PAP-1, a novel target protein of phosphorylation by pim-1 kinase

Role of PIM Kinase Inhibitor in the Treatment of Alzheimer's Disease

Alzheimer's disease (AD), a neurodegenerative disorder, is the most prevalent form of senile dementia, causing progressive deterioration of cognition, behavior, and rational skills. Neuropathologically, AD is characterized by two hallmark proteinaceous aggregates: amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) formed of hyperphosphorylated tau. A significant study has been done to understand how Aβ and/or tau accumulation can alter signaling pathways that affect neuronal function. A conserved protein kinase known as the mammalian target of rapamycin (mTOR) is essential for maintaining the proper balance between protein synthesis and degradation. Overwhelming evidence shows mTOR signaling's primary role in age-dependent cognitive decline and the pathogenesis of AD. Postmortem human AD brains consistently show an upregulation of mTOR signaling. Confocal microscopy findings demonstrated a direct connection between mTOR and intraneuronal Aβ42 through molecular processes of PRAS40 phosphorylation. By attaching to the mTORC1 complex, PRAS40 inhibits the activity of mTOR. Furthermore, inhibiting PRAS40 phosphorylation can stop the Aβ-mediated increase in mTOR activity, indicating that the accumulation of Aβ may aid in PRAS40 phosphorylation. Physiologically, PRAS40 is phosphorylated by PIM1 which is a serine/threonine kinase of proto-oncogene PIM kinase family. Pharmacological inhibition of PIM1 activity prevents the Aβ-induced mTOR hyperactivity in vivo by blocking PRAS40 phosphorylation and restores cognitive impairments by enhancing proteasome function. Recently identified small-molecule PIM1 inhibitors have been developed as potential therapeutic to reduce AD-neuropathology. This comprehensive study aims to address the activity of PIM1 inhibitor that has been tested for the treatment of AD, in addition to the pharmacological and structural aspects of PIM1.

PRPF31-retinitis pigmentosa: Challenges and opportunities for clinical translation

Mutations in pre-mRNA processing factor 31 cause autosomal dominant retinitis pigmentosa (PRPF31-RP), for which there is currently no efficient treatment, making this disease a prime target for the development of novel therapeutic strategies. PRPF31-RP exhibits incomplete penetrance due to haploinsufficiency, in which reduced levels of gene expression from the mutated allele result in disease. A variety of model systems have been used in the investigation of disease etiology and therapy development. In this review, we discuss recent advances in both in vivo and in vitro model systems, evaluating their advantages and limitations in the context of therapy development for PRPF31-RP. Additionally, we describe the latest approaches for treatment, including AAV-mediated gene augmentation, genome editing, and late-stage therapies such as optogenetics, cell transplantation, and retinal prostheses.

Classification of clear cell renal cell carcinoma based on PKM alternative splicing

Clear cell renal cell carcinoma (ccRCC) accounts for 70-80% of kidney cancer diagnoses and displays high molecular and histologic heterogeneity. Hence, it is necessary to reveal the underlying molecular mechanisms involved in progression of ccRCC to better stratify the patients and design effective treatment strategies. Here, we analyzed the survival outcome of ccRCC patients as a consequence of the differential expression of four transcript isoforms of the pyruvate kinase muscle type (PKM). We first extracted a classification biomarker consisting of eight gene pairs whose within-sample relative expression orderings (REOs) could be used to robustly classify the patients into two groups with distinct molecular characteristics and survival outcomes. Next, we validated our findings in a validation cohort and an independent Japanese ccRCC cohort. We finally performed drug repositioning analysis based on transcriptomic expression profiles of drug-perturbed cancer cell lines and proposed that paracetamol, nizatidine, dimethadione and conessine can be repurposed to treat the patients in one of the subtype of ccRCC whereas chenodeoxycholic acid, fenoterol and hexylcaine can be repurposed to treat the patients in the other subtype.

Disrupted alternative splicing for genes implicated in splicing and ciliogenesis causes PRPF31 retinitis pigmentosa

Mutations in pre-mRNA processing factors (PRPFs) cause autosomal-dominant retinitis pigmentosa (RP), but it is unclear why mutations in ubiquitously expressed genes cause non-syndromic retinal disease. Here, we generate transcriptome profiles from RP11 (PRPF31-mutated) patient-derived retinal organoids and retinal pigment epithelium (RPE), as well as Prpf31+/- mouse tissues, which revealed that disrupted alternative splicing occurred for specific splicing programmes. Mis-splicing of genes encoding pre-mRNA splicing proteins was limited to patient-specific retinal cells and Prpf31+/- mouse retinae and RPE. Mis-splicing of genes implicated in ciliogenesis and cellular adhesion was associated with severe RPE defects that include disrupted apical - basal polarity, reduced trans-epithelial resistance and phagocytic capacity, and decreased cilia length and incidence. Disrupted cilia morphology also occurred in patient-derived photoreceptors, associated with progressive degeneration and cellular stress. In situ gene editing of a pathogenic mutation rescued protein expression and key cellular phenotypes in RPE and photoreceptors, providing proof of concept for future therapeutic strategies.

Loss of PIM1 correlates with progression and prognosis of salivary adenoid cystic carcinoma (SACC)

Background

Increasing evidence indicates that PIM1 is a potential prognostic marker and target for cancer treatment but its precise mechanisms of action remain to be determined in salivary adenoid cystic carcinoma (SACC). This study aims to decipher the prognostic and mechanistic role of PIM1 in progression of SACC cells and tumor tissues.

Methods

A SACC cell line (ACC-M) was transfected with shRNA plasmids targeting the PIM1 gene. The expression levels of PIM1, RUNX3 and p21 were measured by quantitative real-time PCR and western blot. Subcellular translocalization of RUNX3 and p21 proteins was assessed using immunofluorescence, and cell cycle phase was quantified using flow cytometry. A total of 97 SACC patients were retrospectively analyzed by clinicopathologic characteristics and survival outcomes.

Results

After down-regulation of PIM1 in ACC-M cells, RUNX3 and p21 proteins were translocated from cytoplasm to nucleus, with a decrease of p21 expression and increase of G0/G1 phase cells. PIM1 and RUNX3 levels show a distinct covariance. PIM1 is associated with T-status, lymph node involvement, nerve invasion, and distant metastasis in SACC tissues. Patients with low PIM1 level had a better outcome than those with higher PIM1 level.

Conclusions

PIM1 is multifunctional in ACC-M cells and it serves as a neoteric therapeutic target and potential prognostic marker for SACC patients.

