EMBO/SourceData huggingface dataset:
Figure 2 (A). Purification of KLF4 protein complex in the presence and absence of DNA damage based on TAP-KLF4 stable expression cells (U2OS). Proteins that interacted with KLF4 were purified from U2OS cells expressing FLAG and HA-tagged KLF4 in the absence and presence of 5 Gy radiation at 4h after the treatment. The accumulated bind induced in response to radiation was isolated for mass spectrometry analysis. PARP1 was identified as a binding partner for KLF4.  (C). The purified complex was further confirmed by Western blot detected by FLAG-KLF4, PARP1(lane 1). The interaction between KLF4 and PARP1 was significantly increased in response to γ-radiation detected by pulldown experiment (lane 3 and 4).  (D) Validation of interaction between ectopically expressed KLF4 and PARP1. 293T cells were transfected with FLAG-KLF4 and Myc-PARP. Whole cell lysates or IP complex pulled down by anti-FLAG antibody were analyzed by Western blotting.  (E) Validation of interaction between endogenous KLF4 and PARP1 in cytosolic lysate and nuclear lysate using immunoprecipitation and Western blotting in MDA-MB-231 cells. The Histone 3 (H3) is the control for nuclear portion, and actin is the control for cytosol portion.  (F) Co-immunoprecipitation of PARP1 with endogenous KLF4 is independent on DNA. The DNA binding inhibitor EtBr was added to the MDA-MB-231 cell lyses followed by immunoprecipitation of KLF4 complex. Co-localization analysis for endogenous PARP1 and KLF4 in MDA-MB-231 cells. PARP1 and KLF4 are co-localized in the nucleus, and this co-localization is increased by in response to radiation. Scale bars, 5 μm. ectopic expressed GFP-PARP1 and DsRed-KLF4 in MDA-MB-231 cells. PARP1 and KLF4 are co-localized in the nucleus, and this co-localization is increased by in response to radiation. Scale bars, 5 μm.  (I). Validation of the interaction between endogenous KLF4 and PARP1 by in situ proximity ligation assay (PLA). No positive staining in KLF4/Rabbit IgG antibody PLA assay. Scale bar, 100 µm. The right panel show the blow-up.  (J) KLF4 was poly(ADP-ribosyl)ated. KLF4 was immunoprecipitated and detected by anti-PAR and anti-KLF4 antibodies in MDA-MB-231 cells.  (K) The PARylation of KLF4 was increased after exposure to DNA damage. KLF4 complex was purified using immunoprecipitation from MDA-MB-231 cells that were treated with 5 µM doxorubicin and were then collected at different times (1h, 2h, 4h and 8h). PARylation was detected by using antibody against PAR.  (L) Loss of PARP1 attenuates KLF4 PARylation. PARP1+/+ and PARP1-/- MEFs cells were transfected with FLAG-KLF4 followed by 4h after 5 Gy radiation, and then the PARylation of KLF4 was detected by pulldown.  (M) PARP1 inhibitors decrease KLF4 PARylation. U2OS cells were pretreated with 10 µM various PARP1 inhibitor niraparib, Olaparib and rucaparib for 1hr followed by exposure to10 Gy radiation for 4 hours. KLF4 was pulled down and the PARylation was detected.
