The methylation of the C-terminal region of hnRNPQ (NSAP1) is important for its nuclear localization

PRMT1 Modulates Alternative Splicing to Enhance HPV18 mRNA Stability and Promote the Establishment of Infection

Only persistent HPV infections lead to the development of cancer. Thus, understanding the virus-host interplay that influences the establishment of viral infection has important implications for HPV biology and human cancers. The ability of papillomaviruses to establish in cells requires the strict temporal regulation of viral gene expression in sync with cellular differentiation. This control primarily happens at the level of RNA splicing and polyadenylation. However, the details of how this spatio-temporal regulation is achieved still need to be fully understood. Until recently, it has been challenging to study the early events of the HPV lifecycle following infection. We used a single-cell genomics approach to identify cellular factors involved in viral infection and establishment. We identify protein arginine N-methyltransferase 1 (PRMT1) as an important factor in viral infection of primary human cervical cells. PRMT1 is the main cellular enzyme responsible for asymmetric dimethylation of cellular proteins. PRMT1 is an enzyme responsible for catalyzing the methylation of arginine residues on various proteins, which influences processes such as RNA processing, transcriptional regulation, and signal transduction. In this study, we show that HPV18 infection leads to increased PRMT1 levels across the viral lifecycle. PRMT1 is critical for the establishment of a persistent infection in primary cells. Mechanistically, PRMT1 inhibition leads to a highly dysregulated viral splicing pattern. Specifically, reduced PRMT1 activity leads to intron retention and a change in the E6 and E7 expression ratio. In the absence of PRMT1, viral transcripts are destabilized and subject to degradation via the nonsense-mediated decay (NMD) pathway. These findings highlight PRMT1 as a critical regulator of the HPV18 lifecycle, particularly in RNA processing, and position it as a potential therapeutic target for persistent HPV18 infections.

Loss of SYNCRIP unleashes APOBEC-driven mutagenesis, tumor heterogeneity, and AR-targeted therapy resistance in prostate cancer

Tumor mutational burden and heterogeneity has been suggested to fuel resistance to many targeted therapies. The cytosine deaminase APOBEC proteins have been implicated in the mutational signatures of more than 70% of human cancers. However, the mechanism underlying how cancer cells hijack the APOBEC mediated mutagenesis machinery to promote tumor heterogeneity, and thereby foster therapy resistance remains unclear. We identify SYNCRIP as an endogenous molecular brake which suppresses APOBEC-driven mutagenesis in prostate cancer (PCa). Overactivated APOBEC3B, in SYNCRIP-deficient PCa cells, is a key mutator, representing the molecular source of driver mutations in some frequently mutated genes in PCa, including FOXA1, EP300. Functional screening identifies eight crucial drivers for androgen receptor (AR)-targeted therapy resistance in PCa that are mutated by APOBEC3B: BRD7, CBX8, EP300, FOXA1, HDAC5, HSF4, STAT3, and AR. These results uncover a cell-intrinsic mechanism that unleashes APOBEC-driven mutagenesis, which plays a significant role in conferring AR-targeted therapy resistance in PCa.

Characterization of the biochemical activity and tumor-promoting role of the dual protein methyltransferase METL-13/METTL13 in Caenorhabditis elegans

The methyltransferase-like protein 13 (METTL13) methylates the eukaryotic elongation factor 1 alpha (eEF1A) on two locations: the N-terminal amino group and lysine 55. The absence of this methylation leads to reduced protein synthesis and cell proliferation in human cancer cells. Previous studies showed that METTL13 is dispensable in non-transformed cells, making it potentially interesting for cancer therapy. However, METTL13 has not been examined yet in whole animals. Here, we used the nematode Caenorhabditis elegans as a simple model to assess the functions of METTL13. Using methyltransferase assays and mass spectrometry, we show that the C. elegans METTL13 (METL-13) methylates eEF1A (EEF-1A) in the same way as the human protein. Crucially, the cancer-promoting role of METL-13 is also conserved and depends on the methylation of EEF-1A, like in human cells. At the same time, METL-13 appears dispensable for animal growth, development, and stress responses. This makes C. elegans a convenient whole-animal model for studying METL13-dependent carcinogenesis without the complications of interfering with essential wild-type functions.

