The q24 band of chromosome 8 （8q24） is frequently amplified in human cancers including breast cancer, and several SNPs （single nucleotide polymorphisms） at 8q24, including rs13281615, have been identified for their association with cancer risks. These SNPs are in a ＂gene desert＂ region, and their functions in cancer development remain to be illustrated, although several of the SNPs appear to influence the genes in the ＂desert＂ in a long-range manner, including the v-myc avian myelocytomatosis viral oncogene homolog （MYC） and the non- protein coding plasmacytoma variant translocation 1 （PVT1）, both of which have been implicated in human cancers. In the current study, we examined rs13281615 for its potential role in breast cancer using normal and cancer tissues from 121 Chinese women with breast cancer. In addition to confirming the association of the GG genotype of rs 13281615 with breast cancer risk, we found that germline GG genotype was significantly associated with estrogen receptor （ER） positivity, higher tumor grade and higher proliferation index. We also found frequent somatic mutations （22/121 or 18.2%） of this SNP in breast cancer. Interestingly, the majority of the mutations （17/22 or 77%） involved a G→ A change, resulting in a decrease in the number of cancers with the GG risk genotype and subsequent loss of GG association with higher tumor grade and proliferation index in cancers. Furthermore, PVT1 expression was increased in cancers, and the increase was associated with the GG genotype of rs13281615. These results suggest that the GG genotype of SNP rs13281615 plays a role in breast cancer likely by influencing PVT1 expression, and that during oncogenesis, ＂protective＂ mutations could occur.
MYC is a potent oncoprotein that modulates multiple cellular processes including proliferation,apoptosis, differentiation, stemness, senescence, and migration. Functioning primarily as a transcriptional factor, MYC interacts with a large number of proteins, and identification and characterization of MYC-interacting proteins are important for understanding how MYC functions. In this study, we used different systems to demonstrate that a novel zinc finger transcription factor, ZNF121, physically interacted with MYC, and the interaction involved their N-terminal regions. Overexpression of ZNF121 increased, while its knockdown decreased, the expression of MYC in multiple epithelial cell lines, and MYC had similar effects on ZNF121 expression. An expression correlation was also detectable in a panel of epithelial cell lines and a cohort of human breast cancer tissues. Functionally, knockdown of ZNF121 in several breast epithelial cell lines attenuated the expressions of MYC and its target genes（e.g., EGR1,CDC2, and nucleolin） and slowed cell proliferation, accompanied by cell cycle arrest in the G1 phase and expression alteration of cell cycle regulators（cyclin D1, p14 and p21）. Analysis of publically available databases showed that ZNF121 expression is up-regulated in human breast cancer, and the up-regulation significantly associates with worse patient survival in the luminal A subtype of breast cancer. These findings establish ZNF121 as a MYC-interacting protein with functional effects on MYC and cell proliferation.
Ang LuoaXuan ZhangaLiya FuaZhengmao ZhuaJin-Tang Dong
