Piwil2 inhibits keratin 8 degradation through promoting p38-induced phosphorylation to resist Fas-mediated apoptosis

PIWIL2 Regulates the Proliferation, Apoptosis and Colony Formation of Colorectal Cancer Cell Line

Background

Tumor cells proliferation and apoptosis inhibition are the mechanisms through which the Colorectal Cancer (CRC) progression, metastasis and chemoresistance are promoted pathologically, offering clinical advantages for characterizing their molecular regulators.

Objectives

In this study, to unravel the role of PIWIL2 as a potential CRC oncogenic regulator, we examined the effect of its overexpression on proliferation, apoptosis and colony formation of SW480 colon cancer cell line.

Material and Methods

Established SW480-P (overexpression of PIWIL2) and SW480-control (SW480-empty vector) cell lines were cultured in DMEM containing 10% FBS with 1% penicillin-streptomycin. The total DNA and RNA was extracted for further experiments. Real-Time PCR and western blotting assay were performed to measure the differential expression of proliferation associated genes including the expression of cell cycle and anti-apoptotic genes as well as Ki-67 and PIWIL2 in both cell lines. Cell proliferation was determined using MTT assay, doubling time assay and the colony formation rate of transfected cells was measured with the 2D colony formation assay.

Results

At the molecular level, PIWIL2 overexpression was associated with significant up-regulation of cyclin D1, STAT3, BCL2-L1, BCL2-L2 and Ki-67 genes. MTT and doubling time assay showed that PIWIL2 expression induced time-related effects on proliferation rate of SW480 cells. Moreover, SW480-P cells had markedly greater capacity to form colonies.

Conclusions

PIWIL2 plays important roles to promote cancer cell proliferation and colonization via the cell cycle acceleration and inhibition of apoptosis, the mechanisms through which this gene seems to contribute to CRC development, metastasis and chemoresistance, hence potentially highlighting PIWIL2 targeted therapy as a valuable tool for CRC treatment.

Identification and Characterization of Piwi-Interacting RNAs for Early Testicular Development in Yak

Normal testicular development plays a crucial role in male reproduction and is the precondition for spermatogenesis. PIWI-interacting RNAs (piRNAs) are novel noncoding RNAs expressed in animal germ cells that form complexes with PIWI family proteins and are involved in germ cell development, differentiation, and spermatogenesis. However, changes in piRNA expression profiles during early testicular development in yak have not been investigated. In this study, we used small RNA sequencing to evaluate the differences and potential functions of piRNA expression profiles in 6-, 18-, and 30-month-old yak testis tissues. Differential expression analysis found 109, 293, and 336 differentially expressed piRNAs in M30 vs. M18, M18 vs. M6, and M30 vs. M6, respectively, and found 30 common differentially expressed piRNAs in the three groups of M6, M18, and M30. In addition, the functional enrichment analysis of differentially expressed piRNAs target genes indicated that they were related to testicular development and spermatogenesis. Finally, we detected the expression of the PIWI protein family in the yak testis at different developmental stages and found that PIWIL1, PIWIL2, PIWIL3, and PIWIL4 were highly expressed in 18- and 30-month-old yak testis and almost not expressed in 6-month-old yak testis. In conclusion, this study summarizes the changes of piRNA expression patterns during the early development of yak testis and provides new clues for the regulatory role of piRNA in yak testis.

