The PHLPP2 phosphatase is a druggable driver of prostate cancer progression

Phlpp1 alters the murine chondrocyte phospho-proteome during endochondral bone formation

Appendicular skeletal growth and bone mass acquisition are controlled by a variety of growth factors, hormones, and mechanical forces in a dynamic process called endochondral ossification. In long bones, chondrocytes in the growth plate proliferate and undergo hypertrophy to drive bone lengthening and mineralization. Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 and 2 (Phlpp1 and Phlpp2) are serine/threonine protein phosphatases that regulate cell proliferation, survival, and maturation via Akt, PKC, Raf1, S6k, and other intracellular signaling cascades. Germline deletion of Phlpp1 suppresses bone lengthening in growth plate chondrocytes. Here, we demonstrate that Phlpp2 does not regulate endochondral ossification, and we define the molecular differences between Phlpp1 and Phlpp2 in chondrocytes. Phlpp2-/- mice were phenotypically indistinguishable from their wildtype (WT) littermates, with similar bone length, bone mass, and growth plate dynamics. Deletion of Phlpp2 had moderate effects on the chondrocyte transcriptome and proteome compared to WT cells. By contrast, Phlpp1/2-/- (double knockout) mice resembled Phlpp1-/- mice phenotypically and molecularly, as the chondrocyte phospho-proteomes of Phlpp1-/- and Phlpp1/2-/- chondrocytes had similarities and were significantly different from WT and Phlpp2-/- chondrocyte phospho-proteomes. Data integration via multiparametric analysis showed that the transcriptome explained less variation in the data as a result of Phlpp1 or Phlpp2 deletion than proteome or phospho-proteome. Alterations in cell proliferation, collagen fibril organization, and Pdpk1 and Pak1/2 signaling pathways were identified in chondrocytes lacking Phlpp1, while cell cycle processes and Akt1 and Aurka signaling pathways were altered in chondrocytes lacking Phlpp2. These data demonstrate that Phlpp1, and to a lesser extent Phlpp2, regulate multiple and complex signaling cascades across the chondrocyte transcriptome, proteome, and phospho-proteome and that multi-omic data integration can reveal novel putative kinase targets that regulate endochondral ossification.

Dietary pro-oxidant therapy by a vitamin K precursor targets PI 3-kinase VPS34 function

Men taking antioxidant vitamin E supplements have increased prostate cancer (PC) risk. However, whether pro-oxidants protect from PC remained unclear. In this work, we show that a pro-oxidant vitamin K precursor [menadione sodium bisulfite (MSB)] suppresses PC progression in mice, killing cells through an oxidative cell death: MSB antagonizes the essential class III phosphatidylinositol (PI) 3-kinase VPS34-the regulator of endosome identity and sorting-through oxidation of key cysteines, pointing to a redox checkpoint in sorting. Testing MSB in a myotubular myopathy model that is driven by loss of MTM1-the phosphatase antagonist of VPS34-we show that dietary MSB improved muscle histology and function and extended life span. These findings enhance our understanding of pro-oxidant selectivity and show how definition of the pathways they impinge on can give rise to unexpected therapeutic opportunities.

Neuronal alterations in AKT isotype expression in schizophrenia

Schizophrenia is characterized by substantial alterations in brain function, and previous studies suggest insulin signaling pathways, particularly involving AKT, are implicated in the pathophysiology of the disorder. This study demonstrates elevated mRNA expression of AKT1-3 in neurons from schizophrenia subjects, contrary to unchanged or diminished total AKT protein expression reported in previous postmortem studies, suggesting a potential decoupling of transcript and protein levels. Sex-specific differential AKT activity was observed, indicating divergent roles in males and females with schizophrenia. Alongside AKT, upregulation of PDPK1, a critical component of the insulin signaling pathway, and several protein phosphatases known to regulate AKT were detected. Moreover, enhanced expression of the transcription factor FOXO1, a regulator of glucose metabolism, hints at possible compensatory mechanisms related to insulin signaling dysregulation. Findings were largely independent of antipsychotic medication use, suggesting inherent alterations in schizophrenia. These results highlight the significance of AKT and related signaling pathways in schizophrenia, proposing that these changes might represent a compensatory response to a primary defect of canonical insulin signaling pathways. This research underscores the need for a detailed understanding of these signaling pathways for the development of effective therapeutic strategies.

Clonal Lineage Tracing with Somatic Delivery of Recordable Barcodes Reveals Migration Histories of Metastatic Prostate Cancer

The patterns by which primary tumors spread to metastatic sites remain poorly understood. Here, we define patterns of metastatic seeding in prostate cancer using a novel injection-based mouse model-EvoCaP (Evolution in Cancer of the Prostate), featuring aggressive metastatic cancer to bone, liver, lungs, and lymph nodes. To define migration histories between primary and metastatic sites, we used our EvoTraceR pipeline to track distinct tumor clones containing recordable barcodes. We detected widespread intratumoral heterogeneity from the primary tumor in metastatic seeding, with few clonal populations instigating most migration. Metastasis-to-metastasis seeding was uncommon, as most cells remained confined within the tissue. Migration patterns in our model were congruent with human prostate cancer seeding topologies. Our findings support the view of metastatic prostate cancer as a systemic disease driven by waves of aggressive clones expanding their niche, infrequently overcoming constraints that otherwise keep them confined in the primary or metastatic site. Significance: Defining the kinetics of prostate cancer metastasis is critical for developing novel therapeutic strategies. This study uses CRISPR/Cas9-based barcoding technology to accurately define tumor clonal patterns and routes of migration in a novel somatically engineered mouse model (EvoCaP) that recapitulates human prostate cancer using an in-house developed analytical pipeline (EvoTraceR).

