Biochemical evidence for conformational variants in the anti-viral and pro-metastatic protein IFITM1

Interferon induced transmembrane proteins (IFITMs) play a dual role in the restriction of RNA viruses and in cancer progression, yet the mechanism of their action remains unknown. Currently, there is no data about the basic biochemical features or biophysical properties of the IFITM1 protein. In this work, we report on description and biochemical characterization of three conformational variants/oligomeric species of recombinant IFITM1 protein derived from an E. coli expression system. The protein was extracted from the membrane fraction, affinity purified, and separated by size exclusion chromatography where two distinct oligomeric species were observed in addition to the expected monomer. These species remained stable upon re-chromatography and were designated as “dimer” and “oligomer” according to their estimated molecular weight. The dimer was found to be less stable compared to the oligomer using circular dichroism thermal denaturation and incubation with a reducing agent. A two-site ELISA and HDX mass spectrometry suggested the existence of structural motif within the N-terminal part of IFITM1 which might be significant in oligomer formation. Together, these data show the unusual propensity of recombinant IFITM1 to naturally assemble into very stable oligomeric species whose study might shed light on IFITM1 anti-viral and pro-oncogenic functions in cells

ΔNp63 transcriptionally regulates ATM to control p53 Serine-15 phosphorylation

Background: Delta Np63 alpha is an epithelial progenitor cell marker that maintains epidermal stem cell self-renewal capacity. Previous studies revealed that UV-damage induced p53 phosphorylation is confined to Delta Np63 alpha-positive cells in the basal layer of human epithelium. Results: We now report that phosphorylation of the p53 tumour suppressor is positively regulated by Delta Np63 alpha in immortalised human keratinocytes. Delta Np63 alpha depletion by RNAi reduces steady-state ATM mRNA and protein levels, and attenuates p53 Serine-15 phosphorylation. Conversely, ectopic expression of Delta Np63 alpha in p63-null tumour cells stimulates ATM transcription and p53 Serine-15 phosphorylation. We show that ATM is a direct Delta Np63 alpha transcriptional target and that the Delta Np63 alpha response element localizes to the ATM promoter CCAAT sequence. Structure-function analysis revealed that the Delta Np63-specific TA2 transactivation domain mediates ATM transcription in coordination with the DNA binding and SAM domains. Conclusions: Germline p63 point mutations are associated with a range of ectodermal developmental disorders, and targeted p63 deletion in the skin causes premature ageing. The Delta Np63 alpha-ATM-p53 damage-response pathway may therefore function in epithelial development, carcinogenesis and the ageing processes

Emergent Role of IFITM1/3 towards Splicing Factor (SRSF1) and Antigen-Presenting Molecule (HLA-B) in Cervical Cancer

The IFITM restriction factors play a role in cancer cell progression through undefined mechanisms. We investigate new protein–protein interactions for IFITM1/3 in the context of cancer that would shed some light on how IFITM1/3 attenuate the expression of targeted proteins such as HLA-B. SBP-tagged IFITM1 protein was used to identify an association of IFITM1 protein with the SRSF1 splicing factor and transporter of mRNA to the ribosome. Using in situ proximity ligation assays, we confirmed a predominant cytosolic protein–protein association for SRSF1 and IFITM1/3. Accordingly, IFITM1/3 interacted with HLA-B mRNA in response to IFNγ stimulation using RNA–protein proximity ligation assays. In addition, RT-qPCR assays in IFITM1/IFITM3 null cells and wt-SiHa cells indicated that HLA-B gene expression at the mRNA level does not account for lowered HLA-B protein synthesis in response to IFNγ. Complementary, shotgun RNA sequencing did not show major transcript differences between IFITM1/IFITM3 null cells and wt-SiHa cells. Furthermore, ribosome profiling using sucrose gradient sedimentation identified a reduction in 80S ribosomal fraction an IFITM1/IFITM3 null cells compared to wild type. It was partially reverted by IFITM1/3 complementation. Our data link IFITM1/3 proteins to HLA-B mRNA and SRSF1 and, all together, our results begin to elucidate how IFITM1/3 catalyze the synthesis of target proteins. IFITMs are widely studied for their role in inhibiting viruses, and multiple studies have associated IFITMs with cancer progression. Our study has identified new proteins associated with IFITMs which support their role in mediating protein expression; a pivotal function that is highly relevant for viral infection and cancer progression. Our results suggest that IFITM1/3 affect the expression of targeted proteins; among them, we identified HLA-B. Changes in HLA-B expression could impact the presentation and recognition of oncogenic antigens on the cell surface by cytotoxic T cells and, ultimately, limit tumor cell eradication. In addition, the role of IFITMs in mediating protein abundance is relevant, as it has the potential for regulating the expression of viral and oncogenic proteins

