Differential microRNA and metabolic expressions in neuroendocrine and cervical carcinomas

Abstract

MicroRNAs (miRNAs) are important regulators of many biological processes involved in cancer development and progression. However, the functional roles of miRNAs in some cancer types are still poorly understood. The aim of this thesis was to investigate the expressions, targets and functions of specific miRNAs in cervical, adrenocortical and Merkel cell carcinoma.

In Paper I, we characterized the functional roles of miR-944, a miRNA with higher expression in cervical cancer. We showed that miR-944 promotes cell proliferation, migration and invasion. Using Ago2 PAR-CLIP sequencing, we identified 58 candidate targets of miR-944 and validated HECW2 and S100PBP as direct targets of miR-944 by luciferase reporter assays. This study reveals the oncogenic role and novel targets of miR-944 in human cervical cancer cells, suggesting its important role in cervical cancer development and its potential implications as a biomarker of cervical carcinoma or as a therapeutic target.

In Paper II, we showed that the IGF2-H19 locus was consistently deregulated in adrenocortical carcinoma (ACC). We used available proteomic data, to identify a subset of proteins inversely correlated to miRNAs of the IGF2-H19 locus. Interestingly, several of the proteins are involved in mitochondrial respiration, such as NDUFC1, a subunit of mitochondrial respiratory complex I. NDUFC1 was observed to be down-regulated in our ACC cohort and was a predicted miR-483-5p target. Inhibition of miR-483-5p in ACC cells increased NDUFC1 expression and reduced both glycolysis and mitochondrial respiration, suggesting that miR-483-5p controls major energy metabolism and its high expression is required to fuel cellular activies in ACC cells.

In Paper III, we demonstrated that over-expression of miR-375 suppressed cell growth and migration, induced cell cycle arrest and apoptosis in Merkel cell polyomavirus-negative (MCPyV-) Merkel cell carcinoma (MCC). Inhibition of miR-375 suppressed cell growth and increased apoptosis in MCPyV-positive (MCPyV+) MCC. Additionally, we showed that LDHB is a target of miR-375 in MCC as shown by its inverse relationship. Low levels of LDHB are required to maintain cell growth and viability in MCPyV+ MCC, while high levels are required for MCPyV- MCC.

In Paper IV, we revealed that MCPyV oncoproteins suppressed LDHB and promoted glycolysis. Intriguingly, LDHB overexpression could revert the growth-promoting effect of sT or truncated LT, indicating that a low LDHB expression is important for maintenance of cell growth and viability in MCPyV+ cells. Inhibition of glycolysis reduced cell growth and induced apoptosis in MCPyV+ MCC cell lines, whereas the MCPyV- MCC cell lines rely on oxidative phosphorylation for cell growth and viability. These data suggest targeting metabolism as a therapeutic strategy in MCC.

Taken together, this thesis work provides new insights into the crucial roles of miRNAs in the molecular mechanisms of cervical, adrenocortical and Merkel cell carcinomas.