Targeting the autophagy-miRNA axis in prostate cancer: toward novel diagnostic and therapeutic strategies

Since prostate cancer is one of the leading causes of cancer-related death, a better understanding of the molecular pathways guiding its development is imperative. A key factor in prostate cancer is autophagy, a cellular mechanism that affects both cell survival and death. Autophagy is essential in maintaining cellular homeostasis. Autophagy is a physiological mechanism wherein redundant or malfunctioning cellular constituents are broken down and recycled. It is essential for preserving cellular homeostasis and is implicated in several physiological and pathological conditions, including cancer. Autophagy has been linked to metastasis, tumor development, and treatment resistance in prostate cancer. The deregulation of miRNAs related to autophagy appears to be a crucial element in the etiology of prostate cancer. These miRNAs influence the destiny of cancer cells by finely regulating autophagic mechanisms. Numerous investigations have emphasized the dual function of specific miRNAs in prostate cancer, which alter autophagy-related pathways to function as either tumor suppressors or oncogenes. Notably, miRNAs have been linked to the control of autophagy and the proliferation, apoptosis, and migration of prostate cancer cells. To create customized therapy approaches, it is imperative to comprehend the dynamic interplay between autophagy and miRNAs in prostate cancer. The identification of key miRNAs provides potential diagnostic and prognostic markers. Unraveling the complex network of lncRNAs, like PCA3, also expands the repertoire of molecular targets for therapeutic interventions. This review explores the intricate interplay between autophagy and miRNAs in prostate cancer, focusing on their regulatory roles in cellular processes ranging from survival to programmed cell death.

LncRNA CCAT1 knockdown suppresses tongue squamous cell carcinoma progression by inhibiting the ubiquitination of PHLPP2

Tongue squamous cell carcinoma (TSCC) is prevailing malignancy in the oral and maxillofacial region, characterized by its high frequency. LncRNA CCAT1 can promote tumorigenesis and progression in many cancers. Here, we investigated the regulatory mechanism by which CCAT1 influences growth and metastasis of TSCC. Levels of CCAT1, WTAP, TRIM46, PHLPP2, AKT, p-AKT, and Ki67 in TSCC tissues and cells were assessed utilizing qRT-PCR, Western blot and IHC. Cell proliferation, migration, and invasion were evaluated utilizing CCK8, colony formation, wound healing and transwell assays. Subcellular localization of CCAT1 was detected utilizing FISH assay. m6A level of CCAT1 was assessed using MeRIP. RNA immunoprecipitation (RIP), Co-immunoprecipitation (Co-IP) and RNA pull down elucidated binding relationship between molecules. Nude mouse tumorigenesis experiments were used to verify the TSCC regulatory function of CCAT1 in vivo. Metastatic pulmonary nodules were observed utilizing hematoxylin and eosin (HE) staining. CCAT1 silencing repressed TSCC cell proliferation, migration and invasion. Expression of CCAT1 was enhanced through N6-methyladenosine (m6A) modification of its RNA, facilitated by WTAP. Moreover, IGF2BP1 up-regulated CCAT1 expression by stabilizing its RNA transcript. CCAT1 bond to PHLPP2, inducing its ubiquitination and activating AKT signaling. CCAT1 mediated the ubiquitination and degradation of PHLPP2 by TRIM46, thereby promoting TSCC growth and metastasis. CCAT1/TRIM46/PHLPP2 axis regulated proliferation and invasion of TSCC cells, implying that CCAT1 would be a novel therapeutic target for TSCC patients.

A germline point mutation in the MYC-FBW7 phosphodegron initiates hematopoietic malignancies

Oncogenic activation of MYC in cancers predominantly involves increased transcription rather than coding region mutations. However, MYC-dependent lymphomas frequently acquire point mutations in the MYC phosphodegron, including at threonine 58 (T58), where phosphorylation permits binding via the FBW7 ubiquitin ligase triggering MYC degradation. To understand how T58 phosphorylation functions in normal cell physiology, we introduced an alanine mutation at T58 (T58A) into the endogenous c-Myc locus in the mouse germline. While MYC-T58A mice develop normally, lymphomas and myeloid leukemias emerge in ∼60% of adult homozygous T58A mice. We found that primitive hematopoietic progenitor cells from MYC-T58A mice exhibit aberrant self-renewal normally associated with hematopoietic stem cells (HSCs) and up-regulate a subset of MYC target genes important in maintaining stem/progenitor cell balance. In lymphocytes, genomic occupancy by MYC-T58A was increased at all promoters compared with WT MYC, while genes differentially expressed in a T58A-dependent manner were significantly more proximal to MYC-bound enhancers. MYC-T58A lymphocyte progenitors exhibited metabolic alterations and decreased activation of inflammatory and apoptotic pathways. Our data demonstrate that a single point mutation stabilizing MYC is sufficient to skew target gene expression, producing a profound gain of function in multipotential hematopoietic progenitors associated with self-renewal and initiation of lymphomas and leukemias.

Neuronal alterations in AKT isotype expression in schizophrenia

Schizophrenia is characterized by substantial alterations in brain function, and previous studies suggest insulin signaling pathways, particularly involving AKT, are implicated in the pathophysiology of the disorder. This study demonstrates elevated mRNA expression of AKT1-3 in neurons from schizophrenia subjects, contrary to unchanged or diminished total AKT protein expression reported in previous postmortem studies, suggesting a potential decoupling of transcript and protein levels. Sex-specific differential AKT activity was observed, indicating divergent roles in males and females with schizophrenia. Alongside AKT, upregulation of PDPK1, a critical component of the insulin signaling pathway, and several protein phosphatases known to regulate AKT were detected. Moreover, enhanced expression of the transcription factor FOXO1, a regulator of glucose metabolism, hints at possible compensatory mechanisms related to insulin signaling dysregulation. Findings were largely independent of antipsychotic medication use, suggesting inherent alterations in schizophrenia. These results highlight the significance of AKT and related signaling pathways in schizophrenia, proposing that these changes might represent a compensatory response to a primary defect of conical insulin signaling pathways. This research underscores the need for a detailed understanding of these signaling pathways for the development of effective therapeutic strategies.

