Snord67 promotes lymph node metastasis and regulates U6-mediated alternative splicing in breast cancer

Small nucleolar RNAs (snoRNAs) have long been considered housekeeping genes, important for ribosomal biogenesis and protein synthesis. However, there is increasing evidence that this largely ignored class of non-coding RNAs (ncRNAs) also have wide-ranging, non-canonical functions in diseases, including cancer. SnoRNAs have been shown to have both oncogenic and tumor suppressor roles, yet whether snoRNAs regulate metastasis is unknown. Here we show that expression of certain snoRNAs are enriched in lymph node (LN) metastases in a micro-surgical, immune-competent mouse model of breast cancer. We identify the snoRNA Snord67 as a key regulator of LN metastasis. Knockout of Snord67 resulted in significantly decreased LN tumor growth and subsequent development of distant metastases. This was associated with loss of targeted methylation on the small nuclear RNA U6, a component of the spliceosome. RNA sequencing revealed distinct alternative splicing patterns in Snord67 knockout cells. Using rapid autopsy breast cancer cases, we found that matched human primary tumor and LN metastases revealed similar alternatively spliced genes, including several that are known to contribute to cancer. These results demonstrate that Snord67 is critical for growth of LN metastases and subsequent spread to distant metastases, and suggest that snoRNA-guided modifications of the spliceosome represent a previously unappreciated, yet targetable pathway in cancer.