HNRNPLL stabilizes mRNA for DNA replication proteins and promotes cell cycle progression in colorectal cancer cells

摘要

Heterogeneous nuclear ribonucleoprotein L‐like (HNRNPLL), an RNA‐binding protein that regulates alternative splicing of pre‐mRNA, has been shown to regulate differentiation of lymphocytes, as well as metastasis of colorectal cancer cells. Here, we show that HNRNPLL promotes cell cycle progression and, hence, proliferation of colorectal cancer cells. Functional annotation analysis of those genes whose expression levels were changed threefold or more in RNA sequencing analysis between SW480 cells overexpressing HNRNPLL and those knocked down for HNRNPLL revealed enrichment of DNA replication‐related genes by HNRNPLL overexpression. Among 13 genes detected in the DNA replication pathway, PCNA,RFC3 and FEN1 showed reproducible upregulation by HNRNPLL overexpression both at mRNA and at protein levels in style="fixed-case">SW480 and style="fixed-case">HT29 cells. Importantly, knockdown of any of these genes alone suppressed the proliferation‐promoting effect induced by style="fixed-case">HNRNPLL overexpression. style="fixed-case">RNA‐immunoprecipitation assay presented a binding of style="fixed-case">FLAG‐tagged style="fixed-case">HNRNPLL to style="fixed-case">mRNA of these genes, and style="fixed-case">HNRNPLL overexpression significantly suppressed the downregulation of these genes during 12 h of actinomycin D treatment, suggesting a role of style="fixed-case">HNRNPLL in style="fixed-case">mRNA stability. Finally, analysis of a public style="fixed-case">RNA sequencing dataset of clinical samples suggested a link between overexpression of style="fixed-case">HNRNPLL and that of style="fixed-case">PCNA, style="fixed-case">RFC3 and style="fixed-case">FEN1. This link was further supported by immunohistochemistry of colorectal cancer clinical samples, whereas expression of style="fixed-case">CDKN1A, which is known to inhibit the cooperative function of style="fixed-case">PCNA, style="fixed-case"> RFC3 and style="fixed-case">FEN1, was negatively associated with style="fixed-case">HNRNPLL expression. These results indicate that style="fixed-case">HNRNPLL stabilizes style="fixed-case">mRNA encoding regulators of style="fixed-case">DNA replication and promotes colorectal cancer cell proliferation.