed a significant enhancement in phosphorylation compared with p85 in UMSCC8 cells. Our findings demonstrate that in carcinoma cells with 11q13 amplification not only overexpression but also post-translational modifications of cortactin coincides with the redistribution from the cytoplasm into cell-matrix contact sites.

Identification of an invasion-inducing gene, Tiam-1, that encodes a protein with homology to GDP-GTP exchangers for Rho-like proteins.

Using proviral tagging in combination with in vitro selection for invasiveness, we have identified a gene, designated Tiam-1, that affects invasion. In the selected invasive T lymphoma variants, proviral insertions were found within coding exons of the Tiam-1 gene, resulting in both truncated 5'-end and 3'-end transcripts that give rise to N- and C-terminal Tiam-1 protein fragments. In one invasive variant, amplification of the Tiam-1 locus was observed with concomitant increase in the amount of normal Tiam-1 protein. Cell clones that were invasive in vitro produced experimental metastases in nude mice, and transfection of truncated Tiam-1 cDNAs into noninvasive cells made these cells invasive. The predicted Tiam-1 protein harbors a Dbl- and Pleckstrin-homologous domain, which it shares with GDP-GTP exchangers for Rho-like proteins that have been implicated in cytoskeletal organization.

Induction of invasive and metastatic potential in mouse T-lymphoma cells (BW5147) by treatment with 5-azacytidine.

Non-invasive, non-metastatic mouse BW5147 T-lymphoma cells were treated with non-mutagenic concentrations of the hypomethylating agent 5-azacytidine (5-aza-C). Subsequently, invasive variants were selected on monolayers of rat embryo fibroblasts. The estimated frequency of induction of invasive variants was smaller than 1 in 10(6) cells. We obtained several independent clones that were stable in the expression of the invasive phenotype. In contrast to the parental cell line, the highly invasive clones produced widespread metastases upon tail vein injection in all the syngeneic AKR mice tested, whereas clones with an intermediate level of invasiveness formed metastases only in part of the mice tested. DNA analysis using the methylation-sensitive and insensitive restriction enzymes, Hpa-II and Msp-I, respectively, showed that the DNA of the invasive variants remained hypomethylated, up to 6 months after 5-aza-C treatment. 5-aza-C is thus able to induce invasive and metastatic potential in the BW5147 T-lymphoma cells, similar to the activated human c-Ha-ras oncogene or human chromosome 7, as studied previously. The acquisition of invasive and metastatic potential is presumably caused by DNA hypomethylation and thus activation of one or more silent invasion controlling genes.

Genetic basis of T-lymphoma invasion.

We have discussed the use of BW5147 T-lymphoma cells as a model system to explore the genetic basis of invasion and metastasis. The degree of invasiveness of these cells in vitro is highly correlated with experimental metastasis formation in vivo upon tail vein injection in syngeneic AKR mice. A powerful in vitro selection system has been developed which allows to select rare invasive cell variants obtained by various experimental manipulations. We found that introduction of the human c-Ha-ras oncogene, the presence of human chromosome 7 from normal activated T-cells, DNA hypomethylation induced by 5-azacytidine treatment, and possibly also retrovirus insertional mutagenesis can convert noninvasive BW5147 T-lymphoma cells into invasive and metastatic cells. Several experimental approaches are discussed to identify the gene(s) involved.