Sinularin stabilizes FOXO3 protein to trigger prostate cancer cell intrinsic apoptosis

Sinularin, a natural product that purified from soft coral, exhibits anti-tumor effects against various human cancers. However, the mechanisms are not well understood. In this study, we demonstrated that Sinularin inhibited the viability of human prostate cancer cells in a dose-dependent manner and displayed significant cytotoxicity only at high concentration against normal prostate epithelial cell RWPE-1. Flow cytometry assay demonstrated that Sinularin induced tumor cell apoptosis. Further investigations revealed that Sinularin exerted anti-tumor activity through intrinsic apoptotic pathway along with up-regulation of pro-apoptotic protein Bax and PUMA, inhibition of anti-apoptotic protein Bcl-2, mitochondrial membrane potential collapses, and release of mitochondrial proteins. Furthermore, we illustrated that Sinularin induced cell apoptosis via up-regulating PUMA through inhibition of FOXO3 degradation by the ubiquitin-proteasome pathway. To explore how Sinularin suppress FOXO3 ubiquitin-proteasome degradation, we tested two important protein kinases AKT and ERK that regulate FOXO3 stabilization. The results revealed that Sinularin stabilized and up-regulated FOXO3 via inhibition of AKT- and ERK1/2-mediated FOXO3 phosphorylation and subsequent ubiquitin-proteasome degradation. Our findings illustrated the potential mechanisms by which Sinularin induced cell apoptosis and Sinularin may be applied as a therapeutic agent for human prostate cancer.

A Germline Point Mutation in the MYC-FBW7 Phosphodegron Initiates Hematopoietic Malignancies

Oncogenic activation of MYC in cancers predominantly involves increased transcription rather than coding region mutations. However, MYC-dependent lymphomas frequently contain point mutations in the MYC phospho-degron, including at threonine-58 (T58), where phosphorylation permits binding by the FBW7 ubiquitin ligase triggering MYC degradation. To understand how T58 phosphorylation functions in normal cell physiology, we introduced an alanine mutation at T58 (T58A) into the endogenous c-Myc locus in the mouse germline. While MYC-T58A mice develop normally, lymphomas and myeloid leukemias emerge in ~60% of adult homozygous T58A mice. We find that primitive hematopoietic progenitor cells from MYC-T58A mice exhibit aberrant self-renewal normally associated with hematopoietic stem cells (HSCs) and upregulate a subset of Myc target genes important in maintaining stem/progenitor cell balance. Genomic occupancy by MYC-T58A was increased at all promoters, compared to WT MYC, while genes differentially expressed in a T58A-dependent manner were significantly more proximal to MYC-bound enhancers. MYC-T58A lymphocyte progenitors exhibited metabolic alterations and decreased activation of inflammatory and apoptotic pathways. Our data demonstrate that a single point mutation in Myc is sufficient to produce a profound gain of function in multipotential hematopoietic progenitors associated with self-renewal and initiation of lymphomas and leukemias.

PHLPP2: A Prognostic Biomarker in Adenocarcinoma of the Rectum

BACKGROUND/AIMS

Adenocarcinoma of the rectum (READ) is typically diagnosed at advanced stages due to a lack of early-onset spe- cific features.

MATERIALS AND METHODS

The study used bioinformatics analysis of READ ribonucleic acid sequencing data from The Cancer Genome Atlas database to identify differentially expressed genes (DEGs). Overlapping genes between DEGs and autophagy-associated genes were screened for prognosis-associated DEGs, which were then validated in the OncoLnc database.

RESULTS

A total of 129 autophagy-associated DEGs were identified, with 17 genes found to be associated with READ prognosis. Multivariate Cox regression analysis revealed that only the PHLPP2 gene was significantly associated with READ prognosis (hazard ratio = 0.442, P = .026), and its low expression correlated with low survival in patients with brain lower-grade glioma (P = .00623) and pancreatic adenocarcinoma (P = .00109).

CONCLUSIONS

PHLPP2 expression may serve as a READ-specific prognostic biomarker and is involved in the PI3K-Akt signaling pathway.

The paracaspase MALT1 is a downstream target of Smad3 and potentiates the crosstalk between TGF-β and NF-kB signaling pathways in cancer cells

TGF-β signaling mediates its biological effects by engaging canonical Smad proteins and crosstalking extensively with other signaling networks, including the NF-kB pathway. The paracaspase MALT1 is an intracellular signaling molecule essential for NF-kB activation downstream of several key cell surface receptors. Despite intensive research on TGF-β and NF-kB interactions, the significance of MALT1 in this context remains undecoded. Here we provide experimental evidence supporting that MALT1 functions to converge these pathways. Using A549 and Huh7 cancer cell line models, we report that TGF-β stimulation enhances MALT1 protein and transcript levels in a time- and dose-dependent manner. Systematic and selective perturbation of TGF-β signaling components identifies MALT1 as a downstream target of Smad3. Rescue experiments in SMAD3 knockout cells confirm that C-terminal phosphorylation of Smad3 is central to MALT1 induction. Corroborating these data, we document that the expression of SMAD3 and MALT1 genes are positively correlated in TCGA cohorts, and we trace the molecular basis of MALT1 elevation to promoter activation. Functional studies in parental as well as NF-kB p65 signaling reporter engineered cells conclusively reveal that MALT1 is paramount for TGF-β-stimulated nuclear translocation and transcriptional activation of NF-kB p65. Furthermore, we find that BCL10 is also implicated in TGF-β activation of NF-kB target genes, potentially coupling the TGF-β-MALT1-NF-kB signaling axis to the CARMA-BCL10-MALT1 (CBM) signalosome. The novel findings of this study indicate that MALT1 is a downstream target of the canonical TGF-β/Smad3 pathway and plays a critical role in modulating TGF-β and NF-kB crosstalk in cancer.

