A peek into the complex realm of histone phosphorylation

Abstract

Although discovered long ago, posttranslational phosphorylation of histones has been in the spotlight only recently. Information is accumulating almost daily on phosphorylation of histones and their roles in cellular physiology and human diseases. An extensive cross talk exists between phosphorylation and other posttranslational modifications, which together regulate various biological processes, including gene transcription, DNA repair, and cell cycle progression. Recent research on histone phosphorylation has demonstrated that nearly all histone types are phosphorylated at specific residues and that these modifications act as a critical intermediate step in chromosome condensation during cell division, transcriptional regulation, and DNA damage repair. As with all young fields, apparently conflicting and sometimes controversial observations about histone phosphorylations and their true functions in different species are found in the literature. Accumulating evidence suggests that instead of functioning strictly as part of a general code, histone phosphorylation probably functions by establishing cross talk with other histone modifications and serving as a platform for recruitment or release of effector proteins, leading to a downstream cascade of events. Here we extensively review published information on the complexities of histone phosphorylation, the roles of proteins recognizing these modifications and the resuting physiological outcome, and, importantly, future challenges and opportunities in this fast-moving field.

Fig. 1.

(Top) Cartoon of the human H2AX histone showing all the serine, threonine, tyrosine, and histidine residues. Residues that have been reported to be phosphorylated are shown with a red “P.” (Bottom) Schematic of some of the events occurring at S139 in mammalian cells. Events that occur in yeast cells at the corresponding S129 are summarized in Table 1. (For details, see Table 1 and the text.)

Fig. 2.

(Top) Cartoon of the human H2B histone showing all the serine, threonine, tyrosine, and histidine residues. Residues that have been reported to be phosphorylated are shown with a red “P.” Yeast has a serine at residue 10 (green), and Drosophila has a serine at residue 33 (yellow), both of which are also phosphorylated. (Bottom) Schematic of the events occurring at S36. (For details, see Table 1 and the text.)

Fig. 3.

(Top) Cartoon of the human H3 histone showing all the serine, threonine, tyrosine, and histidine residues. Residues that have been reported to be phosphorylated are shown with a red “P.” (Bottom) Schematic of some of the events occurring at T11. (For details, see Table 1 and the text.)

Fig. 4.

Cartoon of the human H4 histone showing all the serine, threonine, tyrosine, and histidine residues. Residues that have been reported to be phosphorylated are shown with a red “P.” (Bottom) Schematic of the events occurring at S1. (For details, see Table 1 and the text.)