Highly Selective Red-Emitting Fluorescent Probe for Imaging Cancer Cells in Situ by Targeting Pim-1 Kinase

Based on the fact that enzyme-targeting probes are highly sensitive and selective, a novel red-emitting probe (NB-BF) for Pim-1 kinase including three parts, fluorophore (NB), linker, and inhibitor (BF), has been designed for cancer optical imaging. In its free state, NB-BF is folded and the fluorescence quenched by PET between fluorophore and inhibitor both in PBS buffer and in normal cells. Significantly, it emitted strong red fluorescence in Pim-1 overexpressed cancer cells. The specificity of NB-BF for Pim-1 kinase was directly demonstrated by gene silencing analysis. Furthermore, it is the first time to know where Pim-1 kinase mainly distributes at mitochondria with Pearson's correlation factor (R_r) of 0.965 and to provide a fluorescent tool to verify the function of the Pim-1 kinase. More importantly, NB-BF was applied in tissue imaging and preferentially labeled tumors in vivo.

snRNP proteins in health and disease

Split gene architecture of most human genes requires removal of intervening sequences by mRNA splicing that occurs on large multiprotein complexes called spliceosomes. Mutations compromising several spliceosomal components have been recorded in degenerative syndromes and haematological neoplasia, thereby highlighting the importance of accurate splicing execution in homeostasis of assorted adult tissues. Moreover, insufficient splicing underlies defective development of craniofacial skeleton and upper extremities. This review summarizes recent advances in the understanding of splicing factor function deduced from cryo-EM structures. We combine these data with the characterization of splicing factors implicated in hereditary or somatic disorders, with a focus on potential functional consequences the mutations may elicit in spliceosome assembly and/or performance. Given aberrant splicing or perturbations in splicing efficiency substantially underpin disease pathogenesis, profound understanding of the mis-splicing principles may open new therapeutic vistas. In three major sections dedicated to retinal dystrophies, hereditary acrofacial syndromes, and haematological malignancies, we delineate the noticeable variety of conditions associated with dysfunctional splicing and accentuate recurrent patterns in splicing defects.

Pharmacology of Modulators of Alternative Splicing

More than 95% of genes in the human genome are alternatively spliced to form multiple transcripts, often encoding proteins with differing or opposing function. The control of alternative splicing is now being elucidated, and with this comes the opportunity to develop modulators of alternative splicing that can control cellular function. A number of approaches have been taken to develop compounds that can experimentally, and sometimes clinically, affect splicing control, resulting in potential novel therapeutics. Here we develop the concepts that targeting alternative splicing can result in relatively specific pathway inhibitors/activators that result in dampening down of physiologic or pathologic processes, from changes in muscle physiology to altering angiogenesis or pain. The targets and pharmacology of some of the current inhibitors/activators of alternative splicing are demonstrated and future directions discussed.

Mutations in spliceosomal proteins and retina degeneration

A majority of human genes contain non-coding intervening sequences – introns that must be precisely excised from the pre-mRNA molecule. This event requires the coordinated action of five major small nuclear ribonucleoprotein particles (snRNPs) along with additional non-snRNP splicing proteins. Introns must be removed with nucleotidal precision, since even a single nucleotide mistake would result in a reading frame shift and production of a non-functional protein. Numerous human inherited diseases are caused by mutations that affect splicing, including mutations in proteins which are directly involved in splicing catalysis. One of the most common hereditary diseases associated with mutations in core splicing proteins is retinitis pigmentosa (RP). So far, mutations in more than 70 genes have been connected to RP. While the majority of mutated genes are expressed specifically in the retina, eight target genes encode for ubiquitous core snRNP proteins (Prpf3, Prpf4, Prpf6, Prpf8, Prpf31, and SNRNP200/Brr2) and splicing factors (RP9 and DHX38). Why mutations in spliceosomal proteins, which are essential in nearly every cell in the body, causes a disease that displays such a tissue-specific phenotype is currently a mystery. In this review, we recapitulate snRNP functions, summarize the missense mutations which are found in spliceosomal proteins as well as their impact on protein functions and discuss specific models which may explain why the retina is sensitive to these mutations.

Common mechanisms of onset of cancer and neurodegenerative diseases

Onset of cancer and neurodegenerative disease occurs by abnormal cell growth and neuronal cell death, respectively, and the number of patients with both diseases has been increasing in parallel with an increase in mean lifetime, especially in developed countries. Although both diseases are sporadic, about 10% of the diseases are genetically inherited, and analyses of such familial forms of gene products have contributed to an understanding of the molecular mechanisms underlying the onset and pathogenesis of these diseases. I have been working on c-myc, a protooncogene, for a long time and identified various c-Myc-binding proteins that play roles in c-Myc-derived tumorigenesis. Among these proteins, some proteins have been found to be also responsible for the onset of neurodegenerative diseases, including Parkinson's disease, retinitis pigmentosa and cerebellar atrophy. In this review, I summarize our findings indicating the common mechanisms of onset between cancer and neurodegenerative diseases, with a focus on genes such as DJ-1 and Myc-Modulator 1 (MM-1) and signaling pathways that contribute to the onset and pathogenesis of cancer and neurodegenerative diseases.

EBNA3C augments Pim-1 mediated phosphorylation and degradation of p21 to promote B-cell proliferation

Epstein–Barr virus (EBV), a ubiquitous human herpesvirus, can latently infect the human population. EBV is associated with several types of malignancies originating from lymphoid and epithelial cell types. EBV latent antigen 3C (EBNA3C) is essential for EBV-induced immortalization of B-cells. The Moloney murine leukemia provirus integration site (PIM-1), which encodes an oncogenic serine/threonine kinase, is linked to several cellular functions involving cell survival, proliferation, differentiation, and apoptosis. Notably, enhanced expression of Pim-1 kinase is associated with numerous hematological and non-hematological malignancies. A higher expression level of Pim-1 kinase is associated with EBV infection, suggesting a crucial role for Pim-1 in EBV-induced tumorigenesis. We now demonstrate a molecular mechanism which reveals a direct role for EBNA3C in enhancing Pim-1 expression in EBV-infected primary B-cells. We also showed that EBNA3C is physically associated with Pim-1 through its amino-terminal domain, and also forms a molecular complex in B-cells. EBNA3C can stabilize Pim-1 through abrogation of the proteasome/Ubiquitin pathway. Our results demonstrate that EBNA3C enhances Pim-1 mediated phosphorylation of p21 at the Thr¹⁴⁵ residue. EBNA3C also facilitated the nuclear localization of Pim-1, and promoted EBV transformed cell proliferation by altering Pim-1 mediated regulation of the activity of the cell-cycle inhibitor p21/WAF1. Our study demonstrated that EBNA3C significantly induces Pim-1 mediated proteosomal degradation of p21. A significant reduction in cell proliferation of EBV-transformed LCLs was observed upon stable knockdown of Pim-1. This study describes a critical role for the oncoprotein Pim-1 in EBV-mediated oncogenesis, as well as provides novel insights into oncogenic kinase-targeted therapeutic intervention of EBV-associated cancers.

The oncogenic serine/threonine kinase Pim-1 is upregulated in a number of human cancers including lymphomas, gastric, colorectal and prostate carcinomas. EBV nuclear antigen 3C (EBNA3C) is essential for EBV-induced transformation of human primary B-lymphocytes. Our current study revealed that EBNA3C significantly enhances Pim-1 kinase expression at both the transcript and protein levels. EBNA3C also interacts with Pim-1 and can form a complex in EBV-transformed cells. Moreover, EBNA3C increases nuclear localization of Pim-1 and stabilizes Pim-1 protein levels by inhibiting its poly-ubiquitination. Additionally, EBNA3C augments Pim-1 mediated phosphorylation of p21 and its proteosomal degradation. Stable knockdown of Pim-1 using si-RNA showed a significant decrease in proliferation of EBV transformed lymphoblastoid cell lines and subsequent induction of apoptosis by triggering the intrinsic apoptotic pathway. Therefore, our study demonstrated a new mechanism by which the oncogenic Pim-1 kinase targeted by EBV latent antigen 3C can inhibit p21 function, and is therefore a potential therapeutic target for the treatment of EBV-associated malignancies.