FKBP51 plays an essential role in Akt ubiquitination that requires Hsp90 and PHLPP

FKBP51 plays a relevant role in sustaining cancer cells, particularly melanoma. This cochaperone participates in several signaling pathways. FKBP51 forms a complex with Akt and PHLPP, which is reported to dephosphorylate Akt. Given the recent discovery of a spliced FKBP51 isoform, in this paper, we interrogate the canonical and spliced isoforms in regulation of Akt activation. We show that the TPR domain of FKBP51 mediates Akt ubiquitination at K63, which is an essential step for Akt activation. The spliced FKBP51, lacking such domain, cannot link K63-Ub residues to Akt. Unexpectedly, PHLPP silencing does not foster phosphorylation of Akt, and its overexpression even induces phosphorylation of Akt. PHLPP stabilizes levels of E3-ubiquitin ligase TRAF6 and supports K63-ubiquitination of Akt. The interactome profile of FKBP51 from melanoma cells highlights a relevant role for PHLPP in improving oncogenic hallmarks, particularly, cell proliferation.

Emerging roles of PHLPP phosphatases in the nervous system

It has been more than a decade since the discovery of a novel class of phosphatase, the Pleckstrin Homology (PH) domain Leucine-rich repeat Protein Phosphatases (PHLPP). Over time, they have been recognized as crucial regulators of various cellular processes, such as memory formation, cellular survival and proliferation, maintenance of circadian rhythm, and others, with any deregulation in their expression or cellular localization causing havoc in any cellular system. With the ever-growing number of downstream substrates across multiple tissue systems, a web is emerging wherein the central point is PHLPP. A slight nick in the normal signaling cascade of the two isoforms of PHLPP, namely PHLPP1 and PHLPP2, has been recently found to invoke a variety of neurological disorders including Alzheimer's disease, epileptic seizures, Parkinson's disease, and others, in the neuronal system. Improper regulation of the two isoforms has also been associated with various disease pathologies such as diabetes, cardiovascular disorders, cancer, musculoskeletal disorders, etc. In this review, we have summarized all the current knowledge about PHLPP1 (PHLPP1α and PHLPP1β) and PHLPP2 and their emerging roles in regulating various neuronal signaling pathways to pave the way for a better understanding of the complexities. This would in turn aid in providing context for the development of possible future therapeutic strategies.

Investigating the role of common and rare variants in multiplex multiple sclerosis families reveals an increased burden of common risk variation

Many multiple sclerosis (MS)-associated common risk variants as well as candidate low-frequency and rare variants have been identified; however, approximately half of MS heritability remains unexplained. We studied seven multiplex MS families, six of which with parental consanguinity, to identify genetic factors that increase MS risk. Candidate genomic regions were identified through linkage analysis and homozygosity mapping, and fully penetrant, rare, and low-frequency variants were detected by exome sequencing. Weighted sum score and polygenic risk score (PRS) analyses were conducted in MS families (24 affected, 17 unaffected), 23 sporadic MS cases, 63 individuals in 19 non-MS control families, and 1272 independent, ancestry-matched controls. We found that familial MS cases had a significantly higher common risk variation burden compared with population controls and control families. Sporadic MS cases tended to have a higher PRS compared with familial MS cases, suggesting the presence of a higher rare risk variation burden in the families. In line with this, score distributions among affected and unaffected family members within individual families showed that known susceptibility alleles can explain disease development in some high-risk multiplex families, while in others, additional genetic contributors increase MS risk.

Experimental challenges to modeling prostate cancer heterogeneity

Tumor heterogeneity plays a key role in prostate cancer prognosis, therapy selection, relapse, and acquisition of treatment resistance. Prostate cancer presents a heterogeneous diversity at inter- and intra-tumor and inter-patient levels which are influenced by multiple intrinsic and/or extrinsic factors. Recent studies have started to characterize the complexity of prostate tumors and these different tiers of heterogeneity. In this review, we discuss the most common factors that contribute to tumoral diversity. Moreover, we focus on the description of the in vitro and in vivo approaches, as well as high-throughput technologies, that help to model intra-tumoral diversity. Further understanding tumor heterogeneities and the challenges they present will guide enhanced patient risk stratification, aid the design of more precise therapies, and ultimately help beat this chameleon-like disease.

On the PHLPPside: Emerging roles of PHLPP phosphatases in the heart

PH domain leucine-rich repeat protein phosphatase (PHLPP) is a family of enzymes made up of two isoforms (PHLPP1 and PHLPP2), whose actions modulate intracellular activity via the dephosphorylation of specific serine/threonine (Ser/Thr) residues on proteins such as Akt. Recent data generated in our lab, supported by findings from others, implicates the divergent roles of PHLPP1 and PHLPP2 in maintaining cellular homeostasis since dysregulation of these enzymes has been linked to various pathological states including cardiovascular disease, diabetes, ischemia/reperfusion injury, musculoskeletal disease, and cancer. Therefore, development of therapies to modulate specific isoforms of PHLPP could prove to be therapeutically beneficial in several diseases especially those targeting the cardiovascular system. This review is intended to provide a comprehensive summary of current literature detailing the role of the PHLPP isoforms in the development and progression of heart disease.

