RNA sequencing of pancreatic circulating tumour cells implicates WNT signalling in metastasis

A new method allows the collection of circulating tumour cells (CTCs) despite their rarity; transcriptome sequencing of CTCs could allow identification of pathways involved in metastasis. WNT implicated in metastasis Circulating tumour cells (CTCs) shed from primary tumours are thought to initiate metastasis in distant organs. They are increasingly appreciated as potential biomarkers of disease progression and therapeutic response in patients with cancer. Their low frequency, in comparison with normal blood cells, means that it is a major technological challenge to characterize them fully. Daniel Haber and colleagues have optimized previous microfluidic approaches to capture CTCs from an endogenous mouse pancreatic cancer model. Using RNA sequencing, RNA transcripts enriched in CTCs compared with the primary tumours were identified. The proto-oncogene protein Wnt2 was also identified. The authors were also able to capture CTCs from patients with pancreatic cancer patients, which, like their mouse counterparts, show evidence of upregulation of WNT signalling. Circulating tumour cells (CTCs) shed into blood from primary cancers include putative precursors that initiate distal metastases 1 . Although these cells are extraordinarily rare, they may identify cellular pathways contributing to the blood-borne dissemination of cancer. Here, we adapted a microfluidic device 2 for efficient capture of CTCs from an endogenous mouse pancreatic cancer model 3 and subjected CTCs to single-molecule RNA sequencing 4 , identifying Wnt2 as a candidate gene enriched in CTCs. Expression of WNT2 in pancreatic cancer cells suppresses anoikis, enhances anchorage-independent sphere formation, and increases metastatic propensity in vivo . This effect is correlated with fibronectin upregulation and suppressed by inhibition of MAP3K7 (also known as TAK1) kinase. In humans, formation of non-adherent tumour spheres by pancreatic cancer cells is associated with upregulation of multiple WNT genes, and pancreatic CTCs revealed enrichment for WNT signalling in 5 out of 11 cases. Thus, molecular analysis of CTCs may identify candidate therapeutic targets to prevent the distal spread of cancer.