Coordination of RNA Processing Regulation by Signal Transduction Pathways

Signal transduction pathways transmit the information received from external and internal cues and generate a response that allows the cell to adapt to changes in the surrounding environment. Signaling pathways trigger rapid responses by changing the activity or localization of existing molecules, as well as long-term responses that require the activation of gene expression programs. All steps involved in the regulation of gene expression, from transcription to processing and utilization of new transcripts, are modulated by multiple signal transduction pathways. This review provides a broad overview of the post-translational regulation of factors involved in RNA processing events by signal transduction pathways, with particular focus on the regulation of pre-mRNA splicing, cleavage and polyadenylation. The effects of several post-translational modifications (i.e., sumoylation, ubiquitination, methylation, acetylation and phosphorylation) on the expression, subcellular localization, stability and affinity for RNA and protein partners of many RNA-binding proteins are highlighted. Moreover, examples of how some of the most common signal transduction pathways can modulate biological processes through changes in RNA processing regulation are illustrated. Lastly, we discuss challenges and opportunities of therapeutic approaches that correct RNA processing defects and target signaling molecules.

Protein arginine methyltransferases: promising targets for cancer therapy

Protein methylation, a post-translational modification (PTM), is observed in a wide variety of cell types from prokaryotes to eukaryotes. With recent and rapid advancements in epigenetic research, the importance of protein methylation has been highlighted. The methylation of histone proteins that contributes to the epigenetic histone code is not only dynamic but is also finely controlled by histone methyltransferases and demethylases, which are essential for the transcriptional regulation of genes. In addition, many nonhistone proteins are methylated, and these modifications govern a variety of cellular functions, including RNA processing, translation, signal transduction, DNA damage response, and the cell cycle. Recently, the importance of protein arginine methylation, especially in cell cycle regulation and DNA repair processes, has been noted. Since the dysregulation of protein arginine methylation is closely associated with cancer development, protein arginine methyltransferases (PRMTs) have garnered significant interest as novel targets for anticancer drug development. Indeed, several PRMT inhibitors are in phase 1/2 clinical trials. In this review, we discuss the biological functions of PRMTs in cancer and the current development status of PRMT inhibitors in cancer therapy.

PTBP1 Positively Regulates the Translation of Circadian Clock Gene, Period1

Circadian oscillations of mRNAs and proteins are the main features of circadian clock genes. Among them, Period1 (Per1) is a key component in negative-feedback regulation, which shows a robust diurnal oscillation and the importance of circadian rhythm and translational regulation of circadian clock genes has been recognized. In the present study, we investigated the 5'-untranslated region (5'-UTR) of the mouse core clock gene, Per1, at the posttranscriptional level, particularly its translational regulation. The 5'-UTR of Per1 was found to promote its translation via an internal ribosomal entry site (IRES). We found that polypyrimidine tract-binding protein 1 (PTBP1) binds to the 5'-UTR of Per1 and positively regulates the IRES-mediated translation of Per1 without affecting the levels of Per1 mRNA. The reduction of PTBP1 level also decreased the endogenous levels of the PER1 protein but not of its mRNA. As for the oscillation of PER1 expression, the disruption of PTBP1 levels lowered the PER1 expression but not the phase of the oscillation. PTBP1 also changed the amplitudes of the mRNAs of other circadian clock genes, such as Cryptochrome 1 (Cry1) and Per3. Our results suggest that the PTBP1 is important for rhythmic translation of Per1 and it fine-tunes the overall circadian system.

When SUMO met splicing

Spliceosomal proteins have been revealed as SUMO conjugation targets. Moreover, we have reported that many of these are in a SUMO-conjugated form when bound to a pre-mRNA substrate during a splicing reaction. We demonstrated that SUMOylation of Prp3 (PRPF3), a component of the U4/U6 di-snRNP, is required for U4/U6•U5 tri-snRNP formation and/or recruitment to active spliceosomes. Expanding upon our previous results, we have shown that the splicing factor SRSF1 stimulates SUMO conjugation to several spliceosomal proteins. Given the relevance of the splicing process, as well as the complex and dynamic nature of its governing machinery, the spliceosome, the molecular mechanisms that modulate its function represent an attractive topic of research. We posit that SUMO conjugation could represent a way of modulating spliceosome assembly and thus, splicing efficiency. How cycles of SUMOylation/de-SUMOylation of spliceosomal proteins become integrated throughout the highly choreographed spliceosomal cycle awaits further investigation.