Emerging roles of PHLPP phosphatases in metabolism

Over the last decades, research has focused on the role of pleckstrin homology (PH) domain leucine-rich repeat protein phosphatases (PHLPPs) in regulating cellular signaling via PI3K/Akt inhibition. The PKB/Akt signaling imbalances are associated with a variety of illnesses, including various types of cancer, inflammatory response, insulin resistance, and diabetes, demonstrating the relevance of PHLPPs in the prevention of diseases. Furthermore, identification of novel substrates of PHLPPs unveils their role as a critical mediator in various cellular processes. Recently, researchers have explored the increasing complexity of signaling networks involving PHLPPs whereby relevant information of PHLPPs in metabolic diseases was obtained. In this review, we discuss the current knowledge of PHLPPs on the well-known substrates and metabolic regulation, especially in liver, pancreatic beta cell, adipose tissue, and skeletal muscle in relation with the stated diseases. Understanding the context-dependent functions of PHLPPs can lead to a promising treatment strategy for several kinds of metabolic diseases.

Pleckstrin homology (PH) domain and Leucine Rich Repeat Phosphatase 1 (Phlpp1) Suppresses Parathyroid Hormone Receptor 1 (Pth1r) Expression and Signaling During Bone Growth

Endochondral ossification is tightly controlled by a coordinated network of signaling cascades including parathyroid hormone (PTH). Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 (Phlpp1) affects endochondral ossification by suppressing chondrocyte proliferation in the growth plate, longitudinal bone growth, and bone mineralization. As such, Phlpp1-/- mice have shorter long bones, thicker growth plates, and proportionally larger growth plate proliferative zones. The goal of this study was to determine how Phlpp1 deficiency affects PTH signaling during bone growth. Transcriptomic analysis revealed greater PTH receptor 1 (Pth1r) expression and enrichment of histone 3 lysine 27 acetylation (H3K27ac) at the Pth1r promoter in Phlpp1-deficient chondrocytes. PTH (1-34) enhanced and PTH (7-34) attenuated cell proliferation, cAMP signaling, cAMP response element-binding protein (CREB) phosphorylation, and cell metabolic activity in Phlpp1-inhibited chondrocytes. To understand the role of Pth1r action in the endochondral phenotypes of Phlpp1-deficient mice, Phlpp1-/- mice were injected with Pth1r ligand PTH (7-34) daily for the first 4 weeks of life. PTH (7-34) reversed the abnormal growth plate and long-bone growth phenotypes of Phlpp1-/- mice but did not rescue deficits in bone mineral density or trabecular number. These results show that elevated Pth1r expression and signaling contributes to increased proliferation in Phlpp1-/- chondrocytes and shorter bones in Phlpp1-deficient mice. Our data reveal a novel molecular relationship between Phlpp1 and Pth1r in chondrocytes during growth plate development and longitudinal bone growth. © 2021 American Society for Bone and Mineral Research (ASBMR).

PHLPPing the balance: restoration of protein kinase C in cancer

Protein kinase signalling, which transduces external messages to mediate cellular growth and metabolism, is frequently deregulated in human disease, and specifically in cancer. As such, there are 77 kinase inhibitors currently approved for the treatment of human disease by the FDA. Due to their historical association as the receptors for the tumour-promoting phorbol esters, PKC isozymes were initially targeted as oncogenes in cancer. However, a meta-analysis of clinical trials with PKC inhibitors in combination with chemotherapy revealed that these treatments were not advantageous, and instead resulted in poorer outcomes and greater adverse effects. More recent studies suggest that instead of inhibiting PKC, therapies should aim to restore PKC function in cancer: cancer-associated PKC mutations are generally loss-of-function and high PKC protein is protective in many cancers, including most notably KRAS-driven cancers. These recent findings have reframed PKC as having a tumour suppressive function. This review focusses on a potential new mechanism of restoring PKC function in cancer - through targeting of its negative regulator, the Ser/Thr protein phosphatase PHLPP. This phosphatase regulates PKC steady-state levels by regulating the phosphorylation of a key site, the hydrophobic motif, whose phosphorylation is necessary for the stability of the enzyme. We also consider whether the phosphorylation of the potent oncogene KRAS provides a mechanism by which high PKC expression may be protective in KRAS-driven human cancers.

Pinin promotes tumor progression via activating CREB through PI3K/AKT and ERK/MAPK pathway in prostate cancer

Pinin (PNN), a desmosome associated protein, was demonstrated to be over-expressed and act as a tumor-promoting factor in ovarian cancer, hepatocellular carcinoma and colorectal cancer. However, the precise role of PNN in prostate cancer is still unknown. In the study, we reported that PNN was upregulated in prostate cancer tissues and PNN expression was positively associated with Gleason score, tumor stage and tumor metastasis. PNN promoted cell growth and tumorigenicity in vitro and in vivo, and modulated cell growth through driving G1/S transition via CDK6, CDK2, and Cyclin D1 in prostate cancer cells. Furthermore, PNN accelerated cell invasion, migration and EMT processes of prostate cancer cells, accompanied with the up-regulation of MMP-2, MMP-9, N-cadherin, Vimentin and down-regulation of E-cadherin. Mechanism study demonstrated that the proliferation- and motility-promoting effects of PNN on prostate cancer cells dependent on the activation of CREB, which was reversed by CREB inhibition. More important, PNN activated CREB via PI3K/AKT and ERK/MAPK pathway. Collectively, these findings indicated that PNN plays important roles in prostate cancer tumorigenesis and progression and it is a potential therapeutic target for prostate cancer treatment.