PIM-1 kinase interacts with the DNA binding domain of the vitamin D receptor: a further kinase implicated in 1,25-(OH)2D3 signaling

BACKGROUND

The vitamin D3 receptor (VDR) is responsible for mediating the pleiotropic and, in part, cell-type-specific effects of 1,25-dihydroxyvitamin D3 (calcitriol) on the cardiovascular and the muscle system, on the bone development and maintenance, mineral homeostasis, cell proliferation, cell differentiation, vitamin D metabolism, and immune response modulation.

RESULTS

Based on data obtained from genome-wide yeast two-hybrid screenings, domain mapping studies, intracellular co-localization approaches as well as reporter transcription assay measurements, we show here that the C-terminus of human PIM-1 kinase isoform2 (amino acid residues 135-313), a serine/threonine kinase of the calcium/calmodulin-regulated kinase family, directly interacts with VDR through the receptor's DNA-binding domain. We further demonstrate that PIM-1 modulates calcitriol signaling in HaCaT keratinocytes by enhancing both endogenous calcitriol response gene transcription (osteopontin) and an extrachromosomal DR3 reporter response.

CONCLUSION

These results, taken together with previous reports of involvement of kinase pathways in VDR transactivation, underscore the biological relevance of this novel protein-protein interaction.

The PIM kinases in hematological cancers

The PIM genes represent a family of proto-oncogenes that encode three different serine/threonine protein kinases (PIM1, PIM2 and PIM3) with essential roles in the regulation of signal transduction cascades, which promote cell survival, proliferation and drug resistance. PIM kinases are overexpressed in several hematopoietic tumors and support in vitro and in vivo malignant cell growth and survival, through cell cycle regulation and inhibition of apoptosis. PIM kinases do not have an identified regulatory domain, which means that these proteins are constitutively active once transcribed. They appear to be critical downstream effectors of important oncoproteins and, when overexpressed, can mediate drug resistance to available agents, such as rapamycin. Recent crystallography studies reveal that, unlike other kinases, they possess a hinge region, which creates a unique binding pocket for ATP, offering a target for an increasing number of potent small-molecule PIM kinase inhibitors. Preclinical studies in models of various hematologic cancers indicate that these novel agents show promising activity and some of them are currently being evaluated in a clinical setting. In this review, we profile the PIM kinases as targets for therapeutics in hematologic malignancies.

Inhibition of Pim1 kinase activation attenuates allergen-induced airway hyperresponsiveness and inflammation

Pim kinases are a family of serine/threonine kinases whose activity can be induced by cytokines involved in allergy and asthma. These kinases play a role in cell survival and proliferation, but have not been examined, to the best of our knowledge, in the development of allergic disease. This study sought to determine the role of Pim1 kinase in the development of allergic airway responses. Mice were sensitized and challenged with antigen (primary challenge), or were sensitized, challenged, and rechallenged with allergen in a secondary model. To assess the role of Pim1 kinase, a small molecule inhibitor was administered orally after sensitization and during the challenge phase. Airway responsiveness to inhaled methacholine, airway and lung inflammation, cell composition, and cytokine concentrations were assessed. Lung Pim1 kinase concentrations were increased after ovalbumin sensitization and challenge. In the primary allergen challenge model, treatment with the Pim1 kinase inhibitor after sensitization and during airway challenges prevented the development of airway hyperresponsiveness, eosinophilic airway inflammation, and goblet cell metaplasia, and increased Th2 cytokine concentrations in bronchoalveolar fluid in a dose-dependent manner. These effects were also demonstrated after a secondary allergen challenge, where lung allergic disease was established before treatment. After treatment with the inhibitor, a significant reduction was evident in the number of CD4(+) and CD8(+) T cells and concentrations of cytokines in the airways. The inhibition of Pim1 kinase was effective in preventing the development of airway hyperresponsiveness, airway inflammation, and cytokine production in allergen-sensitized and allergen-challenged mice. These data identify the important role of Pim1 kinase in the full development of allergen-induced airway responses.

PIM serine/threonine kinases in the pathogenesis and therapy of hematologic malignancies and solid cancers

The identification as cooperating targets of Proviral Integrations of Moloney virus in murine lymphomas suggested early on that PIM serine/threonine kinases play an important role in cancer biology. Whereas elevated levels of PIM1 and PIM2 were mostly found in hematologic malignancies and prostate cancer, increased PIM3 expression was observed in different solid tumors. PIM kinases are constitutively active and their activity supports in vitro and in vivo tumor cell growth and survival through modification of an increasing number of common as well as isoform-specific substrates including several cell cycle regulators and apoptosis mediators. PIM1 but not PIM2 seems also to mediate homing and migration of normal and malignant hematopoietic cells by regulating chemokine receptor surface expression. Knockdown experiments by RNA interference or dominant-negative acting mutants suggested that PIM kinases are important for maintenance of a transformed phenotype and therefore potential therapeutic targets. Determination of the protein structure facilitated identification of an increasing number of potent small molecule PIM kinase inhibitors with in vitro and in vivo anticancer activity. Ongoing efforts aim to identify isoform-specific PIM inhibitors that would not only help to dissect the kinase function but hopefully also provide targeted therapeutics. Here, we summarize the current knowledge about the role of PIM serine/threonine kinases for the pathogenesis and therapy of hematologic malignancies and solid cancers, and we highlight structural principles and recent progress on small molecule PIM kinase inhibitors that are on their way into first clinical trials.

Hypoxia-mediated up-regulation of Pim-1 contributes to solid tumor formation

Tumor hypoxia directly promotes genomic instability and facilitates cell survival, resulting in tumors with a more aggressive phenotype. The proto-oncogene pim-1 regulates apoptosis and the cell cycle by phosphorylating target proteins. Overexpression of Pim-1 can cause genomic instability and contribute to lymphomagenesis. It is not clear whether Pim-1 is involved in hypoxia-mediated tumor survival in solid tumors. Here, we show that hypoxia can stabilize Pim-1 by preventing its ubiquitin-mediated proteasomal degradation and can cause Pim-1 translocation from the cytoplasm to the nucleus. Importantly, overexpression of Pim-1 increases NIH3T3 cell transformation exclusively under hypoxic conditions, suggesting that Pim-1 expression under hypoxia may be implicated in the transformation process of solid tumors. Also, blocking Pim-1 function by introduction of dominant negative Pim-1 resensitizes pancreatic cancer cells to apoptosis induced by glucose-deprivation under hypoxia. Introduction of short interfering RNAs for Pim-1 also resensitizes cancer cells to glucose deprivation under hypoxic conditions, while forced overexpression of Pim-1 causes solid tumor cells to become resistant to glucose deprivation. Moreover, dominant negative Pim-1 reduces tumorigenicity in pancreatic cancer cells and HeLa xenograft mouse models. Together, our studies indicate that Pim-1 plays a distinct role in solid tumor formation in vivo, implying that Pim-1 may be a novel target for cancer therapy.