∆Np63/p40 correlates with the location and phenotype of basal/mesenchymal cancer stem-like cells in human ER+ and HER2+ breast cancers

ΔNp63, also known as p40, regulates stemness of normal mammary gland epithelium and provides stem cell characteristics in basal and HER2‐driven murine breast cancer models. Whilst ΔNp63/p40 is a characteristic feature of normal basal cells and basal‐type triple‐negative breast cancer, some receptor‐positive breast cancers express ΔNp63/p40 and its overexpression imparts cancer stem cell‐like properties in ER+ cell lines. However, the incidence of ER+ and HER2+ tumours that express ΔNp63/p40 is unclear and the phenotype of ΔNp63/p40+ cells in these tumours remains uncertain. Using immunohistochemistry with p63 isoform‐specific antibodies, we identified a ΔNp63/p40+ tumour cell subpopulation in 100 of 173 (58%) non‐triple negative breast cancers and the presence of this population associated with improved survival in patients with ER−/HER2+ tumours (p = 0.006). Furthermore, 41% of ER+/PR+ and/or HER2+ locally metastatic breast cancers expressed ΔNp63/p40, and these cells commonly accounted for <1% of the metastatic tumour cell population that localised to the tumour/stroma interface, exhibited an undifferentiated phenotype and were CD44+/ALDH−. In vitro studies revealed that MCF7 and T47D (ER+) and BT‐474 (HER2+) breast cancer cell lines similarly contained a small subpopulation of ΔNp63/p40+ cells that increased in mammospheres. In vivo, MCF7 xenografts contained ΔNp63/p40+ cells with a similar phenotype to primary ER+ cancers. Consistent with tumour samples, these cells also showed a distinct location at the tumour/stroma interface, suggesting a role for paracrine factors in the induction or maintenance of ΔNp63/p40. Thus, ΔNp63/p40 is commonly present in a small population of tumour cells with a distinct phenotype and location in ER+ and/or HER2+ human breast cancers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153532/1/cjp2149_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153532/2/cjp2149.pd

A DHODH inhibitor increases p53 synthesis and enhances tumor cell killing by p53 degradation blockage

ML, CD, IvL, GP, TM, SD, MS, APF, CT, DL, MAH, KL and SL: project grants from the Swedish Research Council, the Swedish Cancer Society and the Swedish Childhood Cancer Foundation. MHi and JC: Cancer Research UK (C8/A6613). MC, EP and WE: Wellcome Trust (073915). MN and BV: projects MEYS-NPS-LO1413 and GACR P206/12/G151. EMC, MP, MMS, ZF and PG: Norwegian Cancer Society (182735, 732200) and Helse Vest (911884, 911789). RB and SC: NIH (R01 CA95684), the Leukemia and Lymphoma Society and the Waxman Foundation. NW, AH, Ad’H: Cancer Research UK (C21383/A6950) and Engineering and Physical Sciences Research Council Doctoral Training Program. JL and YZ: Cancer Research UK (C240/A15751). MH and BW: SARomics Biostructures ABUY, KF: DDDP SciLife, Sweden. LJ, MHa, RS and A-LG: CBCS, Sweden. VP: SciLife fellowship. AT: Breast Cancer Research Scotland.The development of non-genotoxic therapies that activate wild-type p53 in tumors is of great interest since the discovery of p53 as a tumor suppressor. Here we report the identification of over 100 small-molecules activating p53 in cells. We elucidate the mechanism of action of a chiral tetrahydroindazole (HZ00), and through target deconvolution, we deduce that its active enantiomer (R)-HZ00, inhibits dihydroorotate dehydrogenase (DHODH). The chiral specificity of HZ05, a more potent analog, is revealed by the crystal structure of the (R)-HZ05/DHODH complex. Twelve other DHODH inhibitor chemotypes are detailed among the p53 activators, which identifies DHODH as a frequent target for structurally diverse compounds. We observe that HZ compounds accumulate cancer cells in S-phase, increase p53 synthesis, and synergize with an inhibitor of p53 degradation to reduce tumor growth in vivo. We, therefore, propose a strategy to promote cancer cell killing by p53 instead of its reversible cell cycle arresting effect.Publisher PDFPeer reviewe