Emerging roles of PIWI-interacting RNAs (piRNAs) and PIWI proteins in head and neck cancer and their potential clinical implications

Head and neck squamous cell carcinoma (HNSCC) are among the well-known neoplasms originating in the oral cavity, pharynx, and larynx. Despite advancements in chemotherapy, radiotherapy, and surgery, the survival rates of the patients are low, which has posed a major therapeutic challenge. A growing number of non-coding RNAs (ncRNAs), for instance, microRNAs, have been identified whose abnormal expression patterns have been implicated in HNSCC. However, more recently, several seminal research has shown that piwi-interacting RNAs (piRNAs), a promising and young class of small ncRNA, are linked to the emergence and progression of cancer. They can regulate transposable elements (TE) and gene expression through multiple mechanisms, making them potentially more powerful regulators than miRNAs. Hence, they can be more promising ncRNAs candidates for cancer therapeutic intervention. Here, we surveyed the roles and clinical implications of piRNAs and their PIWI proteins partners in tumorigenesis and associated molecular processes of cancer, with a particular focus on HNSCC, to offer a new avenue for diagnosis, prognosis, and therapeutic interventions for the malignancy, improving patient's outcomes.

A novel tumor-specific broad-spectral monoclonal antibody to PL2L60 is highly effective for the treatment of various types of cancers from human and mouse

There are numerous antibodies used for cancer therapy in clinic, but they are essentially less efficacy than expected. None of them has tumor-specific and broad-spectral properties. PIWIL2-like (PL2L) protein 60 (PL2L60) is a product of alienated activation of PIWIL2 gene, and has been found to be specifically and widely expressed in various types of cancers, including hematopoietic and solid ones. Current study aims to investigate whether a monoclonal antibody (mAb) to PL2L60 has both tumor-specific and broad-spectral properties, which can be used universally to treat various types of cancers. The expression of PL2L60 protein in the cell surface and cytoplasm were determined in a panel of human and mouse tumor cell lines by flow cytometry, immunofluorescent microscopy and Western Blotting. The apoptosis and the cell cycle arrest of the tumor cells treated with mAb KAO3 were evaluated by flow cytometry. The tumorigenesis of the mAb KAO3-pretreated tumor cells was determined by tumor incidence and tumor size, and the efficacy of mAb KAO3 treatment on tumor growth in tumors-bearing mice were kinetically evaluated. Complement-dependent cytotoxicity (CDC) assay was used to determine the capacity of mAb KAO3 to kill tumor cells. Treatment of human or mouse tumor cells from hematopoietic or solid tumors with mAb KAO3 at the time of inoculation efficiently inhibited tumorigenesis in the severe combined immunodeficient (SCID) mice. Moreover, injection of mAb KAO3 into established tumors significantly inhibited their growth, and prolonged survival of the tumor-bearing mice, including lymphoma, breast cancer, lung cancer and cervical cancer. The efficacy of mAb KAO3 treatment is likely associated with its binding to PL2L60 expressed on tumor cell surface, which may lead to cancer cell death through blocking cell cycling and/or activation of complement. In conclusion, we have identified a tumor-specific mAb to PL2L60 (KAO3), which may be used potentially to treat all the types of human cancers including from both hematopoietic and solid ones.

The cytoskeleton and connected elements in bone cell mechano-transduction

Bone is a mechano-responsive tissue that adapts to changes in its mechanical environment. Increases in strain lead to increased bone mass acquisition, whereas decreases in strain lead to a loss of bone mass. Given that mechanical stress is a regulator of bone mass and quality, it is important to understand how bone cells sense and transduce these mechanical cues into biological changes to identify druggable targets that can be exploited to restore bone cell mechano-sensitivity or to mimic mechanical load. Many studies have identified individual cytoskeletal components - microtubules, actin, and intermediate filaments - as mechano-sensors in bone. However, given the high interconnectedness and interaction between individual cytoskeletal components, and that they can assemble into multiple discreet cellular structures, it is likely that the cytoskeleton as a whole, rather than one specific component, is necessary for proper bone cell mechano-transduction. This review will examine the role of each cytoskeletal element in bone cell mechano-transduction and will present a unified view of how these elements interact and work together to create a mechano-sensor that is necessary to control bone formation following mechanical stress.

