IPTEN/I, IPTENP1/I, microRNAs, and ceRNA Networks: Precision Targeting in Cancer Therapeutics

The PTEN gene is an important and well-characterised tumour suppressor, known to be altered in many cancer types. Interestingly, the effect of the loss or mutation of PTEN is not dichotomous, and small changes in PTEN cellular levels can promote cancer development. Less well-known mechanisms regulating PTEN, with emerging importance, include the PTEN–miRNA–PTENP1 axis, which has been shown to play a critical role in the fine tuning of PTEN cellular levels. This mechanism, working at the post-transcriptional level, involves the interplay and competition between the PTEN transcript, its pseudogene long non-coding RNA transcripts, PTENP1, and microRNAs. Our growing knowledge of this mechanism has opened avenues for the development of strategies to alter the cellular levels of PTEN, miRNAs, and PTENP1 as a new frontier in cancer therapy. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a well characterised tumour suppressor, playing a critical role in the maintenance of fundamental cellular processes including cell proliferation, migration, metabolism, and survival. Subtle decreases in cellular levels of PTEN result in the development and progression of cancer, hence there is tight regulation of the expression, activity, and cellular half-life of PTEN at the transcriptional, post-transcriptional, and post-translational levels. PTENP1, the processed pseudogene of PTEN, is an important transcriptional and post-transcriptional regulator of PTEN. PTENP1 expression produces sense and antisense transcripts modulating PTEN expression, in conjunction with miRNAs. Due to the high sequence similarity between PTEN and the PTENP1 sense transcript, the transcripts possess common miRNA binding sites with the potential for PTENP1 to compete for the binding, or ‘sponging’, of miRNAs that would otherwise target the PTEN transcript. PTENP1 therefore acts as a competitive endogenous RNA (ceRNA), competing with PTEN for the binding of specific miRNAs to alter the abundance of PTEN. Transcription from the antisense strand produces two functionally independent isoforms (PTENP1-AS-α and PTENP1-AS-β), which can regulate PTEN transcription. In this review, we provide an overview of the post-transcriptional regulation of PTEN through interaction with its pseudogene, the cellular miRNA milieu and operation of the ceRNA network. Furthermore, its importance in maintaining cellular integrity and how disruption of this PTEN–miRNA–PTENP1 axis may lead to cancer but also