Figure 3 (A) Expression of PARP1 and KLF4 in mammary gland epithelial cell and various types of breast cancer cell lines.  (B). Accumulation of PARP1 and KLF4 protein were detected in human breast cancer tissues with 183 breast invasive ductal carcinoma and 10 pairs of primary cancer and adjacent normal tissue specimens by IHC in comparison with adjacent normal breast tissues. Scale bars, 100 μm. Statistic results of KLF4 IHC staining. Normal (n=10), tumor (n=183); p = 4.36x10-7 (KLF4) one-way ANOVA was used for the statistical analysis.Statistic results of PARP1 IHC staining. Normal (n=10), tumor (n=183) p = 0.0473 (PARP1). one-way ANOVA was used for the statistical analysis.(E) Statistical analysis of PARP1 staining among normal (n=10), ER/PR positive (ER/PR) (n=68), HER2 positive (n=62), and triple negative breast cancer (TNBC) (n=48). The p values were labeled in figure, one-way ANOVA was used for the statistical analysis. (F) Statistical analysis of KLF4 protein staining among normal (n=10), ER/PR positive (n=68), HER2 positive (n=62) and TNBC (n=47). The p values were labeled in figure, one-way ANOVA was used for the statistical analysis.  Elevated expression of PARP1 and KLF4 are significantly correlated in 183 breast invasive ductal carcinoma human breast cancer tissue specimens (same batch of staining as (B)). Represents of paired IHC staining of PARP1 and KLF4 (case 1-3) are shown (G). Scale bars, 100 μm.  (H) Statistic analysis of IHC staining indicates that PARP1 expression is positively correlated with KLF4 expression in breast cancer. n=183, r=0.434, p=8.68x10-10, Pearson correlation coefficients.  (I) Survival analysis of KLF4 protein expression in 117 breast cancer patients. Compared to patients with low KLF4 protein expression, patients with high KLF4 levels had an inferior cumulative survival rate (Kaplan-Meier assay, LogRank P=0.012); Low, staining weak and moderate; High, staining strong.  (J) Survival analysis of both KLF4 and PARP1 protein expression in 66 breast cancer patients. Compared to patients with both low KLF4 and PARP1 protein expression levels, patients with both high KLF4 and PARP1 levels had lower cumulative survival rate (Kaplan-Meier assay, LogRank P=0.022).
Figure 4(B) Identification of amino acid stretch 411- 441 on the repression domain of KLF4 as a segment mediating the interaction with PARP1 in 293T cells..(D). Identification of amino acid stretch 411- 441 on the Zinc 2 domain of KLF4 involved in mediating its PARylation modification in 293T cells.. PARylation for Flag tagged KLF4 deletion mutants were analyzed, respectively, by pulldown using PAR antibody followed by Western blotting using antibody against Flag.(E) Dissection of the PARylation region of KLF4 into three zinc finger motif-containing domains, Zinc 1, Zinc 2 and Zinc 3. While no effect was observed on Zinc 1 and Zinc 3 domains, deletion of Zinc 2 domain led to significant attenuation of KLF4 PARylation.(G) Identification of amino acid stretch 829-1014 on the C-terminal segment of PARP1 to be involved in mediating its interaction with KLF4 in 293T cells.
Figure 5(B) The effect of YYR motif mutations on KLF4 PARylation. Constructs of KLF4-Zinc 1-YKH/AAA mutation, KLF4-Zinc 2-YYR/AAA mutation and KLF4-Zinc-2-Y451A mutation were co-transfected with Myc-PARP1 into 293T cells, respectively, and then pulled-down using M2 agarose followed by measuring KLF4 PARylation with anti-PAR antibody. (C) KLF4-Zinc 2-YYR/AAA mutation has only effect on KLF4 PARylation but not on other types posttranslational modifications such as protein methylation, ubiquitylation, acetylation and sumoylation in 293T cells. The FLAG-tagged wild-type or mutant KLF4 were immunoprecipitated with FLAG and detected by anti-SYM10 (methylation), anti-SUMO (sumoylation), Anti-ac-lysine (acetylation), anti-Ub (ubiquitination) and anti-PAR (PARylation).  Effect of PARP1 on the distribution of KLF4 subcellular localization among cytosol, soluble nucleus and chromatin in MDA-MB-231 cells. While the activation of PARP1 in response to genotoxic stress enhances chromatin recruitment of KLF4 ORC2 were the loading control for chromatid fraction. Ponceau S were the control of nuclear soluble fraction.  E) Effect of PARP1 on the distribution of KLF4 subcellular localization among cytosol, soluble nucleus and chromatin in MDA-MB-231 cells. , inhibition of PARP1 by Olaparib attenuates the KLF4 accumulation in chromatin fraction H3 were the loading control for chromatid fraction. PARP1 were the control of nuclear soluble fraction.  (F) KLF4-Zinc 2-YYR/AAA mutation remarkably reduces DNA damage-induced chromatin recruitment of ectopic expressed KLF4 in U2OS cells. ORC2 is the loading control for chromatid fraction.  (G). Confocal analysis of PAR and FLAG-tagged KLF4 showing that KLF4-Zinc 2-YYR/AAA mutation significantly reduces KLF4 PARylation in U2OS cells. Scale bars, 10 μm.  (I) The effect of PARP1 mutations (H909A or T824A) on KLF4 PARylation, confirming the critical role of H909 in mediating KLF4 PARylation in 293T cells. Myc-PARP1 wildtype or mutations (H909A or T824A) and FLAG-KLF4 were co-transfected into 293T cells and then the FLAG-KLF4 was pulldown by anti-FLAG antibody, the PARylation modification of KLF4 was blotted with anti-PAR antibody, and the binding PARP1 was blotted with anti-myc antibody.  (J). Replacement of this histidine by alanine on PARP1 or replacement of the YYR motif of KLF4 by triple alanines leads to the attenuation of KLF4 PARylation. In PARP1-/- MEFs, wild-type or mutant PARP1 (H909A) were co-transfected with FLAG-tagged wild-type or KLF4-Zinc 2-YYR/AAA mutation followed by immunoprecipitation using M2-agarose and Western blotting by anti-PAR antibody.  (K) KLF4 PARylation enhances its transcriptional function demonstrated by p21 promoter luciferase assay. 293T cells were co-transfected with p21 luciferase reporter plasmid with wild-type or mutant KLF4 (YYR/AAA) and wild-type or mutant PARP1 (H909A) and then submitted to luciferase assay. n=3, p=4.74x10-6 (PARP1WT vs PARP1H909A), Data are mean ± SEM; one-way ANOVA was used for the statistical analysis.