Generation of a tissue-specific transgenic model for K8 phosphomutants: A tool to investigate the role of K8 phosphorylation during skin carcinogenesis in vivo

Keratin 8/18, the predominant keratin pair of simple epithelia, is known to be aberrantly expressed in several squamous cell carcinomas (SCCs), where its expression is often correlated with increased invasion, neoplastic progression, and poor prognosis. The majority of keratin 8/18 structural and regulatory functions are governed by posttranslational modifications, particularly phosphorylation. Apart from filament reorganization, cellular processes including cell cycle, cell growth, cellular stress, and apoptosis are known to be orchestrated by K8 phosphorylation at specific residues in the head and tail domains. Even though deregulation of K8 phosphorylation at two significant sites (Serine⁷³ /Serine⁴³¹ ) has been implicated in neoplastic progression of SCCs by various in vitro studies, including ours, it is reported to be highly context-dependent. Therefore, to delineate the precise role of Kereatin 8 phosphorylation in cancer initiation and progression, we have developed the tissue-specific transgenic mouse model expressing Keratin 8 wild type and phosphodead mutants under Keratin 14 promoter. Subjecting these mice to 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate-mediated skin carcinogenesis revealed that Keratin 8 phosphorylation may lead to an early onset of tumors compared to Keratin 8 wild-type expressing mice. Conclusively, the transgenic mouse model developed in the present study ascertained a positive impact of Keratin 8 phosphorylation on the neoplastic transformation of skin-squamous cells.

PIWIL2 interacting with IKK to regulate autophagy and apoptosis in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies and cause of death from cancer in China. Previous studies showed that autophagy and apoptosis inhibition are critical for the survival of ESCC cells. However, the underlying mechanisms remain to be clarified. Recently, we found that PIWIL2, a novel cancer testis protein, is highly expressed in ESCC and associated with high T-stage and poor 5-year survival rate in patients. Our further study showed that PIWIL2 can directly bind to IKK and promote its phosphorylation, leading to phosphorylation of IκB and subsequently nuclear translocation of NF-κB for apoptosis inhibition. Meanwhile, PIWIL2 competitively inhibits binding of IKK to TSC1, and thus deactivate mTORC1 pathway which suppresses ULK1 phosphorylation and initiation of autophagy. The mouse xenograft model suggested that PIWIL2 can promote ESCC growth in an IKK-dependent manner. This present work firstly revealed that PIWIL2 can play a role in regulating autophagy and apoptosis, and is associated with poor prognosis in ESCC patients, providing novel insights into the roles of PIWIL2 in tumorigenesis.

A Comprehensive Molecular and Clinical Analysis of the piRNA Pathway Genes in Ovarian Cancer

Simple Summary

Although ovarian cancer (OC) is one of the most lethal gynecological cancers, its development and progression remain poorly understood. The piRNA pathway is important for transposon defense and genome stability. piRNA maturation and function involve a number of genes known as the piRNA pathway genes. These genes have recently been implicated in cancer development and progression but information about their role in OC is limited. Our work aimed to provide a better understanding of the roles of piRNA pathway genes in OC. Through analyzing changes in the abundance of 10 piRNA pathway genes, we discovered gene expression differences in benign vs. cancer, chemosensitive vs. chemoresistant and post hormone treatment in OC samples and cells. Furthermore, we observed the differential effects of these genes on patient survival and OC cell invasion. Overall, this work supports a role of the piRNA pathway genes in OC progression and encourages further study of their clinical relevance.

