Myeloproliferative disorders: the centrosome connection

Myeloproliferative Neoplasm-like Mutations of Calreticulin Induce Phenotypes Associated with Calreticulin Dysfunction in C. elegans

In previous research, we created a C. elegans model with homozygous mutations in calreticulin similar to those found in patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF), two myeloproliferative neoplasms (MPNs). This model, lacking JAK orthologs, enabled us to examine the transcriptomic effects caused by mutant calreticulin without the influence of JAK/STAT activation, the primary pathogenic mechanism associated with calreticulin mutations known to date. Most of the gene expression changes observed seemed to be due to a partial loss of protein function, with the alteration of the extracellular matrix being particularly notable. In this study, our aim was to determine whether this model exhibited any phenotype related to these transcriptomic alterations. The results demonstrate that these strains exhibit multiple phenotypes related to the alteration of the extracellular matrix, fat levels, and fertility, which could be a possible consequence of a partial loss of calreticulin function. These phenotypes resemble some of the clinical and molecular characteristics described in patients with MPNs, but they had never before been linked to a loss of protein function in humans. Thus, these results collectively suggest that CALR mutations could have significant effects on MPNs due to loss of protein function. Delving deeper into these effects to develop innovative therapies for these patients offers considerable potential and interest, given that targeted therapies for these patients have not yielded very promising results so far.

Transcriptomic Analysis Reveals JAK2/MPL-Independent Effects of Calreticulin Mutations in a C. elegans Model

There is growing evidence that Ph-negative myeloproliferative neoplasms (MPNs) are disorders in which multiple molecular mechanisms are significantly disturbed. Since their discovery, CALR driver mutations have been demonstrated to trigger pathogenic mechanisms apart from the well-documented activation of JAK2/MPL-related pathways, but the lack of experimental models harboring CALR mutations in a JAK2/MPL knockout background has hindered the research on these non-canonical mechanisms. In this study, CRISPR/Cas9 was performed to introduce homozygous patient-like calreticulin mutations in a C. elegans model that naturally lacks JAK2 and MPL orthologs. Whole-genome transcriptomic analysis of these worms was conducted, and some of the genes identified to be associated with processes involved in the pathogenesis of MPNs were further validated by qPCR. Some of the transcriptomic alterations corresponded to typically altered genes and processes in cancer and Ph-negative MPN patients that are known to be triggered by mutant calreticulin without the intervention of JAK2/MPL. However, interestingly, we have also found altered other processes described in these diseases that had not been directly attributed to calreticulin mutations without the intervention of JAK2 or MPL. Thus, these results point to a new experimental model for the study of the JAK2/MPL-independent mechanisms of mutant calreticulin that induce these biological alterations, which could be useful to study unknown non-canonical effects of the mutant protein. The comparison with a calreticulin null strain revealed that the alteration of all of these processes seems to be a consequence of a loss of function of mutant calreticulin in the worm, except for the dysregulation of Hedgehog signaling and flh-3. Further analysis of this model could help to delineate these mechanisms, and the verification of these results in mammalian models may unravel new potential therapeutic targets in MPNs. As far as we know, this is the first time that a C. elegans strain with patient-like mutations is proposed as a potential model for leukemia research.

The SH2 domain and kinase activity of JAK2 target JAK2 to centrosome and regulate cell growth and centrosome amplification

JAK2 is cytokine-activated non-receptor tyrosine kinase. Although JAK2 is mainly localized at the plasma membrane, it is also present on the centrosome. In this study, we demonstrated that JAK2 localization to the centrosome depends on the SH2 domain and intact kinase activity. We created JAK2 mutants deficient in centrosomal localization ΔSH2, K882E and (ΔSH2, K882E). We showed that JAK2 WT clone strongly enhances cell proliferation as compared to control cells while JAK2 clones ΔSH2, K882E and (ΔSH2, K882E) proliferate slower than JAK2 WT cells. These mutant clones also progress much slower through the cell cycle as compared to JAK2 WT clone and the enhanced proliferation of JAK2 WT cells is accompanied by increased S -> G2 progression. Both the SH2 domain and the kinase activity of JAK2 play a role in prolactin-dependent activation of JAK2 substrate STAT5. We showed that JAK2 is an important regulator of centrosome function as the SH2 domain of JAK2 regulates centrosome amplification. The cells overexpressing ΔSH2 and (ΔSH2, K-E) JAK2 have almost three-fold the amplified centrosomes of WT cells. In contrast, the kinase activity of JAK2 is dispensable for centrosome amplification. Our observations provide novel insight into the role of SH2 domain and kinase activity of JAK2 in centrosome localization of JAK2 and in the regulation of cell growth and centrosome biogenesis.

