Nucleophosmin is essential for ribosomal protein L5 nuclear export

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Nucleophosmin (NPM/B23) is a crucial regulator of cell processes like ribosome biogenesis and genomic integrity.
• NPM's precise functions and mechanisms remain largely unknown.
• NPM loss leads to significant developmental and growth disruptions.

Purpose of the Study:

• To elucidate the mechanisms of NPM function, particularly its role in nucleocytoplasmic shuttling.
• To identify NPM trafficking targets and understand their functional implications.
• To investigate NPM's role in ribosome biogenesis and nuclear export.

Main Methods:

• Biochemical purification of NPM-bound protein complexes from HeLa cell lysates.
• Analysis of NPM-rpL5 interaction and colocalization.
• Assessment of NPM shuttling inhibition and NPM loss effects on rpL5 and 5S rRNA nuclear export.

Main Results:

• NPM utilizes a CRM1-dependent nuclear export sequence for nucleocytoplasmic shuttling.
• Ribosomal protein L5 (rpL5) was identified as an NPM-binding partner.
• NPM directly interacts with rpL5, facilitating its colocalization with ribosomal subunits and polysomes.
• Inhibition of NPM shuttling or NPM depletion blocked rpL5 and 5S rRNA nuclear export, causing cell cycle arrest.

Conclusions:

• NPM plays a vital role in the nuclear export of rpL5 and 5S rRNA.
• NPM's nucleocytoplasmic shuttling provides essential chaperoning activity for rpL5/5S.
• This chaperoning function is critical for ribosome biogenesis and cell cycle progression.