Mammalian WDR12 is a novel member of the Pes1–Bop1 complex and is required for ribosome biogenesis and cell proliferation

Abstract

Target genes of the protooncogene c-myc are implicated in cell cycle and growth control, yet the linkage of both is still unexplored. Here, we show that the products of the nucleolar target genes Pes1 and Bop1 form a stable complex with a novel member, WDR12 (PeBoW complex). Endogenous WDR12, a WD40 repeat protein, is crucial for processing of the 32S precursor ribosomal RNA (rRNA) and cell proliferation. Further, a conditionally expressed dominant-negative mutant of WDR12 also blocks rRNA processing and induces a reversible cell cycle arrest. Mutant WDR12 triggers accumulation of p53 in a p19ARF-independent manner in proliferating cells but not in quiescent cells. Interestingly, a potential homologous complex of Pes1–Bop1–WDR12 in yeast (Nop7p–Erb1p–Ytm1p) is involved in the control of ribosome biogenesis and S phase entry. In conclusion, the integrity of the PeBoW complex is required for ribosome biogenesis and cell proliferation in mammalian cells.

The balance between rRNA and ribosomal protein synthesis up- and downregulates the tumour suppressor p53 in mammalian cells

“…Analysis of polysomal profiles of both starved and rapamycintreated cells (Figures 3c and g) indicated that the global rRNA transcription modulates p53 G Donati et al level of protein synthesis also was reduced in these conditions, in comparison with control cells. These data were consistent with the absence of p53 stabilisation after serum deprivation observed in TGR-1 cells (Ho¨lzel et al, 2005), but not with the reported activation of p53 in WI-38 cells after serum starvation (Bhat et al, 2004), thus suggesting that serum starvation may induce a cell-specific p53 activation.…”

Ribosome biogenesis surveillance: probing the ribosomal protein-Mdm2-p53 pathway

“…Together, the studies on Bop1 show how a nucleolar RNA processing factor involved in discrete steps in rRNA processing can transduce stress signals to p53 through a mediator that has yet to be determined. WDR12, a WD40 repeat protein reported to bind to a Pes1-Bop1 complex, is also essential for rRNA processing, and much like Bop1, alteration of WRD12 function can trigger a reversible p53-induced arrest of the cell cycle (Holzel et al, 2005). As Bop1 and WDR12 are part of a complex, it seems reasonable to speculate that disruption of Pes1-Bop1-WDR12 functional activity may render a similar stress response.…”

Interactions among Ytm1, Erb1, and Nop7 Required for Assembly of the Nop7-Subcomplex in Yeast Preribosomes

“…Two-hybrid assays and GST pulldown experiments show that Nop7 and Ytm1 interact directly with Erb1, but not with each other (Miles et al, 2005). Mammalian counterparts of these three proteins, Pes1, WDR12, and Bop1, also associate with each other to form the PeBoW complex (Hö lzel et al, 2005). Each of these proteins is essential, conserved among eukaryotes, located primarily in the nucleolus, and required for the assembly of 60S ribosomal subunits (Strezoska et al, 2000;Pestov et al, 2001;Adams et al, 2002;Lerch-Gaggl et al, 2002;Oeffinger et al, 2002;Miles et al, 2005;Hö lzel et al, 2005).…”

“…Mammalian counterparts of these three proteins, Pes1, WDR12, and Bop1, also associate with each other to form the PeBoW complex (Hö lzel et al, 2005). Each of these proteins is essential, conserved among eukaryotes, located primarily in the nucleolus, and required for the assembly of 60S ribosomal subunits (Strezoska et al, 2000;Pestov et al, 2001;Adams et al, 2002;Lerch-Gaggl et al, 2002;Oeffinger et al, 2002;Miles et al, 2005;Hö lzel et al, 2005). The Nop7-subcomplex is also a member of a "functional cluster" in yeast; depletion of each of these three proteins causes identical defects in rRNA precursor (pre-rRNA) processing: altered conversion of 27SA 3 pre-rRNA to 27SB S pre-rRNA (Adams et al, 2002;Miles et al, 2005;Oeffinger et al, 2002;Pestov et al, 2001).…”