PIM kinases phosphorylate lactate dehydrogenase A at serine 161 and suppress its nuclear ubiquitination.

Lactate dehydrogenase A (LDHA) is a glycolytic enzyme catalysing the reversible conversion of pyruvate to lactate. It has been implicated as a substrate for PIM kinases, yet the relevant target sites and functional consequences of phosphorylation have remained unknown. Here, we show that all three PIM family members can phosphorylate LDHA at serine 161. When we investigated the physiological consequences of this phosphorylation in PC3 prostate cancer and MCF7 breast cancer cells, we noticed that it suppressed ubiquitin-mediated degradation of nuclear LDHA and promoted interactions between LDHA and 14-3-3 proteins. By contrast, in CRISPR/Cas9-edited knock-out cells lacking all three PIM family members, ubiquitination of nuclear LDHA was dramatically increased followed by its decreased expression. Our data suggest that PIM kinases support nuclear LDHA expression and activities by promoting phosphorylation-dependent interactions of LDHA with 14-3-3ε, which shields nuclear LDHA from ubiquitin-mediated degradation.

PIM kinases inhibit AMPK activation and promote tumorigenicity by phosphorylating LKB1.

BACKGROUND: The oncogenic PIM kinases and the tumor-suppressive LKB1 kinase have both been implicated in the regulation of cell growth and metabolism, albeit in opposite directions. Here we investigated whether these kinases interact with each other to influence AMPK activation and tumorigenic growth of prostate and breast cancer cells. METHODS: We first determined how PIM and LKB1 kinases affect AMPK phosphorylation levels. We then used in vitro kinase assays to demonstrate that LKB1 is phosphorylated by PIM kinases, and site-directed mutagenesis to identify the PIM target sites in LKB1. The cellular functions of PIM and LKB1 kinases were evaluated using either pan-PIM inhibitors or CRISPR/Cas9 genomic editing, with which all three PIM family members and/or LKB1 were knocked out from PC3 prostate and MCF7 breast cancer cell lines. In addition to cell proliferation assays, we examined the effects of PIM and/or LKB1 loss on tumor growth using the chick embryo chorioallantoic membrane (CAM) xenograft model. RESULTS: We provide both genetic and pharmacological evidence to demonstrate that inhibition of PIM expression or activity increases phosphorylation of AMPK at Thr172 in both PC3 and MCF7 cells, but not in their derivatives lacking LKB1. This is explained by our observation that all three PIM family kinases can phosphorylate LKB1 at Ser334. Wild-type LKB1, but not its phosphodeficient derivative, can restore PIM inhibitor-induced AMPK phosphorylation in LKB1 knock-out cells. In the CAM model, loss of LKB1 enhances tumorigenicity of PC3 xenografts, while cells lacking both LKB1 and PIMs exhibit slower proliferation rates and form smaller tumors. CONCLUSION: PIM kinases are novel negative regulators of LKB1 that affect AMPK activity in an LKB1-dependent fashion. The impairment of cell proliferation and tumor growth in cells lacking both LKB1 and PIMs indicates that these kinases possess a shared signaling role in the context of cancer. These data also suggest that PIM inhibitors may be a rational therapeutic option for LKB1-deficient tumors. Video Abstract.

PIM1 accelerates prostate cancer cell motility by phosphorylating actin capping proteins.

BACKGROUND: The PIM family kinases promote cancer cell survival and motility as well as metastatic growth in various types of cancer. We have previously identified several PIM substrates, which support cancer cell migration and invasiveness. However, none of them are known to regulate cellular movements by directly interacting with the actin cytoskeleton. Here we have studied the phosphorylation-dependent effects of PIM1 on actin capping proteins, which bind as heterodimers to the fast-growing actin filament ends and stabilize them. METHODS: Based on a phosphoproteomics screen for novel PIM substrates, we have used kinase assays and fluorescence-based imaging techniques to validate actin capping proteins as PIM1 substrates and interaction partners. We have analysed the functional consequences of capping protein phosphorylation on cell migration and adhesion by using wound healing and real-time impedance-based assays. We have also investigated phosphorylation-dependent effects on actin polymerization by analysing the protective role of capping protein phosphomutants in actin disassembly assays. RESULTS: We have identified capping proteins CAPZA1 and CAPZB2 as PIM1 substrates, and shown that phosphorylation of either of them leads to increased adhesion and migration of human prostate cancer cells. Phosphorylation also reduces the ability of the capping proteins to protect polymerized actin from disassembly. CONCLUSIONS: Our data suggest that PIM kinases are able to induce changes in actin dynamics to support cell adhesion and movement. Thus, we have identified a novel mechanism through which PIM kinases enhance motility and metastatic behaviour of cancer cells. Video abstract.

Rapid and efficient generation of neural progenitors from adult bone marrow stromal cells by hypoxic preconditioning.

BACKGROUND: Bone marrow stromal cells (BMSCs) are attractive as a source of neural progenitors for ex vivo generation of neurons and glia. Limited numbers of this subpopulation, however, hinder translation into autologous cell-based therapy. Here, we demonstrate rapid and efficient conditioning with hypoxia to enrich for these neural progenitor cells prior to further expansion in neurosphere culture. METHOD: Adherent cultures of BMSCs (rat/human) were subjected to 1 % oxygen for 24 h and then subcultured as neurospheres with epidermal growth factor (EGF) and basic fibroblast growth factor supplementation. Neurospheres and cell progeny were monitored immunocytochemically for marker expression. To generate Schwann cell-like cells, neurospheres were plated out and exposed to gliogenic medium. The resulting cells were co-cultured with purified dorsal root ganglia (rat) neurons and then tested for commitment to the Schwann cell fate. Fate-committed Schwann cells were subjected to in vitro myelination assay. RESULTS: Transient hypoxic treatment increased the size and number of neurospheres generated from both rat and human BMSCs. This effect was EGF-dependent and attenuated with the EGF receptor inhibitor erlotinib. Hypoxia did not affect the capacity of neurospheres to generate neuron- or glia-like precursors. Human Schwann cell-like cells generated from hypoxia-treated BMSCs demonstrated expression of S100ß /p75 and capacity for myelination in vitro. CONCLUSION: Enhancing the yield of neural progenitor cells with hypoxic preconditioning of BMSCs in vitro but without inherent risks of genetic manipulation provides a platform for upscaling production of neural cell derivatives for clinical application in cell-based therapy.