Hemmingsson, O. | bioRxiv Science

bioRxiv2023

MET functions in tumour progression and therapy resistance are repressed by intronic polyadenylation

Intronic polyadenylation (IPA) leads to the production of transcript isoforms with alternative last exons in thousands of mammalian genes. Widespread regulation of IPA isoforms was observed during oncogenic transformation and in tumours versus healthy tissues, and several IPA isoforms were involved in oncogenesis. However, little is known about the potential involvement of IPA in tumour progression, such as cancer cell invasiveness and metastasis, and in resistance to anticancer therapies. Here, we show that an IPA isoform of MET (short MET) whose production is inhibited by U1 snRNP (U1), an essential ribonucleoprotein complex that recognizes the 5 exon-intron junction of pre-mRNA, is associated with better prognosis in breast cancer. Induction of the short MET isoform, using a steric-blocking antisense oligonucleotide targeting the U1 binding site in the vicinity of the short MET alternative polyadenylation site, antagonizes cell invasiveness. U1 blockade with an antisense oligonucleotide targeting the U1 snRNA also decreases breast cancer cell invasiveness, in both human and mouse cancer cell models, and this effect involves IPA induction in MET and several genes belonging to the RAS/RAF/MAPK signalling pathway. Finally, short MET relieves melanoma cell resistance to MAPK cascade-targeted therapy in vitro and in vivo. IPA isoform levels of MET and a few other genes (mTOR, EGFR and CTNNA1) help predict such resistance in patients. Altogether, our findings provide evidence for a role of IPA in both cancer cell invasiveness and resistance to therapy. This suggests that IPA isoforms can be exploited as biomarkers and therapeutic targets to combat tumour progression.

molecular biology↗

bioRxiv2019

ASNA-1 oxidation induced by cisplatin exposure enhances its cytotoxicity by selectively perturbing tail anchored protein targeting

Cisplatin is a frontline cancer treatment, but intrinsic or acquired resistance is common. We previously showed that ASNA-1/TRC40 inactivation increases cisplatin sensitivity in mammalian cells and a Caenorhabditis elegans asna-1 knockdown model. ASNA-1 has conserved tail-anchored protein (TAP) targeting and insulin secretion functions. Here we examined the mechanism of ASNA-1 action. We show that ASNA-1 exists in two physiologically-responsive redox states with separable TAP-targeting and insulin secretion functions. Cisplatin-generated ROS targeted ASNA-1 oxidation, resulting in a selective targeting defect of an ASNA-1-dependent TAP. Increased ASNA-1 oxidation sensitized worms to cisplatin cytotoxicity. Mutants with a redox balance favoring oxidized ASNA-1 were cisplatin sensitive as null mutants by diverting ASNA-1 away from its TAP-targeting role and instead perturbing endoplasmic reticulum (ER) function. Mutations in the ASNA-1 receptor required for TAP insertion induced equivalent cisplatin sensitivity. We reveal a previously undescribed cellular dysfunction induced by cisplatin, identify a cisplatin target, and show that drug exposure causes TAP targeting-induced ER dysfunction. Therapeutic oxidation of ASNA-1 could be a clinically useful means to increase cisplatin sensitivity, reduce cytotoxic drug doses, and counteract cisplatin resistance.\n\nAUTHOR SUMMARYCisplatin is a very effective anti-cancer drug and is widely used as a frontline treatment. However, tumor resistance limits its use. Tumor re-sensitization would improve cancer treatment. ASNA-1/TRC40 knockdown in Caenorhabditis elegans and mammals results in cisplatin hypersensitivity, but the underlying mechanistic details are largely unknown. We show that in C. elegans ASNA-1 mutants, increased cisplatin killing is coupled with delocalization of a tail-anchored protein, SEC-61{beta}, a membrane protein that should reach the ER and is instead mistargeted. Like its homologs, the reduced form of worm ASNA-1 is needed for targeting activity. Targeting is blocked upon ASNA-1 oxidation after cisplatin treatment, likely via reactive oxygen species (ROS) generated by cisplatin treatment. Nevertheless, the oxidized form of the protein can execute other functions like insulin secretion. We show also that mutants with high oxidized ASNA-1 levels are cisplatin sensitive. Additionally, cisplatin induced mistargeting strictly acts through ASNA-1 inactivation. Thus, we define a pathway from cisplatin exposure that targets protein (ASNA-1) inactivation, consequently leading to mis-targeting of proteins that need ASNA-1 for their maturation. This multi-step process provides vital information about likely proteins that can be targeted by drugs to enhance cisplatin mediated killing and improve chemotherapy.\n\nSUMMARY STATEMENTSensitizing tumors to cisplatin would be of considerable therapeutic benefit. Here we show a novel mechanism of cisplatin sensitization via oxidation of ASNA-1 in a Caenorhabditis elegans model.

cell biology↗