PCa is a major malignancy affecting the male population worldwide, and effective therapeutic options for advanced-stage PCa, especially metastatic PCa, are still scarce . As the most wide-ranging posttranscriptional modification, N6-methyladenosine (m6A) is strongly correlated with cancer cell proliferation, progression and metastasis . In PCa, however, relevant studies are lacking, and there are no prediction models based on m6A regulators to evaluate the prognosis of metastatic PCa.
In this study, we found that the mRNA expression of most genes did not exhibit prominent differences between primary and metastatic samples, except for a few genes, such as FMR1 and FTO. We also performed integrative analyses on CNVs and mutation alterations and mRNA expression of m6A regulators in primary, metastatic and NEPC samples. Although few mutations were observed, their biological significance has been verified to be vital during tumour progression. A mutation in METTL14 could facilitate tumour proliferation via the AKT signalling pathway . There is a paucity of studies targeting mutations in m6A regulators in PCa, but in acute myeloid leukaemia, mutations of m6A regulators were predictive of unfavourable prognosis . CNVs are strongly related to mRNA expression. Specifically, copy number gain could foster amplification of genes, and copy number reduction inhibits the expression of genes. Except for a few regulators, such as YTHDF2, FTO and RBM15B, most of them experienced CNV amplification. Amplification of FTO was reported to significantly improve the prognosis of prostate cancer .
However, the same m6A regulator may exert different roles in distinct tumours through diverse mechanisms. Herein, two distinct molecular subgroups of metastatic prostate cancer with obviously distinct characteristics were shown based on 21 m6A regulators related to prognosis. m6Acluster.A was significantly enriched in lysine degradation and the mTOR signalling pathway. While the m6Acluster.B was mainly enriched in arachidonic acid metabolism and steroid hormone biosynthesis. We know that activating mTOR signalling can enhance tumour proliferation and progression via distinct mechanisms, including the enhancement of angiogenesis, glyolytic and lipid metabolism, and inhibition of autophagy . Additionally, m6A regulator expression was higher in m6A clusters. A than in m6Acluster.B. To further investigate the relationship between the expression of m6A regulators and PCa prognosis, METTL14-overexpressing or METTL14 knockdown PC3 and DU145 cell lines were constructed. Similar to previous studies, METTL14 ablation inhibited the proliferation and metastasis capability, while upregulating METTL14 enhanced the proliferation and metastasis of PCa cells .
Furthermore, in this study, the transcriptomic heterogeneity among distinct subgroups of metastatic prostate cancer was found to be markedly related to shearing and RNA transportation. A total of 2330 DEGs were presented as m6A phenotype-related genes. Similar to the m6A regulator clustering results, two distinct genomic subtypes were identified based on m6A phenotype-related genes (2330). Prognosis in m6AGenecluster.A type tumour was dismal, and most m6A regulators were expressed in the m6A cluster. A were higher than in m6AGenecluster.B. Next, we selected the most category-related genes based on the above DEGs and then constructed a prognostic model to provide a reference for treating patients with metastatic prostate cancer. We observed that m6Ascore was significantly correlated with biological functions such as DNA repair and mismatch repair. Similarly, m6Ascores of samples upregulated m6Acluster.A or m6Agenecluster.A were distinctively higher than those in samples overexpressing m6Acluster.B or m6Agenecluster.B. This work implied that m6A regulators play an essential role in the prognosis of metastatic PCa, and patients with high m6A scores may be more appropriate for pharmacy therapy targeted for DNA repair, such as poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis).
In the high m6Ascore groups, the ARscore, mutation and CNV numbers, which were unfavourable factors for prognosis, were correspondingly elevated. In this model, CSNK1D is located on chromosome 17. Gene expression and activity changes in CSNK1D have been observed in distinct cancers . In metastatic HCC, the expression level of CSNK1D was higher than that in nonmetastatic HCC . SLC35E1 (solute carrier family 35, member E1) is a nucleotide sugar transporter carrier. It has been reported that for colorectal liver metastases, SLC35E1 could be predictive of the therapeutic effect of 5-fluorouracil–based chemotherapy . In our validation experiment, silencing CSNK1D or SLC35E1 reduced the proliferation and metastasis of DU145 and PC3 cells, which showed similar effects to the vehicle groups administered olaparib. Furthermore, KDM1A, the first identified demethylase, also termed LSD1 or KIAA0601, can regulate the initiation of tumours . CCCTC-binding factor (CTCF) is a well-known regulator facilitating chromatin into topologically associated domains by enhancing cohesin-mediated loop formation , which is strongly associated with cancer initiation . RBBP4 could promote the malignant progression of colon cancer through the Wnt/β-catenin pathway . CDC23 regulates the tumour cell phenotype and is upregulated in papillary thyroid cancer . Cell division cycle 5-like (CDC5L) protein, a cell phase regulator of the G2/M transition, has been demonstrated to improve bladder cancer cell proliferation, migration and invasion . As an RNA-binding protein, hnRNPA1 can regulate the expression and translation of several mediators involved in tumour initiation and progression .