PAPA-1 Is a nuclear binding partner of IGFBP-2 and modulates its growth-promoting actions

IGF-binding proteins (IGFBPs) have multiple cellular effects, which occur by both IGF-dependent and -independent mechanisms. IGFBP-2 is involved in the regulation of both normal and carcinogenic cell growth. To further understand the actions of IGFBP-2, we carried out a yeast two-hybrid screen to search for intracellular partner proteins using a human prostate cDNA library. We isolated Pim-1-associated protein-1 (PAP-1)-associated protein-1 (PAPA-1) as an IGFBP-2-binding protein, whose expression and subcellular localization is regulated by both IGFBP-2 and androgens. Coimmunoprecipitation and glutathione S-transferase pull-down assay confirmed the interaction in vitro, and confocal microscopy showed the colocalization of IGFBP-2 and PAPA-1 in the nucleus. Suppression of PAPA-1 by small interfering RNA treatment enhanced the growth-promoting effect of IGFBP-2. Conversely, IGFBP-2-promoted bromodeoxyuridine incorporation into LNCaP cells was abrogated by the simultaneous overexpression of myc-hPAPA-1. Mouse embryonic fibroblasts from IGFBP-2 knockout mouse showed diminished growth activity compared with wild type, and expression of FLAG-mPAPA-1 decreased cell proliferation in IGFBP-2 knockout, but not control mouse embryonic fibroblasts. These studies suggest that the growth-promoting role of IGFBP-2 in prostate cancer is inhibited by its intracellular interaction with PAPA-1.

Potential roles for the PIM1 kinase in human cancer - a molecular and therapeutic appraisal

In vitro experiments have shown the PIM1 kinase to have diverse biological roles in cell survival, proliferation and differentiation. In humans, PIM1 is often expressed in both normal and transformed cells. The PIM1 kinase is a true oncogene implicated in early transformation and tumour progression in haematopoietic malignancies and prostate carcinomas. It is associated with aggressive subgroups of lymphoma, is a marker of poor prognosis in prostate carcinomas and has been suggested to have a role in hormone insensitivity of prostate malignancies. PIM1 has a possible role in other carcinomas with 6p21 genomic alterations. On one hand, PIM1 (due to its role in malignancy) appears to be a promising target for drug development programmes but, on the other hand, the complexity of its molecular structure has posed challenges in the development of PIM1 inhibitors. In this review we discuss PIM1 expression in human tissues (including some new data from our laboratory), its role in human malignancies, as well as the possibilities and challenges in the development of target therapy for PIM1.

Pim-1 kinase-dependent phosphorylation of p21Cip1/WAF1 regulates its stability and cellular localization in H1299 cells

Previous studies from our laboratory showed that p21Cip1/WAF1 can be phosphorylated by Pim-1 kinase in vitro, implying that part of the function of Pim-1 might involve influencing the cell cycle. In the present study, site-directed mutagenesis and phosphorylated-specific antibodies were used as tools to identify the sites phosphorylated by Pim-1 and the consequences of this phosphorylation. What we found was that Pim-1 can efficiently phosphorylate p21 on Thr145 in vitro using recombinant protein and in vivo in intact cells. Unexpectedly, we found that Ser146 is a second site that is phosphorylated in vivo, but this phosphorylation event seems to be an indirect result of Pim-1 expression. More importantly, the consequences of phosphorylation of either Thr145 or Ser146 are distinct. When p21 is phosphorylated on Thr145, it localizes to the nucleus and results in the disruption of the association between proliferating cell nuclear antigen and p21. Furthermore, phosphorylation of Thr145 promotes stabilization of p21. On the other hand, when p21 is phosphorylated on Ser146, it localizes primarily in the cytoplasm and the effect of phosphorylation on stability is minimal. Cotransfection of wild-type Pim-1 with p21 increases the rate of proliferation compared with cotransfection of p21 with kinase-dead Pim-1. Knocking down Pim-1 expression greatly decreases the rate of proliferation of H1299 cells and their ability to grow in soft agar. These data suggest that Pim-1 overexpression may contribute to tumorigenesis in part by influencing the cellular localization and stability of p21 and by promoting cell proliferation.

Comparative molecular field analysis of flavonoid inhibitors of the PIM-1 kinase

The PIM-1 protein, the product of the pim-1 oncogene, is a serine/threonine kinase. Dysregulation of the PIM-1 kinase has been implicated in the development of human malignancies including lymphomas, leukemias, and prostate cancer. Comparative molecular field analysis (CoMFA) is a 3-D QSAR technique that has been widely used, with notable success, to correlate biological activity with the steric and electrostatic properties of ligands. We have used a set of 15 flavonoid inhibitors of the PIM-1 kinase, aligned de novo by common substructure, to generate a CoMFA model for the purpose of elucidating the steric and electrostatic properties involved in flavonoid binding to the PIM-1 kinase. Partial least squares correlation between observed and predicted inhibitor potency (expressed as -logIC50), using a non-cross-validated partial least squares analysis, generated a non-cross-validated q2=0.805 for the training set (n=15) of flavonoids. The CoMFA generated steric map indicated that the PIM-1-binding site was sterically hindered, leading to more efficient binding of planar molecules over (R) or (S) compounds. The electrostatic map identified that positive charges near the flavonoid atom C8 and negative charges near C4' increased flavonoid binding. The CoMFA model accurately predicted the potency of a test set of flavonoids (n=6), generating a correlation between observed and predicted potency of q2=0.825. CoMFA models generated from additional alignment rules, which were guided by co-crystal structure ligand orientations, did not improve the correlative value of the model. Superimposing the PIM-1 kinase crystal structure onto the CoMFA contours validated the steric and electrostatic maps, elucidating the amino acid residues that potentially contribute to the CoMFA fields. Thus we have generated the first predictive model that may be used for the rational design of small-molecule inhibitors of the PIM-1 kinase.

Pim-1 kinase inhibits the activation of reporter gene expression in Elk-1 and c-Fos reporting systems but not the endogenous gene expression: an artifact of the reporter gene assay by transient co-transfection

We have studied the molecular mechanism and signal transduction of pim-1, an oncogene encoding a serine-threonine kinase. This is a true oncogene which prolongs survival and inhibits apoptosis of hematopoietic cells. In order to determine whether the effects of Pim-1 occur by regulation of the mitogen-activated protein kinase pathway, we used a transcriptional reporter assay by transient co-transfection as a screening method. In this study, we found that Pim-1 inhibited the Elk-1 and NFkappaB transcriptional activities induced by activation of the mitogen-activated protein kinase cascade in reporter gene assays. However, Western blots showed that the induction of Elk-1-regulated expression of endogenous c-Fos was not affected by Pim-1. The phosphorylation and activation of neither Erk1/2 nor Elk-1 was influenced by Pim-1. Also, in the gel shift assay, the pattern of endogenous NFkappaB binding to its probe was not changed in any manner by Pim-1. These data indicate that Pim-1 does not regulate the activation of Erk1/2, Elk-1 or NFkappaB. These contrasting results suggest a pitfall of the transient co-transfection reporter assay in analyzing the regulation of transcription factors outside of the chromosome context. It ensures that results from reporter gene expression assay should be verified by study of endogenous gene expression.

