N6-methyladenosine (m6A) modification in osteosarcoma: expression, function and interaction with noncoding RNAs – an updated review

Figures & data

Figure 1. Dynamic regulation of RNA m6A levels by m6A and the known functions of m6A in the regulation of RNA metabolism. m6A modifications are catalysed by the methyltransferase complex consisting of METTL3 and METTL14, as well as their cofactors WTAP, KIAA1429 and RBM15/15B (writers). The removal of m6A modifications relies on the demethylases FTO and ALKBH5 (erasers). m6A modifications are functionally facilitated by the m6A binding proteins YTHDF1–3, YTHDC1–2, IGF2BP1–3, ELAV1, and HNRNPs (readers).

Figure 2. METTL3 regulates osteosarcoma biology by acting on TRAF6, ATAD2 and LEF1. METTL14 regulates osteosarcoma biological processes by acting on MN1 and caspase-3. WTAP regulates osteosarcoma biological processes through HMBOX1. METTL3, METTL14 and YTHDF regulate osteosarcoma biological processes through TRIM7. FTO regulates osteosarcoma biological processes through KLF3 and DACT1. ALKBH5 regulates the biological process of osteosarcoma through SOCS3 and USP22/RNF40. YTHDF1 regulates the biological process of osteosarcoma through CONT7. ELAVL1 regulates the biological process of osteosarcoma through DRG1.

Table 1. Roles of m6A regulators in osteosarcoma.

m6A regulators	Type	m6A component	Targeted genes/signal pathway	Function	Mechanisms	Reference
METTL3	writer	oncogene	ATAD2	Proliferation↑, invasion and metastasis↑, apoptosis↓	METTL3 knockdown inhibited the protein expression of ATAD2 in osteosarcoma cells	[33]
		oncogene	DRG1	Proliferation↑, invasion and metastasis↑, colony formation abilities↑, apoptosis↓	METTL3 knockdown impaired the stability of DRG1 mRNA	[34]
		oncogene	TRAF6	Proliferation↑, invasion and metastasis↑, apoptosis↓	METTL3 can increase TRAF6 transcript levels	[35]
		oncogene	LEF1/Wnt/β-catenin	Proliferation↑, invasion and metastasis↑	METTL3 silence decreased the m6A methylation and total mRNA level of LEF1, then inhibited the activity of Wnt/β-catenin signalling pathway y	[36]
		oncogene	CONT7	Proliferation↑, invasion and metastasis↑	METTL3 could promote the expression of pre-CONT7 and mature mRNA	[37]
		oncogene	TRIM7/BRMS1	Chemoresistance↑, invasion and migration↑	METTL3 modifies the 3 ’- UTR region of TRIM7, TRIM7 ubiquitinates the k184 site of BRMS1	[38]
		oncogene	ATG5	autophagy↑	METTL3 increasesATG5 mRNA stabilization	[39]
WTAP	writer	oncogene	HMBOX1/PI3K/AKT	Proliferation↑, migration and invasion↑	WTAP repressed HMBOX1 expressed with WTAP-dependent m6A modification at the 3´UTR of HMBOX1	[40]
METTL14	writer	oncogene	MN1	Proliferation↑, migration, and invasion↑	METTL14 enhances MN1 mRNA stability and promotes its translation	[16]
		tumor suppressor	Caspase-3	Proliferation↓, migration, and invasion↓, apoptosis↑	METTL14 can make caspase-3 forms lysed caspase-3	[41]
		tumor suppressor	TRIM7/BRMS1	Chemoresistance↑, invasion, and migration↑	METTL14 modifies the 3 ’- UTR region of TRIM7, TRIM7 ubiquitinates the k184 site of BRMS1	[38]
METTL16	Writer	oncogene	VPS33B	Proliferation↑, migration, and invasion↑	METTL16 facilitating the degradation of VPS33B	[42]
KIAA1429	Writer	oncogene	JAK2/STAT3	Proliferation↑, migration, and invasion↑	/	[43]
FTO	eraser	oncogene	DACT1/Wnt	growth↑, metastasis↑	reducing the RNA stability and protein expression of DACT1	[44]
		oncogene	KLF3	Proliferation↑, migration, and invasion↑	FTO-induced decay of KLF3 mRNA	[45]
ALKBH5	eraser	oncogene	USP22/RNF40	cell-cycle↑, replication↑, and DNA damage repair↑	ALKBH5 destabilizes USP22 and RNF40	[46]
		oncogene	SOCS3	cell-cycle↓, Proliferation↓, and apoptosis↑	ALKBH5 enhances SOCS3 mRNA stability	[47]
YTHDF1	reader	oncogene	YAP	Proliferation↑, invasion, and metastasis↑, colony-formation abilities↑, apoptosis↓	YTHDF1 can promote the recognition and translation of methylated YAP transcripts	[17]
		oncogene	CONT7	Proliferation↑, migration, and invasion↑	YTHDF1 promote CONT7 transcription	[37]
YTHDF2	reader	Tumor suppressor	TRIM7	Chemoresistance↑, invasion, and migration↑	Knocking down YTHDF2 increased the mRNA level and stability of TRIM7	[38]
YTHDF3	reader	oncogene	PGK1	proliferation↑, and aerobic glycolysis↑	YTHDF3 enhances the stability of PGK1 mRNA	[48]
IGF2BP1	reader	oncogene	ERRα	ATP production↑, glucose depletion↑, lactate production↑, and Dox resistance↑	IGF2BP1 enhances the stability of ERRα mRNA	[49]
IGF2BP2	reader	oncogene	MN1	Proliferation↑, invasion, and metastasis↑	IGF2BP2 promotes MN1 translation	[16]
ELAVL1	reader	oncogene	DRG1	Proliferation↑, invasion, and metastasis↑	ELAVL1 mediates the stability of DRG1 mRNA	[34]