Molecular Action of Polyphenols in Leukaemia and Their Therapeutic Potential

Leukaemia is a malignant disease of the blood. Current treatments for leukaemia are associated with serious side-effects. Plant-derived polyphenols have been identified as potent anti-cancer agents and have been shown to work synergistically with standard chemotherapy agents in leukaemia cell lines. Polyphenols have multiple mechanisms of action and have been reported to decrease cell proliferation, arrest cell cycle and induce apoptosis via the activation of caspase (3, 8 and 9); the loss of mitochondrial membrane potential and the release of cytochrome c. Polyphenols have been shown to suppress activation of transcription factors, including NF-kB and STAT3. Furthermore, polyphenols have pro-oxidant properties, with increasing evidence that polyphenols inhibit the antioxidant activity of glutathione, causing oxidative DNA damage. Polyphenols also induce autophagy-driven cancer cell death and regulate multidrug resistance proteins, and thus may be able to reverse resistance to chemotherapy agents. This review examines the molecular mechanism of action of polyphenols and discusses their potential therapeutic targets. Here, we discuss the pharmacological properties of polyphenols, including their anti-inflammatory, antioxidant, anti-proliferative, and anti-tumour activities, and suggest that polyphenols are potent natural agents that can be useful therapeutically; and discuss why data on bioavailability, toxicity and metabolism are essential to evaluate their clinical use.

DLGAP1 directs megakaryocytic growth and differentiation in an MPL dependent manner in hematopoietic cells

Background

The MPL protein is a major regulator of megakaryopoiesis and platelet formation as well as stem cell regulation. Aberrant MPL and downstream Jak/STAT signaling results in the development of the Myeloproliferative Neoplasms (MPN). The pathogenetic and phenotypic features of the classical MPNs cannot be explained by the known mutations and genetic variants associated with the disease.

Methods

In order to identify potential pathways involved in MPN development, we have performed a functional screen using retroviral insertional mutagenesis in cells dependent on MPL activation. We have used viral transduction and plasmid transfections to test the effects of candidate gene overexpression on growth and differentiation of megakaryocytic cells. The shRNA approach was used to test for the effects of candidate gene downregulation in cells. All effects were tested with candidate gene alone or in presence of hematopoietic relevant kinases in the growth medium. We assayed the candidate gene cellular localization in varying growth conditions by immunofluorescence. Flow Cytometry was used for testing of transduction efficiency and for sorting of positive cells.

Results

We have identified the DLGAP1 gene, a member of the Scribble cell polarity complex, as one of the most prominent positive candidates. Analyses in hematopoietic cell lines revealed DLGAP1 centrosomal and cytoplasmic localization. The centrosomal localization of DLGAP1 was cell cycle dependent and hematopoietic relevant tyrosine kinases: Jak2, SRC and MAPK as well as the CDK1 kinase promoted DLGAP1 dissociation from centrosomes. DLGAP1 negatively affected the growth rate of MPL dependent hematopoietic cells and supported megakaryocytic cells polyploidization, which was correlated with its dissociation from centrosomes.

Conclusions

Our data support the conclusion that DLGAP1 is a novel, potent factor in MPL signaling, affecting megakaryocytic growth and differentiation, relevant to be investigated further as a prominent candidate in MPN development.

Electronic supplementary material

The online version of this article (10.1186/s40364-019-0165-z) contains supplementary material, which is available to authorized users.

Platelet-derived growth factor receptors (PDGFRs) fusion genes involvement in hematological malignancies

PURPOSE

To investigate oncogenic platelet-derived growth factor receptor(PDGFR) fusion genes involvement in hematological malignancies, the advances in the PDGFR fusion genes diagnosis and development of PDGFR fusions inhibitors.

METHODS

Literature search was done using terms "PDGFR and Fusion" or "PDGFR and Myeloid neoplasm" or 'PDGFR and Lymphoid neoplasm' or "PDGFR Fusion Diagnosis" or "PDGFR Fusion Targets" in databases including PubMed, ASCO.org, and Medscape.

RESULTS

Out of the 36 fusions detected, ETV6(TEL)-PDGFRB and FIP1L1-PDGFRA fusions were frequently detected, 33 are as a result of chromosomal translocation, FIP1L1-PDGFRA and EBF1-PDGFRB are the result of chromosomal deletion and CDK5RAP2- PDGFRΑ is the result of chromosomal insertion. Seven of the 34 rare fusions have detectable reciprocals.

