Pim-3 promotes the growth of human pancreatic cancer in the orthotopic nude mouse model through vascular endothelium growth factor

PIM3 Kinase: A Promising Novel Target in Solid Cancers

PIM3 (provirus-integrating Moloney site 3) is a serine/threonine kinase and belongs to the PIM family (PIM1, PIM2, and PIM3). PIM3 is a proto-oncogene that is frequently overexpressed in cancers originating from endoderm-derived tissues, such as the liver, pancreas, colon, stomach, prostate, and breast cancer. PIM3 plays a critical role in activating multiple oncogenic signaling pathways promoting cancer cell proliferation, survival, invasion, tumor growth, metastasis, and progression, as well as chemo- and radiation therapy resistance and immunosuppressive microenvironment. Genetic inhibition of PIM3 expression suppresses in vitro cell proliferation and in vivo tumor growth and metastasis in mice with solid cancers, indicating that PIM3 is a potential therapeutic target. Although several pan-PIM inhibitors entered phase I clinical trials in hematological cancers, there are currently no FDA-approved inhibitors for the treatment of patients. This review provides an overview of recent developments and insights into the role of PIM3 in various cancers and its potential as a novel molecular target for cancer therapy. We also discuss the current status of PIM-targeted therapies in clinical trials.

Direct phosphorylation and stabilization of HIF-1α by PIM1 kinase drives angiogenesis in solid tumors

Angiogenesis is essential for the sustained growth of solid tumors. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of angiogenesis and constitutive activation of HIF-1 is frequently observed in human cancers. Therefore, understanding the mechanisms governing the activation of HIF-1 is critical for successful therapeutic targeting of tumor angiogenesis. Herein, we establish a new regulatory mechanism responsible for the constitutive activation of HIF-1α in cancer, irrespective of oxygen tension. PIM1 kinase directly phosphorylates HIF-1α at threonine 455, a previously uncharacterized site within its oxygen-dependent degradation domain. This phosphorylation event disrupts the ability of prolyl hydroxylases to bind and hydroxylate HIF-1α, interrupting its canonical degradation pathway and promoting constitutive transcription of HIF-1 target genes. Moreover, phosphorylation of the analogous site in HIF-2α (S435) stabilizes the protein through the same mechanism, indicating post-translational modification within the oxygen-dependent degradation domain as a mechanism of regulating the HIF-α subunits. In vitro and in vivo models demonstrate that expression of PIM1 is sufficient to stabilize HIF-1α and HIF-2α in normoxia and stimulate angiogenesis in a HIF-1-dependent manner. CRISPR mutants of HIF-1α (Thr455D) promoted increased tumor growth, proliferation, and angiogenesis. Moreover, HIF-1α-T455D xenograft tumors were refractory to the anti-angiogenic and cytotoxic effects of PIM inhibitors. These data identify a new signaling axis responsible for hypoxia-independent activation of HIF-1 and expand our understanding of the tumorigenic role of PIM1 in solid tumors.

Pim-3 alleviates lipopolysaccharide-stimulated AR42J pancreatic acinar cell injury via improving the inflammatory microenvironment

Acute pancreatitis (AP) is a common acute abdominal disease characterized by pancreatic aseptic inflammation, with ~20% of patients progressing to severe AP (SAP) with a high mortality rate. The aim of this study was to explore the protective effects of Pim-3 proto-oncogene, serine/threonine kinase (Pim-3) on rat pancreatic acinar AR4-2J cells damaged by lipopolysaccharide (LPS). The recombinant plasmid p-enhanced green fluorescent protein (pEGFP)-N2/Pim-3 was transiently transfected into AR42J cells and the AR42J cells were then treated with 2 µg/ml LPS. Subsequently, the proliferation of AR42J cells was detected using MTT assay. The cell cycle progression and apoptosis rate of the AR42J cells were examined using flow cytometry. AR42J cell migration was assessed using wound healing assays. Additionally, RT-semi quantitative PCR and western blot analyses were used to detect the mRNA and protein expression levels, respectively, of Pim-3, interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, intercellular adhesion molecule (ICAM)-1 and Occludin in AR42J cells. The results revealed that proliferation of AR42J cells was significantly enhanced and cell apoptosis was markedly reduced in the pEGFP-N2/Pim-3 + LPS group. The proportion of AR42J cells in G1 phase in the pEGFP-N2/Pim-3 + LPS group was decreased, whereas the proportion of cells in the G2 and S phases was increased. The wound healing assays demonstrated that AR42J cell migration was significantly increased in the pEGFP-N2/Pim-3 + LPS group. Finally, the expression levels of IL-6, IL-1β, TNF-α and ICAM-1 were significantly decreased in the pEGFP-N2/Pim-3 + LPS group, whereas the expression of Occludin was significantly increased. The present study demonstrated that raised expression levels of Pim-3 can protect AR42J cells from LPS-induced injury by modifying the inflammatory microenvironment, suggesting that Pim-3 may be a potential target for AP or SAP therapy.

