MYBL2 Drives Prostate Cancer Plasticity: Inhibiting Its Transcriptional Target CDK2 for RB1-Deficient Neuroendocrine Prostate Cancer.

Phenotypic plasticity is a recognized mechanism driving therapeutic resistance in patients with prostate cancer. Although underlying molecular causations driving phenotypic plasticity have been identified, therapeutic success is yet to be achieved. To identify putative master regulator transcription factors (MR-TF) driving phenotypic plasticity in prostate cancer, this work utilized a multiomic approach using genetically engineered mouse models of prostate cancer combined with patient data to identify MYB proto-oncogene like 2 (MYBL2) as a significantly enriched transcription factor in prostate cancer exhibiting phenotypic plasticity. Genetic inhibition of Mybl2 using independent murine prostate cancer cell lines representing phenotypic plasticity demonstrated Mybl2 loss significantly decreased in vivo growth as well as cell fitness and repressed gene expression signatures involved in pluripotency and stemness. Because MYBL2 is currently not druggable, a MYBL2 gene signature was employed to identify cyclin-dependent kinase-2 (CDK2) as a potential therapeutic target. CDK2 inhibition phenocopied genetic loss of Mybl2 and significantly decreased in vivo tumor growth associated with enrichment of DNA damage. Together, this work demonstrates MYBL2 as an important MR-TF driving phenotypic plasticity in prostate cancer. Furthermore, high MYBL2 activity identifies prostate cancer that would be responsive to CDK2 inhibition. SIGNIFICANCE: Prostate cancers that escape therapy targeting the androgen receptor signaling pathways via phenotypic plasticity are currently untreatable. Our study identifies MYBL2 as a MR-TF in phenotypic plastic prostate cancer and implicates CDK2 inhibition as a novel therapeutic target for this most lethal subtype of prostate cancer.

Phenotypic Plasticity - Alternate Transcriptional Programs Driving Treatment Resistant Prostate Cancer.

Androgen deprivation therapy (ADT) that antagonizes androgen receptor (AR) signaling has made significant increases to overall survival of prostate cancer patients. However, ADT is not curative, and patients eventually progress to castration resistant disease (CRPC). It has become evident that a subset of prostate cancers acquire ADT resistance through mechanisms independent of AR alteration or reprogramming of AR signaling. This approximately involves a quarter of prostate cancers progressing on ADT. Collectively, these tumors evolve via phenotypic plasticity and display the activation of developmental and stemness gene signatures as well as transitional programs including an epithelial-mesenchymal phenotype. Currently, no successful treatments exist for prostate cancer patients to inhibit or reverse prostate tumor progression that utilizes mechanisms of epi-plasticity. This overview will discuss epigenetic mechanisms that mediate phenotypic plasticity and the potential for targeting the epigenome to create a novel direction for combination strategies involving epigenetic therapy to provide durable response.

An RNAi-independent role of AP1-like stress response factor Pap1 in centromere and mating-type silencing in Schizosaccaromyces pombe.

Gene silencing in S. pombe occurs by heterochromatin formation at the centromere (cen), mating-type (mat) and telomere loci. It is mediated by silencing factors including Swi6, Clr1-4, Rhp6 and Pola. RNAi pathway also plays a role in establishment of silencing at the mat and cen loci. Recently, the stress response factors, Atf1 and Pcr1were shown to play an RNAi-independent role in silencing at the mat3 locus through a cis-acting Atf1-binding site located within the repression element REIII and recruitment of the silencing factors Clr3 and Clr6. Another cis-acting site, named repression element REII abutting the mat2 locus, also establishes heterochromatin structure through Clr5 and histone deacetylases but independently of H3-Lys9-methylation and RNAi. Here, we report the occurrence of binding sites for another oxidative response factor, the pombe AP1- like factor Pap1, at the mating-type, centromere and telomere loci. By genetic studies we show that these sites play a role in silencing at the outer repeats of centromeres as well as mating-type locus and this effect is mediated through Pap1 binding site and interaction with and recruitment of the HP1/Swi6. Importantly, pap1Δ cells display a silencing defect even in absence of the oxidative stress. Such a role of Pap1 in heterochromatin formation may be evolutionarily conserved.

