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MicroRNA-mediated suppression of the TGF-β pathway confers transmissible and reversible CDK4/6 inhibitor resistance (RNA-Seq)

ABSTRACT: CDK4/6 inhibition is now part of the standard armamentarium for patients with estrogen receptor (ER)-positive breast cancer, so that defining mechanisms of resistance is a pressing issue. Here, we identify increased CDK6 expression as a key determinant of acquired resistance after exposure to palbociclib in ER-positive breast cancer cells. Increased CDK6 in resistant cells was dependent on TGF-β pathway suppression via miR-432-5p expression. Exosomal miR-432-5p expression mediated transfer of the resistance phenotype between neighboring cell populations. We confirmed these data in pre-treatment and post-progression biopsies from a parotid cancer patient who had responded to ribociclib, demonstrating clinical relevance of this mechanism. Additionally, the CDK4/6 inhibitor resistance phenotype can be reversed in vitro and in vivo by a prolonged drug holiday.

ORGANISM(S): Homo sapiens

PROVIDER: GSE117746 | GEO | 2019/03/04

REPOSITORIES: GEO

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Project description:The p53 tumour suppressor is a transcription factor that can regulate the expression of numerous genes encoding either proteins or microRNAs (miRNAs). The predominant outcomes of a typical p53 response are the initiation of apoptotic cascades and the activation of cell cycle checkpoints. HT29-tsp53 cells express a temperature sensitive variant of p53 and in the absence of exogenous DNA damage, these cells preferentially undergo G1 phase cell cycle arrest at the permissive temperature that correlates with increased expression of the cyclin-dependent kinase inhibitor p21WAF1. Recent evidence also suggests that a variety of miRNAs can induce G1 arrest by inhibiting the expression of proteins like CDK4 and CDK6. Here we used oligonucleotide microarrays to identify p53-regulated miRNAs that are induced in these cells undergoing G1 arrest. At the permissive temperature, the expression of several miRNAs was increased through a combination of either transcriptional or post-transcriptional regulation. In particular, miR-34a-5p, miR-143-3p and miR-145-5p were strongly induced and they reached levels comparable to that of reference miRNAs (miR-191 and miR-103). Importantly, miR-34a-5p and miR-145-5p are known to silence the Cdk4 and/or Cdk6 G1 cyclin-dependent kinases (cdks). Surprisingly, there was no p53-dependent decrease in the expression of either of these G1 cdks. To search for other potential targets of p53-regulated miRNAs, p53-downregulated mRNAs were identified through parallel microarray analysis of mRNA expression. Once again, there was no clear effect of p53 on the repression of mRNAs under these conditions despite a remarkable increase in p53-induced mRNA expression. Therefore, despite a strong p53 transcriptional response, there was no clear evidence that p53-responsive miRNA contributed to gene silencing. Taken together, the changes in cell cycle distribution in this cell line at the permissive temperature is likely attributable to transcriptional upregulation of the CDKN1A mRNA and p21WAF1 protein and not to the down regulation of CDK4 or CDK6 by p53-regulated miRNAs. Two independent experiments were performed with 2 samples in each experiment (1 control and 1 treatment condition). In the control sample, RNA was isolated cells maintained at the restrictive temperature (37ËC). The treatment treated sample, was incubated for 16 hours at the permissive temperature (32ËC).

Project description:Cdk4 and Cdk6 are two related kinases that bind D-type cyclins and regulate cell cycle progression. Due to their relevance in cancer, Cdk4/6 inhibitors are currently in advanced clinical trials in multiple tumor types. Cdk4/6 are inhibited by INK4 proteins that exert tumor suppressing functions. To test the significance of this inhibitory mechanism we have generated knock-in mice that express a Cdk6 mutant (Cdk6 R31C) insensitive to INK4-mediated inhibition. Cdk6R/R mice display altered development of the hematopoietic system without resulting in enhanced tumor susceptibility, either in the presence or absence of p53. The presence of the Cdk6 R31C allele results in defective potential of hematopoietic progenitors in adoptive transfer assays or after induced damage. These defects are rescued after complete insensitivity to INK4 inhibitors in Cdk4R/R; Cdk6R/R double mutant mice, and INK4-resistant mice display increased susceptibility to hematopoietic and endocrine tumors. In BCR-ABL-transformed hematopoietic cells, the presence of the Cdk6 R31C allele results in increased binding of p16INK4a to wild-type Cdk4, whereas the double mutant is fully insensitive to INK4 inhibitors resulting in accelerated disease onset. Our observations reveal that Cdk4 and Cdk6 cooperate in tumor development and suggest a role for Cdk6 in buffering INK4 protein levels thus contributing to the development of hematopoietic tumors. The presence of the Cdk4 R24C and Cdk6 R31C alleles results in relevant changes in the expression profiles of cancer cells including deregulation of apoptosis and other processes. p185BCR-ABL1 was used to transform wild-type or double knock-in Cdk4 R24C; Cdk6 R31C fetal livers. Cell lines were isolated as spontaneous immortal and transformed clones after transduction of fetal liver with a p185 BCR-ABL1-transgene. RNA was isolated from asynchronous cultures. Two-condition experiment, Cdk4R-Cdk6R cells versus wild-type cells. Biological replicates: 3 control replicates, 3 transfected replicates.

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MicroRNA-mediated suppression of the TGF-β pathway confers transmissible and reversible CDK4/6 inhibitor resistance (RNA-Seq)

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