MDM2 and neoplasm: Assuming that the MDM2/p53 autoregulatory negative feedback loop is functional at the protein level in astrocytic tumours with amplified copies of the MDM2 gene, one would expect the P1 promoter to give rise to high MDM2 mRNA and protein levels in these neoplasms, as all MDM2 gene coded proteins with a p53-binding domain would inhibit the transcriptional activation of the P2 promoter by p53, reducing MDM2 mRNA expression from this promoter.