Pim kinase isoforms: devils defending cancer cells from therapeutic and immune attacks

Pim kinases are being implicated in oncogenic process in various human cancers. Pim kinases primarily deal with three broad categories of functions such as tumorigenesis, protecting cells from apoptotic signals and evading immune attacks. Here in this review, we discuss the regulation of Pim kinases and their expression, and how these kinases defend cancer cells from therapeutic and immune attacks with special emphasis on how Pim kinases maintain their own expression during apoptosis and cellular transformation, defend mitochondria during apoptosis, defend cancer cells from immune attack, defend cancer cells from therapeutic attack, choose localization, self-regulation, activation of oncogenic transcription, metabolic regulation and so on. In addition, we also discuss how Pim kinases contribute to tumorigenesis by regulating cellular transformation and glycolysis to reinforce the importance of Pim kinases in cancer and cancer stem cells.

Pim-3 Regulates Stemness of Pancreatic Cancer Cells via Activating STAT3 Signaling Pathway

Due to its aggressiveness and unusual resistance to conventional therapies, pancreatic cancer is a highly lethal gastrointestinal malignancy with poor prognosis. According to the cancer stem cell hypothesis, there exists a fraction of cancer cells, that is, cancer stem cells, responsible for tumor maintenance and therapeutic failure. Herein we investigated the involvement of proto-oncogene Pim-3 in driving the stemness properties in pancreatic cancer. Expression levels of several stemness-associated markers were examined in several pancreatic cancer cell lines. The double positive (CD24+ESA+) and double negative (CD24-ESA-) pancreatic cancer cells were isolated from PANC-1 and L3.6pl, and their self-renewal ability, tumorigenicity as well as sensitivity to gemcitabine were then evaluated. Results showed that there existed heterogeneity in expression levels of stemness-associated surface markers among pancreatic cancer cell lines. CD24+ESA+ pancreatic cancer cells exhibited increased tumorigenicity and decreased chemosensitivity to gemcitabine as compared to CD24-ESA- cells. Besides, the double positive (CD24+ESA+) subpopulation also exhibited greater expression level of Pim-3 when compared with the double negative (CD24-ESA-) ones. Furthermore, silencing of Pim-3 in pancreatic cancer cells leads to decreased proportions of both single positive (CD24+ and ESA+) and double positive (CD24+ESA+) pancreatic cancer cells. Overexpression of Pim-3 was associated with increased levels of some stemness-associated transcription factors (STAT3, etc.). Moreover, the phosphorylation level and transcriptional activity of STAT3 were decreased in Pim-3 silenced pancreatic cancer cells and restoration of its activity results in restitution of stem cell-like phenotypes. Therefore, Pim-3 maintains stemness of pancreatic cancer cells via activating STAT3 signaling pathway and might be used as a novel therapeutic target in pancreatic cancer.

Pim-3 is a Critical Risk Factor in Development and Prognosis of Prostate Cancer

BACKGROUND Pim-3 kinase is a highly homologous serine/threonine kinase that is overexpressed in hematological malignancies and solid tumors. Few studies have been conducted to define the role of Pim-3 in solid tumors, especially in prostate cancer. The aim of this study was to define the role of Pim-3 in development and prognosis of prostate cancer. MATERIAL AND METHODS We collected specimens from 160 patients with prostate cancer, as well as 100 patients with benign prostatic hyperplasia. Realtime polymerase chain reaction was used for the assessment of Pim-3 expression at the RNA level and Western blot was used to quantify the Pim-3 protein synthesis in 3 different cell lines. RESULTS We found that Pim-3 mRNA expression in prostate cancer tissue was significantly higher than that in benign prostatic hyperplasia tissue (p<0.05). Accordingly, the protein level expression of Pim-3 in prostate cancer cell lines was also significantly higher than that in control cells. In addition, the expression status of Pim-3 mRNA was significantly associated with pathological parameters such as pre-surgery prostate specific antigen, Gleason score, pathological stage, and lymphoid metastasis. High expression of Pim-3 also significantly decreased the survival rate of patients after surgery. CONCLUSIONS Pim-3 expression is an important risk factor for prostate cancer; we are the first team to report Pim-3 as a valuable biomarker in Chinese.