Abstract

Ovarian cancer (OC) is one of the most lethal gynecological malignancies, yet molecular mechanisms underlying its origin and progression remain poorly understood. With increasing reports of piRNA pathway deregulation in various cancers, we aimed to better understand its role in OC through a comprehensive analysis of key genes: PIWIL1-4, DDX4, HENMT1, MAEL, PLD6, TDRD1,9 and mutants of PIWIL1 (P1∆17) and PIWIL2 (PL2L60). High-throughput qRT-PCR (n = 45) and CSIOVDB (n = 3431) showed differential gene expression when comparing benign ovarian tumors, low grade OC and high grade serous OC (HGSOC). Significant correlation of disparate piRNA pathway gene expression levels with better progression free, post-progression free and overall survival suggests a complex role of this pathway in OC. We discovered PIWIL3 expression in chemosensitive but not chemoresistant primary HGSOC cells, providing a potential target against chemoresistant disease. As a first, we revealed that follicle stimulating hormone increased PIWIL2 expression in OV-90 cells. PIWIL1, P1∆17, PIWIL2, PL2L60 and MAEL overexpression in vitro and in vivo decreased motility and invasion of OVCAR-3 and OV-90 cells. Interestingly, P1∆17 and PL2L60, induced increased motility and invasion compared to PIWIL1 and PIWIL2. Our results in HGSOC highlight the intricate role piRNA pathway genes play in the development of malignant neoplasms.

The role of Nrf2/PIWIL2/purine metabolism axis in controlling radiation-induced lung fibrosis

NF-E2-related factor 2 (Nrf2) is a key transcription factor recently implicated in the control of radiation-induced lung fibrosis (RILF). However, the molecular mechanism of Nrf2 in the pathogenesis of RILF is still unclear. The purpose of this study was to evaluate the regulatory effect and mechanism of Nrf2 in the pathogenesis of RILF. The effects of different Nrf2 expression levels on RILF were explored in vitro and in vivo. The RILF model of Nrf2 knockout mice was established for in vivo study. In the study of the mechanism of action, ChIP-seq assay and metabolomics analysis were performed. The discovered mechanism of Nrf2-mediated RILF alleviation was further validated in vitro and in vivo. We found that overexpression of Nrf2 significantly alleviated the fibrosis caused by irradiation in vivo and in vitro. Conversely, Nrf2 silencing strongly aggravated the development of RILF. Mechanistically, Nrf2 signaling increased the expression of piwi-like RNA-mediated gene silencing 2 (PIWIL2), leading to the alteration of purine metabolism and contributing to the relief of RILF. These results suggest that Nrf2 promotes the attenuation of RILF in vivo and in vitro by directly targeting PIWIL2 and activating purine metabolism.

Piwi-like 1 and -2 protein expression levels are prognostic factors for muscle invasive urothelial bladder cancer patients

Piwi-like proteins are essential for stem-cell maintenance and self-renewal in multicellular organisms. We analyzed the expression of Piwi-like 1 and Piwi-like 2 by immunohistochemistry (IHC) in 95 muscle invasive bladder cancer (MIBC) samples using tissue microarray. Application of an immunoreactive score (IRS) revealed 37 and 45 patients who were Piwi-like 1 and -2 positive (IRS > 2). IHC results were correlated with clinico-pathological and survival data. The expression of both proteins was positively correlated with each other, lymph node metastasis and expression of CK20 and GATA 3. A negative correlation for both proteins was detected for disease-specific survival (DSS), recurrence, Ki67/MIB1 proliferation index, and CK5 expression. Detection of Piwi-like 1 protein positivity was associated with poor DSS (P = 0.019; log rank test, Kaplan-Meier analysis), and in multivariate Cox’s analysis (adjusted to tumor stage and tumor grade), it was an independent prognostic factor for DSS (RR = 2.16; P = 0.011). Piwi-like 2 positivity was associated with DSS (P = 0.008) and recurrence-free survival (RFS; P = 0.040), and in multivariate Cox’s analysis, Piwi-like 2 positivity was an independent prognostic factor for DSS (RR = 2.46; P = 0.004) and RFS (RR = 3.0; P = 0.003). Most interestingly, in the basal type patient subgroup (CK5+/GATA3−), Piwi-like 2 positivity was associated with poorer DSS, OS and RFS (P < 0.001, P = 0.004 and P = 0.05; log rank test). In multivariate analysis, Piwi-like 2 positivity was an independent prognostic factor for DSS (RR = 12.70; P = 0.001), OS (RR = 6.62;  = 0.008) and RFS (RR=13.0; P = 0.040). In summary, Piwi-like 1 and -2 positivity are associated with clinico-pathological factors and survival. Both Piwi-like proteins are suggested as biomarkers for MIBC patients.