Identification of Genes Required for Enzalutamide Resistance in Castration-Resistant Prostate Cancer Cells In Vitro.

Castration-resistant prostate cancer can be treated with the antiandrogen enzalutamide, but responses and duration of response are variable. To identify genes that support enzalutamide resistance, we performed a short hairpin RNA (shRNA) screen in the bone-homing, castration-resistant prostate cancer cell line, C4-2B. We identified 11 genes (TFAP2C, CAD, SPDEF, EIF6, GABRG2, CDC37, PSMD12, COL5A2, AR, MAP3K11, and ACAT1) whose loss resulted in decreased cell survival in response to enzalutamide. To validate our screen, we performed transient knockdowns in C4-2B and 22Rv1 cells and evaluated cell survival in response to enzalutamide. Through these studies, we validated three genes (ACAT1, MAP3K11, and PSMD12) as supporters of enzalutamide resistance in vitro Although ACAT1 expression is lower in metastatic castration-resistant prostate cancer samples versus primary prostate cancer samples, knockdown of ACAT1 was sufficient to reduce cell survival in C4-2B and 22Rv1 cells. MAP3K11 expression increases with Gleason grade, and the highest expression is observed in metastatic castration-resistant disease. Knockdown of MAP3K11 reduced cell survival, and pharmacologic inhibition of MAP3K11 with CEP-1347 in combination with enzalutamide resulted in a dramatic increase in cell death. This was associated with decreased phosphorylation of AR-Serine650, which is required for maximal AR activation. Finally, although PSMD12 expression did not change during disease progression, knockdown of PSMD12 resulted in decreased AR and AR splice variant expression, likely contributing to the C4-2B and 22Rv1 decrease in cell survival. Our study has therefore identified at least three new supporters of enzalutamide resistance in castration-resistant prostate cancer cells in vitro.

Increased nuclear factor I/B expression in prostate cancer correlates with AR expression.

BACKGROUND: Most prostate cancers express androgen receptor (AR), and our previous studies have focused on identifying transcription factors that modify AR function. We have shown that nuclear factor I/B (NFIB) regulates AR activity in androgen-dependent prostate cancer cells in vitro. However, the status of NFIB in prostate cancer was unknown. METHODS: We immunostained a tissue microarray including normal, hyperplastic, prostatic intraepithelial neoplasia, primary prostatic adenocarcinoma, and castration-resistant prostate cancer tissue samples for NFIB, AR, and synaptophysin, a marker of neuroendocrine differentiation. We interrogated publically available data sets in cBioPortal to correlate NFIB expression and AR and neuroendocrine prostate cancer (NEPCa) activity scores. We analyzed prostate cancer cell lines for NFIB expression via Western blot analysis and used nuclear and cytoplasmic fractionation to assess where NFIB is localized. We performed co-immunoprecipitation studies to determine if NFIB and AR interact. RESULTS: NFIB increased in the nucleus and cytoplasm of prostate cancer samples versus matched normal controls, independent of Gleason score. Similarly, cytoplasmic AR and synaptophysin increased in primary prostate cancer. We observed strong NFIB staining in primary small cell prostate cancer. The ratio of cytoplasmic-to-nuclear NFIB staining was predictive of earlier biochemical recurrence in prostate cancer, once adjusted for tumor margin status. Cytoplasmic AR was an independent predictor of biochemical recurrence. There was no statistically significant difference between NFIB and synaptophysin expression in primary and castration-resistant prostate cancer, but cytoplasmic AR expression was increased in castration-resistant samples. In primary prostate cancer, nuclear NFIB expression correlated with cytoplasmic NFIB and nuclear AR, while cytoplasmic NFIB correlated with synaptophysin, and nuclear and cytoplasmic AR. In castration-resistant prostate cancer samples, NFIB expression correlated positively with an AR activity score, and negatively with the NEPCa score. In prostate cancer cell lines, NFIB exists in several isoforms. We observed NFIB predominantly in the nuclear fraction of prostate cancer cells with increased cytoplasmic expression seen in castration-resistant cell lines. We observed an interaction between AR and NFIB through co-immunoprecipitation experiments. CONCLUSION: We have described the expression pattern of NFIB in primary and castration-resistant prostate cancer and its positive correlation with AR. We have also demonstrated AR interacts with NFIB.