Arginine methylation enhances the RNA chaperone activity of the West Nile virus host factor AUF1 p45

A prerequisite for the intracellular replication process of the Flavivirus West Nile virus (WNV) is the cyclization of the viral RNA genome, which enables the viral replicase to initiate RNA synthesis. Our earlier studies indicated that the p45 isoform of the cellular AU-rich element binding protein 1 (AUF1) has an RNA chaperone activity, which supports RNA cyclization and viral RNA synthesis by destabilizing a stem structure at the WNV RNA's 3'-end. Here we show that in mammalian cells, AUF1 p45 is consistently modified by arginine methylation of its C terminus. By a combination of different experimental approaches, we can demonstrate that the methyltransferase PRMT1 is necessary and sufficient for AUF1 p45 methylation and that PRMT1 is required for efficient WNV replication. Interestingly, in comparison to the nonmethylated AUF1 p45, the methylated AUF1 p45(aDMA) exhibits a significantly increased affinity to the WNV RNA termini. Further data also revealed that the RNA chaperone activity of AUF1 p45(aDMA) is improved and the methylated protein stimulates viral RNA synthesis considerably more efficiently than the nonmethylated AUF1 p45. In addition to its destabilizing RNA chaperone activity, we identified an RNA annealing activity of AUF1 p45, which is not affected by methylation. Arginine methylation of AUF1 p45 thus represents a specific determinant of its RNA chaperone activity while functioning as a WNV host factor. Our data suggest that the methylation modifies the conformation of AUF1 p45 and in this way affects its RNA binding and restructuring activities.

Post-Translational Modifications and RNA-Binding Proteins

RNA-binding proteins affect cellular metabolic programs through development and in response to cellular stimuli. Though much work has been done to elucidate the roles of a handful of RNA-binding proteins and their effect on RNA metabolism, the progress of studies to understand the effects of post-translational modifications of this class of proteins is far from complete. This chapter summarizes the work that has been done to identify the consequence of post-translational modifications to some RNA-binding proteins. The effects of these modifications have been shown to increase the panoply of functions that a given RNA-binding protein can assume. We will survey the experimental methods that are used to identify the presence of several protein modifications and methods that attempt to discern the consequence of these modifications.

Control of translation and miRNA-dependent repression by a novel poly(A) binding protein, hnRNP-Q

The heterogeneous nuclear ribonucleoprotein Q2 competitively binds mRNA poly(A) tails to regulate translational and miRNA-related functions of PABP.

Translation control often operates via remodeling of messenger ribonucleoprotein particles. The poly(A) binding protein (PABP) simultaneously interacts with the 3′ poly(A) tail of the mRNA and the eukaryotic translation initiation factor 4G (eIF4G) to stimulate translation. PABP also promotes miRNA-dependent deadenylation and translational repression of target mRNAs. We demonstrate that isoform 2 of the mouse heterogeneous nuclear protein Q (hnRNP-Q2/SYNCRIP) binds poly(A) by default when PABP binding is inhibited. In addition, hnRNP-Q2 competes with PABP for binding to poly(A) in vitro. Depleting hnRNP-Q2 from translation extracts stimulates cap-dependent and IRES-mediated translation that is dependent on the PABP/poly(A) complex. Adding recombinant hnRNP-Q2 to the extracts inhibited translation in a poly(A) tail-dependent manner. The displacement of PABP from the poly(A) tail by hnRNP-Q2 impaired the association of eIF4E with the 5′ m⁷G cap structure of mRNA, resulting in the inhibition of 48S and 80S ribosome initiation complex formation. In mouse fibroblasts, silencing of hnRNP-Q2 stimulated translation. In addition, hnRNP-Q2 impeded let-7a miRNA-mediated deadenylation and repression of target mRNAs, which require PABP. Thus, by competing with PABP, hnRNP-Q2 plays important roles in the regulation of global translation and miRNA-mediated repression of specific mRNAs.

The regulation of mRNA translation and stability is of paramount importance for almost every cellular function. In eukaryotes, the poly(A) binding protein (PABP) is a central regulator of both global and mRNA-specific translation. PABP simultaneously interacts with the 3′ poly(A) tail of the mRNA and the eukaryotic translation initiation factor 4G (eIF4G). These interactions circularize the mRNA and stimulate translation. PABP also regulates specific mRNAs by promoting miRNA-dependent deadenylation and translational repression. A key step in understanding PABP's functions is to identify factors that affect its association with the poly(A) tail. Here we show that the cytoplasmic isoform of the mouse heterogeneous nuclear ribonucleoprotein Q (hnRNP-Q2/SYNCRIP), which exhibits binding preference to poly(A), interacts with the poly(A) tail by default when PABP binding is inhibited. In addition, hnRNP-Q2 competes with PABP for binding to the poly(A) tail. Depleting hnRNP-Q2 stimulates translation in cell-free extracts and in cultured cells, in agreement with its function as translational repressor. In addition, hnRNP-Q2 impeded miRNA-mediated deadenylation and repression of target mRNAs, which requires PABP. Thus, competition from hnRNP-Q2 provides a novel mechanism by which multiple functions of PABP are regulated. This regulation could play important roles in various biological processes, such as development, viral infection, and human disease.