Figure 8 (A) Depletion of KLF4 significantly enhances the efficacy of Olaparib in killing TNBC cells (4T1). 4T1 cells with stable expression of shKLF4 were implanted into mammary fat pad of BALB/c Nude mice. Drug treatment was started at 10th day. Placebo or Olaparib at the dose of 100 mg/kg was administrated daily for twelve days. Tumor volumes were measured every other day. Tumor volumes were measured every other day. n=9 per group, p values were labeled in figure, one-way ANOVA assay.  (B & C) The image of 4T1 xenograft tumors (B) and tumors were weighed and summarized (C). n=9 per group, p values were labeled in figure, one-way ANOVA assay.  The combination effect when combine of Olaparib with ABT-263 and dasatinib in suppression MDA-MB-231 xenograft tumor growth. 8 weeks SCID/Beige female mice were injected 8x106 MDA-MB-231 cells in matrigel (1:1 volume). When tumor reach to 50mm3, 100mg/kg Olaparib (dissolve in 2%DMSO+30%PEG400+saline) was administrated by oral gavage daily, 30mg/kg ABT-263 (dissolve in 5%DMSO) was administrated by intraperitoneal injection every other day, 50mg/kg Olaparib (dissolve in 2%DMSO+30%PEG400+saline) or placebo (2%DMSO+30%PEG400+saline) were administrated by oral gavage every other day. Mice were treated with single or combination drugs for four weeks. Tumor volumes were measured every other day (F). The image of MDA-MB-231 xenograft tumors  The combination effect when combine of Olaparib with ABT-263 and dasatinib in suppression MDA-MB-231 xenograft tumor growth. 8 weeks SCID/Beige female mice were injected 8x106 MDA-MB-231 cells in matrigel (1:1 volume). When tumor reach to 50mm3, 100mg/kg Olaparib (dissolve in 2%DMSO+30%PEG400+saline) was administrated by oral gavage daily, 30mg/kg ABT-263 (dissolve in 5%DMSO) was administrated by intraperitoneal injection every other day, 50mg/kg Olaparib (dissolve in 2%DMSO+30%PEG400+saline) or placebo (2%DMSO+30%PEG400+saline) were administrated by oral gavage every other day. Mice were treated with single or combination drugs for four weeks. Tumor volumes were measured every other day (G). The tumors were weighed and summarized (H). Placebo (n=7), ABT263 (n=9), Dasatinib (n=8), Olaparib (n=6), Olaparib+ABT263 (n=9), Olaparib+Dasatinib (n=10), p values were labeled in figure, one-way ANOVA assay. (I) Staining of H & E, KLF4, PARP1, p21 and Bax in MDA-MB-231 xenograft tumors. Scale bars, 100 μm. Combination of ABT-263 or dasatinib with Olaparib treatment decrease KLF4 and p21expression, but increase Bax expression in xenograft tumors.