Role of Cdc23/Mcm10 in generating the ribonucleotide imprint at the mat1 locus in fission yeast.

The developmental asymmetry of fission yeast daughter cells derives from inheriting 'older Watson' versus 'older Crick' DNA strand from the parental cell, strands that are complementary but not identical with each other. A novel DNA strand-specific 'imprint', installed during DNA replication at the mating-type locus (mat1), imparts competence for cell type inter-conversion to one of the two chromosome replicas. The catalytic subunit of DNA Polymerase α (Polα) has been implicated in the imprinting process. Based on its known biochemical function, Polα might install the mat1 imprint during lagging strand synthesis. The nature of the imprint is not clear: it is either a nick or a ribonucleotide insertion. Our investigations do not support a direct role of Polα in nicking through putative endonuclease domains but confirm its indirect role in installing an alkali-labile moiety as the imprint. While ruling out the role of the primase subunit of Polα holoenzyme, we find that mutations in the Polα-recruitment and putative primase homology domain in Mcm10/Cdc23 abrogate the ribonucleotide imprint formation. These results, while confirming the ribonucleotide nature of the imprint suggest the possibility of a direct role of Mcm10/Cdc23 in installing it in cooperation with Polα and Swi1.

Translational initiation factor eIF5 replaces eIF1 on the 40S ribosomal subunit to promote start-codon recognition.

In eukaryotic translation initiation, AUG recognition of the mRNA requires accommodation of Met-tRNAi in a 'PIN' state, which is antagonized by the factor eIF1. eIF5 is a GTPase activating protein (GAP) of eIF2 that additionally promotes stringent AUG selection, but the molecular basis of its dual function was unknown. We present a cryo-electron microscopy (cryo-EM) reconstruction of a yeast 48S pre-initiation complex (PIC), at an overall resolution of 3.0 Å, featuring the N-terminal domain (NTD) of eIF5 bound to the 40S subunit at the location vacated by eIF1. eIF5 interacts with and allows a more accommodated orientation of Met-tRNAi. Substitutions of eIF5 residues involved in the eIF5-NTD/tRNAi interaction influenced initiation at near-cognate UUG codonsin vivo, and the closed/open PIC conformation in vitro, consistent with direct stabilization of the codon:anticodon duplex by the wild-type eIF5-NTD. The present structure reveals the basis for a key role of eIF5 in start-codon selection.

eIF1A residues implicated in cancer stabilize translation preinitiation complexes and favor suboptimal initiation sites in yeast.

The translation pre-initiation complex (PIC) scans the mRNA for an AUG codon in favorable context, and AUG recognition stabilizes a closed PIC conformation. The unstructured N-terminal tail (NTT) of yeast eIF1A deploys five basic residues to contact tRNAi, mRNA, or 18S rRNA exclusively in the closed state. Interestingly, EIF1AX mutations altering the human eIF1A NTT are associated with uveal melanoma (UM). We found that substituting all five basic residues, and seven UM-associated substitutions, in yeast eIF1A suppresses initiation at near-cognate UUG codons and AUGs in poor context. Ribosome profiling of NTT substitution R13P reveals heightened discrimination against unfavorable AUG context genome-wide. Both R13P and K16D substitutions destabilize the closed complex at UUG codons in reconstituted PICs. Thus, electrostatic interactions involving the eIF1A NTT stabilize the closed conformation and promote utilization of suboptimal start codons. We predict UM-associated mutations alter human gene expression by increasing discrimination against poor initiation sites.

Competition between translation initiation factor eIF5 and its mimic protein 5MP determines non-AUG initiation rate genome-wide.

