Abstract
Specificity protein 1 (Sp1) transcription factor (TF) regulates expression of long non-coding RNAs (lncRNAs) in hepatocellular carcinoma (HCC) cells. RNA interference (RNAi) studies showed that among several lncRNAs expressed in HepG2, SNU-449 and SK-Hep-1 cells, highly upregulated in liver cancer (HULC) was regulated not only by Sp1 but also Sp3 and Sp4 in the three cell lines. Knockdown of Sp transcription factors and HULC by RNAi showed that they play important roles in HCC cell proliferation, survival and migration. The relative contribution of Sp1, Sp3, Sp4 and HULC on these responses in HepG2, SNU-449 and SK-Hep-1 cells were cell context- and response-dependent. In the poorly differentiated SK-Hep-1 cells, knockdown of Sp1 or HULC resulted in genomic and morphological changes, indicating that Sp1 and Sp1-regulated HULC are important for maintaining the mesenchymal phenotype in this cell line. Genomic analysis showed an inverse correlation between expression of genes after knockdown of HULC and expression of those genes in liver tumors from patients. The antidiabetic drug metformin down-regulates Sp proteins in pancreatic cancer, and similar results including decreased HULC expression were observed in HepG2, SNU-449 and SK-Hep-1 cells treated with metformin, indicating that metformin and other antineoplastic agents that target Sp proteins may have clinical applications for HCC chemotherapy.
Highlights
Hepatocellular carcinoma (HCC) is one of the leading causes of cancer deaths worldwide and over 500,000 new cases are diagnosed each year [1,2,3]
Using knockdown of specificity protein 1 (Sp1) by RNA interference (RNAi) as a model, we initially investigated the effects of loss of Sp1 on expression of long non-coding RNA (lncRNA) highly expressed in HCC cells, namely Highly upregulated in liver cancer (HULC), lncRNA-high expression in HCC (HEIH), AY129027, DQ786243 and HOTAIR [5] (Fig. 1C)
Sp transcription factors are overexpressed in multiple tumors and cancer cell lines and there is evidence that Sp1 is a negative prognostic factor for patients with several different cancers including HCC [20,21,22,23,24,25,26]
Summary
Hepatocellular carcinoma (HCC) is one of the leading causes of cancer deaths worldwide and over 500,000 new cases are diagnosed each year [1,2,3]. The incidence of HCC is highest in less developed countries where there is widespread hepatitis B virus (HBV) infection. The incidence of HCC in the United States has tripled over the past two decades and this is due, in part, to increased infection with hepatitis C virus (HCV) [1, 2]. Upregulated in liver cancer (HULC) and high expression in HCC (HEIH) are two lncRNAs overexpressed in liver tumors. Both HULC and HEIH play a role in the proliferation of liver cancer cells.
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