Figure 1Kaplan-Meier survival graph indicates prolonged life span of Wwox knockout mice injected with AAV9-hSynI-mWwox [total n=18, spontaneously dead n=6, mice taken out for electrophysiology/electron microscopy/analysis, are shown in yellow, n=12] compared to mice injected with AAV9-hSynI-GFP (n=6) or the non-injected (n=8 (P <0.0001, Log-rank Mantel-Cox test).Immunofluorescence images showing the expression of WWOX (red) in brain tissue (cortex) at P17 from WT and Wwox null mice that were injected with AAV9-hSynI-mWwox (2x1010). Neurons are labelled with anti-NeuN antibody (green). The square white box shows the magnified area. White arrows show the transgene expression in NeuN positive cells. Graph showing the percentage of NeuN and WWOX double positive cells in different parts of the brain (Cortex, Hippocampus and Cerebellum) from KO mice injected with AAV-mWwox at P17. NeuN and WWOX double positive cells were calculated from 3 identical sagittal sections of the AAV-mWwox injected mice (n=3) brains.
Figure 2Kaplan-Meier survival graph indicates prolonged life span of Wwox knockout mice injected with AAV9-hWWOX [total n=16, alive n=6, spontaneously dead n=6, 4 mice (shown in yellow) were taken out for analysis) compared to the non-injected (n=8)] (P <0.0001, Log-rank Mantel-Cox test).D-F. Immunofluorescence images showing the expression of WWOX (magenta) in cortex (D), Hippocampus (E) and Cerebellum (F) at P19 from WT and Wwox null mice that were injected with AAV-hWWOX (2x1010) or Wwox null alone. Neurons are labelled with anti-NeuN antibody (green). The square white box shows the magnified area.   Graph represents the percentage of neurons showing the transgene (NeuN and WWOX positive) expression at different parts (cortex, hippocampus and cerebellum) of the KO brain at P19 after AAV injection. NeuN and WWOX double positive cells were calculated from 3 identical sagittal sections of the AAV-hWWOX injected mice (n=3) brains.
Figure 3Representative traces of cell-attached recordings performed in WT (blue), KO (red) and KO injected with either with AAV9-hSynI-mWwox (KO+A-mW shown in purple) or AAV9-hSynI-hWWOX (KO+A-hW shown in green) pups at P18-21 days. Traces represent spontaneous neocortical activity (action potentials shown). The panels represent 12 s recording with an inset presenting a zoom-in of an 0.5 s interval.   The graph shows the recordings (P18-21) averages over 30 neurons from WT (n=3), 30 neurons from KO+A-mWwox (n=3), 30 neurons from KO+A-hWWOX (n=3), and 45 neurons from KO (n=3).   Immunofluorescence staining with anti-GFAP (shown in green) and anti-Iba1 (shown in magenta) antibodies showing the expression of astrocytes and microglia at P19 from WT, KO and KO+A-hWWOX. The square white box shows the magnified area from CA3 regions of hippocampus from all the genotypes. F, G. Graphs represents the quantification of GFAP (F) and Iba1 (G) positive cells from the images shown in E. The number of GFAP or Iba1 cells were counted from 3 identical sagittal sections from CA3 region per group (n=3 per each genotype). H. Immunocytochemical images showing astrocytes (anti-GFAP) and microglia (anti-Iba1) in CA3 region of hippocampus from WT (n=3) and rescued (KO+AAV-hWWOX) (n=3) mice at 9 months. Magnified area is shown with square box. I, J. Graphs represents the quantification of GFAP (I) and Iba1 (J) positive cells from the images shown in H. The number of GFAP or Iba1 cells were counted from 3 identical sagittal sections (paraffin embedded) from CA3 region per group (n=3 per each genotype).
Figure 4Images of whole brain sagittal sections that were immunolabelled with anti-MBP at P17 from indicated mice (n=3 for each group). MBP staining (shown in gray) in cortex (green dotted line represents the border of the cortex), hippocampus and cerebellum is presented (magnified from the top panel).Sagittal section of the brain (P17) tissues immunostained for CC1 (green) and PDGFRα (magenta). Images showing increased number of matured oligodendrocytes in corpus callosum of the Wwox null after treatment with AAV-mWwox compared to Wwox null injected with AAV-GFP virus.   Graph represents the quantification of CC1 and PDGFRα positive cells in corpus callosum (area 0.5 mm2) of WT (n=3), KO (n=3) and KO+A-mWwox (n=3) counted from three similar brain sagittal sections per mouse in each genotype.