A Y2H-seq approach defines the human protein methyltransferase interactome

To accelerate high-density interactome mapping, we developed a yeast two-hybrid interaction screening approach involving short-read second-generation sequencing (Y2H-seq) with improved sensitivity and a quantitative scoring readout allowing rapid interaction validation. We applied Y2H-seq to investigate enzymes involved in protein methylation, a largely unexplored post-translational modification. The reported network of 523 interactions involving 22 methyltransferases or demethylases is comprehensively annotated and validated through coimmunoprecipitation experiments and defines previously undiscovered cellular roles of nonhistone protein methylation.

Identification and characterization of new molecular partners for the protein arginine methyltransferase 6 (PRMT6)

PRMT6 is a protein arginine methyltransferase that has been implicated in transcriptional regulation, DNA repair, and human immunodeficiency virus pathogenesis. Only few substrates of this enzyme are known and therefore its cellular role is not well understood. To identify in an unbiased manner substrates and potential regulators of PRMT6 we have used a yeast two-hybrid approach. We identified 36 new putative partners for PRMT6 and we validated the interaction in vivo for 7 of them. In addition, using invitro methylation assay we identified 4 new substrates for PRMT6, extending the involvement of this enzyme to other cellular processes beyond its well-established role in gene expression regulation. Holistic approaches create molecular connections that allow to test functional hypotheses. The assembly of PRMT6 protein network allowed us to formulate functional hypotheses which led to the discovery of new molecular partners for the architectural transcription factor HMGA1a, a known substrate for PRMT6, and to provide evidences for a modulatory role of HMGA1a on the methyltransferase activity of PRMT6.

Protein arginine methylation of SERBP1 by protein arginine methyltransferase 1 affects cytoplasmic/nuclear distribution

Protein arginine methylation regulates a broad array of cellular processes. SERBP1 implicated in tumor progression through its putative involvement in the plaminogen activator protease cascade, is an RNA-binding protein containing an RG-rich domain and an RGG box domain that might be methylated by protein arginine N-methyltransferases (PRMTs). Asymmetric dimethylarginine (aDMA) was detected in SERBP1 and an indirect methyltransferase inhibitor adenosine dialdehyde (AdOx) significantly reduced the methylation signals. Arginines in the middle RG and C-terminal RGG region of SERBP1 are methylated based on the analyses of different deletion constructs. The predominant type I protein arginine methyltransferase PRMT1 co-immunoprecipitated with SERBP1 and the level of bound PRMT1 decreased upon the addition of AdOx. Recombinant PRMT1 methylated SERBP1 and knockdown of PRMT1 significantly reduced the aDMA level of SERBP1, indicating that SERBP1 is specifically methylated by PRMT1. Immunofluorescent analyses of endogenous SERBP1 showed predominant cytoplasmic localization of SERBP1. Treatment of AdOx or PRMT1 siRNA increased the nuclear localization of SERBP1. Analyses of different deletions indicated that the middle RG region is important for the nuclear localization while both N- and C- terminus are required for nuclear export. Low methylation of the C-terminal RGG region also favors nuclear localization. In conclusion, the RG-rich and RGG box of SERBP1 is asymmetrically dimethylated by PRMT1 and the modification affects protein interaction and intracellular localization of the protein. These findings provide the basis for dissecting the roles of SERBP1.

