Interplay between LARP1 and MYC - a two-way regulation?

Abstract

There is increasing evidence that several steps of carcinogenesis including initiation, progression and chemotherapy resistance are regulated by post-transcriptional mechanisms. One such example is the RNA-binding protein LARP1 which has been shown to drive tumorigenesis and is highly expressed in several epithelial cancers, where it correlates with poor prognosis. Interestingly, there is huge overlap between the transcriptome of MYC and the interactome of LARP1. In this project, I investigated whether there was co-regulation between MYC and LARP1, which could explain the mechanism through which LARP1 promotes cancer progression. In order to determine whether MYC drives the transcription of LARP1, siRNA knockdown of MYC was conducted in the cisplatin-resistant ovarian cancer cell lines OVCAR-3 and OVCAR- 8. While there are numerous ChIP- and RNA-seq datasets available suggesting a strong regulatory mechanism of MYC in various cell lines, only a modest change in LARP1 levels was observed after MYC depletion. To investigate whether MYC directly binds to the LARP1 promoter, chromatin immunoprecipitation was performed and analysed by qPCR. Indeed, MYC strongly binds the long isoform of LARP1, compared to IgG control. The knockdown experiment was repeated with a LARP1 targeting siRNA to analyse a potential stabilisation of MYC by LARP1. Upon LARP1 depletion, there was no significant effect on MYC levels or localisation, assessed by western blot and immunocytochemistry. While MYC had a modest impact on LARP1 expression, this thesis did not demonstrate a direct regulation of MYC by LARP1. Future work will elaborate on the idea that LARP1 regulates the translation of MYC target genes and is therefore a regulator of the âMYC signalâ. Should this prove to be the case, this could evolve as another option to target the â currently â âundruggableâ MYC. Finally, this interaction would implicate LARP1 as a promising target for rational drug design in MYC driven cancers.</p