Adipocyte PHLPP2 inhibition prevents obesity-induced fatty liver

Increased adiposity confers risk for systemic insulin resistance and type 2 diabetes (T2D), but mechanisms underlying this pathogenic inter-organ crosstalk are incompletely understood. We find PHLPP2 (PH domain and leucine rich repeat protein phosphatase 2), recently identified as the Akt Ser473 phosphatase, to be increased in adipocytes from obese mice. To identify the functional consequence of increased adipocyte PHLPP2 in obese mice, we generated adipocyte-specific PHLPP2 knockout (A-PHLPP2) mice. A-PHLPP2 mice show normal adiposity and glucose metabolism when fed a normal chow diet, but reduced adiposity and improved whole-body glucose tolerance as compared to Cre- controls with high-fat diet (HFD) feeding. Notably, HFD-fed A-PHLPP2 mice show increased HSL phosphorylation, leading to increased lipolysis in vitro and in vivo. Mobilized adipocyte fatty acids are oxidized, leading to increased peroxisome proliferator-activated receptor alpha (PPARα)-dependent adiponectin secretion, which in turn increases hepatic fatty acid oxidation to ameliorate obesity-induced fatty liver. Consistently, adipose PHLPP2 expression is negatively correlated with serum adiponectin levels in obese humans. Overall, these data implicate an adipocyte PHLPP2-HSL-PPARα signaling axis to regulate systemic glucose and lipid homeostasis, and suggest that excess adipocyte PHLPP2 explains decreased adiponectin secretion and downstream metabolic consequence in obesity.

Obesity can be associated with an increased risk of metabolic complications. Here, the authors show that adipocyte-specific ablation of the phosphatase PHLPP2 improves glucose homeostasis in high-fat diet fed obese mice, and that this may be due at least in part to PHLPP2 dephosphorylation of HSL.

PHLPPing the Script: Emerging Roles of PHLPP Phosphatases in Cell Signaling

Whereas protein kinases have been successfully targeted for a variety of diseases, protein phosphatases remain an underutilized therapeutic target, in part because of incomplete characterization of their effects on signaling networks. The pleckstrin homology domain leucine-rich repeat protein phosphatase (PHLPP) is a relatively new player in the cell signaling field, and new roles in controlling the balance among cell survival, proliferation, and apoptosis are being increasingly identified. Originally characterized for its tumor-suppressive function in deactivating the prosurvival kinase Akt, PHLPP may have an opposing role in promoting survival, as recent evidence suggests. Additionally, identification of the transcription factor STAT1 as a substrate unveils a role for PHLPP as a critical mediator of transcriptional programs in cancer and the inflammatory response. This review summarizes the current knowledge of PHLPP as both a tumor suppressor and an oncogene and highlights emerging functions in regulating gene expression and the immune system. Understanding the context-dependent functions of PHLPP is essential for appropriate therapeutic intervention.

The MD Anderson Prostate Cancer Patient-derived Xenograft Series (MDA PCa PDX) Captures the Molecular Landscape of Prostate Cancer and Facilitates Marker-driven Therapy Development

PURPOSE

Advances in prostate cancer lag behind other tumor types partly due to the paucity of models reflecting key milestones in prostate cancer progression. Therefore, we develop clinically relevant prostate cancer models.

EXPERIMENTAL DESIGN

Since 1996, we have generated clinically annotated patient-derived xenografts (PDXs; the MDA PCa PDX series) linked to specific phenotypes reflecting all aspects of clinical prostate cancer.

RESULTS

We studied two cell line-derived xenografts and the first 80 PDXs derived from 47 human prostate cancer donors. Of these, 47 PDXs derived from 22 donors are working models and can be expanded either as cell lines (MDA PCa 2a and 2b) or PDXs. The histopathologic, genomic, and molecular characteristics (androgen receptor, ERG, and PTEN loss) maintain fidelity with the human tumor and correlate with published findings. PDX growth response to mouse castration and targeted therapy illustrate their clinical utility. Comparative genomic hybridization and sequencing show significant differences in oncogenic pathways in pairs of PDXs derived from different areas of the same tumor. We also identified a recurrent focal deletion in an area that includes the speckle-type POZ protein-like (SPOPL) gene in PDXs derived from seven human donors of 28 studied (25%). SPOPL is a SPOP paralog, and SPOP mutations define a molecular subclass of prostate cancer. SPOPL deletions are found in 7% of The Cancer Genome Atlas prostate cancers, which suggests that our cohort is a reliable platform for targeted drug development.

CONCLUSIONS

The MDA PCa PDX series is a dynamic resource that captures the molecular landscape of prostate cancers progressing under novel treatments and enables optimization of prostate cancer-specific, marker-driven therapy.

The PI3K-AKT-mTOR Pathway and Prostate Cancer: At the Crossroads of AR, MAPK, and WNT Signaling

Oncogenic activation of the phosphatidylinositol-3-kinase (PI3K), protein kinase B (PKB/AKT), and mammalian target of rapamycin (mTOR) pathway is a frequent event in prostate cancer that facilitates tumor formation, disease progression and therapeutic resistance. Recent discoveries indicate that the complex crosstalk between the PI3K-AKT-mTOR pathway and multiple interacting cell signaling cascades can further promote prostate cancer progression and influence the sensitivity of prostate cancer cells to PI3K-AKT-mTOR-targeted therapies being explored in the clinic, as well as standard treatment approaches such as androgen-deprivation therapy (ADT). However, the full extent of the PI3K-AKT-mTOR signaling network during prostate tumorigenesis, invasive progression and disease recurrence remains to be determined. In this review, we outline the emerging diversity of the genetic alterations that lead to activated PI3K-AKT-mTOR signaling in prostate cancer, and discuss new mechanistic insights into the interplay between the PI3K-AKT-mTOR pathway and several key interacting oncogenic signaling cascades that can cooperate to facilitate prostate cancer growth and drug-resistance, specifically the androgen receptor (AR), mitogen-activated protein kinase (MAPK), and WNT signaling cascades. Ultimately, deepening our understanding of the broader PI3K-AKT-mTOR signaling network is crucial to aid patient stratification for PI3K-AKT-mTOR pathway-directed therapies, and to discover new therapeutic approaches for prostate cancer that improve patient outcome.