The oncogenic serine/threonine kinase Pim-1 directly phosphorylates and activates the G2/M specific phosphatase Cdc25C

The proto-oncogene Pim-1 encodes a serine-threonine kinase which is a downstream effector of cytokine signaling and can enhance cell cycle progression by altering the activity of several cell cycle regulators among them the G1 specific inhibitor p21(Waf), the phosphatase Cdc25A and the kinase C-TAK1. Here, we demonstrate by using biochemical assays that Pim-1 can interact with the phosphatase Cdc25C and is able to directly phosphorylate the N-terminal region of the protein. Cdc25C is functionally related to Cdc25A but acts specifically at the G2/M cell cycle transition point and can be inactivated by C-TAK1-mediated phosphorylation. Immuno-fluorescence experiments showed that Pim-1 and Cdc25C co-localize in the cytoplasm of both epithelial and myeloid cells. We find that phosphorylation by Pim-1 enhances the phosphatase activity of Cdc25C and in transfected cells that are arrested in G2/M by bleomycin, Pim-1 can enhance progression into G1. Therefore, we propose that Pim-1 activates Cdc25C by a direct phosphorylation and can thereby assume the function of a positive cell cycle regulator at the G2/M transition.

Pim-1 kinase stability is regulated by heat shock proteins and the ubiquitin-proteasome pathway

Elevated expression of the serine/threonine kinase Pim-1 increases the incidence of lymphomas in Pim-1 transgenic mice and has also been found to occur in some human cancers. Pim-1 acts as a cell survival factor and may prevent apoptosis in malignant cells. It was therefore of interest to understand to what extent maintenance and degradation of Pim-1 protein is affected by heat shock proteins (Hsp) and the ubiquitin-proteasome pathway in K562 and BV173 human leukemic cells. The half-life of Pim-1 protein in these cells was found to increase from 1.7 to 3.1 hours when induced by heat shock or by treating the cells with the proteasome inhibitor PS-341 (bortezomib). The Hsp90 inhibitor geldanamycin prevented the stabilization of Pim-1 by heat shock. Using immunoprecipitation, it was determined that Pim-1 is targeted for degradation by ubiquitin and that Hsp70 is associated with Pim-1 under these circumstances. Conversely, Hsp90 was found to protect Pim-1 from proteasomal degradation. A luminescence-based kinase assay showed that Pim-1 kinase bound to Hsp70 or Hsp90 remains active, emphasizing the importance of its overall cellular levels. This study shows how Pim-1 levels can be modulated in cells through degradation and stabilization.

The serine/threonine kinase Pim-1

The human pim-1 gene encodes a serine/threonine kinase, which belongs to the group of calcium/calmodulin-regulated kinases (CAMK). It contains a characteristic kinase domain, a so-called ATP anchor and an active site. In mouse and human, two Pim-1 proteins are produced from the same gene by using an alternative upstream CUG initiation codon, a 44 kD and another, shorter 34 kD form that both contain the kinase domain. Expression of Pim-1 is widespread and ranges from the hematopoietic and lymphoid system to prostate, testis and oral epithelial cells. Two other proteins with significant sequence similarities exist, Pim-2 and Pim-3; both are also serine/threonine kinases and have largely overlapping functions. Pim-1 is able to phosphorylate different targets, most of which are involved in cell cycle progression or apoptosis. Pim-1 expression can be induced by several external stimuli in particular by a number of cytokines relevant in the immune system, which led to the labeling of Pim-1 as a "booster" for the immune response.

Crystal structures of proto-oncogene kinase Pim1: a target of aberrant somatic hypermutations in diffuse large cell lymphoma

Pim1, a serine/threonine kinase, is involved in several biological functions including cell survival, proliferation, and differentiation. While pim1 has been shown to be involved in several hematopoietic cancers, it was also recently identified as a target of aberrant somatic hypermutation in diffuse large cell lymphoma (DLCL), the most common form of non-Hodgkin's lymphoma. The crystal structures of Pim1 in apo form and bound with AMPPNP have been solved and several unique features of Pim1 were identified, including the presence of an extra beta-hairpin in the N-terminal lobe and an unusual conformation of the hinge connecting the two lobes of the enzyme. While the apo Pim1 structure is nearly identical with that reported recently, the structure of AMPPNP bound to Pim1 is significantly different. Pim1 is unique among protein kinases due to the presence of a proline residue at position 123 that precludes the formation of the canonical second hydrogen bond between the hinge backbone and the adenine moiety of ATP. One crystal structure reported here shows that changing P123 to methionine, a common residue that offers the backbone hydrogen bond to ATP, does not restore the ATP binding pocket of Pim1 to that of a typical kinase. These unique structural features in Pim1 result in novel binding modes of AMP and a known kinase inhibitor scaffold, as shown by co-crystallography. In addition, the kinase activities of five Pim1 mutants identified in DLCL patients have been determined. In each case, the observed effects on kinase activity are consistent with the predicted consequences of the mutation on the Pim1 structure. Finally, 70 co-crystal structures of low molecular mass, low-affinity compounds with Pim1 have been solved in order to identify novel chemical classes as potential Pim1 inhibitors. Based on the structural information, opportunities for optimization of one specific example are discussed.

Pim-1 Ligand-bound Structures Reveal the Mechanism of Serine/Threonine Kinase Inhibition by LY294002

Pim-1 is an oncogene-encoded serine/threonine kinase primarily expressed in hematopoietic and germ cell lines. Pim-1 kinase was originally identified in Maloney murine leukemia virus-induced T-cell lymphomas and is associated with multiple cellular functions such as proliferation, survival, differentiation, apoptosis, and tumorigenesis (Wang, Z., Bhattacharya, N., Weaver, M., Petersen, K., Meyer, M., Gapter, L., and Magnuson, N. S. (2001) J. Vet. Sci. 2, 167-179). The crystal structures of Pim-1 complexed with staurosporine and adenosine were determined. Although a typical two-domain serine/threonine protein kinase fold is observed, the inter-domain hinge region is unusual in both sequence and conformation; a two-residue insertion causes the hinge to bulge away from the ATP-binding pocket, and a proline residue in the hinge removes a conserved main chain hydrogen bond donor. Without this hydrogen bond, van der Waals interactions with the hinge serve to position the ligand. The hinge region of Pim-1 resembles that of phosphatidylinositol 3-kinase more closely than it does other protein kinases. Although the phosphatidylinositol 3-kinase inhibitor LY294002 also inhibits Pim-1, the structure of the LY294002.Pim-1 complex reveals a new binding mode that may be general for Ser/Thr kinases.

STATs as critical mediators of signal transduction and transcription: lessons learned from STAT5

Signal transducers and activators of transcription (Stats) comprise a family of seven transcription factors that are activated by a variety of cytokines, hormones and growth factors. Stats are activated through tyrosine phosphorylation, mainly by Jak kinases, that lead to their dimerization, nuclear translocation and regulation of target gene expression. Stat5 was originally identified as a transcription factor that regulates the beta-casein gene in response to prolactin (PRL), but Stat5 is activated also by several other cytokines and growth factors. The molecular mechanisms that underlie Stat5-mediated transcription involve interactions and cooperation with sequence specific transcription factors and transcriptional coregulators. Our studies identified p100 protein as a coactivator for Stat5, and suggest the existence of a positive regulatory loop in PRL-induced transcription, where PRL stabilizes p100 protein, which in turn can cooperate with Stat5 in transcriptional activation. Suppressors of cytokine signaling (SOCS) proteins are important negative regulators of Stats. A target gene for Stat5, the serine/threonine kinase Pim-1, was found to cooperate with SOCS-1 and SOCS-3 to inhibit Stat5 activity suggesting that Pim-1 together with SOCS-1 and SOCS-3 are components of a negative feedback mechanism that allows Stat5 to regulate its own activation.

