MDM2 and neoplasm: In cultured HaCaT cells, arsenic exposure induced a change in the expression of p53 and the p53 regulatory protein, murine double minute 2 (MDM2).20 In p53-compromised cells (with either p53 dysfunction or inhibition), arsenic exposure was reported to induce centrosomal abnormality and colony formation.21 In p53 heterozygous knockout and wild-type C57BL/6 J mice, tumor induction by DMA (a major metabolite of ingested inorganic arsenics in most mammals), particularly of malignant lymphomas and sarcomas, was similar in treated- and control-p53(±) knockout mice.22