PIWI proteins contribute to apoptosis during the UPR in human airway epithelial cells

Small noncoding microRNAs (miRNAs) post-transcriptionally regulate a large portion of the human transcriptome. miRNAs have been shown to play an important role in the unfolded protein response (UPR), a cellular adaptive mechanism that is important in alleviating endoplasmic reticulum (ER) stress and promoting cell recovery. Another class of small noncoding RNAs, the Piwi-interacting RNAs (piRNAs) together with PIWI proteins, was originally shown to play a role as repressors of germline transposable elements. More recent studies, however, indicate that P-element induced WImpy proteins (PIWI proteins) and piRNAs also regulate mRNA levels in somatic tissues. Using genome-wide small RNA next generation sequencing, cell viability assays, and caspase activity assays in human airway epithelial cells, we demonstrate that ER stress specifically up-regulates total piRNA expression profiles, and these changes correlate with UPR-induced apoptosis as shown by up-regulation of two pro-apoptotic factor mRNAs, CHOP and NOXA. Furthermore, siRNA knockdown of PIWIL2 and PIWIL4, two proteins involved in piRNA function, attenuates UPR-related cell death, inhibits piRNA expression, and inhibits the up-regulation of CHOP and NOXA mRNA expression. Hence, we provide evidence that PIWIL2 and PIWIL4 proteins, and potentially the up-regulated piRNAs, constitute a novel epigenetic mechanism that control cellular fate during the UPR.

CLOCK and BMAL1 stabilize and activate RHOA to promote F-actin formation in cancer cells

Circadian genes control most of the physiological functions in cancer cells, including cell proliferation, migration, and invasion. The CLOCK and BMAL1 complex plays a central role in circadian rhythms. Previous studies have shown that circadian genes may act as oncogenes or tumor-suppressor genes. In addition, F-actin, regulated by RHOA, has been shown to participate in tumor progression. However, the roles of the CLOCK and BMAL1 genes in the regulation of tumor progression via the RHOA-ROCK-CFL pathway remain largely unclear. Here we first indicate that the rearrangement of F-actin is regulated by CLOCK and BMAL1. We found that CLOCK and BMAL1 can upregulate RHOA expression by inhibiting CUL3-mediated ubiquitination and activate RHOA by reducing the interaction between RHOA and RhoGDI. Consequently, CLOCK and BMAL1 control the expression of the components of the RHOA-ROCK-CFL pathway, which alters the dynamics of F-actin/G-actin turnover and promotes cancer cell proliferation, migration, and invasion. In conclusion, our research proposes a novel insight into the role of CLOCK and BMAL1 in tumor cells.

The role of 17β‑estradiol‑induced upregulation of Piwi‑like 4 in modulating gene expression and motility in breast cancer cells

