Neuroblastoma (NB), a sympathetically derived childhood tumour, shows characteristics of neuronal precursor cells, suggesting a halted differentiation process. We have previously shown that the Notch signalling cascade, a key player during normal neurogenesis, also might be involved in NB differentiation. Valproic acid (VPA), a well-tolerated antiepileptic drug, has been shown to induce differentiation and cell death of NB cells, possibly associated with its recently described HDAC inhibiting activity. Stimulation of NB cells with VPA led to increased cell death and phenotypic changes associated with differentiation, that is, neurite extension and upregulation of neuronal markers. VPA treatment also led to an activated Notch signalling cascade as shown by increased levels of intracellular Notch-1 and Hes-1, mimicking the initial phase of induced differentiation. These results reinforce that VPA potentially could be used in differentiation therapy of NB and that the effects in part could be a consequence of interference with the Notch signalling cascade.

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ID proteins have been implicated in the regulation of cell proliferation and differentiation in various cell types during normal development as well as in the formation of cancer. Our aim was to delineate the expression of ID2 by immunohistochemistry in primary breast cancer in order to detect potential associations with cell cycle regulatory proteins and/or clinicopathologic parameters. We further overexpressed ID2 in a breast cancer cell line to elaborate potential effects on proliferation and invasiveness. We observed large variations in ID2 expression in primary breast cancer, and the protein was localised to both the nucleus and cytoplasm. Interestingly, a high cytoplasmic ID2 protein level correlated with a favourable prognosis. Overexpressing ID2 in the MDA-MB-468 breast cancer cell line generated a marked cytoplasmic localisation of the protein and reduced the invasive capacity of cells. Modest enhancement of cell proliferation was further detected in ID2-overexpressing cells. In conclusion, ID2 protein expression varies substantially within primary breast tumours and high cytoplasmic levels of ID2 might reflect a less aggressive breast tumour phenotype. ' 2005 Wiley-Liss, Inc.Key words: ID2; breast cancer; proliferation; invasion The cell cycle regulatory machinery is a highly complex and delicate system that often is abrogated in cancer, and tumour cells consequently override one or more cell cycle checkpoints. One important checkpoint is the G 1 -S transition, where cells are committed to DNA replication and subsequent division. The cell cycle regulatory machinery is dependent on the activity of different CDKs and their associated cyclins, whose expression is tightly regulated over the cell cycle. Regulators of kinase activity are inhibitory proteins like p21, p27 and p16. One of the major substrates for the CDKs is pRb. Overexpression or inactivation of cell cycle regulatory proteins leads to abnormal proliferation and lack of checkpoint control. For example, inactivation of pRb has been noted in about 60% of all human cancers either by mutation and gene deletions or by deregulated phosphorylation, sequestration by oncoproteins or loss of cooperating factors.ID2 is a multipotent regulatory molecule harbouring an HLH motif. Through the HLH domain, ID proteins (ID1-ID4 in mammals) bind and sequester the DNA binding bHLH proteins known as E proteins, thereby preventing them from binding DNA alone or in complex with tissue-specifically expressed bHLH proteins. Since these latter bHLH proteins often are associated with differentiation and decreased proliferation, elevated ID protein levels often lead to maintained proliferation, whereas decreased ID protein levels are associated with differentiation.In the normal mammary epithelium, ID2 has been linked to critical steps in the development of functional mammary glands.2 The phenotype of homozygous ID2 knockout mice reveals lactation defects due to poor expansion of lobulo-alveolar tissue in the mammary glands, possibly caused by decreased proliferation of...

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The disintegrin and metalloproteases (ADAMs) are emerging as therapeutic targets in human disease, but specific drug design is hampered by potential redundancy. Unlike other metzincins, ADAM prodomains remain bound to the mature enzyme to regulate activity. Here ADAM12, a protease that promotes tumor progression and chondrocyte proliferation in osteoarthritic cartilage, is shown to possess a prodomain/catalytic domain cationic molecular switch, regulated by exogenous heparan sulfate and heparin but also endogenous cell surface proteoglycans and the polyanion, calcium pentosan polysulfate. Sheddase functions of ADAM12 are regulated by the switch, as are proteolytic functions in placental tissue and sera of pregnant women. Moreover, human heparanase, an enzyme also linked to tumorigenesis, can promote ADAM12 sheddase activity at the cell surface through cleavage of the inhibitory heparan sulfate. These data present a novel concept that might allow targeting of ADAM12 and suggest that other ADAMs may have specific regulatory activity embedded in their prodomain and catalytic domain structures.