Mdm2 and Mdm4 which is also known as MdmX can act as oncogenes if there is any mutation or deregulation in their functions. The overexpression or amplification of these genes results in the inhibition of p53 even in case of stresses. The inhibition of p53 results in uncontrollable cell division and proliferation. In this way Mdm2 and Mdm4 act as oncogenes. There can be many ways by which these genes can act as oncogenes. They can either become mutated or up-regulated. They are actually the negative regulators of the p53 protein. The p53 protein is usually needed at the time of stresses and kept under check and control during normal situations so that the normal process of cell division could be carried out. This Mdm2 protein act as an inhibitor of p53 transcriptional activation. It recognizes trans-activation domain (TAD) at N-terminal and act as E3-ubiquitin ligase. The regulation of Mdm2 at the time of stresses is made possible by different mechanisms. The most important mechanism is the phosphorylation of Mdm2. The phosphorylation inactivates the Mmd2 and hence stopping its property of blocking p53 and regulating the cellular responses in case of stresses. Mdm4 also shows similar mechanism, but its level in thymus cells is more as compared to the other cells.

Keywords: Oncogenes; Proliferation; Upregulation; Transcriptional Activation; Phosphorylation; Thymus