Association of PAP-1 and Prp3p, the products of causative genes of dominant retinitis pigmentosa, in the tri-snRNP complex

PAP-1 has been identified by us as a Pim-1-binding protein and has recently been implicated as the defective gene in RP9, one type of autosomal dominant retinitis pigmentosa (adRP). We have then shown that PAP-1 plays a role in pre-mRNA splicing. Because four causative genes for adRP, including PAP-1, Prp31, Prp8, and Prp3, encode proteins that function as splicing factors or splicing-modulating factors, we investigated the interaction of PAP-1 with Prp3p and Prp31p in this study. The results showed that PAP-1 interacted with Prp3p but not Prp31p in human cells and yeast, and that the basic region of PAP-1 and the C-terminal region of Prp3p, regions beside spots found in adRP mutations, were needed for binding. Furthermore, both Prp3p and a part of PAP-1 were found to be components of the U4/U6.U5-tri-snRNP complex, one form of the spliceosome, in Ba/F3 and K562 cells by analysis of sucrose density gradients, suggesting that PAP-1 is weakly associated with the spliceosome. These results also suggest that splicing factors implicated in adRP contribute alone or mutually to proper splicing in the retina and that loss of their functions leads to onset of adRP.

IL-5 and granulocyte-macrophage colony-stimulating factor activate STAT3 and STAT5 and promote Pim-1 and cyclin D3 protein expression in human eosinophils

Allergic inflammation is characterized by elevated eosinophil numbers and by the increased production of the cytokines IL-5 and GM-CSF, which control several eosinophil functions, including the suppression of apoptosis. The JAK/STAT pathway is important for several functions in hemopoietic cells, including the suppression of apoptosis. We report in this study that STAT3, STAT5a, and STAT5b are expressed in human eosinophils and that their signaling pathways are active following IL-5 or GM-CSF treatment. However, in airway eosinophils, the phosphorylation of STAT5 by IL-5 is reduced, an event that may be related to the reduced expression of the IL-5Ralpha on airway eosinophils. Furthermore, IL-5 and GM-CSF induced the protein expression of cyclin D3 and the kinase Pim-1, both of which are regulated by STAT-dependent processes in some cell systems. Pim-1 is more abundantly expressed in airway eosinophils than in blood eosinophils. Because Pim-1 reportedly has a role in the modulation of apoptosis, these results suggest that Pim-1 action is linked to the suppression of eosinophil apoptosis by these cytokines. Although cyclin D3 is known to be critical for cell cycle progression, eosinophils are terminally differentiated cells that do not proceed through the cell cycle. Thus, this apparent cytokine regulation of cyclin D3 suggests that there is an alternative role(s) for cyclin D3 in eosinophil biology.

PAP-1, the mutated gene underlying the RP9 form of dominant retinitis pigmentosa, is a splicing factor

PAP-1 is an in vitro phosphorylation target of the Pim-1 oncogene. Although PAP-1 binds to Pim-1, it is not a substrate for phosphorylation by Pim-1 in vivo. PAP-1 has recently been implicated as the defective gene in RP9, one type of autosomal dominant retinitis pigmentosa (adRP). However, RP9 is a rare disease and only two missense mutations have been described, so the report of a link between PAP-1 and RP9 was tentative. The precise cellular role of PAP-1 was also unknown at that time. We now report that PAP-1 localizes in nuclear speckles containing the splicing factor SC35 and interacts directly with another splicing factor, U2AF35. Furthermore, we used in vitro and in vivo splicing assays to show that PAP-1 has an activity, which alters the pattern of pre-mRNA splicing and that this activity is dependent on the phosphorylation state of PAP-1. We used the same splicing assay to examine the activities of two mutant forms of PAP-1 found in RP9 patients. The results showed that while one of the mutations, H137L, had no effect on splicing activity compared with that of wild-type PAP-1, the other, D170G, resulted in both a defect in splicing activity and a decreased proportion of phosphorylated PAP-1. The D170G mutation may therefore cause RP by altering splicing of retinal genes through a decrease in PAP-1 phosphorylation. These results demonstrate that PAP-1 has a role in pre-mRNA splicing and, given that three other splicing factors have been implicated in adRP, this finding provides compelling further evidence that PAP-1 is indeed the RP9 gene.

CIR, a corepressor of CBF1, binds to PAP-1 and effects alternative splicing

We have reported that PAP-1, a product of a causative gene for autosomal retinitis pigmentosa, plays a role in splicing. In this study, CIR, a protein originally identified as a CBF1-interacting protein and reported to act as a transcriptional corepressor, was identified as a PAP-1 binding protein and its function as a splicing factor was investigated. In addition to a basic lysine and acidic serine-rich (BA) domain and a zinc knuckle-like motif, CIR has an arginine/serine dipeptide repeat (RS) domain in its C terminal region. The RS domain has been reported to be present in the superfamily of SR proteins, which are involved in splicing reactions. We generated CIR mutants with deletions of each BA and RS domain and studied their subcellular localizations and interactions with PAP-1 and other SR proteins, including SC35, SF2/ASF, and U2AF35. CIR was found to interact with U2AF35 through the BA domain, with SC35 and SF2/ASF through the RS domain, and with PAP-1 outside the BA domain in vivo and in vitro. CIR was found to be colocalized with SC35 and PAP-1 in nuclear speckles. Then the effect of CIR on splicing was investigated using the E1a minigene as a reporter in HeLa cells. Ectopic expression of CIR with the E1a minigene changed the ratio of spliced isoforms of E1a that were produced by alternative selection of 5'-splice sites. These results indicate that CIR is a member of the family of SR-related proteins and that CIR plays a role in splicing regulation.

Pim-1 is up-regulated by constitutively activated FLT3 and plays a role in FLT3-mediated cell survival

Constitutively activating internal tandem duplication (ITD) mutations of the receptor tyrosine kinase FLT3 (Fms-like tyrosine kinase 3) play an important role in leukemogenesis, and their presence is associated with poor prognosis in acute myeloid leukemia (AML). To better understand FLT3 signaling in leukemogenesis, we have examined the changes in gene expression induced by FLT3/ITD or constitutively activated wild-type FLT3 expression. Microarrays were used with RNA harvested before and after inhibition of FLT3 signaling. Pim-1 was found to be one of the most significantly down-regulated genes upon FLT3 inhibition. Pim-1 is a proto-oncogene and is known to be up-regulated by signal transducer and activator of transcription 5 (STAT5), which itself is a downstream target of FLT3 signaling. Quantitative polymerase chain reaction (QPCR) confirmed the microarray results and demonstrated approximately 10-fold decreases in Pim-1 expression in response to FLT3 inhibition. Pim-1 protein also decreased rapidly in parallel with decreasing autophosphorylation activity of FLT3. Enforced expression of either the 44-kDa or 33-kDa Pim-1 isotypes resulted in increased resistance to FLT3 inhibition-mediated cytotoxicity and apoptosis. In contrast, expression of a dominant-negative Pim-1 construct accelerated cytotoxicity in response to FLT3 inhibition and inhibited colony growth of FLT3/ITD-transformed BaF3 cells. These findings demonstrate that constitutively activated FLT3 signaling up-regulates Pim-1 expression in leukemia cells. This up-regulation contributes to the proliferative and antiapoptotic pathways induced by FLT3 signaling.