In the human genome, translation initiation from non-AUG codons plays an important role in various gene regulation programs. However, mechanisms regulating the non-AUG initiation rate remain poorly understood. Here, we show that the non-AUG initiation rate is nearly consistent under a fixed nucleotide context in various human and insect cells. Yet, it ranges from <1% to nearly 100% compared to AUG translation, depending on surrounding sequences, including Kozak, and possibly additional nucleotide contexts. Mechanistically, this range of non-AUG initiation is controlled in part, by the eIF5-mimic protein (5MP). 5MP represses non-AUG translation by competing with eIF5 for the Met-tRNAi-binding factor eIF2. Consistently, eIF5 increases, whereas 5MP decreases translation of NAT1/EIF4G2/DAP5, whose sole start codon is GUG. By modulating eIF5 and 5MP1 expression in combination with ribosome profiling we identified a handful of previously unknown non-AUG initiation sites, some of which serve as the exclusive start codons. If the initiation rate for these codons is low, then an AUG-initiated downstream ORF prevents the generation of shorter, AUG-initiated isoforms. We propose that the homeostasis of the non-AUG translatome is maintained through balanced expression of eIF5 and 5MP.

Ablation of RNA interference and retrotransposons accompany acquisition and evolution of transposases to heterochromatin protein CENPB.

Inactivation of retrotransposons is accompanied by the emergence of centromere-binding protein-B (CENPB) in Schizosaccharomyces, as well as in metazoans. The RNA interference (RNAi)-induced transcriptional silencing (RITS) complex, comprising chromodomain protein-1 (Chp1), Tas3 (protein with unknown function), and Argonaute (Ago1), plays an important role in RNAi-mediated heterochromatinization. We find that whereas the Ago1 subunit of the RITS complex is highly conserved, Tas3 is lost and Chp1 is truncated in Schizosaccharomyces cryophilus and Schizosaccharomyces octosporus We show that truncated Chp1 loses the property of heterochromatin localization and silencing when transformed in Schizosaccharomyces pombe Furthermore, multiple copies of CENPB, related to Tc1/mariner and Tc5 transposons, occur in all Schizosaccharomyces species, as well as in humans, but with loss of transposase function (except Schizosaccharomyces japonicus). We propose that acquisition of Tc1/mariner and Tc5 elements by horizontal transfer in S. pombe (and humans) is accompanied by alteration of their function from a transposase/endonuclease to a heterochromatin protein, designed to suppress transposon expression and recombination. The resulting redundancy of RITS may have eased the selection pressure, resulting in progressive loss or truncation of tas3 and chp1 genes in S. octosporus and S. cryophilus and triggered similar evolutionary dynamics in the metazoan orthologues.

Active yeast ribosome preparation using monolithic anion exchange chromatography.

In vitro studies of translation provide critical mechanistic details, yet purification of large amounts of highly active eukaryotic ribosomes remains a challenge for biochemists and structural biologists. Here, we present an optimized method for preparation of highly active yeast ribosomes that could easily be adapted for purification of ribosomes from other species. The use of a nitrogen mill for cell lysis coupled with chromatographic purification of the ribosomes results in 10-fold-increased yield and less variability compared with the traditional approach, which relies on sedimentation through sucrose cushions. We demonstrate that these ribosomes are equivalent to those made using the traditional method in a host of in vitro assays, and that utilization of this new method will consistently produce high yields of active yeast ribosomes.

Topical Delivery of Protein and Peptide Using Novel Cell Penetrating Peptide IMT-P8.

Skin, being the largest organ of the body, is an important site for drug administration. However, most of the drugs have poor permeability and thus drug delivery through the skin is very challenging. In this study, we examined the transdermal delivery capability of IMT-P8, a novel cell-penetrating peptide. We generated IMT-P8-GFP and IMT-P8-KLA fusion constructs and evaluated their internalization into mouse skin after topical application. Our results demonstrate that IMT-P8 is capable of transporting green fluorescent protein (GFP) and proapoptotic peptide, KLA into the skin and also in different cell lines. Interestingly, uptake of IMT-P8-GFP was considerably higher than TAT-GFP in HeLa cells. After internalization, IMT-P8-KLA got localized to the mitochondria and caused significant cell death in HeLa cells signifying an intact biological activity. Further in vivo skin penetration experiments revealed that after topical application, IMT-P8 penetrated the stratum corneum, entered into the viable epidermis and accumulated inside the hair follicles. In addition, both IMT-P8-KLA and IMT-P8-GFP internalized into the hair follicles and dermal tissue of the skin following topical application. These results suggested that IMT-P8 could be a potential candidate to be used as a topical delivery vehicle for various cosmetic and skin disease applications.