Figure 5Electron micrograph (EM) images from mid sagittal section of corpus callosum showing increased number of myelinated axons in AAV9-hSynI-mWwox-injected mice compared to Wwox-null mice (KO) at P17.   Graph showing average number of myelinated axons in corpus callosum from WT (n=3), KO (n=3) or KO mice injected with AAV9-hSynI-mWwox (n=3) per field of view (FOV).   g-ratio analysis showing reduced myelin thickness of axons in corpus callosum KO (n=3) compared to the KO+AAV-Wwox (n=3). Axon diameter and myelin thickness was calculated from the electron micrograph images of corpus callosum (total no of axons n=350 per each group).   EM images showing increased number of myelinated axons in optic nerve in AAV9-hSynI-mWwox injected mice compared to KO mice at P17.   Graph showing the average number of myelinated axons (counted per FOV) in optic nerve from WT (n=3), KO (n=3) and KO+AAV-mWwox(n=3).   g-ratio's of myelinated axons from optic nerves showing improved myelin thickness (less g-ratio) after WWOX restoration (KO+AAV-mWwox) compared to KO alone (n=3 per genotype, total no of axons n=200 per each group).
Figure 6Representative images of open field test showing tracking pattern (open arena) of WT (females, n=7, males n=6) and AAV-mWwox-injected KO mice (females n=7, males n=5) at 8-10 weeks. Dot plot graphs represent the velocity (B), total distance travelled (C)
Figure 2A. Western analysis of nuclear (N) or cytoplasmic (C) fractions from whole cell lysates (W) from A549 cells (RL WT), RNase L knock out A549 cells (RL KO), or A549 cells with either wild-type RNase L (NLS-RL-WT) or RNase L-R667A (NLS-RL-CM) fused to a nuclear localization signal sequence. Short and long exposure with anti-RL antibody. GAPDH protein used as cytoplasmic marker. Histone H3 protein used as nuclear marker. B. Graph depicting the fraction of RNase L found in the nucleus or cytoplasm. Mean and SEM of two experiments with individual experiment values plotted.C. FISH with probes to GAPDH mRNA or oligo(dT) to detect poly(A)+ RNA in A549 cells without or with either NLS-RL-WT or NLS-RL-CM either mock transfected or transfected with poly(I:C) for 4 hours. Scale bar 5 micron.D. Graph depicting median and the value of the intensity of oligo(dT) fluorescence in individual nuclei divided by nuclear volume in the indicated cell types either mock transfected or transfected with poly(I:C) for 4 hours. At least 43 nuclei analyzed per condition.
Figure 3Analysis of nuclear RNA granules in A549 cells with RNase L targeted to the nucleus (NLS-RL-WT) either mock transfected or treated with poly(I:C) (PIC) for 4 to 5 hours. A. FISH analysis to detect poly(A)+ RNA and nucleolar-localized snoRD3A RNA. IF analysis to detect nucleolar granular component protein nucleophosmin (NPM1). B. Graph of the mean and value of the average volume of individual snoRD3A foci in nuclei. 17 nuclei mock treated cells, 31 nuclei PIC treated cells. C. Fraction of nuclei with NPM1 protein enriched in ring structures classified as granular component assemblies or dispersed in nucleoplasm. 17 nuclei mock treated cells, 31 nuclei PIC treated cells.Analysis of nuclear RNA granules in A549 cells with RNase L targeted to the nucleus (NLS-RL-WT) either mock transfected or treated with poly(I:C) (PIC) for 4 to 5 hours. D. IF analysis to detect dense fibrillar component protein, ribosome processing factor 1 (RPF1). E. Graph of the mean and value of the average volume of individual snoRD3A foci in nuclei. 43 nuclei mock treated cells, 69 nuclei PIC treated cells. F. Graph of the mean and value of the average volume of RPF1 foci in 43 mock treated cells and 69 nuclei PIC treated cells.Analysis of nuclear RNA granules in A549 cells with RNase L targeted to the nucleus (NLS-RL-WT) either mock transfected or treated with poly(I:C) (PIC) for 4 to 5 hours. G. FISH analysis to detect poly(A)+ RNA and nuclear speckle-localized MALAT1 RNA and IF analysis with anti-sc35 antibody to detect nuclear speckle protein SRRM2. H. Graph of the mean and value of the intensity of MALAT1 signal divided by the nuclear volume of individual nuclei. 51 nuclei mock treated cells, 56 nuclei PIC treated cells. I. Graph of the median and value of the volume of individual SRRM2 foci in nuclei. Mock 1526 SRRM2 foci in 51 nuclei. PIC 136 SRRM2 foci in 20 nuclei that contain <10 SRRM2 foci.Analysis of nuclear RNA granules in A549 cells with RNase L targeted to the nucleus (NLS-RL-WT) either mock transfected or treated with poly(I:C) (PIC) for 4 to 5 hours. J. FISH analysis to detect poly(A)+ RNA and IF analysis to detect Cajal body protein coilin. K. Graph depicting the fraction of nuclei in mock and PIC treated cells with decreased oligo(dT) with different distributions of coilin protein. 90 nuclei in mock treated cells, 192 nuclei in PIC treated cells.