Arginine methylation of the nuclear poly(a) binding protein weakens the interaction with its nuclear import receptor, transportin

The nuclear poly(A) binding protein, PABPN1, promotes mRNA polyadenylation in the cell nucleus by increasing the processivity of poly(A) polymerase and contributing to poly(A) tail length control. In its C-terminal domain, the protein carries 13 arginine residues that are all asymmetrically dimethylated. The function of this modification in PABPN1 has been unknown. Part of the methylated domain serves as nuclear localization signal, binding the import receptor transportin. Here we report that arginine methylation weakens the affinity of PABPN1 for transportin. Recombinant, unmethylated PABPN1 binds more strongly to transportin than its methylated counterpart from mammalian tissue, and in vitro methylation reduces the affinity. Transportin and RNA compete for binding to PABPN1. Methylation favors RNA binding. Transportin also inhibits in vitro methylation of the protein. Finally, a peptide corresponding to the nuclear localization signal of PABPN1 competes with transportin-dependent nuclear import of the protein in a permeabilized cell assay and does so less efficiently when it is methylated. We hypothesize that transportin binding might delay methylation of PABPN1 until after nuclear import. In the nucleus, arginine methylation may favor the transition of PABPN1 to the competing ligand RNA and serve to reduce the risk of the protein being reexported to the cytoplasm by transportin.

The Role of Protein Arginine Methylation in mRNP Dynamics

In eukaryotes, messenger RNA biogenesis depends on the ordered and precise assembly of a nuclear messenger ribonucleoprotein particle (mRNP) during transcription. This process requires a well-orchestrated and dynamic sequence of molecular recognition events by specific RNA-binding proteins. Arginine methylation is a posttranslational modification found in a plethora of RNA-binding proteins responsible for mRNP biogenesis. These RNA-binding proteins include both heterogeneous nuclear ribonucleoproteins (hnRNPs) and serine/arginine-rich (SR) proteins. In this paper, I discuss the mechanisms of action by which arginine methylation modulates various facets of mRNP biogenesis, and how the collective consequences of this modification impart the specificity required to generate a mature, translational- and export-competent mRNP.

The predominant protein arginine methyltransferase PRMT1 is critical for zebrafish convergence and extension during gastrulation

Protein arginine methyltransferase (PRMT)1 is the predominant type I methyltransferase in mammals. In the present study, we used zebrafish (Danio rerio) as the model system to elucidate PRMT1 expression and function during embryogenesis. Zebrafish prmt1 transcripts were detected from the zygote period to the early larva stage. Knockdown of prmt1 by antisense morpholino oligo (AMO) resulted in delayed growth, shortened body-length, curled tails and cardiac edema. PRMT1 protein level, type I protein arginine methyltransferase activity, specific asymmetric protein arginine methylation and histone H4 R3 methylation all decreased in the AMO-injected morphants. The morphants showed defective convergence and extension and the abnormalities were more severe at the posterior than the anterior parts. Cell migration defects suggested by the phenotypes were not only observed in the morphant embryos, but also in a cellular prmt1 small-interfering RNA knockdown model. Rescue of the phenotypes by co-injection of wild-type but not catalytic defective prmt1 mRNA confirmed the specificity of the AMO and the requirement of methyltransferase activity in early development. The results obtained in the present study demonstrate a direct link of early development with protein arginine methylation catalyzed by PRMT1.

Arginine methylation analysis of the splicing-associated SR protein SFRS9/SRP30C

The human SFRS9/SRp30c belongs to the SR family of splicing regulators. Despite evidence that members of this protein family may be targeted by arginine methylation, this has yet to be experimentally addressed. In this study, we found that SFRS9 is a target for PRMT1-mediated arginine methylation in vitro, and that it is immunoprecipitated from HEK-293 lysates by antibodies that recognize both mono- and dimethylated arginines. We further observed that upon treatment with the methylation inhibitor Adox, the fluorescent EGFP-SFRS9 re-localizes to dot-like structures in the cell nucleus. In subsequent confocal analyses, we found that EGFP-SFRS9 localizes to nucleoli in Adox-treated cells. Our findings indicate the importance of arginine methylation for the subnuclear localization of SFRS9.

Functional association of human Ki-1/57 with pre-mRNA splicing events

The cytoplasmic and nuclear protein Ki-1/57 was first identified in malignant cells from Hodgkin's lymphoma. Despite studies showing its phosphorylation, arginine methylation, and interaction with several regulatory proteins, the functional role of Ki-1/57 in human cells remains to be determined. Here, we investigated the relationship of Ki-1/57 with RNA functions. Through immunoprecipitation assays, we verified the association of Ki-1/57 with the endogenous splicing proteins hnRNPQ and SFRS9 in HeLa cell extracts. We also found that recombinant Ki-1/57 was able to bind to a poly-U RNA probe in electrophoretic mobility shift assays. In a classic splicing test, we showed that Ki-1/57 can modify the splicing site selection of the adenoviral E1A minigene in a dose-dependent manner. Further confocal and fluorescence microscopy analysis revealed the localization of enhanced green fluorescent proteinKi-1/57 to nuclear bodies involved in RNA processing and or small nuclear ribonucleoprotein assembly, depending on the cellular methylation status and its N-terminal region. In summary, our findings suggest that Ki-1/57 is probably involved in cellular events related to RNA functions, such as pre-mRNA splicing.