MiR-377 inhibits the proliferation of pancreatic cancer by targeting Pim-3

MicroRNAs (miRNAs) play important roles in the regulation of various tumor biological processes including proliferation and apoptosis. MiR-377 has been implicated in many types of cancer, whereas its expressional feature and potential biological function in pancreatic ductal adenocarcinoma (PDAC) remains unclear. In this study, we scanned the global miRNA expression profiles in PDAC from The Cancer Genome Atlas (TCGA) and found miR-377 was down-regulated significantly in PDAC. Then, its expression was measured in both pancreatic cancer tissues and cells; the data showed that miR-377 was de-regulated and inversely correlated with pathologic parameters of tumor growth or metastasis. We generated PDAC cell lines with stable overexpression or inhibition of miR-377, and our results indicated that miR-377 up-regulation significantly promoted cell viability, proliferation, and migration in PDAC cells, and also induced cell apoptosis and cell cycle arrest simultaneously. Binding-site predictions by bioinformatics showed that Pim-3 might be a potential target of miR-377. Luciferase reporter assay ulteriorly identified that miR-377 suppressed Pim-3 expression by binding the 3'-UTR. In tumor tissues, we also showed that the Pim-3 expression was inversely correlated with that of miR-377. Furthermore, stable ectopic miR-377 expression in pancreatic cancer cell lines suppressed Pim-3 expression, leading to the attenuation of Bad phosphorylation level at its Ser112 and promoting cell apoptosis. Overall, these results reveal that miR-377 may have tumor growth suppression function by down-regulating Pim-3 kinase expression to inhibit both pancreatic tumor growth and migration, and induce cell apoptosis. Hence, miR-377 may be a potential diagnostic marker and therapeutic target.

PIM-1 contributes to the malignancy of pancreatic cancer and displays diagnostic and prognostic value

Background

The effects of PIM-1 on the progression of pancreatic cancer remain unclear, and the prognostic value of PIM-1 levels in tissues is controversial. Additionally, the expression levels and clinical value of PIM-1 in plasma have not been reported.

Methods

The effects of PIM-1 on biological behaviours were analysed. PIM-1 levels in tissues and plasma were detected, and the clinical value was evaluated.

Results

We found that PIM-1 knockdown in pancreatic cancer cells suppressed proliferation, induced cell cycle arrest, enhanced apoptosis, resensitized cells to gemcitabine and erlotinib treatment, and inhibited ABCG2 and EZH2 mRNA expression. Our results indicated that PIM-1 and the EGFR pathway formed a positive feedback loop. We also found that PIM-1 expression in pancreatic cancer tissues was significantly upregulated and that a high level of expression was negatively associated with prognosis (P = 0.025, hazard ratio [HR] =2.113, 95 % confidence interval: 1.046–4.266). Additionally, we found that plasma PIM-1 levels in patients with pancreatic cancer were significantly increased and could be used in the diagnosis of pancreatic cancer. High plasma PIM-1 expression was an independent adverse prognostic factor for pancreatic cancer (P = 0.037, HR = 1.87, 95 % CI: 1.04–3.35).

Conclusion

Our study suggests that PIM-1 contributes to malignancy and has diagnostic and prognostic value in pancreatic cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0406-z) contains supplementary material, which is available to authorized users.

PIM kinases: an overview in tumors and recent advances in pancreatic cancer

The PIM kinases represent a family of serine/threonine kinases, which is composed of three different members (PIM1, PIM2 and PIM3). Aberrant expression of PIM kinases is observed in variety of tumors, including pancreatic cancer. The PIM kinases play pivotal roles in the regulation of cell cycle, apoptosis, properties of stem cells, metabolism, autophagy, drug resistance and targeted therapy. The roles of PIM kinases in pancreatic cancer include the regulation of proliferation, apoptosis, cell cycle, formation, angiogenesis and prediction prognosis. Blocking the activities of PIM kinases could prevent pancreatic cancer development. PIM kinases may be a novel target for cancer therapy.

Pathophysiological roles of Pim-3 kinase in pancreatic cancer development and progression