CONCLUSION

RNA aptamers are promising therapeutic target of PDGFRs and diagnostic tools of PDGFRs fusion genes. Also, PDGFRs have variable prospective therapeutic strategies including small molecules, RNA aptamers, and interference therapeutics as well as development of adaptor protein Lnk mimetic drugs.

Fusion of PDGFRB to MPRIP, CPSF6, and GOLGB1 in three patients with eosinophilia-associated myeloproliferative neoplasms

In eosinophilia-associated myeloproliferative neoplasms (MPN-eo), constitutive activation of protein tyrosine kinases (TK) as consequence of translocations, inversions, or insertions and creation of TK fusion genes is recurrently observed. The most commonly involved TK and their potential TK inhibitors include PDGFRA at 4q12 or PDGFRB at 5q33 (imatinib), FGFR1 at 8p11 (ponatinib), and JAK2 at 9p24 (ruxolitinib). We here report the identification of three new PDGFRB fusion genes in three male MPN-eo patients: MPRIP-PDGFRB in a case with t(5;17)(q33;p11), CPSF6-PDGFRB in a case with t(5;12)(q33;q15), and GOLGB1-PDGFRB in a case with t(3;5)(q13;q33). The fusion proteins identified by 5'-rapid amplification of cDNA ends polymerase chain reaction (PCR) or DNA-based long distance inverse PCR are predicted to contain the TK domain of PDGFRB. The partner genes contain domains like coiled-coil structures, which are likely to cause dimerization and activation of the TK. In all patients, imatinib induced rapid and durable complete remissions.

JAK2 tyrosine kinase phosphorylates and is negatively regulated by centrosomal protein Ninein

JAK2 is a cytoplasmic tyrosine kinase critical for cytokine signaling. In this study, we have identified a novel centrosome-associated complex containing ninein and JAK2. We have found that active JAK2 localizes around the mother centrioles, where it partly colocalizes with ninein, a protein involved in microtubule (MT) nucleation and anchoring. We demonstrated that JAK2 is an important regulator of centrosome function. Depletion of JAK2 or use of JAK2-null cells causes defects in MT anchoring and increased numbers of cells with mitotic defects; however, MT nucleation is unaffected. We showed that JAK2 directly phosphorylates the N terminus of ninein while the C terminus of ninein inhibits JAK2 kinase activity in vitro. Overexpressed wild-type (WT) or C-terminal (amino acids 1179 to 1931) ninein inhibits JAK2. This ninein-dependent inhibition of JAK2 significantly decreases prolactin- and interferon gamma (IFN-γ)-induced tyrosyl phosphorylation of STAT1 and STAT5. Downregulation of ninein enhances JAK2 activation. These results indicate that JAK2 is a novel member of centrosome-associated complex and that this localization regulates both centrosomal function and JAK2 kinase activity, thus controlling cytokine-activated molecular pathways.

Identification and functional characterization of imatinib-sensitive DTD1-PDGFRB and CCDC88C-PDGFRB fusion genes in eosinophilia-associated myeloid/lymphoid neoplasms

Eosinophilia-associated myeloid neoplasms with rearrangement of chromosome bands 5q31-33 are frequently associated with PDGFRB fusion genes, which are exquisitely sensitive to treatment with imatinib. In search for novel fusion partners of PDGFRB, we analyzed three cases with translocation t(5;20)(q33;p11), t(5;14)(q33;q32), and t(5;17;14)(q33;q11;q32) by 5′-rapid amplification of cDNA ends polymerase chain reaction (5′-RACE-PCR) and DNA-based long-distance inverse PCR (LDI-PCR) with primers derived from PDGFRB. LDI-PCR revealed a fusion between CCDC88C exon 25 and PDGFRB exon 11 in the case with t(5;17;14)(q33;q11;q32) while 5′-RACE-PCR identified fusions between CCDC88C exon 10 and PDGFRB exon 12 and between DTD1 exon 4 and PDGFRB exon 12 in the cases with t(5;14)(q33;q32) and t(5;20)(q33;p11), respectively. The PDGFRB tyrosine-kinase domain is predicted to be retained in all three fusion proteins. The partner proteins contained coiled-coil domains or other domains, which putatively lead to constitutive activation of the PDGFRB fusion protein. In vitro functional analyses confirmed transforming activity and imatinib-sensitivity of the fusion proteins. All three patients achieved rapid and durable complete hematologic remissions on imatinib.

