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  • br significantly decreased by more than


    significantly decreased, by more than 12-fold, upon treatment with PDMP, and by approximately 5-fold upon treatments with siGb3S, STxB, PP2 or FH535, as compared to vehicle treatments (Fig. 5C).
    4. Discussion
    Our present study elucidated that methylation of adenosine in TP53 codon R273H RNA transcripts promotes the selection of m6A-R273H
    TP53-Dox Cells
    Vehicle PDMP NPC
    p53 antibody-IP
    pp53 antibody-IP P
    Western Blot::
    Vehicle PDMP
    Vehicle PDMP
    E. MS Assessment of p53 Following IP with pp53 antibody
    ID probability Peptide sequence
    Mascot Ion score Mascot ID score
    pre-mRNA for splicing and mutant protein expression, which in turn results in drug resistance in cancer SCH 58261 heterozygously carrying TP53 R273H mutation. Both accumulation of genetic mutations and dysre-gulated RNA processing occur in cancer cells, and it has become in-creasingly clear that the latter contributes key components of cancerous behaviors and tumor progression. Recent studies showed that RNA methylation converting adenosine into m6A, and preferential pre-mRNA splicing brought about as a consequence of enhanced pre-mRNA recognition and processing by YTHDF1, YTHDF2 and other m6A-readers, can globally either upregulate or down-regulate expression of genes, including NANOG, POU5F1, KLF4, SOX2, c-MYC, EGFR, ASB2 and RARA, in ways that enrich cancer stem cells and promote tumor progression [49,50]. Our present study, for the first time, indicates that methylation of a single transited adenosine in a mutant codon of pre-mRNA can determine mutant protein expression from heterozygous TP53 R273H mutation. To wit, selective expression of the R273H mu-tant protein in cancer cells relies on the m6A at codon 273, and relevant pre-mRNA structure, which together confer preference for binding to spliceosome and splicing [51]. G-to-A transition is the most common base substitution in gene mutation, and has been reported in other codons (R175H, R248Q) of TP53 missense mutations, as well as in many other genes [7,9,52]. Whether or not m6A production in these cases also leads to preferential splicing to regulate mutant protein ex-pression needs to be investigated in further studies. 
    TP53 missense mutation is an attractive specific target for im-proving cancer treatments, and abolishing preferential p53 mutant protein expression might prove to be more an efficacious strategy thereto. DNA damage stress in cancer cells exposed to anticancer drugs can upregulate expression of mutant proteins, such as R273H, when mutated genes coding for them are present, which at minimum in-variably results in drug resistance, thereby compromising the efficacy of treatments [53] (Fig. 1, Table 1). We hereby advance suppression of m6A levels as a possible approach for quashing mutant p53 protein expression while restoring wt p53 protein expression and function, so as to efficaciously sensitize cancer cells that carry heterozygous R273H mutation (Fig. 1, Table 1). Our current studies also revealed that glycosphingolipids, in parti-cular Gb3, can upregulate the expression of METTL3 via promotion of cSrc/β-catenin signaling, thereby enhancing RNA methylation so as to facilitate or favor mutant protein expression and consequent drug re-sistance. Devising suitable ways of targeting these pivotal pathways, perhaps most profitably in combination, should provide the basis for clinically viable and valuable therapeutic approaches that will improve treatments of cancers found to carry comparably activating mutations of tumor suppressor genes.