A non-catalytic role for inositol 1,3,4,5,6-pentakisphosphate 2-kinase in the synthesis of ribosomal RNA

TY - JOUR

T1 - A non-catalytic role for inositol 1,3,4,5,6-pentakisphosphate 2-kinase in the synthesis of ribosomal RNA

AU - Brehm, Maria A

AU - Wundenberg, Torsten

AU - Williams, Jason

AU - Mayr, Georg W

AU - Shears, Stephen B

PY - 2013/1/15

Y1 - 2013/1/15

N2 - Fundamental to the life and destiny of every cell is the regulation of protein synthesis through ribosome biogenesis, which begins in the nucleolus with the production of ribosomal RNA (rRNA). Nucleolar organization is a highly dynamic and tightly regulated process; the structural factors that direct nucleolar assembly and disassembly are just as important in controlling rRNA synthesis as are the catalytic activities that synthesize rRNA. Here, we report that a signaling enzyme, inositol 1,3,4,5,6-pentakisphosphate 2-kinase (IP5K) is also a structural component in the nucleolus. We demonstrate that IP5K has functionally significant interactions with three proteins that regulate rRNA synthesis: protein kinase CK2, TCOF1 and upstream-binding-factor (UBF). Through molecular modeling and mutagenic studies, we identified an Arg-Lys-Lys tripeptide located on the surface of IP5K that mediates its association with UBF. Nucleolar IP5K spatial dynamics were sensitive to experimental procedures (serum starvation or addition of actinomycin D) that inhibited rRNA production. We show that IP5K makes stoichiometrically sensitive contributions to the architecture of the nucleoli in intact cells, thereby influencing the degree of rRNA synthesis. Our study adds significantly to the biological significance of IP5K; previously, it was the kinase activity of this protein that had attracted attention. Our demonstration that IP5K 'moonlights' as a molecular scaffold offers an unexpected new example of how the biological sophistication of higher organisms can arise from gene products acquiring multiple functions, rather than by an increase in gene number.

AB - Fundamental to the life and destiny of every cell is the regulation of protein synthesis through ribosome biogenesis, which begins in the nucleolus with the production of ribosomal RNA (rRNA). Nucleolar organization is a highly dynamic and tightly regulated process; the structural factors that direct nucleolar assembly and disassembly are just as important in controlling rRNA synthesis as are the catalytic activities that synthesize rRNA. Here, we report that a signaling enzyme, inositol 1,3,4,5,6-pentakisphosphate 2-kinase (IP5K) is also a structural component in the nucleolus. We demonstrate that IP5K has functionally significant interactions with three proteins that regulate rRNA synthesis: protein kinase CK2, TCOF1 and upstream-binding-factor (UBF). Through molecular modeling and mutagenic studies, we identified an Arg-Lys-Lys tripeptide located on the surface of IP5K that mediates its association with UBF. Nucleolar IP5K spatial dynamics were sensitive to experimental procedures (serum starvation or addition of actinomycin D) that inhibited rRNA production. We show that IP5K makes stoichiometrically sensitive contributions to the architecture of the nucleoli in intact cells, thereby influencing the degree of rRNA synthesis. Our study adds significantly to the biological significance of IP5K; previously, it was the kinase activity of this protein that had attracted attention. Our demonstration that IP5K 'moonlights' as a molecular scaffold offers an unexpected new example of how the biological sophistication of higher organisms can arise from gene products acquiring multiple functions, rather than by an increase in gene number.

KW - Amino Acid Sequence

KW - Cell Line, Tumor

KW - Cell Nucleolus

KW - HeLa Cells

KW - Humans

KW - Inositol

KW - MCF-7 Cells

KW - Microscopy, Fluorescence

KW - Models, Molecular

KW - Molecular Sequence Data

KW - Phosphorylation

KW - Phosphotransferases (Alcohol Group Acceptor)

KW - RNA, Ribosomal

U2 - 10.1242/jcs.110031

DO - 10.1242/jcs.110031

M3 - SCORING: Journal article

C2 - 23203802

VL - 126

SP - 437

EP - 444

JO - J CELL SCI

JF - J CELL SCI

SN - 0021-9533

IS - Pt 2

ER -