Effects of the TP53 p.R249S mutant on proliferation and clonogenic properties in human hepatocellular carcinoma cell lines: interaction with hepatitis B virus X protein.

Aflatoxin B(1) (AFB(1)) is a risk factor for hepatocellular carcinoma (HCC) in many low-resource countries. Although its metabolites bind at several positions in TP53, a mutation at codon 249 (AGG to AGT, arginine to serine, p.R249S) accounts for 90% of TP53 mutations in AFB(1)-related HCC. This specificity suggests that p.R249S confers a selective advantage during hepatocarcinogenesis. Using HCC cell lines, we show that p.R249S has lost the capacity to bind to p53 response elements and to transactivate p53 target genes. In p53-null Hep3B cells, stable transfection of p.R249S or of another mutant, p.R248Q, did not induce significant changes in cell proliferation and survival after cytotoxic stress. In contrast, in a cell line that constitutively expresses both p.R249S and the hepatitis B virus antigen HBx (PLC/PRF/5), silencing of either p.R249S or HBx by RNA interference slowed down proliferation, with no additive effects when both factors were silenced. Furthermore, the two proteins appear to form a complex. In human HCC samples, mutation at codon 249 did not correlate with p.R249S protein accumulation or HBx truncation status. We suggest that p.R249S may contribute to hepatocarcinogenesis through interaction with HBx, conferring a subtle growth advantage at early steps of the transformation process, but that this interaction is not required for progression to advanced HCC.

A prostate cancer susceptibility allele at 6q22 increases RFX6 expression by modulating HOXB13 chromatin binding.

Genome-wide association studies have identified thousands of SNPs associated with predisposition to various diseases, including prostate cancer. However, the mechanistic roles of these SNPs remain poorly defined, particularly for noncoding polymorphisms. Here we find that the prostate cancer risk-associated SNP rs339331 at 6q22 lies within a functional HOXB13-binding site. The risk-associated T allele at rs339331 increases binding of HOXB13 to a transcriptional enhancer, conferring allele-specific upregulation of the rs339331-associated gene RFX6. Suppression of RFX6 diminishes prostate cancer cell proliferation, migration and invasion. Clinical data indicate that RFX6 upregulation in human prostate cancers correlates with tumor progression, metastasis and risk of biochemical relapse. Finally, we observe a significant association between the risk-associated T allele at rs339331 and increased RFX6 mRNA levels in human prostate tumors. Together, our results suggest that rs339331 affects prostate cancer risk by altering RFX6 expression through a functional interaction with the prostate cancer susceptibility gene HOXB13.