A majority of breast cancer cases are positive for the estrogen receptor (ER), which means that they can respond to the estrogen hormone to achieve growth. Hence, the ER signaling pathway has been extensively targeted in pharmaceutical research and development in order to suppress tumor growth. However, prevalent hormone therapy and targeted therapy often become ineffective as cancer cells ultimately develop resistance, suggesting that there could be unidentified signaling molecules and events that regulate breast cancer growth. Notably, recent studies have uncovered that Piwi-like (Piwil) proteins, which were initially found in germline cells, are expressed in a wide spectrum of human cancers, including breast cancers. Although Piwil proteins have been well established to silence retrotransposons and to promote heterochromatin formation in germline cells, their somatic functions in cancer cells remain largely unknown. In the present study, we profiled the expression of four Piwi homologs in an ER-positive breast cancer cell line, MCF-7, and found that only Piwil4 was upregulated by 17β-estradiol treatment. Notably, Piwil4 upregulation was not observed in an ER-positive but non-tumorigenic breast cancer cell line, MCF-12A. In addition, the induced expression of Piwil4 was dependent on estrogen/ERα signaling. To explore the biological significance of Piwil4 in breast cancer growth, we knocked down Piwil4 with multiple siRNAs and observed the suppressed expression of some canonical targets of ER. The knockdown of Piwil4 expression also decreased the migration and invasion capabilities of MCF-7 cells. Furthermore, the loss-of-function of Piwil4 reduced the motility of MCF-7 cells in wound-healing assays, which could be associated to decreased expression of vimentin and N-cadherin. Collectively, these findings revealed that Piwil4 is a novel regulator of ER signaling that could be targeted to inhibit breast cancer growth and migration.

An unusual intragenic promoter of PIWIL2 contributes to aberrant activation of oncogenic PL2L60

PIWIL2-like (PL2L) protein 60 (PL2L60), a product of aberrantly activated PIWIL2 gene, is widely expressed in various types of tumors and may promote tumorigenesis. However, the mechanisms underlying the activation of expression of PL2L60 remain unknown. In this study, an intragenic promoter responsible for the activation of PL2L60 within the human PIWIL2 gene has been identified, cloned and characterized. The promoter of PL2L60 is located in the intron 10 of the host gene PIWIL2. Bioinformatic and mutagenic analysis reveals that this intragenic promoter within the sequence of 50 nucleotides contains two closely arranged cis-acting elements specific for the hepatic leukemia factor (HLF) in the positive strand and signal transducer and activator of transcription 3 (STAT3) in the negative strand. Chromatin immunoprecipitation analysis demonstrates that both the HLF and polymerase II (Pol II), a hallmark of active promoters, directly bind to the sequence, although STAT3 does not. Knockdown of HLF and STAT3 alone or both by RNA interference significantly reduced both promoter activity and the PL2L60 protein expression, although there is no additive effect. The expression of PL2L60 proteins was enhanced when host gene Piwil2 was genetically disrupted in a murine cell model. Taken together, we have identified a PL2L60-specific intragenic promoter in the host gene of PIWIL2, which is interdependently activated by HLF and STAT3 through steric interaction. This activation is dependent on cellular milieu rather than the integrity of host gene PIWIL2, highlighting a novel, important mechanism for a cancer-causing gene to be activated during tumorigenesis.

PIWIL2 suppresses Siah2-mediated degradation of HDAC3 and facilitates CK2α-mediated HDAC3 phosphorylation

HDAC3 is involved in deacetylation of histone and non-histone proteins, having a key role in the regulation of gene transcription and also in the process of tumorgenesis. However, how HDAC3 is regulated in cancer remains largely unclear. Here, we showed that PIWIL2 can interact with HDAC3, leading to stabilization of HDAC3 from ubiquitin-mediated degradation by competitive association with E3 ubiquitin ligase Siah2. Furthermore, we found that expression of PIWIL2 enhanced HDAC3 activity via CK2α. PIWIL2 facilitated the interaction between HDAC3 and CK2α, thus exhibiting a promotion on the HDAC3 phosphorylation by CK2α. Further work showed that PIWIL2 could promote cell proliferation and suppress cell apoptosis via regulating HDAC3. Our present study firstly revealed that PIWIL2 can play a role in HDAC3-mediated epigenetic regulation on cancer cell proliferation and apoptosis. These findings provide a novel insight into the roles of PIWIL2 in tumorigenesis.

