The epitranscriptome: At the crossroad of cancer prognosis

FRA-1 as a Regulator of EMT and Metastasis in Breast Cancer

Among FOS-related components of the dimeric AP-1 transcription factor, the oncoprotein FRA-1 (encoded by FOSL1) is a key regulator of invasion and metastasis. The well-established FRA-1 pro-invasive activity in breast cancer, in which FOSL1 is overexpressed in the TNBC (Triple Negative Breast Cancer)/basal subtypes, correlates with the FRA-1-dependent transcriptional regulation of EMT (Epithelial-to-Mesenchymal Transition). After summarizing the major findings on FRA-1 in breast cancer invasiveness, we discuss the FRA-1 mechanistic links with EMT and cancer cell stemness, mediated by transcriptional and posttranscriptional interactions between FOSL1/FRA-1 and EMT-regulating transcription factors, miRNAs, RNA binding proteins and cytokines, along with other target genes involved in EMT. In addition to the FRA-1/AP-1 effects on the architecture of target promoters, we discuss the diagnostic and prognostic significance of the EMT-related FRA-1 transcriptome, along with therapeutic implications. Finally, we consider several novel perspectives regarding the less explored roles of FRA-1 in the tumor microenvironment and in control of the recently characterized hybrid EMT correlated with cancer cell plasticity, stemness, and metastatic potential. We will also examine the application of emerging technologies, such as single-cell analyses, along with animal models of TNBC and tumor-derived CTCs and PDXs (Circulating Tumor Cells and Patient-Derived Xenografts) for studying the FRA-1-mediated mechanisms in in vivo systems of EMT and metastasis.

MFAP2, upregulated by m1A methylation, promotes colorectal cancer invasiveness via CLK3

BACKGROUND

Distant metastasis is the main cause of mortality in colorectal cancer (CRC) patients. N1-methyladenosine (m1A) is a type of epitranscriptome modification. While its regulatory effect on mRNA and its role in CRC metastasis remain unclear.

METHODS

The m1A methylation profile of mRNAs in CRC was revealed by m1A methylated RNA immunoprecipitation sequencing. The expression of MFAP2 in tumor tissues was measured by immunohistochemistry and then correlated with the clinical characteristics and prognosis of CRC patients. The role of MFAP2 in the invasiveness of CRC cells was evaluated by transwell assays and peritoneal metastatic model in nude mice. The downstream targets of MFAP2 was screened by mass spectrometry analysis. Then the role of MFAP2-CLK3 signaling axis was verified by cotransfecting MFAP2 siRNA and CLK3 plasmid in CRC cells.

RESULTS

Microfibril associated protein 2 (MFAP2) mRNA was overexpressed and m1A-hypermethylated in CRC. High expression of MFAP2 was closely related to lymph node metastasis and distant metastasis, leading to poor prognosis in patients with CRC. In vivo and in vitro studies showed that silencing of MFAP2 inhibited the migration, invasion and metastasis of CRC cells. CDC Like Kinase 3 (CLK3) was a potential downstream target of MFAP2. Further studies showed that MFAP2 depletion might induce autophagic degradation of CLK3, and the role of MFAP2 in the invasiveness of CRC cells was dependent on CLK3.

CONCLUSIONS

Our results uncover a newly identified MFAP2-CLK3 signaling axis, which is a potential therapeutic target for CRC metastasis.

Long Non-Coding RNA H19 Expression Correlates with Autophagy Process in Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) is characterized by poor prognosis and high mortality. The suppression of the long-non-coding RNA H19, counterbalanced by IGF2 over-expression, leads to down-regulation of the autophagy markers, high proliferation rate and metastatic potential in patients affected by ACC. The administration of the deacetylase inhibitors (DACi) panobinostat, trichostatin A (TSA) and SAHA affected the cell viability of H295R monolayer and spheroids and induced the over-expression of H19 and autophagy transcripts. H19 knock down in H295R cells was not able to modulate the expression level of autophagy transcripts. Instead, H19 knock down was able to impede the ability of DACi to modulate the protein level of the autophagy markers. Furthermore, the administration of higher concentration of DACi was able to down-regulate the protein level of Beclin1 and p62 and to induce the conversion of LC3B-I into the active LC3B-II form, thus confirming an active autophagic process. Neither the active protein level nor the activity of caspases 8 and 3 was prompted by the DACi, thus excluding the involvement of the executioners of apoptosis in H295R decay. The DACi restore H19, the autophagy markers and trigger cell death in ACC cells. The re-activation of autophagy would represent a novel strategy for the treatment of patients affected by this severe malignancy.