Pim-3 is a member of the provirus integration site for Moloney murine leukemia virus (Pim) family proteins that exhibit serine/threonine kinase activity. Similar to the other Pim kinases (Pim-1 and Pim-2), Pim-3 is involved in many cellular processes, including cell proliferation, survival, and protein synthesis. Although Pim-3 is expressed in normal vital organs, it is overexpressed particularly in tumor tissues of endoderm-derived organs, including the liver, pancreas, and colon. Silencing of Pim-3 expression can retard in vitro cell proliferation of hepatocellular, pancreatic, and colon carcinoma cell lines by promoting cell apoptosis. Pim-3 lacks the regulatory domains similarly as Pim-1 and Pim-2 lack, and therefore, Pim-3 can exhibit its kinase activity once it is expressed. Pim-3 expression is regulated at transcriptional and post-transcriptional levels by transcription factors (e.g., Ets-1) and post-translational modifiers (e.g., translationally-controlled tumor protein), respectively. Pim-3 could promote growth and angiogenesis of human pancreatic cancer cells in vivo in an orthotopic nude mouse model. Furthermore, a Pim-3 kinase inhibitor inhibited cell proliferation when human pancreatic cancer cells were injected into nude mice, without inducing any major adverse effects. Thus, Pim-3 kinase may serve as a novel molecular target for developing targeting drugs against pancreatic and other types of cancer.

Pim-3 promotes human pancreatic cancer growth by regulating tumor vasculogenesis

Pim-3, a proto-oncogene with serine/threonine kinase activity, is aberrantly expressed in malignant lesions, but not in normal pancreatic tissues. To assess the role of Pim-3 in human pancreatic carcinogenesis in vivo and to determine the underlying Pim-3 signaling regulatory mechanisms, we established MiaPaca-2 cells overexpressing wild-type Pim-3 or Pim-3 kinase dead mutants (K69M-Pim-3) as well as PCI55 cells stably expressing Pim-3 shRNA or scrambled shRNA in a tetracycline-inducible manner. In addition, we conducted studies utilizing a nude mouse tumor xenograft model. Our results demonstrated that cells stably overexpressing wild-type Pim-3 exhibited functionally enhanced phosphorylation of Bad at Ser112 and increased proliferation. In contrast, the stable inactivation of Pim-3 by K69M-Pim-3 or silencing of Pim-3 expression by Pim-3 shRNA resulted in functionally decreased phosphorylation of Bad at Ser112 and higher apoptotic cells. Following subcutaneous injection of these stable cell lines, nude mice injected with Pim-3 overexpressing cells developed 100% subcutaneous tumors, together with increased PCNA-positive cells and enhanced intratumoral CD31-positive vascular areas. On the other hand, intratumoral neovascularization and tumor cell proliferation was attenuated in mice injected with Pim-3 kinase inactive cells, eventually reducing tumorigenicity in these mice to 46.6%. Moreover, Pim-3 overexpression upregulated the intratumoral levels of pSTAT3Try705, pSurvivinThr34, HGF, EGF, FGF-2 and VEGF, while the increases were markedly diminished on Pim-3 kinase inactivation. Collectively, the Pim-3 kinase emerges as being involved in accelerating human pancreatic cancer development and in promoting tumor neovascularization and subsequent tumor growth. Targeting Pim-3 may play a dual role in halting tumor progression, by promoting tumor cell death and blocking angiogenesis.

A novel regulatory mechanism of Pim-3 kinase stability and its involvement in pancreatic cancer progression

Translationally controlled tumor protein (TCTP/TPT1) was identified from a yeast 2-hybrid screen and shown to interact with Pim-3, a member of the proto-oncogene Pim family with serine/threonine kinase activity. TCTP was aberrantly expressed in human pancreatic cancer cells and malignant ductal epithelial cells, but not in normal pancreatic duct epithelial cells adjacent to tumor foci of human pancreatic cancer tissue. Moreover, TCTP colocalized with Pim-3 both in human pancreatic cancer cells and in clinical tissues. Mapping studies revealed that the interaction between Pim-3 and TCTP occurred through the C-terminal region of Pim-3 and N-terminal region of TCTP. Although Pim-3 had no effect on TCTP expression or phosphorylation, overexpression of TCTP increased the amount of Pim-3 in a dose-dependent manner. Interestingly, RNAi-mediated ablation of TCTP expression reduced Pim-3 protein but not mRNA, through a mechanism involving the ubiquitin-proteasome degradation system. As a consequence of Pim-3 instability and subsequent degradation, tumor growth in vitro and in vivo was inhibited by arresting cell-cycle progression and enhancing apoptosis. Furthermore, TCTP and Pim-3 expression were significantly correlated in pancreatic adenocarcinoma specimens, and patients with highly expressed TCTP and Pim-3 presented with a more advanced tumor stage. These observations indicate that TCTP enhances Pim-3 stability to simultaneously promote and prevent cell-cycle progression and apoptosis, respectively. Hence, TCTP and Pim-3 serve a pivotal role in human pancreatic cancer with important ramifications for clinical diagnostic and therapeutic implications.

IMPLICATIONS

The present study provides a new idea and experimental evidence for recognizing TCTP/Pim-3 pathway as a target for therapy in human pancreatic cancer.