The phosphatase and tensin homologue deleted on chromosome 10 (PTEN) phosphatase dephosphorylates PIP3, the lipid product of the class I PI 3-kinases, and suppresses the growth and proliferation of many cell types. It has been heavily studied, in large part due to its status as a tumour suppressor, the loss of function of which is observed through diverse mechanisms in many tumour types. Here we present a concise review of our understanding of the PTEN protein and highlight recent advances, particularly in our understanding of its localization and regulation by ubiquitination and SUMOylation.

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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still adapting to its new human host. Attention has focussed on the viral spike protein, but substantial variation has been seen in the ORF8 gene. Here, we show that SARS-CoV-2 ORF8 protein undergoes signal peptide-mediated processing through the endoplasmic reticulum and is secreted as a glycosylated, disulphide-linked dimer. The secreted protein from the prototype SARS-CoV-2 virus had no major effect on viability of a variety of cell types, or on IFN or NF-κB; signalling. However, it modulated cytokine expression from primary CSF1-derived human macrophages, most notably by decreasing IL-6 and IL-8 secretion. Furthermore, a sequence polymorphism L84S that appeared early in the pandemic associated with the Clade S lineage of virus, showed a markedly different effect, of increasing IL-6 production. We conclude that ORF8 sequence polymorphisms can potentially affect SARS-CoV-2 virulence and should therefore be monitored in sequencing-based surveillance.

The lipid and protein tyrosine phosphatase, PTEN, is one of the most frequently mutated tumor suppressors in human cancers and is essential for regulating the oncogenic pro-survival PI3K/AKT signaling pathway. Because of its diverse physiological functions, PTEN has attracted great interest from researchers in multiple research fields. The functional diversity of PTEN demands a collection of delicate regulatory mechanisms, including transcriptional control and posttranslational mechanisms that include ubiquitination. Addition of ubiquitin to PTEN can have several effects on PTEN function, potentially regulating its stability, localization, and activity. In cell and in vitro ubiquitination assays are employed to study the ubiquitination-mediated regulation of PTEN. However, PTEN ubiquitination assays are challenging to perform and the data published from these assays has been of mixed quality. Here we describe protocols to detect PTEN ubiquitination in cultured cells expressing epitope tagged ubiquitin (in cell PTEN ubiquitination assay) and also using purified proteins (in vitro PTEN ubiquitination assay).