Prioritization of anticancer drugs against a cancer using genomic features of cancer cells: A step towards personalized medicine.

In this study, we investigated drug profile of 24 anticancer drugs tested against a large number of cell lines in order to understand the relation between drug resistance and altered genomic features of a cancer cell line. We detected frequent mutations, high expression and high copy number variations of certain genes in both drug resistant cell lines and sensitive cell lines. It was observed that a few drugs, like Panobinostat, are effective against almost all types of cell lines, whereas certain drugs are effective against only a limited type of cell lines. Tissue-specific preference of drugs was also seen where a drug is more effective against cell lines belonging to a specific tissue. Genomic features based models have been developed for each anticancer drug and achieved average correlation between predicted and actual growth inhibition of cell lines in the range of 0.43 to 0.78. We hope, our study will throw light in the field of personalized medicine, particularly in designing patient-specific anticancer drugs. In order to serve the scientific community, a webserver, CancerDP, has been developed for predicting priority/potency of an anticancer drug against a cancer cell line using its genomic features (http://crdd.osdd.net/raghava/cancerdp/).

dbEM: A database of epigenetic modifiers curated from cancerous and normal genomes.

We have developed a database called dbEM (database of Epigenetic Modifiers) to maintain the genomic information of about 167 epigenetic modifiers/proteins, which are considered as potential cancer targets. In dbEM, modifiers are classified on functional basis and comprise of 48 histone methyl transferases, 33 chromatin remodelers and 31 histone demethylases. dbEM maintains the genomic information like mutations, copy number variation and gene expression in thousands of tumor samples, cancer cell lines and healthy samples. This information is obtained from public resources viz. COSMIC, CCLE and 1000-genome project. Gene essentiality data retrieved from COLT database further highlights the importance of various epigenetic proteins for cancer survival. We have also reported the sequence profiles, tertiary structures and post-translational modifications of these epigenetic proteins in cancer. It also contains information of 54 drug molecules against different epigenetic proteins. A wide range of tools have been integrated in dbEM e.g. Search, BLAST, Alignment and Profile based prediction. In our analysis, we found that epigenetic proteins DNMT3A, HDAC2, KDM6A, and TET2 are highly mutated in variety of cancers. We are confident that dbEM will be very useful in cancer research particularly in the field of epigenetic proteins based cancer therapeutics. This database is available for public at URL: http://crdd.osdd.net/raghava/dbem.

Conformational changes in the P site and mRNA entry channel evoked by AUG recognition in yeast translation preinitiation complexes.

The translation preinitiation complex (PIC) is thought to assume an open conformation when scanning the mRNA leader, with AUG recognition evoking a closed conformation and more stable P site interaction of Met-tRNAi; however, physical evidence is lacking that AUG recognition constrains interaction of mRNA with the 40S binding cleft. We compared patterns of hydroxyl radical cleavage of rRNA by Fe(II)-BABE tethered to unique sites in eIF1A in yeast PICs reconstituted with mRNA harboring an AUG or near-cognate (AUC) start codon. rRNA residues in the P site display reduced cleavage in AUG versus AUC PICs; and enhanced cleavage in the AUC complexes was diminished by mutations of scanning enhancer elements of eIF1A that increase near-cognate recognition in vivo. This suggests that accessibility of these rRNA residues is reduced by accommodation of Met-tRNAi in the P site (PIN state) and by their interactions with the anticodon stem of Met-tRNAi. Our cleavage data also provide evidence that AUG recognition evokes dissociation of eIF1 from its 40S binding site, ejection of the eIF1A-CTT from the P-site and rearrangement to a closed conformation of the entry channel with reduced mobility of mRNA.