Identification of the RGG box motif in Shadoo: RNA-binding and signaling roles?

Using comparative genomics and in-silico analyses, we previously identified a new member of the prion-protein (PrP) family, the gene SPRN, encoding the protein Shadoo (Sho), and suggested its functions might overlap with those of PrP. Extended bioinformatics and conceptual biology studies to elucidate Sho’s functions now reveal Sho has a conserved RGG-box motif, a well-known RNA-binding motif characterized in proteins such as FragileX Mental Retardation Protein. We report a systematic comparative analysis of RGG-box containing proteins which highlights the motif’s functional versatility and supports the suggestion that Sho plays a dual role in cell signaling and RNA binding in brain. These findings provide a further link to PrP, which has well-characterized RNA-binding properties.

The host protein Staufen1 interacts with the Pr55Gag zinc fingers and regulates HIV-1 assembly via its N-terminus

Background

The formation of new infectious human immunodeficiency type 1 virus (HIV-1) mainly relies on the homo-multimerization of the viral structural polyprotein Pr55^Gag and on the recruitment of host factors. We have previously shown that the double-stranded RNA-binding protein Staufen 1 (Stau1), likely through an interaction between its third double-stranded RNA-binding domain (dsRBD3) and the nucleocapsid (NC) domain of Pr55^Gag, participates in HIV-1 assembly by influencing Pr55^Gag multimerization.

Results

We now report the fine mapping of Stau1/Pr55^Gag association using co-immunoprecipitation and live cell bioluminescence resonance energy transfer (BRET) assays. On the one hand, our results show that the Stau1-Pr55^Gag interaction requires the integrity of at least one of the two zinc fingers in the NC domain of Pr55^Gag but not that of the NC N-terminal basic region. Disruption of both zinc fingers dramatically impeded Pr55^Gag multimerization and virus particle release. In parallel, we tested several Stau1 deletion mutants for their capacity to influence Pr55^Gag multimerization using the Pr55^Gag/Pr55^Gag BRET assay in live cells. Our results revealed that a molecular determinant of 12 amino acids at the N-terminal end of Stau1 is necessary to increase Pr55^Gag multimerization and particle release. However, this region is not required for Stau1 interaction with the viral polyprotein Pr55^Gag.

Conclusion

These data highlight that Stau1 is a modular protein and that Stau1 influences Pr55^Gag multimerization via 1) an interaction between its dsRBD3 and Pr55^Gag zinc fingers and 2) a regulatory domain within the N-terminus that could recruit host machineries that are critical for the completion of new HIV-1 capsids.

Over-expression of GFP-FEZ1 causes generation of multi-lobulated nuclei mediated by microtubules in HEK293 cells

FEZ1 (Fasciculation and elongation protein zeta 1) is an ortholog of the Caenorhabditis elegans protein UNC-76, involved in neuronal development and axon outgrowth, in that worm. Mammalian FEZ1 has already been reported to cooperate with PKC-zeta in the differentiation and polarization of PC12 neuronal cells. Furthermore, FEZ1 is associated with kinesin 1 and JIP1 to form a cargo-complex responsible for microtubule based transport of mitochondria along axons. FEZ1 can also be classified as a hub protein, since it was reported to interact with over 40 different proteins in yeast two-hybrid screens, including at least nine nuclear proteins. Here, we transiently over-expressed GFP-FEZ1full in human HEK293 and HeLa cells in order to study the sub-cellular localization of GFP-FEZ1. We observed that over 40% of transiently transfected cells at 3 days post-transfection develop multi-lobulated nuclei, which are also called flower-like nuclei. We further demonstrated that GFP-FEZ1 localizes either to the cytoplasm or the nuclear fraction, and that the appearance of the flower-like nuclei depends on intact microtubule function. Finally, we show that FEZ1 co-localizes with both, alpha- and especially with gamma-tubulin, which localizes as a centrosome like structure at the center of the multiple lobules. In summary, our data suggest that FEZ1 has an important centrosomal function and supply new mechanistic insights to the formation of flower-like nuclei, which are a phenotypical hallmark of human leukemia cells.