The p53 Negative Regulator, MDM4 but Not MDM2, Is Frequently Activated in Hepatocellular Carcinoma
Xiaoping Zhou, Mark Bloomston, Lawrence A Shirley, Arletta Lozanski, Gerard Lozanski, Wendy L Frankel. Ohio State University, Columbus, OH
Background: The p53 tumor suppressor pathway is frequently inactivated in human cancers including hepatocellular carcinoma (HCC). MDM2 and MDM4 are the primary negative regulators of p53. Amplification or over-expression of MDM2 and MDM4 abolish the p53 mediated response by inactivating the wild-type p53 protein. A functional single nucleotide polymorphism of the MDM2 (SNP-309 T/G) enhances the Sp1 binding to MDM2 promoter and MDM2 expression resulting in attenuation of p53 and has been associated with the development and prognosis of a number of tumors. We hypothesized that over-expression of MDM2 and MDM4 may be the common mechanism of p53 inactivation in HCC and thus a potential therapeutic target.
Design: Tissue microarrays of HCC were constructed and immunohistochemically stained for MDM2, MDM4 and p53. Expression intensity was scored as 0 (absent), 1+ (modest) or 2+ (high). Genotyping of MDM2 SNP-309 was performed on genomic DNA extracted from tumor by PCR amplification flanking the corresponding promoter region followed by temperature gradient capillary electrophoresis and direct sequencing. We evaluated the association between MDM2 SNP-309 and the risk of HCC by comparing the genotype frequency with that of controls. We also investigated the relationships between MDM2 SNP-309 genotype, MDM2, MDM4 and p53 expression and median overall survival time.
Results: MDM4 expression was detected in 42 of 93 HCC (45%; 1+ in 33, 2+ in 9), p53 was detected in 6 (6%; 1+ in 4, 2+ in 2), and no MDM2 immunoreactivity was found. The MDM2 SNP-309 genotypes of HCC were not statistically different from those of 100 controls.
|HCC (n = 69)||Control (n = 100)|
|G/G||7 (10%)||12 (12%)|
|T/G||30 (43.5%)||40 (40%)|
|T/T||32 (46.4%)||48 (48%)|