Transcriptional Profiles of Skeletal Muscle Associated With Increasing Severity of White Striping in Commercial Broilers

Development of the white striping (WS) abnormality adversely impacts overall quality of broiler breast meat. Its etiology remains unclear. This study aimed at exploring transcriptional profiles of broiler skeletal muscles exhibiting different WS severity to elucidate molecular mechanisms underlying the development and progression of WS. Total RNA was isolated from pectoralis major of male 7-week-old Ross 308 broilers. The samples were classified as mild (n = 6), moderate (n = 6), or severe (n = 4), based on number and thickness of the white striations on the meat surface. The transcriptome was profiled using a chicken gene expression microarray with one-color hybridization technique. Gene expression patterns of each WS severity level were compared against each other; hence, there were three comparisons: moderate vs. mild (C1), severe vs. moderate (C2), and severe vs. mild (C3). Differentially expressed genes (DEGs) were identified using the combined criteria of false discovery rate ≤ 0.05 and absolute fold change ≥1.2. Differential expression of 91, 136, and 294 transcripts were identified in C1, C2, and C3, respectively. There were no DEGs in common among the three comparisons. Based on pathway analysis, the enriched pathways of C1 were related with impaired homeostasis of macronutrients and small biochemical molecules with disrupted Ca²⁺-related pathways. Decreased abundance of the period circadian regulator suggested the shifted circadian phase when moderate WS developed. The enriched pathways uniquely obtained in C2 were RNA degradation, Ras signaling, cellular senescence, axon guidance, and salivary secretion. The DEGs identified in those pathways might play crucial roles in regulating cellular ion balances and cell-cycle arrest. In C3, the pathways responsible for phosphatidylinositol 3-kinase-Akt signaling, p53 activation, apoptosis, and hypoxia-induced processes were modified. Additionally, pathways associated with a variety of diseases with the DEGs involved in regulation of [Ca²⁺], collagen formation, microtubule-based motor, and immune response were identified. Eight pathways were common to all three comparisons (i.e., calcium signaling, Ras-associated protein 1 signaling, ubiquitin-mediated proteolysis, vascular smooth muscle contraction, oxytocin signaling, and pathway in cancer). The current findings support the role of intracellular ion imbalance, particularly Ca²⁺, oxidative stress, and impaired programmed cell death on WS progression.

PTEN and PHLPP crosstalk in cancer cells and in TGFβ-activated stem cells

Akt kinase regulates several cellular processes, among them growth, proliferation and survival, and has been correlated to neoplastic disease. We report here crosstalk between several Akt regulatory phosphatases that controls the level of the activated form (phosphorylated) of Akt and affects tumor cell aggressiveness. In prostate cancer cell lines, we observed that transient transfection of PTEN decreased the endogenous level of PHLPPs and in contrast, the transient transfection of PHLPPs decreased the endogenous level of PTEN. Furthermore, silencing of PTEN by siRNA resulted in increased PHLPP levels. This phenomenon was not seen in non-transformed cells or in prostate stem cells. This crosstalk promoted cancer cell invasion and was controlled by epigenetically regulated processes where activation of miRs (miR-190 and miR214), the polycomb group of proteins and DNA methylation were involved. The purinergic P2X4 receptor, which has been shown to have a role in wound healing, was identified to be the mediator of this crosstalk. We also studied prostate stem cells and found this crosstalk in the TGFβ1-activated epithelial-mesenchymal transition (EMT). The crosstalk seemed to be a natural part of EMT. In summary, we identify a crosstalk between Akt phosphatases which is not present in non-transformed prostate cells but occurs in cancer cells and stem cells transformed by TGFβ-1. This crosstalk is important for cellular invasion.

BACKGROUND

Phosphatases regulate the Akt oncogene.

RESULTS

Crosstalk between Akt phosphatases in prostate cancer cells and in TGF-β1 activated stem cells but not in non-transformed cells.

CONCLUSION

This back-up mechanism facilitates invasive migration of prostate stem and cancer cells.

SIGNIFICANCE

Characterization of Akt regulation may lead to a better understanding of tumor development and to novel strategies for treatment.

Endothelial Scaffolding Protein ENH (Enigma Homolog Protein) Promotes PHLPP2 (Pleckstrin Homology Domain and Leucine-Rich Repeat Protein Phosphatase 2)-Mediated Dephosphorylation of AKT1 and eNOS (Endothelial NO Synthase) Promoting Vascular Remodeling

OBJECTIVE

A decrease in nitric oxide, leading to vascular smooth muscle cell proliferation, is a common pathological feature of vascular proliferative diseases. Nitric oxide synthesis by eNOS (endothelial nitric oxide synthase) is precisely regulated by protein kinases including AKT1. ENH (enigma homolog protein) is a scaffolding protein for multiple protein kinases, but whether it regulates eNOS activation and vascular remodeling remains unknown. Approach and Results: ENH was upregulated in injured mouse arteries and human atherosclerotic plaques and was associated with coronary artery disease. Neointima formation in carotid arteries, induced by ligation or wire injury, was greatly decreased in endothelium-specific ENH-knockout mice. Vascular ligation reduced AKT and eNOS phosphorylation and nitric oxide production in the endothelium of control but not ENH-knockout mice. ENH was found to interact with AKT1 and its phosphatase PHLPP2 (pleckstrin homology domain and leucine-rich repeat protein phosphatase 2). AKT and eNOS activation were prolonged in VEGF (vascular endothelial growth factor)-induced ENH- or PHLPP2-deficient endothelial cells. Inhibitors of either AKT or eNOS effectively restored ligation-induced neointima formation in ENH-knockout mice. Moreover, endothelium-specific PHLPP2-knockout mice displayed reduced ligation-induced neointima formation. Finally, PHLPP2 was increased in the endothelia of human atherosclerotic plaques and blood cells from patients with coronary artery disease.

