The human box C/D snoRNAs U3 and U8 are required for pre-rRNA processing and tumorigenesis

Area of Science:

• Molecular Biology
• Cancer Research
• Genetics

Background:

• Small nucleolar RNAs (snoRNAs) are increasingly recognized for their roles in both promoting and suppressing tumors, but their precise functions in tumorigenesis are not fully understood.
• Specific box C/D snoRNAs, U3 and U8, are found at higher levels in breast cancers, suggesting a potential link to cancer development.

Purpose of the Study:

• To investigate the roles of human U3 and U8 snoRNAs in ribosome biogenesis, nucleolar structure, and their impact on tumorigenesis.
• To elucidate the mechanisms by which U3 and U8 influence cancer cell behavior and tumor growth.

Main Methods:

• Functional characterization of U3 and U8 in human breast (MCF-7) and lung (H1944) cancer cell lines.
• Assessment of pre-ribosomal RNA (rRNA) processing and its effect on ribosomal subunit synthesis.
• Analysis of p53-dependent anti-tumor stress responses involving ribosomal proteins uL5 and uL18.
• Evaluation of tumor growth and metabolic activity in a mouse xenograft model following U3 or U8 depletion.

Main Results:

• U3 and U8 are essential for pre-rRNA processing, critical for the synthesis of both small and large ribosomal subunits.
• Depletion of U3 or U8 activates a potent p53-dependent anti-tumor stress response mediated by ribosomal proteins uL5 and uL18.
• Nucleolar structure integrity is more sensitive to U3/U8 perturbations in lung cancer cells compared to breast cancer cells.
• U3 suppression reduced tumor growth and metabolic activity, while U8 depletion abolished tumorigenic potential in vivo.
• U3-suppressed tumors exhibited heterogeneous metabolic tracer uptake, suggesting novel regulatory roles in mRNA metabolism.

Conclusions:

• U3 and U8 play critical roles in ribosome biogenesis and are implicated in regulating tumor growth and metabolic activity.
• The p53 pathway is a key mediator of the anti-tumor effects observed upon U3 or U8 depletion.
• Further research into the non-conventional functions of U3, potentially in mRNA metabolism, is warranted for a comprehensive understanding of its role in cancer.