Figure 5Analysis of A549 cells with NLS-RL-WT or NLS-RL-CM either mock transfected or treated with poly(I:C) (PIC) for 5 hours. A. FISH analysis to detect poly(A)+ RNA and IF analysis against FUS protein. Images are a single 0.2 micron Z section.Analysis of A549 cells with NLS-RL-WT or NLS-RL-CM either mock transfected or treated with poly(I:C) (PIC) for 5 hours. B. Graph depicting the fraction of nuclei with FUS dispersed in the nucleoplasm or in foci in cells with reduced nuclear oligo(dT) signal. All the nuclei (total) in which nuclear RNA was degraded (N=64) or the same nuclei classified as to whether or not they contained residual poly(A) foci. Nuclei with poly(A) foci (N=14). Nuclei without poly(A) foci (N=50).Analysis of A549 cells with NLS-RL-WT either mock transfected or treated with poly(I:C) (PIC) for 5 hours. C. FISH analysis to detect poly(A)+ RNA and IF analysis against mediator complex protein, MED1, to detect super-enhancer condensates. D. Number of MED1 foci in mock and PIC treated NLS-RL-WT cells. E. Average volume of individual MED1 foci in mock and PIC treated NLS-RL-WT cells.Analysis of A549 cells with NLS-RL-WT either mock transfected or treated with poly(I:C) (PIC) for 5 hours. F. FISH analysis to detect poly(A)+ RNA and IF analysis against BRD4, to detect super-enhancer condensates. G. Number of BRD4 foci in mock and PIC treated NLS-RL-WT cells. H. Average volume of individual BRD4 foci in mock and PIC treated NLS-RL-WT cells.
Figure 1B) Volcano plot of quantified proteins. Log2 fold change was determined as the difference between the mean LFQ intensity of the four replicates of telomeric to control sequence and p-values were calculated with a Welch t-test. Proteins above the threshold p=0.05, s0=1, c=0.5 (dashed line) are considered enriched. Abbreviations: LFQ: Label free quantificationD) Heatmap of LFQ intensity of proteins enriched at DNA baits. Telomere interactors are indicated on the right side of the heatmap. Color code indicates measured log2 LFQ intensities in the telomere pull-down. RNA binding proteins are marked with a black box on the left side of the figure. Abbreviations: LFQ: Label free quantification RBP: RNA binding proteinE) Critically short telomeres arise after 90 population doublings in the absence of telomerase (tlc1). Genomic DNA was extracted at indicated population doublings and digested with XhoI. A radioactive probe was used to recognize telomeric DNA in a southern blot. Abbreviations: PD: population doubling.F) tlc1 cells reach senescence at PD 80-100. %viability of indicated strains after propagation in YPD is indicated at different population doublings n=3. Asterisk indicates population doubling used in G) to determine binding of Npl3 to short telomeres by TAP-ChIP. 3 independent spores from the indicated genotypes were used. Population doublings are counted from germination of meiotic products and hence begin at approx. PD40. Abbreviations: TAP: tandem affinity purification tagG) Npl3-TAP associates strongly to short telomeres. Cross-linked samples from indicated strains were used in a TAP-ChIP. Enrichment at telomeres was determined by quantitative PCR on indicated telomeres. Data represents mean % input +/- SEM n=3 (paired t-test one tailed *p<0.05, **p<0.01). PD90 refers to 90 population doublings in the absence of TLC1 (telomerase RNA subunit). The no tag control serves as an indicator of non-specific background signal. Abbreviations: TAP: tandem affinity purification tag, PD: population doubling.