Molecularly-targeted Strategy and NF-κB in lymphoid malignancies

Molecularly-targeted therapy is a promising strategy for the treatment of cancer. Nuclear factor (NF)-κB is a transcription factor that is constitutively activated in various lymphoid malignancies and may therefore be a good therapeutic target. Lymphoid malignancies arise from different stages of normal lymphocyte differentiation and acquire distinct pathways for constitutive NF-κB activation. However, no NF-κB inhibitor has yet been successfully applied in clinical medicine. This review focuses on the concept of molecularly-targeted therapeutics with small molecule drugs, molecular mechanisms of constitutive NF-κB activation in lymphoid malignancies, and the development of NF-κB inhibitors. A future perspective regarding the development of NF-κB inhibitors is also included.

Centrosome-kinase fusions promote oncogenic signaling and disrupt centrosome function in myeloproliferative neoplasms

Chromosomal translocations observed in myeloproliferative neoplasms (MPNs) frequently fuse genes that encode centrosome proteins and tyrosine kinases. This causes constitutive activation of the kinase resulting in aberrant, proliferative signaling. The function of centrosome proteins in these fusions is not well understood. Among others, kinase centrosome localization and constitutive kinase dimerization are possible consequences of centrosome protein-kinase fusions. To test the relative contributions of localization and dimerization on kinase signaling, we targeted inducibly dimerizable FGFR1 to the centrosome and other subcellular locations and generated a mutant of the FOP-FGFR1 MPN fusion defective in centrosome localization. Expression in mammalian cells followed by western blot analysis revealed a significant decrease in kinase signaling upon loss of FOP-FGFR1 centrosome localization. Kinase dimerization alone resulted in phosphorylation of the FGFR1 signaling target PLCγ, however levels comparable to FOP-FGFR1 required subcellular targeting in addition to kinase dimerization. Expression of MPN fusion proteins also resulted in centrosome disruption in epithelial cells and transformed patient cells. Primary human MPN cells showed masses of modified tubulin that colocalized with centrin, Smoothened (Smo), IFT88, and Arl13b. This is distinct from acute myeloid leukemia (AML) cells, which are not associated with centrosome-kinase fusions and had normal centrosomes. Our results suggest that effective proliferative MPN signaling requires both subcellular localization and dimerization of MPN kinases, both of which may be provided by centrosome protein fusion partners. Furthermore, centrosome disruption may contribute to the MPN transformation phenotype.

FOP is a centriolar satellite protein involved in ciliogenesis

Centriolar satellites are proteinaceous granules that are often clustered around the centrosome. Although centriolar satellites have been implicated in protein trafficking in relation to the centrosome and cilium, the details of their function and composition remain unknown. FOP (FGFR1 Oncogene Partner) is a known centrosome protein with homology to the centriolar satellite proteins FOR20 and OFD1. We find that FOP partially co-localizes with the satellite component PCM1 in a cell cycle-dependent manner, similarly to the satellite and cilium component BBS4. As for BBS4, FOP localization to satellites is cell cycle dependent, with few satellites labeled in G1, when FOP protein levels are lowest, and most labeled in G2. FOP-FGFR1, an oncogenic fusion that causes a form of leukemia called myeloproliferative neoplasm, also localizes to centriolar satellites where it increases tyrosine phosphorylation. Depletion of FOP strongly inhibits primary cilium formation in human RPE-1 cells. These results suggest that FOP is a centriolar satellite cargo protein and, as for several other satellite-associated proteins, is involved in ciliogenesis. Localization of the FOP-FGFR1 fusion kinase to centriolar satellites may be relevant to myeloproliferative neoplasm disease progression.

Centrosomal targeting of tyrosine kinase activity does not enhance oncogenicity in chronic myeloproliferative disorders

Constitutive tyrosine kinase activation by reciprocal chromosomal translocation is a common pathogenetic mechanism in chronic myeloproliferative disorders. Since centrosomal proteins have been recurrently identified as translocation partners of tyrosine kinases FGFR1, JAK2, PDGFRα and PDGFRβ in these diseases, a role for the centrosome in oncogenic transformation has been hypothesized. In this study, we addressed the functional role of centrosomally targeted tyrosine kinase activity. First, centrosomal localization was not routinely found for all chimeric fusion proteins tested. Second, targeting of tyrosine kinases to the centrosome by creating artificial chimeric fusion kinases with the centrosomal targeting domain of AKAP450 failed to enhance the oncogenic transforming potential in both Ba/F3 and U2OS cells, although phospho-tyrosine-mediated signal transduction pathways were initiated at the centrosome. We conclude that the centrosomal localization of constitutively activated tyrosine kinases does not contribute to disease pathogenesis in chronic myeloproliferative disorders.

