Highly Expressed miR-375 is not an Intracellular Oncogene in Merkel Cell Polyomavirus-Associated Merkel Cell Carcinoma

Abstract

miR-375 is a highly abundant miRNA in Merkel cell carcinoma (MCC). In other cancers, it acts as either a tumor suppressor or oncogene. While free-circulating miR-375 serves as a surrogate marker for tumor burden in patients with advanced MCC, its function within MCC cells has not been established. Nearly complete miR-375 knockdown in MCC cell lines was achieved using antagomiRs via nucleofection. The cell viability, growth characteristics, and morphology were not altered by this knockdown. miR-375 target genes and related signaling pathways were determined using Encyclopedia of RNA Interactomes (ENCORI) revealing Hippo signaling and epithelial to mesenchymal transition (EMT)-related genes likely to be regulated. Therefore, their expression was analyzed by multiplexed qRT-PCR after miR-375 knockdown, demonstrating only a limited change in expression. In summary, highly effective miR-375 knockdown in classical MCC cell lines did not significantly change the cell viability, morphology, or oncogenic signaling pathways. These observations render miR-375 an unlikely intracellular oncogene in MCC cells, thus suggesting that likely functions of miR-375 for the intercellular communication of MCC should be addressed.

MicroRNAs as Guardians of the Prostate: Those Who Stand before Cancer. What Do We Really Know about the Role of microRNAs in Prostate Biology?

“…For example, two studies argue that miR-375 suppresses growth in PC-3 cells and two studies claim the opposite. Furthermore, the sobering lack of a phenotype from loss of miR-375 expression in MCC cell lines suggests that miR-375 may have functions outside the tumor cells, as suggested by Fan et al [99] and supported by studies in prostate cancer [114]. An exosomal function of miR-375 must be explored in more detail, as well as the idea that exosomes loaded with sufficient amounts of miR-375 can be transferred to adjacent cells to mediate an effect in the recipient cells.…”

“…The starkest example for the lack of any major effect of miR-375 inhibition comes from Merkel cell carcinoma (MCC) cell lines that express high levels of miR-375. Even almost complete inhibition of miR-375 had almost no effect on the cells in vitro [99]. Only three studies (two on breast cancer cell lines MDA-MB231 and MCF7 and one on miR375 knockout in mouse pancreas) indicate an oncogenic or at least pro-growth effect of miR-375 [100][101][102][103][104][105][106][107][108][109][110][111].…”

“…For example, massive un-physiological overexpression of miR-375 may "always" result in a growth-suppressive phenotype in vitro in prostate cancer cells or for that matter any cancer cell (e.g., oral cancer). To explore this issue in a more unbiased fashion and shed light on the unsatisfactory conclusions about miR-375's role in cancer, we selected ten of the most recent publications [93][94][95][96][97][98][99][100][101][102] and ten of the most cited publications [103][104][105][106][107][108][109][110][111][112] that deal with miR-375 and determined the pro-or anti-growth outcomes of its overexpression or inhibition in these studies. Overexpression using a miR-375 mimic produced growth inhibition and/or induction of apoptosis in 16 of the 17 studies, while miR-375 inhibition had either no effect or mild pro-growth effects in 7 of 10 studies.…”

Expression and Regulatory Network Analysis of Function of Small Nucleolar RNA Host Gene 4 in Hepatocellular Carcinoma

“…20 The Encyclopedia of RNA Interactomes (ENCORI) is an open-source web tool used for studying the ncRNA interactions of CLIP-seq, degradome-seq, and RNA-RNA interactome and RBPs data. 21 The RBPs relevant to SNHG4 were downloaded from the CirclncRNAnet and ENCORI. Subsequently, RBPs coexistent in both databases and which were expressed in HepG2 cells (Human hepatoma cell lines), were screened.…”

New Insights into the Biological and Clinical Aspects of Merkel Cell Carcinoma

“…They show that artesunate represses MCPyV T-antigen expression and inhibits cell growth in vitro and in vivo, suggesting its potential treatment for MCC. Fan et al [5] concede that miR-375 is unlikely an intracellular oncogene in MCC cells and thus may rather serve for intercellular communication; indeed they subsequently published that miR-375 is functional in polarizing cancer associated fibroblasts [6]. Kervarrec et al [7] take on the complexity of cell of origin in MCC, in which they conclude that MCPyV T antigens contribute to the acquisition of Merkel cell-like phenotype in epithelial cells.…”