Intracellular distribution of the ΔNp73 protein isoform in medulloblastoma cells: a study with newly generated rabbit polyclonal antibodies

The p73 protein is a member of the p53 family of transcription factors that has two N-terminal isoforms: the TAp73 isoform is reported to have a tumor suppressor function, whereas the ΔNp73 isoform likely has oncogenic potential. The expression of these isoforms and the differences in their intracellular distribution have been described in many cancer types; however, little is known about the p73 isoforms in brain tumors. Our study is focused on the intracellular localization of ΔNp73 in medulloblastoma cell lines. Due to a lack of suitable anti-ΔNp73 antibodies, we developed two new rabbit polyclonal antibodies, ΔNp73- 26 and Δ Np73-27, with sufficient specificity, as demonstrated by immunodetection methods using transiently transfected cell lines. Both of these new antibodies were subsequently used for analysis of the ΔNp73 distribution in medulloblastoma cells using immunofluorescence, immunoblotting and immunogold labeling for transmission electron microscopy. We found a nuclear localization of the ΔNp73 isoform in all of the medulloblastoma cell lines included in this study. Furthermore, a non-random accumulation of the ΔNp73 isoform near the cell nuclei was observable in all of these cell lines. By double-labeling with ΔNp73 and golgin-97, we showed the co-localization of the ΔNp73 isoform with the Golgi apparatus. Nevertheless, further detailed analyses of possible interactions of ΔNp73 with the proteins accumulated in the Golgi apparatus should be performed to explain the dynamics of ΔNp73 outside the cell nucleus

The diverse oncogenic and tumour suppressor roles of p63 and p73 in cancer: a review by cancer site

p63 and p73, the two other members of the p53 family, were identified almost 15 years ago. Here, we review their potential use for diagnosis, prognosis and prediction of response to therapy in various cancers. The two genes show distinct expression patterns in both normal and cancer tissues and each gene gives rise to multiple protein isoforms with different activities, including those with tumour-suppressor or oncogenic effects. Despite such complexity, some common themes emerge; p63 is commonly overexpressed as the ΔNp63 isoform and sometimes associated with TP63 amplification, whereas p73 is often reduced (by methylation or gene loss), or there is an increase in the ratio of ΔNp73 to TAp73. These generalisations do not apply universally; TAp63 is overexpressed in haematological malignancies, TP63 mis-sense mutations have been reported in squamous cancers and TP63 translocations occur in lymphomas and some lung adenocarcinomas. There are associations with disease prognosis and response to specific therapies in individual cancer types for both p63 and p73, making their analysis of clinical relevance. We also discuss their utility for aiding in differential diagnosis, which has been demonstrated for p63, but not yet for p73. Throughout, we highlight the discrepant nature of many studies due to the variable methodologies employed, the lack of systematic evaluation of isoforms and the problems of poor antibody characterization and crossreactions within the p63/p73 family. Finally, we emphasize the value of recently developed isoformspecific reagents that have clear advantages for the study of p63 and p73 experimentally and clinically