The driver of malignancy in KG-1a leukemic cells, FGFR1OP2-FGFR1, encodes an HSP90 addicted oncoprotein

The KG-1a cell line is developed from a human stem cell myeloproliferative neoplasm as the result of intragenic disruption and a chromosomal translocation of the FGFR1 gene and the FGFR1OP2 gene encoding a protein of unknown function called FOP2 (FGFR1 Oncogene Partner 2). The resulting fusion protein FOP2-FGFR1 is soluble and has constitutive tyrosine kinase activity. Since the heat shock protein HSP90 and its co-chaperone CDC37 have been shown to stabilize many oncogenic proteins, we investigated the requirement for HSP90 or HSP90-CDC37 assistance to maintain the stability or activity of FOP2-FGFR1 expressed in KG-1a cells. We found that HSP90-CDC37 forms a permanent complex with FOP2-FGFR1. This results in protection against degradation of FOP2-FGFR1 and holds the oncoprotein in a permanently active conformation. Inhibition of HSP90 or depletion of CDC37 or heat shock factor 1 (HSF1) reduced the expression level of FOP2-FGFR1 and was sufficient to block the oncoprotein induced proliferation of KG-1a cells. We conclude that the driver of malignancy in KG-1a leukemic cells, FOP2-FGFR1, is an HSP90 addicted oncoprotein. This provides a rationale for the therapeutic use of HSP90 inhibitors in myeloid leukemias that contain FGFR fusion proteins.

Abnormal centrosome-centriole cycle in chronic myeloid leukaemia?

Abnormal numbers, structures and functions of centrosomes in chronic myeloid leukaemia (CML) may influence cell proliferation and genomic instability, which are features of the disease. Centrosomes are regulators of mitotic spindle orientation and can act as scaffolds for centrosome-associated regulators of the cell cycle. This study showed, for the first time, that p210(BCR-ABL1) and p145(ABL1) are both centrosome-associated proteins, as demonstrated by co-immunoprecipitation with the pericentriolar protein, pericentrin. Furthermore, when CML cells were treated with imatinib there was a 55% and 20% reduction of p210(BCR-ABL1) and p145(ABL1) binding to pericentrin, respectively. Cell lines expressing p210(BCR-ABL1) and primary CD34(+) cells from CML patients exhibited more numerical and structural centrosomal abnormalities than p210(BCR-ABL1) negative cells. Primary cells from CML blast crisis (BC) patients exhibited a distinctive amorphous staining pattern of pericentrin compared to normal and CML chronic phase (CP) patients, suggesting a possible defect in pericentrin localisation at the centrosomes. Proteins, such as aurora kinases, pericentrin, survivin and separase, regulate centrosome structure and function, cell cycle and mitotic spindle formation. Levels of the protease, separase are abnormally high in CML CP and BC cells in comparison to normal CD34(+) cells. The data imply that expression of p210(BCR-ABL1) is associated with abnormalities in the centrosome-centriole cycle and increased separase expression.

Myeloproliferative disorder FOP-FGFR1 fusion kinase recruits phosphoinositide-3 kinase and phospholipase Cgamma at the centrosome

Background

The t(6;8) translocation found in rare and agressive myeloproliferative disorders results in a chimeric gene encoding the FOP-FGFR1 fusion protein. This protein comprises the N-terminal region of the centrosomal protein FOP and the tyrosine kinase of the FGFR1 receptor. FOP-FGFR1 is localized at the centrosome where it exerts a constitutive kinase activity.

Results

We show that FOP-FGFR1 interacts with the large centrosomal protein CAP350 and that CAP350 is necessary for FOP-FGFR1 localisation at centrosome. FOP-FGFR1 activates the phosphoinositide-3 kinase (PI3K) pathway. We show that p85 interacts with tyrosine 475 of FOP-FGFR1, which is located in a YXXM consensus binding sequence for an SH2 domain of p85. This interaction is in part responsible for PI3K activation. Ba/F3 cells that express FOP-FGFR1 mutated at tyrosine 475 have reduced proliferative ability. Treatment with PI3K pathway inhibitors induces death of FOP-FGFR1 expressing cells. FOP-FGFR1 also recruits phospholipase Cγ1 (PLCγ1) at the centrosome. We show that this enzyme is recruited by FOP-FGFR1 at the centrosome during interphase.