Eukaryotic translation initiation factor eIF5 promotes the accuracy of start codon recognition by regulating Pi release and conformational transitions of the preinitiation complex.

eIF5 is the GTPase activating protein (GAP) for the eIF2 · GTP · Met-tRNAi (Met) ternary complex with a critical role in initiation codon selection. Previous work suggested that the eIF5 mutation G31R/SUI5 elevates initiation at UUG codons by increasing GAP function. Subsequent work implicated eIF5 in rearrangement of the preinitiation complex (PIC) from an open, scanning conformation to a closed state at AUG codons, from which Pi is released from eIF2 · GDP · Pi. To identify eIF5 functions crucial for accurate initiation, we investigated the consequences of G31R on GTP hydrolysis and Pi release, and the effects of intragenic G31R suppressors on these reactions, and on the partitioning of PICs between open and closed states. eIF5-G31R altered regulation of Pi release, accelerating it at UUG while decreasing it at AUG codons, consistent with its ability to stabilize the closed complex at UUG. Suppressor G62S mitigates both defects of G31R, accounting for its efficient suppression of UUG initiation in G31R,G62S cells; however suppressor M18V impairs GTP hydrolysis with little effect on PIC conformation. The strong defect in GTP hydrolysis conferred by M18V likely explains its broad suppression of Sui(-) mutations in numerous factors. We conclude that both of eIF5's functions, regulating Pi release and stabilizing the closed PIC conformation, contribute to stringent AUG selection in vivo.

Labeling of a protein with fluorophores using maleimide derivitization.

Maleimide derivitization of a protein is an essential tool for putting probes such as fluorescent labels at different sites within a polypeptide chain. This allows one to better understand protein-protein or protein-nucleic acid interactions using various biophysical approaches such as fluorescence anisotropy and fluorescence resonance energy transfer (FRET).

Labeling a protein with fluorophores using NHS ester derivitization.

N-hydroxysuccinimde (NHS) ester-mediated derivitization involves the reaction of this amine-reactive group with the primary amines of a protein or a biomolecule. Using NHS chemistry allows one to conjugate various fluorescent probes, biotin, and cross-linkers to primary amines. For example, we use NHS ester chemistry to fluorescently label the amino terminus of a protein with the dye, 5-(and-6)-carboxyfluorescein, succinimidyl ester (5(6)-FAM, SE).

Enhanced eIF1 binding to the 40S ribosome impedes conformational rearrangements of the preinitiation complex and elevates initiation accuracy.

In the current model of translation initiation by the scanning mechanism, eIF1 promotes an open conformation of the 40S subunit competent for rapidly loading the eIF2·GTP·Met-tRNAi ternary complex (TC) in a metastable conformation (POUT) capable of sampling triplets entering the P site while blocking accommodation of Met-tRNAi in the PIN state and preventing completion of GTP hydrolysis (Pi release) by the TC. All of these functions should be reversed by eIF1 dissociation from the preinitiation complex (PIC) on AUG recognition. We tested this model by selecting eIF1 Ssu(-) mutations that suppress the elevated UUG initiation and reduced rate of TC loading in vivo conferred by an eIF1 (Sui(-)) substitution that eliminates a direct contact of eIF1 with the 40S subunit. Importantly, several Ssu(-) substitutions increase eIF1 affinity for 40S subunits in vitro, and the strongest-binding variant (D61G), predicted to eliminate ionic repulsion with 18S rRNA, both reduces the rate of eIF1 dissociation and destabilizes the PIN state of TC binding in reconstituted PICs harboring Sui(-) variants of eIF5 or eIF2. These findings establish that eIF1 dissociation from the 40S subunit is required for the PIN mode of TC binding and AUG recognition and that increasing eIF1 affinity for the 40S subunit increases initiation accuracy in vivo. Our results further demonstrate that the GTPase-activating protein eIF5 and ß-subunit of eIF2 promote accuracy by controlling eIF1 dissociation and the stability of TC binding to the PIC, beyond their roles in regulating GTP hydrolysis by eIF2.