HNRNPLL, a newly identified colorectal cancer metastasis suppressor, modulates alternative splicing of CD44 during epithelial-mesenchymal transition.

OBJECTIVE: Despite the recent advances in treatment of colon cancer, the prognosis is unfavourable for patients with distant metastases. The aim of this study was to identify targets for prevention and/or therapy of colon cancer metastasis.

DESIGN: CMT93 cells, a murine rectal cancer cell line with poor metastasising activity, were transduced with lentiviral shRNA library and transplanted into the rectum of syngeneic C57BL/6 mice. Genomic DNA was collected from metastatic lesions, and the integrated shRNA were retrieved by PCR for sequencing, followed by identification of the candidate genes targeted by the shRNA.

RESULTS: The genome-wide shRNA library screen identified Hnrnpll ( heterogeneous nuclear ribonucleoprotein L-like ) encoding a pre-mRNA splicing factor as a candidate metastasis suppressor gene. Knockdown of Hnrnpll enhanced matrigel invasion activity of colon cancer cells in vitro, as well as their metastatic ability in vivo. An RNA-immunoprecipitation analysis showed Hnrnpll-binding to Cd44 pre-mRNAs, and the level of Cd44 variable exon 6 ( Cd44v6 ) , a poor prognosis marker of colorectal cancer, was increased by knocking down Hnrnpll . A neutralising Cd44v6 antibody suppressed the matrigel invasion ability induced by Hnrnpll knockdown. HNRNPLL expression was downregulated when colon cancer cells were induced to undergo epithelial-mesenchymal transition (EMT). Immunohistochemistry of clinical samples indicated that colorectal cancer cells with low E-cadherin expression at the invasion front exhibited decreased HNRNPLL expression.

CONCLUSIONS: HNRNPLL is a novel metastasis suppressor of colorectal cancer, and modulates alternative splicing of CD44 during EMT.