Conclusion

These results delineate a particular type of oncogenic mechanism by which an ectopic kinase recruits its substrates at the centrosome whence unappropriate signaling induces continuous cell growth and MPD.

Combined translocation with ZNF198-FGFR1 gene fusion and deletion of potential tumor suppressors in a myeloproliferative disorder

Tyrosine kinases activated by mutation or translocation are involved in the chronic phase of myeloproliferative disorders. Complementary or alternative events are not so well characterized. We report here a case of t(8;13) generating a ZNF198-FGFR1 fusion kinase gene on the derivative chromosome 13. ZNF198-FGFR1 mRNA, but not FGFR1-ZNF198, was detected by polymerase chain reaction amplification. By using fluorescence in situ hybridization with BAC clones, we mapped a deletion of about 2 megabases on the derivative chromosome 8, including the reciprocal FGFR1-ZNF198 fusion gene and the surrounding genes from 8p11 and 13q12. Potential tumor suppressor genes affected by the deletion by loss (IFT88, CRYL1, TACC1) or break (LATS2) may participate in the malignant process.

Structure of the N-terminal domain of the FOP (FGFR1OP) protein and implications for its dimerization and centrosomal localization

The fibroblast growth factor receptor 1 (FGFR1) oncogene partner, FOP, is a centrosomal protein that is involved in the anchoring of microtubules (MTS) to subcellular structures. The protein was originally discovered as a fusion partner with FGFR1 in oncoproteins that give rise to stem cell myeloproliferative disorders. A subsequent proteomics screen identified FOP as a component of the centrosome. FOP contains a Lis-homology (LisH) motif found in more than 100 eukaryotic proteins. LisH motifs are believed to be involved in microtubule dynamics and organization, cell migration, and chromosome segregation; several of them are associated with genetic diseases. We report here a 1.6A resolution crystal structure of the N-terminal dimerization domain of FOP. The structure comprises an alpha-helical bundle composed of two antiparallel chains, each of them having five alpha-helices. The central part of the dimer contains the LisH domain. We further determined that the FOP LisH domain is part of a longer N-terminal segment that is required, albeit not sufficient, for dimerization and centrosomal localization of FOP.

Targeting NF-κB in hematologic malignancies

The transcription factor nuclear factor kappa B (NF-kappaB) can intervene in oncogenesis by virtue of its capacity to regulate the expression of a plethora of genes that modulate apoptosis, and cell survival as well as proliferation, inflammation, tumor metastasis and angiogenesis. Different reports demonstrate the intrinsic activation of NF-kappaB in lymphoid and myeloid malignancies, including preneoplastic conditions such as myelodysplastic syndromes, underscoring its implication in malignant transformation. Targeting intrinsic NF-kappaB activation, as well as its upstream and downstream regulators, may hence constitute an additional approach to the oncologist's armamentarium. Several small inhibitors of the NF-kappaB-activatory kinase IkappaB kinase, of the proteasome, or of the DNA binding of NF-kappaB subunits are under intensive investigation. Currently used cytotoxic agents can induce NF-kappaB activation as an unwarranted side effect, which confers apoptosis suppression and hence resistance to these drugs. Thus, NF-kappaB inhibitory molecules may be clinically useful, either as single therapeutic agents or in combination with classical chemotherapeutic agents, for the treatment of hematological malignancies.

A complex of two centrosomal proteins, CAP350 and FOP, cooperates with EB1 in microtubule anchoring

The anchoring of microtubules (MTs) to subcellular structures is critical for cell shape, polarity, and motility. In mammalian cells, the centrosome is a prominent MT anchoring structure. A number of proteins, including ninein, p150Glued, and EB1, have been implicated in centrosomal MT anchoring, but the process is far from understood. Here we show that CAP350 and FOP (FGFR1 oncogene partner) form a centrosomal complex required for MT anchoring. We show that the C-terminal domain of CAP350 interacts directly with FOP and that both proteins localize to the centrosome throughout the cell cycle. FOP also binds to EB1 and is required for localizing EB1 to the centrosome. Depletion of either CAP350, FOP, or EB1 by siRNA causes loss of MT anchoring and profound disorganization of the MT network. These results have implications for the mechanisms underlying MT anchoring at the centrosome and they attribute a key MT anchoring function to two novel centrosomal proteins, CAP350 and FOP.