Changes of chromatin structure are mainly regulated by epigenetic regulations including ATP-dependent remodeling of nucleosomes, the incorporation of variants histones into nucleosomes and posttranslational modifications of histones . Post-translational modifications of the N-terminal tails of histones include acetylation, methylation, phosphorylation, ubiquitination, sumoylation, and ADP-ribosylation [2, 3]. Histone acetylation as one of the best characterized epigenetic modifications is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDAC). The balance between histone acetylation and deacetylation serves as a key epigenetic mechanism for gene expression, DNA repair, developmental processes and tumorigenesis [4–6]. Thus, any reason to make this imbalance can lead to abnormal cell function, even cancer.
MYST1 (also known as hMOF), is the human ortholog of the Drosophila MOF protein containing chromodomain and acetyl-CoA binding motif which is one of the key components of the dosage compensation complex (DCC) or the male specific lethal (d MSL) complex . Recent biochemical purifications revealed that hMOF forms at least two distinct multi-protein complexes in mammalian cells. One complex is the evolutionary conserved human MSL complex which is responsible for the majority of histone H4 acetylation at lysine 16 [8, 9]. The other hMOF-containing complex is the human n on-s pecific l ethal (NSL) complex which is recently characterized by Cai Y et al. . hNSL complex can also acetylate histone H4 at lysine 5 and 8 on the recombinant polynucleosomes with the exception of histone H4K16. Although the functions of hMSL and hNSL complexes in human cells are not very clear, both complexes can acetylate histone H4 at lysine 16, suggesting the importance of acetylation of H4K16 in cells. Except for acetylation of H4K16, NSL complex was found to be able to acetylate the tumor suppressor protein p53, and this acetylation is able to affect the behavior of p53 in response to DNA damage . It has been reported that depletion of hMOF in human cells leads to genomic instability, spontaneous chromosomal aberrations, cell cycle defects, reduced transcription of certain genes, and defective DNA damage repair and early embryonic lethality [4–7]. This suggests a critical role for hMOF in fundamental processes such as gene transcription, cell proliferation, differentiation and DNA repair response. It is worth mentioning that depletion of hMOF also leads to global reduction of histone H4K16 acetylation in human cells [8, 12]. However, recent studies suggest that the global modification status of H4K16Ac is also affected by Gcn-5-containing HAT and SIRT-LSD1 HDAC complexes [13, 14], indicating hMOF might not be the only HAT fulfilling acetylation of H4K16 in cells. Although the role of histone H4K16 acetylation in transcription regulation is not completely understood, loss of H4K16 acetylation has been found in certain cancers. Pfister et al.  found that frequent downregulation of hMOF in large series of primary breast carcinomas and medulloblastomas and hMOF protein expression tightly correlated with acetylation of H4K16 in both cancers. In addition, analysis of the tissue microarray slides revealed low or absent histone H4K16 acetylation in majority of breast cancer tissues .
Renal cell carcinoma (RCC) is one of the most common genitourinary malignancies, accounting for about 3% of all cancers worldwide . With the improved imaging diagnostic technology, more RCC cases have been diagnosed at an early stage. However, there is a considerable number of RCC patients at the time of diagnosis has been transferred . Research efforts have found various biomarkers of diagnostic and prognostic of RCC such as hypoxia-induced factor 1alpha (HIF1α), vascular endothelial growth factor (VEGF), and carbonic anhydrase IX (CA9), but they are not specific and sensitive enough to accurately predict the survival of RCC patients [19–21]. Recent studies indicate that epigenetic alterations play an important role in carcinogenesis, and global histone modifications as predictors of cancer recurrence in various tumor entities has begun to study. Patients with RCC have been found that total acetylation levels of histone H3 were inversely correlated with pT-stage, distant metastasis, Fuhrman grading and RCC progression, whereas total histone H4Ac deacetylation was correlated with pT-stage and grading . All the above observations strongly suggest that histone modifications might be involved in the development and progression of RCC. However, it is not clear which particular enzyme or specific modified lysine residue is responsible for tumorigenesis in RCC. This study aims to assess hMOF expression and its corresponding acetylation of histone H4K16 in the RCC via qRT-PCR, western blotting and immunohistochemistry. Simultaneously, we also investigated the correlation between the expression of hMOF and CA9.