The Effect of UVB Irradiation on Histone H4

Abstract

Histone modifications such as phosphorylation, alter chromatin and accessibility to transcription factors. Consequently, they play an important role in gene expression. During normal cell development, histone H4 serine 1 becomes phosphorylated and arginine 3 becomes methylated. Using different proteins, studies have established a crosstalk relationship between these two modifications whereby methylation will block phosphorylation. In histone H4, serine 1 becomes phosphorylated in response to DNA damage. In addition, there is evidence that exposure to ultraviolet light increases the activity of protein arginine methyltransferase 1 (PRMT1), the enzyme responsible for arginine 3 methylation. However, whether phosphorylation or methylation can directly respond to environmental stresses, such as ultraviolet B (UVB) irradiation, remains unknown. It is also not known whether phosphorylation or neighboring arginine methylation respond synergistically or antagonistically to UVB irradiation. Preliminary in vitro studies have confirmed that histone H4 is methylated by PRMT1 at arginine 3. The effects of UVB irradiation will be assessed by directly measuring the amount of serine 1 phosphorylation and arginine 3 methylation of histone H4 under set conditions. In vitro modification reactions and HeLa cells incubated with kinase and methyltransferase inhibitors, will undergo UVB (280 – 315 nm) irradiation through a homemade beam collimating device. Histone H4 will be purified and the amount of phosphorylation and methylation will be detected by immunoblotting. We hypothesize that methylation of arginine 3 at histone H4 will increase in response to UVB irradiation and block neighboring phosphorylation of serine 1. PRMT1 is implicated (along with p300, a lysine acetyltransferase) in a signal transduction pathway that is responsible for the production and function of p53, a tumor suppressor. If the amount of arginine methylation increases in response to ultraviolet light, it will confirm that PRMT1 plays an indirect role in the suppression of tumors via histone modification. Finally, the effect of this modification on serine 1 phosphorylation will lead to a greater understanding of the histone code.Support or Funding InformationThis research was funded through the Minority Access to Research Careers Undergraduate Student Training in Academic Research Fellowship Program (NIH Grant GM008228)