Identification and verification of potential piRNAs from domesticated yak testis

PIWI-interacting RNAs (piRNA) are small non-coding RNA molecules expressed in animal germ cells that interact with PIWI family proteins to form RNA–protein complexes involved in epigenetic and post-transcriptional gene silencing of retrotransposons and other genetic elements in germ line cells, including reproductive stem cell self-sustainment, differentiation, meiosis and spermatogenesis. In the present study, we performed high-throughput sequencing of piRNAs in testis samples from yaks in different stages of sexual maturity. Deep sequencing of the small RNAs (18–40 nt in length) yielded 4,900,538 unique reads from a total of 53,035,635 reads. We identified yak small RNAs (18–30 nt) and performed functional characterization. Yak small RNAs showed a bimodal length distribution, with two peaks at 22 nt and >28 nt. More than 80% of the 3,106,033 putative piRNAs were mapped to 4637 piRNA-producing genomic clusters using RPKM. 6388 candidate piRNAs were identified from clean reads and the annotations were compared with the yak reference genome repeat region. Integrated network analysis suggested that some differentially expressed genes were involved in spermatogenesis through ECM–receptor interaction and PI3K-Akt signaling pathways. Our data provide novel insights into the molecular expression and regulation similarities and diversities in spermatogenesis and testicular development in yaks at different stages of sexual maturity.

Cancer/testis antigen PIWIL2 suppresses circadian rhythms by regulating the stability and activity of BMAL1 and CLOCK

Circadian rhythms are regulated by transcriptional and post-translational feedback loops generated by appropriate functions of clock proteins. Rhythmic degradation of the circadian clock proteins is critical for maintenance of the circadian oscillations. Notably, circadian clock does not work during spermatogenesis and can be disrupted in tumors. However, the underlying mechanism that suppresses circadian rhythms in germ cells and cancer cells remains largely unknown. Here we report that the cancer/testis antigen PIWIL2 can repress circadian rhythms both in the testis and cancer cells. By facilitating SRC binding with PI3K, PIWIL2 activates the PI3K-AKT pathway to phosphorylate and deactivate GSK3β, suppressing GSK3β-induced phosphorylation and degradation of circadian protein BMAL1 and CLOCK. Meanwhile, PIWIL2 can bind with E-Box sequences associated with the BMAL1/CLOCK complex to negatively regulate the transcriptional activation activity of promoters of clock-controlled genes. Taken together, our results first described a function for the germline-specific protein PIWIL2 in regulation of the circadian clock, providing a molecular link between spermatogenesis as well as tumorigenesis to the dysfunction of circadian rhythms.

HILI destabilizes microtubules by suppressing phosphorylation and Gigaxonin-mediated degradation of TBCB

Human PIWIL2, aka HILI, is a member of PIWI protein family and overexpresses in various tumors. However, the underlying mechanisms of HILI in tumorigenesis remain largely unknown. TBCB has a critical role in regulating microtubule dynamics and is overexpressed in many cancers. Here we report that HILI inhibits Gigaxonin-mediated TBCB ubiquitination and degradation by interacting with TBCB, promoting the binding between HSP90 and TBCB, and suppressing the interaction between Gigaxonin and TBCB. Meanwhile, HILI can also reduce phosphorylation level of TBCB induced by PAK1. Our results showed that HILI suppresses microtubule polymerization and promotes cell proliferation, migration and invasion via TBCB for the first time, revealing a novel mechanism for HILI in tumorigenesis.

