The METTL3 RNA Methyltransferase Regulates Transcriptional Networks in Prostate Cancer

Abstract

Prostate cancer (PCa) is a leading cause of cancer-related deaths and is driven by aberrant androgen receptor (AR) signalling. For this reason, androgen deprivation therapies (ADTs) that suppress androgen-induced PCa progression either by preventing androgen biosynthesis or via AR signalling inhibition (ARSi) are common treatments. The N6-methyladenosine (m6A) RNA modification is involved in regulating mRNA expression, translation, and alternative splicing, and through these mechanisms has been implicated in cancer development and progression. RNA-m6A is dynamically regulated by the METTL3 RNA methyltransferase complex and the FTO and ALKBH5 demethylases. While there is evidence supporting a role for aberrant METTL3 in many cancer types, including localised PCa, the wider contribution of METTL3, and by inference m6A, in androgen signalling in PCa remains poorly understood. Therefore, the aim of this study was to investigate the expression of METTL3 in PCa patients and study the clinical and functional relevance of METTL3 in PCa. It was found that METTL3 is aberrantly expressed in PCa patient samples and that siRNA-mediated METTL3 knockdown or METTL3-pharmacological inhibition significantly alters the basal and androgen-regulated transcriptome in PCa, which supports targeting m6A as a novel approach to modulate androgen signalling in PCa.

Clinical and molecular significance of the RNA m6A methyltransferase complex in prostate cancer

“…In agreement with a number of other studies in distinct PCa cohorts (Ji et al, 2020;Li B. et al, 2020;Yuan et al, 2020;Haigh et al, 2022), METTL3 expression was significantly higher in PCa compared with non-malignant prostate tissue in the current study. Elevated METTL3 expression was also associated with extraprostatic extension, and by inference associated with poorer patient outcomes (Ball et al, 2015).…”

“…All four components of the m 6 A methylation complex investigated were expressed at both the mRNA and protein level in all cell lines. METTL3 expression was significantly higher in all PCa cell lines relative to the non-malignant PNT1A ( Figure 4A ), as we reported previously ( Haigh et al, 2022 ). Similarly, CBLL1 expression was found to be significantly higher in all PCa cell lines expressing AR ( Figure 4D ), with METTL14 and WTAP expression higher in LNCaP, 22Rv1 and DU145 when compared with PNT1A ( Figures 4B, C , respectively).…”

“…The highest levels of mRNA expression of all four genes were seen in the castrate-sensitive LNCaP and castrate-resistant 22Rv1 cell lines ( p ≤ .01). METTL3 [as previously reported in Haigh et al (2022) ], METTL14, WTAP and CBLL1 protein was expressed in all prostate cell lines examined ( Figure 4E ). Uncropped western blots are presented ( Supplementary Figures S2–S10 ).…”

“… METTL3, METTL14, WTAP and CBLL1 expression in non-malignant and prostate cancer cell lines; mRNA expression analysed by qRT-PCR relative to β-actin (A–D) and protein expression analysed using western blot (E) . METTL3 protein expression as previously reported in Haigh et al (2022) . * p ≤ .05, ** p ≤ .005, *** p ≤ .001, **** p ≤ .0001 by unpaired t -test.…”

“…Given the implication of METTL3 in the development and progression of numerous cancer types, there has been considerable interest in small molecule METTL3 inhibitors, that have recently demonstrated preclinical proof of concept evidence for the treatment of leukaemia ( Yankova et al, 2021 ). Such METTL3 inhibitors may also have utility in solid tumours, including PCa ( Haigh et al, 2022 ).…”