To be able to investigate the mechanism of mutation induction by DNA-damaging agents, it is important to know the variability in spontaneous mutation induction. The group of Simons has investigated the rate of spontaneous mutations in undamaged cells under different growth conditions.
The Sarasin group has investigated the mechanism of induction of point mutations in human cells. The research was focused on the question whether UV-induced mutation spectra differ in fibroblasts from Xeroderma pigmentosum group D (XP-D) patients, who are prone to UV-induced skin cancer (as most XP patients), and in fibroblasts from Trichothiodystrophy (TTD)/XP-D patients who are not tumour-prone.
The laboratory of Herrlich has investigated several aspects of the cellular response to radiation. UV light induces the activation of pre-existing transcription factors, including the AP-1 factors cJun and cFos. Activation of these factors appeared to depend on signal transduction pathways triggered by growth-factor receptors. Therefore, the crucial question has been investigated how growth-factor receptors are activated by UV radiation.
In the course of a study of the biological and genetical properties of XP and TTD cells, the group of Bertazzoni has identified a clonal chromosomal rearrangement in an XP-C fibroblast strain, which apparently reflected a preneoplastic state (anchorage-independent growth). Selection for anchorage independent growth has now led to the isolation of several more XP clones with chromosomal abnormalities.
The Rommelaere group has focused on the mechanism of radiation-induced DNA amplification, using Parvoviruses and a model. Parvoviruses can undergo viral DNA amplification in carcinogen-treated cells in the absence of viral replication proteins. Since p53 is known to protect cells against amplification of cellular genes, the group has investigated whether p53 plays a role in selective viral DNA amplification.
The laboratory of Thomou-Politi has investigated the effects of low doses of IR on expression of the CD(2) gene, which codes for a T-cell-specific surface antigen. Expression of CD(2) is enhanced by IR, and it may serve as a sensitive indicator for exposure to low radiation doses. Since CD(2) appears to be involved in cell-cell adhesion, signal transduction and T-cell differentiation, the effect of IR on stimulation of T-cell activation was studied. Low doses of IR indeed not only cause an increase in the level of CD(2) mRNA in T-lymphocytes but also enhance the response of the cells to mitogenic stimulation.
Finally, in the summer of 1994 the group of Russev from Sofia, Bulgaria, joined the contract. The research of this group deals with the mechanism of inhibition of replicon initiation of gamma irradiation or topoisomerase II inhibitors. Specifically, the group focussed on (1) the effect of gamma-rays and topo II poisons on chromatin structure, (2) the effect of protein synthesis inhibitors and protein phosphorylation on replicon initiation suppression by these treatments.
THE OBJECTIVE OF THIS RESEARCH PROPOSAL IS TO GAIN AN UNDERSTANDING OF THE CELLULLAR RESPONSES TO DNA DAMAGE. BOTH UV-LIGHT AND IONIZING RADIATION INDUCE A VARIETY OF REACIONS WHICH ARE COLLECTIVELY CALLED "STRESS RESPON SES". THESE CAN BE DIVIDED INTO THE EARLY REACTIONS AND WHICH CULMINATE IN MUTAGENESIS AND CARCINOGENESIS.
IN THE PRESENT RESEARCH PROPOSAL, 6 EUROPEAN LABORATORIES, THAT ALREADY COLLABORATE IN THE CURRENT PROJECT (BI7034) WITH THE OBJECTIVE OF INVESTI GATING VARIOUS ASPECTS OF THE INDUCTION OF STRESS RESPONSES, WILL JOIN FOR CES WITH 2 ADDITIONAL LABORATORIES, THOSE OF DRS. P. HERRLICH AND J.W.I.M. SIMONS. TOGETHER, THE 8 GROUPS WITH THEIR SPECIALISMS COVER THE MAJOR AREAS OF RESEARCH WITHIN THE FIELD. THE SEQUENCE OF REACTIONS FOLLOWING DNA DAMA GE STARTS WITH THE INITIAL RESPONSES WHICH INCLUDE ACTIVATION OF TRANS CRIPTION FACTORS, ACTIVATION OF GENE TRANSCRIPTION AND SECRETION OF GROWTH FACTORS (COVERED BY THE GROUPS OF HERRLICH, DEVORET, BERTAZONNI, VAN DER EB). THESE EVENTS SOMEHOW MODIFY THE CELL, IN SUCH A WAY THAT A TRANSIENT STATE OF GENETIC INSTABILITY IS INDUCED, WHICH RESULT IN ALTERNATIONS AT THE DNA LEVEL. THE CELLULAR PROCESSES LEADING TO THESE GENETIC ALTERNATIONS ARE NOT YET ELUCIDATED, BUT IT IS THOUGHT THAT PROTEINS E.G. WITH FUNCTIONS SIMILAR TO THE BACTERIAL RECA PROTEIN, AND POLY(ADP-RIBOSE) POLYMERASE ARE INVOLVED (COVERED BY THE GROUPS OF DEVORET AND BERTAZZONI). THE END-POINT EFFECTS ARE A VARIETY OF ALTERNATIONS AT THE DNA LEVEL, SUCH AS POINT MUTA TION, GENE AMPLIFICATION AND OTHERJ DNA REARRANGEMENTS. THESE SUBJECTS WILL BE INVESTIGATED BY THE GROUPS OF SARASIN, BERTAZZONI, DEVORET, SINONS, VAN DER EB AND HERRLICH. THE ULTIMATE CONSEQUENCES OF THESE EVENTS MAY BE NEO PLASTIC TRANSFORMATION (COVERED BY VAN DER EB, SIMONS, SARASIN AND OTHER GROUPS). OTHER BIOLOGICAL EFFECTS, WHICH CAN BE USED TO MONITOR AND STUDY STRESS RESPONSES, INCLUDE ALTERNATIONS IN THE PERMISSIVENESS TO ONCOLYTIC PARVOVIRUS REPLICATION (ROMMELAERE) OR ALTERED EXPRESSION OF CELL SURFACE PROTEINS (THOMOU-POLITI).
THE SIGNIFICANCE OF THIS JOINED PROPOSAL IS EMPHASIZED BY THE FACT THAT THE RADIATION-INDUCED STRESS RESPONSES APPEAR TO REPRESENT THE MOLECULAR BASIS OF BOTH TUMOR INITIATION AND PROMOTION, AND POSSIBLY ALSO OF TUMOR PROGRESSION, STEPS THAT PLAY A CENTRAL ROLE IN CARCINOGENESIS.
Funding SchemeCSC - Cost-sharing contracts
2300 RA Leiden