CstF64: Cell Cycle Regulation and Functional Role in 3′ End Processing of Replication-Dependent Histone mRNAs

Abstract

The 3′ end processing of animal replication-dependent histone mRNAs is activated during G₁/S-phase transition. The processing site is recognized by stem-loop binding protein and the U7 snRNP, but cleavage additionally requires a heat-labile factor (HLF), composed of cleavage/polyadenylation specificity factor, symplekin, and cleavage stimulation factor 64 (CstF64). Although HLF has been shown to be cell cycle regulated, the mechanism of this regulation is unknown. Here we show that levels of CstF64 increase toward the S phase and its depletion affects histone RNA processing, S-phase progression, and cell proliferation. Moreover, analyses of the interactions between CstF64, symplekin, and the U7 snRNP-associated proteins FLASH and Lsm11 indicate that CstF64 is important for recruiting HLF to histone precursor mRNA (pre-mRNA)-resident proteins. Thus, CstF64 is central to the function of HLF and appears to be at least partly responsible for its cell cycle regulation. Additionally, we show that misprocessed histone transcripts generated upon CstF64 depletion mainly accumulate in the nucleus, where they are targets of the exosome machinery, while a small cytoplasmic fraction is partly associated with polysomes.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00791-14.

ACKNOWLEDGMENTS

We are grateful to Judith Trüb for excellent technical support, Gian-Reto Lohrer for performing statistical analyses, and Marc Ruepp and Pamela Nicholson (all associated with the University of Bern) for various materials and discussions. Moreover, we thank Silvia Barabino (University of Milano Bicocca) and Marc Ruepp for helpful comments on the manuscript.

This work was supported by the Swiss National Science Foundation (grants 31003A-120064 and 31003A-135644 to D.S.) and the Kanton Bern.

We have no conflicts of interest.

V.R. performed experimental procedures under the guidance of D.S. E.G. performed experimental procedures under the guidance of D.S. and V.R. V.R. and D.S. conducted the project, designed experiments, and wrote the manuscript.