CD44-SLC1A2 fusion transcripts in primary colorectal cancer

A CD44-SLC1A2 fusion has recently been discovered in a subset of primary gastric cancers, and an APIP-SLC1A2 fusion has been described in a colon cancer cell line (SNU-C1); however, whether such SLC1A2 fusions occur in primary colorectal cancer (CRC) and whether such fusions are specific for gastrointestinal cancers remain uncertain. In the present study, we examined 90 primary CRCs and 112 primary non-small cell lung cancers (NSCLCs) for CD44-SLC1A2 and APIP-SLC1A2 fusion transcripts using RT-PCR and subsequent sequencing analyses. Although the expression of both types of SLC1A2 fusion transcripts was not detected in any of the NSCLCs, the expression of CD44-SLC1A2, but not the APIP-SLC1A2 fusion transcript, was detected in one (1.1 %) CRC. The CD44-SLC1A2 fusion transcript was expressed in cancerous tissue but not in corresponding non-cancerous tissue, and the fusion occurred between exon 1 of CD44 and exon 2 of SLC1A2; it was expected that a slightly truncated but functional SLC1A2 protein would be produced under the CD44 promoter. A quantitative RT-PCR analysis revealed that SLC1A2 mRNA expression was upregulated in CRC containing SLC1A2 fusion transcripts, while it was downregulated in most other CRCs. The SLC1A2 fusion-positive carcinoma was located on the right-side of colon, was a mucinous adenocarcinoma, was immunohistochemically negative for MSH2 mismatch repair protein, and contained no APC or KRAS mutations. Together, these results suggest that the expression of SLC1A2 fusion transcripts is related to a subset of primary CRCs and may contribute to the elucidation of the characteristics of SLC1A2 fusion-positive CRCs in the future.