Role of cytoplasmic acetyltransferases, NAA60 and HAT1, in cellular protection against genotoxic agents

Histone acetyltransferases (HATs) are separated into two types. Type A HATs act on nucleosomal histones and thus primarily function in transcriptional regulation, while cytoplasmic HATs (type B) are known as enzymes that modify free histones before their assembly into chromatin, and may also function outside the nucleus. N-alpha-acetyltransferase 60 (NAA60) is the most recently discovered type B HATs, which are also known as N-terminal acetyltransferases (NATs) and are found only in multicellular eukaryotes. NAA60 localizes to the Golgi complex and possesses a unique ability to catalyze the acetylation of membrane-anchored proteins at the N-terminus and free histones at the lysine side chains, the biological significance of which remains unclear. To investigate the cellular functions of NAA60 and its relation to other cytoplasmic HATs, Hat1, we generated NAA60- or HAT1-deficient cells and NAA60/HAT1-double deficient cells using a chicken B lymphocyte leukemia DT40 cell line. Although NAA60-deficient cells did not show any impairment in cell growth and showed a slight sensitivity to DNA damage agents, NAA60/HAT1-double deficient cells exhibited an additive increase in sensitivity to methyl methanesulfonate (MMS) and 4-nitroquinoline 1-oxide (4-NQO) when compared to HAT1-deficient cells, which were previously reported to be moderately sensitive to these agents. These results predict that each type B HATs might contribute differently in regulation of repair of chemical induced DNA lesions.