Bovine piRNA-like RNAs are associated with both transposable elements and mRNAs

PIWI proteins and their associated piRNAs have been the focus of intensive research in the past decade; therefore, their participation in the maintenance of genomic integrity during spermatogenesis has been well established. Recent studies have suggested important roles for the PIWI/piRNA system outside of gametogenesis, based on the presence of piRNAs and PIWI proteins in several somatic tissues, cancers, and the early embryo. Here, we investigated the small RNA complement present in bovine gonads, gametes, and embryos through next-generation sequencing. A distinct piRNA population was present in the testis as expected. However, we also found a large population of slightly shorter, 24–27 nt piRNA-like RNA (pilRNAs) in pools of oocytes and zygotes. These oocyte and embryo pilRNAs exhibited many of the canonical characteristics of piRNAs including a 1U bias, the presence of a ‘ping-pong’ signature, genomic clustering, and transposable element targeting. Some of the major transposons targeted by oocyte and zygote pilRNA were from the LINE RTE and ERV1 classes. We also identified pools of pilRNA potentially derived from, or targeted at, specific mRNA sequences. We compared the frequency of these gene-associated pilRNAs to the fold change in the expression of respective mRNAs from two previously reported transcriptome datasets. We observed significant negative correlations between the number of pilRNAs targeting mRNAs, and their fold change in expression between the 4–8 cell and 8–16 cell stages. Together, these results represent one of the first characterizations of the PIWI/piRNA pathway in the translational bovine model, and in the novel context of embryogenesis.

Phosphorylation Impacts N-end Rule Degradation of the Proteolytically Activated Form of BMX Kinase

Cellular signaling leading to the initiation of apoptosis typically results in the activation of caspases, which in turn leads to the proteolytic generation of protein fragments with new or altered cellular functions. Increasing numbers of reports are demonstrating that the activity of many of these proteolytically activated protein fragments can be attenuated by their selective degradation by the N-end rule pathway. Here we report the first evidence that selective degradation of a caspase product by the N-end rule pathway can be modulated by phosphorylation. We demonstrate that the pro-apoptotic fragment of the bone marrow kinase on chromosome X (BMX) generated by caspase cleavage in the prostate cancer-derived PC3 cell line is metabolically unstable in cells because its N-terminal tryptophan targets it for proteasomal degradation via the N-end rule pathway. In addition, we have demonstrated that phosphorylation of tyrosine 566 relatively inhibits degradation of the C-terminal BMX catalytic fragment, and this phosphorylation is crucial for its pro-apoptotic function. Overall, our results demonstrate that cleaved BMX is a novel N-end rule substrate, and its degradation exhibits a novel interplay between substrate phosphorylation and N-end rule degradation, revealing an increasing complex regulatory network of apoptotic proteolytic signaling cascades.

Piwil 2 expression is correlated with disease-specific and progression-free survival of chemotherapy-treated bladder cancer patients

Piwi-like 2 (Piwil 2) belongs to the family of Argonaute genes/proteins. The expression of Piwil 2 is associated with stem cells. A role in tumorigenesis and/or tumor progression is proposed for different cancers but not yet for bladder cancer (BCa). We investigated the Piwil 2 expression by immunohistochemistry in a cohort of 202 BCa patients treated by cystectomy and adjuvant chemotherapy. The association between Piwil 2 expression and disease-specific (DSS) or progression-free survival (PFS) was calculated using Kaplan Meier analyses and univariate/multivariate Cox's regression hazard models.In a multivariate Cox's regression, Piwil 2 expression, either in the cytoplasm or the nucleus, was significantly associated with DSS and PFS. A weak cytoplasmic staining pattern was associated with poor DSS and tumor progression (RR=2.7; P=0.004 and RR=2.4; P=0.027). Likewise,, absent nuclear Piwil 2 immunoreactivity was associated with poor DSS and tumor progression (RR=2.3; P=0.023 and RR=2.2; P=0.022). BCa patients whose tumors exhibited a combination of weak cytoplasmic and absent nuclear immunoreactivity had a 6-fold increased risk of tumor-related death (P=0.005) compared to patients with strong expression. Considering only patients with high grade G3 tumors, a 7.8-fold risk of tumor-associated death and a 3.6-fold risk of tumor progression were detected independently of the histologic tumor subtype or the chemotherapy regimen. In summary, a combination of weak cytoplasmic and absent nuclear expression of Piwil 2 is significantly associated with an increased risk of DSS and tumor progression. This implicates that Piwil 2 could be a valuable prognostic marker for high-risk BCa patients.