Altered expression of the suppressors PML and p53 in glioblastoma cells with the antisense-EGF-receptor

Gene amplification and enhanced expression of the epidermal growth factor receptor (EGFR) represent the major molecular genetic alteration in glioblastomas and it may play an essential role in cell growth and in the carcinogenic process. On the other hand, the nuclear suppressor proteins PML and p53 are also known to play critical roles in cancer development and in suppressing cell growth. Here we report that, in glioblastoma cells with defective EGFR function, the expressions of both promyelocytic leukaemia (PML) and p53 were altered. Cells that were transfected with the antisense-cDNA of EGFR were found to have more cells in G1 and fewer cells in S phase. In addition, the transfected cells were found to be non-responsive to EGF-induced cell growth. Interestingly, the expression of the suppressors p53 and PML were found to be significantly increased by immunohistochemical assay in the antisense-EGFR cells. Moreover, the PML expression in many of the cells was converted from the nuclear dot pattern into fine-granulated staining pattern. In contrast, the expressions of other cell cycle regulated genes and proto-oncogene, including the cyclin-dependent kinase 4 (cdk4), retinoblastoma, p16INK4a and p21H-ras, were not altered. These data indicate that there are specific inductions of PML and p53 proteins which may account for the increase in G1 and growth arrest in antisense-EGFR treated cells. It also indicates that the EGF, p53 and PML transduction pathways were linked and they may constitute an integral part of an altered growth regulatory programme. The interactions and cross-talks of these critical molecules may be very important in regulating cell growth, differentiation and cellular response to treatment in glioblastomas. © 1999 Cancer Research Campaig

Oral uracil-tegafur: an alternative to intravenous 5-fluorouracil?

The fluoropyrimidines have been used in the treatment of a number of tumour types over the past 40 years. Particular attention has focused on the use of 5-fluorouracil (5-FU) in colorectal cancer for which, until recently, there has been a lack of other effective chemotherapy. In an attempt to optimise the efficacy of fluoropyrimidines, a number of approaches have been used. These include alternative methods of iv. scheduling, the use of co-factors and the development of oral compounds. The aim of oral agents is to satisfy patient preference while maintaining the efficacy of sustained drug exposure seen with prolonged or continuous infusions of iv. 5-FU. One such oral compound is uracil-tegafur (UFT), which combines tegafur (ftorafur, a 5-FU prodrug) and uracil in a 1:4 molar ratio. UFT first entered Phase I trials in Japan over 20 years ago but has only recently received significant exposure in Phase II and III trials. Results from a number of Phase III studies in Europe and in the US are now becoming available. With UFT recently approved for colorectal cancer in many European countries, although not in the US, it is timely to review the current situation and future prospects for this agent

The complexity of p53 stabilization and activation

A number of proteins are activated by stress stimuli but none so spectacularly or with the degree of complexity as the tumour suppressor p53 (human p53 gene or protein). Once stabilized, p53 is responsible for the transcriptional activation of a series of proteins involved in cell cycle control, apoptosis and senescence. This protein is present at low levels in resting cells but after exposure to DNA-damaging agents and other stress stimuli it is stabilized and activated by a series of post-translational modifications that free it from MDM2 (mouse double minute 2 but used interchangeably to denote human also), a ubiquination ligase that ubiquitinates it prior to proteasome degradation. The stability of p53 is also influenced by a series of other interacting proteins. In this review, we discuss the post-translational modifications to p53 in response to different stresses and the consequences of these changes