A novel nucleolar protein, PAPA-1, induces growth arrest as a result of cell cycle arrest at the G1 phase

We have identified a novel nucleolar protein, PAP-1-associated protein-1 (PAPA-1), after screening the interacting proteins with Pim-1-associated protein-1 (PAP-1), a protein that is a phosphorylation target of Pim-1 kinase. PAPA-1 comprises 345 amino acids with a basic amino-acid cluster. PAPA-1 was found to be localized in the nucleolus in transfected HeLa cells, and the lysine/histidine cluster was essential for nucleolar localization of PAPA-1. PAPA-1 protein and mRNA expression decreased upon serum restimulation of starvation-synchronized cells, which displayed maximum level of PAPA-1 expression at G0 and early G1 phase of the cell cycle. Ectopic expression of PAPA-1 induced growth suppression of cells, and the effect was dependent on its nucleolar localization in established HeLa cell lines that inducibly express PAPA-1 or its deletion mutant under the control of a tetracycline-inducible promoter. Furthermore, when PAPA-1-inducible HeLa cells were synchronized by thymidine, colcemid or mimosine, and then PAPA-1 was expressed, the proportion of cells at the G1 phase was obviously increased. These results suggest that PAPA-1 induces growth and cell cycle arrests at the G1 phase of the cell cycle.

The oncogenic serine/threonine kinase Pim-1 phosphorylates and inhibits the activity of Cdc25C-associated kinase 1 (C-TAK1): a novel role for Pim-1 at the G2/M cell cycle checkpoint

The Pim-1 oncogene encodes a serine-threonine kinase that relays signals from cytokine receptors and contributes to the formation of lymphoid tumors when expressed at high levels. Here we show that the protein kinase Cdc25 C-associated kinase 1 (C-TAK1) is a binding partner and a substrate of Pim-1. A physical interaction of Pim-1 and C-TAK1 could be shown biochemically and in yeast two-hybrid assays. Immunofluorescence experiments suggested that Pim-1.C-TAK1 complexes are predominantly cytoplasmic. When transiently transfected, Pim-1 was also found in the nucleus and could recruit C-TAK1 to this compartment. Both Pim-1 and C-TAK1 underwent autophosphorylation, but only Pim-1 was able to phosphorylate C-TAK1 but not vice versa. Mass spectrometry analysis of C-TAK1 suggested that the sites of autophosphorylation and Pim-1-mediated phosphorylation are distinct and not overlapping. Phosphorylation by Pim-1 decreased C-TAK1 kinase activity significantly, in particular its ability to phosphorylate and inactivate Cdc25C, a protein that actively promotes cell cycle progression at the G(2)/M phase. Hence our findings directly suggest a novel role for Pim-1 as a positive regulator at the G(2)/M transition of the cell cycle.

The PIM-2 kinase phosphorylates BAD on serine 112 and reverses BAD-induced cell death

Hematopoietic growth factors mediate the survival and proliferation of blood-forming cells, but the mechanisms through which these proteins produce their effects are incompletely known. Recent studies have identified the pim family of kinases as mediators of cytokine-dependent survival signals. Several studies have identified substrates for the pim-1 kinase, but little is known about the other family members, pim-2 and pim-3. We have investigated potential functions for the pim-2 kinase in factor-dependent murine hematopoietic cells. We find that pim-2 mRNA and protein expression are regulated by cytokines similarly to pim-1. Three PIM-2 protein isoforms are produced in cytokine-treated cells. All three forms are active kinases, and the short (PIM-2(34 kDa)) form is the most active at enhancing survival of FDCP1 cells after cytokine withdrawal. This pro-survival function involves inhibition of apoptosis and caspase activation. Enforced expression of PIM-2(34 kDa) kinase does not appear to regulate expression of BCL-2, BCL-xL, BIM, or BAX proteins. However, the kinase can phosphorylate the pro-apoptotic protein BAD on serine 112, which accounts in part for its ability to reverse Bad-induced cell death. Our results indicate that pim-2 functions similarly to pim-1 as a pro-survival kinase and suggest that BAD is a legitimate PIM-2 substrate.

Retroviral insertional mutagenesis: tagging cancer pathways

Slow transforming retroviruses, such as the Moloney murine leukemia virus (M-MuLV), induce tumors upon infection of a host after a relatively long latency period. The underlying mechanism leading to cell transformation is the activation of proto-oncogenes or inactivation of tumor suppressor genes as a consequence of proviral insertions into the host genome. Cells carrying proviral insertions that confer a selective advantage will preferentially grow out. This means that proviral insertions mark genes contributing to tumorigenesis, as was demonstrated by the identification of numerous proto-oncogenes in retrovirally induced tumors in the past. Since cancer is a complex multistep process, the proviral insertions in one clone of tumor cells also represent oncogenic events that cooperate in tumorigenesis. Novel advances, such as the launch of the complete mouse genome, high-throughput isolation of proviral flanking sequences, and genetically modified animals have revolutionized proviral tagging into an elegant and efficient approach to identify signaling pathways that collaborate in cancer.

Expression of depolarization-induced immediate early gene proteins in PC12 cells

Immediate early genes induced by depolarization are thought to be important in mediating neuronal functional plasticity. We previously identified a group of immediate early genes that are preferentially induced by depolarization and forskolin but not by nerve growth factor or epidermal growth factor in PC12 pheochromocytoma cells. These depolarization-induced genes include synaptotagmin 4; the protein kinases KID-1, PIM-1, and SIK; an orphan transcription factor, Nurr-1; and a transcription corepressor, rTLE-3. All these genes are also induced in the hippocampus in response to kainic-acid induced depolarization. To characterize further the unique functions of these genes in plasticity, we used recombinant proteins to generate and purify antibodies against KID-1 and SIK proteins. Immunoblotting experiments were performed to examine the induced expression of the KID-1 and SIK proteins in PC12 cells. PIM-1 and Nurr-1 protein expression was also examined following stimulation, using commercially available antibodies. There is an increase in synthesis, in PC12 cells, of these four IEG proteins after KCl plus forskolin treatment. Nurr-1 protein peaks between 2 and 4 hr and decreases by 6 hr after the treatment. PIM-1 and KID-1 proteins rise by 1 hr, peak between 2 and 4 hr, and return to their basal levels at 6 hr. SIK protein increases significantly at 2 hr after treatment, peaks between 4 and 6 hr, and returns to the basal level at 8 hr. Immunofluorescence studies demonstrate distinct distribution patterns of each of these depolarization-induced IEG proteins in PC12 cells.

Phosphorylation of the cell cycle inhibitor p21Cip1/WAF1 by Pim-1 kinase

The serine/threonine kinase, Pim-1, appears to be involved in regulating proliferation, differentiation and cell survival of lymphoid and myeloid cells. In this study, we have found that amino acid residues 140-147 (RKRRQTSM) at the C-terminal end of p21(Cip1/WAF1), a cyclin-dependent kinase (CDK) inhibitor, constitute an ideal phosphorylation consensus sequence for Pim-1. We demonstrate that Pim-1 efficiently phosphorylates this peptide sequence as well as the p21 protein in vitro. We also demonstrate by pull-down assay and by immunoprecipitation that Pim-1 associates with p21. During phorbol ester-induced differentiation of U937 cells, both Pim-1 and p21 expression levels increase with Pim-1 levels increasing in both the nucleus and cytoplasm while p21 remains primarily cytoplasmic. Co-transfection of wild type p21 with wild type Pim-1 results in cytoplasmic localization of p21 while co-transfection of wild type p21 with kinase dead Pim-1 results in nuclear localization of p21. Consistent with the results from the phosphoamino acid assay, Pim-1 phosphorylates transfected p21 only on Thr(145) in p21-deficient human fibroblasts and this phosphorylation event results in the cytoplasmic localization of p21. These findings demonstrate that Pim-1 associates with and phosphorylates p21 in vivo, which influences the subcellular localization of p21.

