Background: Myeloid Cell Leukemia 1 (MCL1), an anti-apoptotic Bcl-2 family protein, is a key regulator of intrinsic apoptosis. Normal cells require strict control over MCL1 expression and aberrant MCL1 expression has been shown linked to the emergence of various diseases and chemoresistance. Previous studies have detailed how MCL1 expression is regulated by multiple mechanisms both transcriptionally and translationally. However, characterization of the post-transcriptional regulators of MCL1 mRNA is limited. Polypyrimidine tract binding protein 1 (PTBP1) is a known regulator of post-transcriptional gene expression that can control mRNA splicing, translation, stability, and localization. In the described study we characterize the impact that PTBP1 has on MCL1 expression, its molecular mechanisms, and its roles on cellular apoptosis.

Methods: Cross-linking Immunoprecipitation (CLIP)-seq data analysis and RNA immunoprecipitation (RIP) were performed to analyze protein interactions with RNA and map the RNA binding sites on the genes of interests. RNA half-life was measured by treating cells with Actinomycin D and extracting total RNA at different time point. Cell viability was measured by the MTS assay and apoptosis was assessed by Annexin V/Propidium Iodide (PI) staining followed by flow cytometry analysis.

Results: Our studies demonstrate that PTBP1 binds to MCL1 mRNA and that knockdown of PTBP1 up-regulates MCL1 expression in cancer. Mechanistically, PTBP1 silencing stabilizes MCL1 mRNA and increases MCL1 mRNA accumulation in cytoplasm. We further identify that this post-transcriptional regulation is mediated by microRNAs and Argonaute2 (Ago2). Moreover, we show that PTBP1 down-regulation is anti-apoptotic to antitubulin chemotherapeutics in a MCL1-dependent manner.

Conclusions: Our findings suggest that PTBP1 is a novel post-transcriptional regulator of MCL1 mRNA by which it controls apoptotic response to antitubulin chemotherapeutics.

Note: This abstract was not presented at the meeting.

Citation Format: William J. Placzek, Jia Cui. PTBP1 modulation of MCL1 mRNA regulates sensitivity to antitubulin chemotherapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4315. doi:10.1158/1538-7445.AM2017-4315