CONCLUSIONS

ENH forms a complex with AKT1 and its phosphatase PHLPP2 to negatively regulate AKT1 activation in the artery endothelium. AKT1 deactivation, a decrease in nitric oxide generation, and subsequent neointima formation induced by vascular injury are mediated by ENH and PHLPP2. ENH and PHLPP2 are thus new proatherosclerotic factors that could be therapeutically targeted.

PHLPP2 is a novel biomarker and epigenetic target for the treatment of vitamin C in pancreatic cancer

Epigenetic dysregulations are closely associated with the development of pancreatic ductal adenocarcinoma (PDAC), which is one of the most aggressive malignancies and currently has limited treatment options. Vitamin C (VC), an epigenetic mediator, exerts antitumor effects on several types of cancer. However, the clinical application of VC is limited, particularly in PDAC. Thus, to investigate the antitumor effects and explore the potential clinical application of VC in PDAC, the survival of patients from The Cancer Genome Atlas database were analyzed, and proliferation, apoptosis and migration assays were performed in the present study. It was first established that high expression levels of the sodium‑dependent VC transporter 2, a critical VC transporter, predicted a good prognosis in patients with pancreatic adenocarcinoma. It was further confirmed that VC directly inhibited proliferation, induced apoptosis and suppressed migration of human pancreatic cancer cells. Global 5‑hydroxymethylcytosine (5hmC) content was significantly upregulated in pancreatic cancer cells following VC treatment, predominantly relying on ten‑eleven translocation 2. Furthermore, VC could specifically increase 5hmC levels at the promotor region on PH domain leucine‑rich repeat protein phosphatase 2 (PHLPP2) and enhance PHLPP2 expression levels. When PHLPP2 expression levels were knocked down, VC was able to partially overcome the inhibition of pancreatic cancer cells. These results illustrated a novel and precise mechanism of action of epigenetic alterations that underly the inhibition of VC in pancreatic cancer, and emphasized that PHLPP2 may be a new biomarker and epigenetic target for the clinical treatment of VC in PDAC.

Mutant p53 drives cancer chemotherapy resistance due to loss of function on activating transcription of PUMA

P53 is a critical tumor suppressor gene, activating p53 and its downstream targets to induce apoptosis is a promising way for cancer therapy. However, more than 50% of cancer patients have p53 mutations, which may cause cancer therapy resistance, and the underline mechanism is poorly understood. Here, we found that cell viability decrease and apoptosis induced by p53-dependent traditional drugs in colon cancer cells were eliminated in p53 mutant cells. Mutant p53 did not up-regulate the expression of its direct downstream targets PUMA and p21, due to the inhibition of PUMA transcription. Furthermore, mutant p53 could not bind to the promoter of PUMA to activate its transcription like WT p53 did, while overexpressed WT p53 rescued PUMA-induced subsequent apoptosis. In conclusion, our findings demonstrate mutant p53 may cause chemo-resistance of tumor because of inactivating PUMA transcription, which prompts some new insights for clinical therapy of cancer patients with mutant p53.Abbreviations: CRC: Colorectal cancer; CDKs: Cyclin-dependent kinases; PUMA: p53 up-regulated modulator of apoptosis; PDGF: the platelet-derived growth factor; WT p53: wild-type p53 protein; mutp53: mutant p53 proteins; BAX: Bcl-2-associated X protein; NOXA: Phorbol-12-myristate-13-acetate-induced protein 1.

PHLPP2 as a novel metastatic and prognostic biomarker in non-small cell lung cancer patients

Background

PH domain and leucine‐rich repeat protein phosphatase 2 (PHLPP2) has been reported to be a potent tumor suppressor in many human cancers. However, PHLPP2 has not been fully researched as a putative clinical prognostic biomarker of lung cancer.

Methods

The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases including data on 1383 non‐small cell lung cancer (NSCLC) patients were used to determine PHLPP2 expression. PHLPP2 expression was then examined by immunohistochemistry, and its clinical significance analyzed in 134 NSCLC patients, including 73 patients with adenocarcinoma and 81 with squamous cell carcinoma.

Results

We found PHLPP2 expression to be less pronounced in NSCLC tissue samples than that in nontumoral lung tissues according to data taken from TCGA and GEO datasets; this outcome was further validated by immunohistochemistry assay. The low PHLPP2 expression level was found to be associated with the presence of lymph node metastasis (P = 0.003). Importantly, PHLPP2 was found to be an independent indicator of prognosis for overall (hazard ratio [HR] = 0.520, 95% confidence interval [Cl] = 0.327–0.827; P = 0.006) and disease‐free survival (HR = 0.489, 95% Cl = 0.308–0.775; P = 0.002) in patients with surgically‐resected NSCLC by multivariate analysis.

Conclusion

Taken together, our findings show that PHLPP2 is a robust clinical marker for NSCLC survival and could serve as a potential therapeutic target.

A balancing act: PHLPP2 fine tunes AKT activity and MYC stability in prostate cancer

PTEN loss stimulates prostate tumor progression by sustaining AKT activation. Nowak et al. (2019. J. Cell Biol https://doi.org/10.1083/jcb.201902048) surprisingly show that the AKT-suppressing phosphatase PHLPP2 promotes disease progression in the context of dual PTEN and p53 loss by increasing MYC stability.