Mutations in a protein target of the Pim-1 kinase associated with the RP9 form of autosomal dominant retinitis pigmentosa

The RP9 form of autosomal dominant retinitis pigmentosa (adRP) maps to a locus on human chromosome 7p14. We now report two different disease associated mutations in a previously unidentified human gene, the mouse orthologue of which has been characterised by its interaction with the Pim-1 oncogene. In the original linked family we identified the missense mutation H137L. A second missense mutation, D170G, was found in a single RP patient. The putative RP9 gene appears to be expressed in a wide range of tissues, but its function is unknown and a pathogenic mechanism remains to be determined.

CD40 signaling in B cells regulates the expression of the Pim-1 kinase via the NF-kappa B pathway

The ability of CD40 signaling to regulate B cell growth, survival, differentiation, and Ig class switching involves many changes in gene expression. Using cDNA expression arrays and Northern blotting, we found that CD40 signaling increased the mRNA levels for pim-1, a protooncogene that encodes a serine/threonine protein kinase. Subsequent experiments showed that CD40 engagement also increased both Pim-1 protein levels and Pim-1 kinase activity in B cells. We then investigated the signaling pathways by which CD40 regulates Pim-1 expression and found that CD40 up-regulates Pim-1 primarily via the activation of NF-kappaB. Inhibiting the activation of NF-kappaB, either by treating cells with a chemical inhibitor, BAY11-7082, or by inducibly expressing a superrepressor form of IkappaBalpha, significantly impaired the ability of CD40 to increase Pim-1 protein levels. Because Pim-1 expression is associated with cell proliferation and survival, we asked whether this correlated with the ability of CD40 signaling to prevent anti-IgM-induced growth arrest in the WEHI-231 murine B cell line, a model for Ag-induced clonal deletion. We found that the anti-IgM-induced growth arrest in WEHI-231 cells correlated with a substantial decrease in Pim-1 levels. In contrast, culturing WEHI-231 cells with either anti-CD40 Abs or with the B cell mitogen LPS, both of which prevent the anti-IgM-induced growth arrest, also prevented the rapid decline in Pim-1 levels. This suggests that Pim-1 could regulate the survival and proliferation of B cells.

Pim-1 translocates sorting nexin 6/TRAF4-associated factor 2 from cytoplasm to nucleus

Pim-1, an oncogene product of serine/threonine kinase, has been found to play roles in apoptosis induction/suppression, cell-cycle progression and transcriptional regulation by phosphorylating the target proteins involved in these processes. The target proteins phosphorylated by Pim-1, including p100, Cdc25A, PAP-1 and heterochromatin protein 1, have been identified. The precise functions of Pim-1, however, are still poorly understood. In this study, we identified tumor necrosis factor receptor-associated factor 4-associated factor 2/sorting nexin 6 (TFAF2/SNX6) as a Pim-1-binding protein, and we found that TFAF2/SNX6 was phosphorylated and translocated from the cytoplasm to nucleus by Pim-1. This translocation of the protein was not affected by Pim-1-dependent phosphorylation. Since sorting nexins, including TFAF2/SNX6, have been reported to be located in the cytoplasm or membrane by association with several receptors of tyrosine- or serine/threonine-kinase, this is the first report of TFAF2/SNX6 being located in the nucleus after binding to Pim-1.

Pim-1 negatively regulates the activity of PTP-U2S phosphatase and influences terminal differentiation and apoptosis of monoblastoid leukemia cells

The levels of Pim-1, a serine/threonine kinase, increase during phorbol myristate acetate (PMA)-induced myeloid cell differentiation. The tyrosine phosphatase PTP-U2S is also associated with PMA-induced differentiation of myeloid cells and has been shown to enhance differentiation and the onset of apoptosis. PTP-U2S contains a Pim-1 phosphorylation consensus sequence, KKRKLTN, which is efficiently phosphorylated by Pim-1. Immunoprecipitated PTP-U2S from U937 cells was phosphorylated by recombinant Pim-1, resulting in a decrease in its phosphatase activity. During PMA-induced differentiation, U937 cells transfected with the dominant negative Pim-1 underwent rapid differentiation and accelerated apoptosis. The opposite effect was observed for wild-type Pim-1. Our results, therefore, provide compelling evidence that Pim-1 functions to negatively regulate PMA-induced differentiation in part through the phosphorylation of PTP-U2S. Together these data suggest that Pim-1 phosphorylates PTP-U2S in vivo to decrease the phosphatase activity that may be necessary to prevent the premature onset of apoptosis following differentiation.

Regulation of Pim-1 by Hsp90

The protooncogene Pim-1 encodes serine/threonine protein kinases that are involved in cytokine-mediated cell proliferation and in lymphoma- and leukemogenesis. It is largely unknown how Pim-1 executes its biological effects. Here we show that Pim-1 physically interacts with heat shock protein 90 alpha and beta (Hsp90alpha and beta). The Hsp90-specific inhibitor geldanamycin (GA) induced a rapid degradation of Pim-1 and reduced its kinase activity. The expression of Hsp90alpha was regulated by a signal from the cytokine receptor gp130, as is Pim-1's expression. These results indicate that Hsp90 is coordinately regulated with Pim-1 and is involved in the stabilization and function of Pim-1.

cDNA cloning, sequencing and characterization of bovine pim-1

The cDNA clone of bovine pim-1 has been isolated from phorbol-12-myristate-13-acetate (PMA) and concanavalin A (ConA)-activated peripheral blood lymphocytes (PBLs). The full-length cDNA contains a 411bp 5' untranslated region (5'-UTR), followed by a 939bp coding region and a 3' untranslated region (3'-UTR) that contains 1403bp. Comparison of the bovine pim-1 coding sequence with the human, rat, mouse, frog and zebrafish counterparts reveals 94, 90, 89, 67 and 40% homology at the nucleotide level, respectively. The predicted amino acid sequence of bovine Pim-1 shares 98.7, 97.1, 93.3, 68.8, and 52.4% similarity with the sequences of human, rat, mouse, frog, and zebrafish, respectively. The 5'-UTR of bovine pim-1 shares high sequence similarity to the human and mouse counterparts and is G/C-rich (75%) which may promote a high degree of secondary structure. The 3'-UTR of bovine pim-1 contains two potential polyadenylation sites and an A/T-rich motif which has been shown to decrease the stability of polyA mRNA molecules. Southern blot results indicate that a single copy of the gene exists in the bovine genome. Northern blot results show that PMA stimulation of PBLs increases the expression of the pim-1 mRNA. In addition, examination of Pim-1 protein expression in PBLs stimulated with a variety of mitogens including ConA, PMA, anti-CD3 and purified protein derivative (PPD) from Mycobacterium tuberculosis, reveals two different types of expression patterns during the course of a 24h period of stimulation. ConA and PPD gave a biphasic pattern of expression while PMA and anti-CD3 gave single transient pattern of expression suggesting that expression is controlled by more than one signaling pathway.