Figure 3. Mutual regulation between m6A and ncRNA in osteosarcoma. (a) ALKBH5 weakens the m6A methylation modification of pre-miR-181b-1 and enhances the expression levels of both pre-miR-181b-1 and miR-181-5p. YTHDF2 recognizes pre-miR-181b-1 and enhances its stability, and YTHDF1 recognizes downstream YAP and promotes its translation, together regulating osteosarcoma progression. miR-451a regulates osteosarcoma progression by activating the AKT/mTOR pathway through regulation of YTHDC1-mediated m6A methylation. (b) pre-mRNA forms circRNA by back splicing. circ_0001105 regulation of osteosarcoma progression by sponging miR-766 and activating YTHDF2 expression. METTL3 enhances circNRIP1 expression through m6A modification, and circNRIP1 regulates osteosarcoma progression by sponging miR-199a to promote FOXC2 expression. circ0024831 directly binds to the tudor structural domain of SND1, blocking the recognition of m6A-modified RNA by SND1 and regulating osteosarcoma progression. circ-CTnNB1 interacts with RBM15 and subsequently promotes the expression of HK2, GPI and PGK1 through m6A modification to regulate osteosarcoma progression. (c) ALKBH5 inhibits the degradation of PVT1 and inhibits the binding of YTHDF2 to PVT1, regulating osteosarcoma progression. WTAP increases the stability of FOXD2-AS1 and regulates osteosarcoma progression. METTL3 increases the stability of DANCR and regulates osteosarcoma progression.

Table 2. Mutual regulation between m6A and ncRNA in osteosarcoma.

ncRNA		m6A component	Roles in osteosarcoma	Interplay	Downstream targets	Function	Mechanism	Reference
miRNA	miR-181b-5p	ALKBH5/YTHDF2	Tumor suppressor	ALKBH5/YTHDF2 regulate miR-181b-5p	YAP	Proliferation↓, invasion, and metastasis↓, colony-formation abilities↓, apoptosis↑	YTHDF2 recognizes and degrades pre-miR-181b-1 demethylated by ALKBH5	[17]
	miR − 451a	YTHDC1	Oncogene	miR − 451a target YTHDC1	Akt/mTOR signalling pathway	Proliferation↑, invasion, and metastasis↑	miR-451a-mediated YTHDC1 stabilizes PDPK1 mRNA via the m6A-dependent regulation	[61]
	miR-766	YTHDF2	Oncogene	miR-766 target YTHDF2	/	Proliferation↑, invasion, and metastasis↑	circ_0001105 may act as a ceRNA of miR-766 to relieve the repressive effect of miR-766 on its target YTHDF2.	[64]
circRNA	circNRIP1	METTL3	Oncogene	METTL3 regulate circNRIP1	FOCX2	Proliferation↑, invasion, metastasis↑, and apoptosis↓	circNRIP1 contributed to FOXC2 expression by sponging miR-199a	[65]
	circ-CTNNB1	RBM15	Oncogene	circ-CTNNB1 regulate RBM15		Proliferation↑, invasion, metastasis↑, apoptosis↓	circ-CTNNB1 and RBM15 interact through the RRM1 structural	[56]
	circ_ 0001105	YTHDF2	Tumor suppressor	circ_0001105 target YTHDF2	miR-766	Proliferation↓, invasion, and metastasis↓	circ_0001105 may act as a ceRNA of miR-766 to relieve the repressive effect of miR-766 on its target YTHDF2.	[64]
	circ0024831	SND1	Oncogene	circ0024831 target SND1	COX-2/PGE2	Proliferation↑	SND1 can recognize m6A-modified mRNA and regulate target mRNA stability.	[63]
lncRNA	DANCR	METTL3	Oncogene	METTL3 regulate DANCR	/	Proliferation↑, invasion, and metastasis↑	METTL3 contributes to progression by increasing DANCR mRNA stability via m6A modification	[51]
	PVT1	ALKBH5/YTHDF2	Oncogene	ALKBH5/YTHDF2 regulate PVT1	/	Proliferation↑	ALKBH5 demethylates PVT1, which is subsequently recognized by YTHDF2 and inhibits its degradation	[59]
	FOXD2-AS1	WTAP	Oncogene	WTAP regulate FOXD2-AS1	FOXM1	Proliferation↑, invasion and metastasis↑	WTAP enhanced the stability of FOXD2-AS1	[54]

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