Binding efficacy of aminobenzoic acid derivatives with DNA duplex: drug binding sites and DNA structure and dynamics

Communicated by Ramaswamy H. Sarma.

Biomolecular study and conjugation of two para-aminobenzoic acid derivatives with serum proteins: drug binding efficacy and protein structural analysis

Two aminobenzoic acid derivatives DAB-0 and DAB-1 showed distinct biological properties on murine bladder cancer (BCa) cell line MB49-I. In contrast to DAB-1, DAB-0 does not possess any anti-inflammatory activity and is less toxic. Furthermore, DAB-0 does not interfere with INFγ-induced STAT1 activation and TNFα-induced IκB phosphorylation, while DAB-1 does. In order to rationalize these results, the binding efficacy of DAB-0 and DAB-1 with serum proteins such a human serum albumin (HSA), bovine serum albumin (BSA) and beta-lactoglobulin (β-LG) was investigated in aqueous solution at physiological pH. Multiple spectroscopic methods and thermodynamic analysis were used to determine the binding efficacy of DAB-0 and DAB-1 with serum proteins. Drug-protein conjugation was observed via through ionic contacts. DAB-1 forms stronger adducts than DAB-0, while β-LG shows more affinity with the order of stability β-LG > BSA > HSA. The stronger complexation of DAB-1 with serum proteins might account for its biological potential and transport in the blood. The binding efficacy ranged from 40 to 60%. Major alterations of protein secondary structures were detected upon drug complexation. Serum proteins are capable of delivering DAB-1 in vitro.Communicated by Ramaswamy H. Sarma.

Complexation of cis-Pt and trans-Pt(NH3)2Cl2 with serum proteins: A potential application for drug delivery

AbbreviationsHAShuman serum albuminBSAbovine serum albuminβ-LGbeta-lactoglobulincis-Pt and trans-PtPt(NH₃)₂Cl₂FTIRFourier transform infraredCommunicated by Ramaswamy H. Sarma.

Location of multiple binding sites for testo and testo-Pt(II) with tRNA

We report the binding of testo and testo-Pt(II) complexes (testosterone derivatives) with tRNA in aqueous solution at physiological pH. Thermodynamic parameter ΔH₀ -8 to -3 (kJ mol^-1), ΔS₀ 35 to 18 (J mol^-1K^-1) and ΔG₀ -14 to -13 (kJ mol^-1) and other spectroscopic results showed drug-tRNA binding occurs via ionic contacts with testo-Pt(II) forming more stable tRNA complexes in comparison to testo: K_testo-Pt(II)-tRNA= 3.2 (± 0.9) × 10⁵ M^-1 > K_testo-tRNA= 2.1 (± 0.7) × 10⁵ M^-1. Molecular modeling showed multiple binding sites for testo and testo-Pt(II) on tRNA molecule. Some of the useful molecular descriptors are calculated. Major structural changes were observed for biopolymers upon drug complexation, while tRNA remains in the A-family structures.

PAMAM dendrimers in drug delivery: loading efficacy and polymer morphology

The binding efficacy of anticancer drugs doxorubicin and tamoxifen with polyamidoamine (PAMAM-G4) dendrimers was studied in aqueous solution at physiological pH. The results of multiple spectroscopic methods, transmission electron microscopy (TEM), and molecular modeling of conjugated drug–polymer were examined. Structural analysis showed that drug–polymer conjugation occurs mainly via H-bonding and hydrophilic and hydrophobic contacts. Doxorubicin forms a more stable conjugate with PAMAM-G4 than tamoxifen. The drug loading efficacy was 40%–50%. The TEM images showed major changes in the PAMAM morphology upon drug encapsulation. Modeling showed that drug is located in the polymer surface and in the internal cavities. PAMAM nanoparticles are capable of transporting doxorubicin and tamoxifen in vitro. This minireview presents the most recent work performed with the dendrimers demonstrating their usefulness for drug delivery in cancer therapy.

Testosterone and its dimers alter tRNA morphology

The morphology of tRNA was studied upon conjugation with testosterone and its aliphatic and aromatic dimers, using multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling. Structural analysis showed that testosterone binds tRNA through A62, A64, C60, C61, C63, G51, U50 and U59 bases. The binding affinity was testosterone dimer-aromatic>testosterone dimer-aliphatic>testosterone. The steroid loading efficacy was 35-45%. Transmission electron microscopy showed major changes in tRNA morphology upon testosterone interaction with an increase in the diameter of the tRNA aggregate, indicating encapsulation of testosterone by tRNA.

Review on the delivery of steroids by carrier proteins

Due to the poor solubility of steroids in aqueous solution, delivery of these biomaterials is of major biomedical importance. We have reviewed the conjugation of testosterone and it aliphatic dimer and aromatic dimer with several carrier proteins, human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) in aqueous solution at physiological pH. The results of multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were compared here. Steroid-protein bindings are via hydrophilic and H-bonding contacts. HSA forms more stable conjugate than BSA and b-LG. The stability of steroid-protein conjugates is testosterone>dimer-aromatic>dimer-aliphatic. Encapsulation of steroids by protein is shown by TEM images. Modeling showed the presence of H-bonding, which stabilized testosterone-protein complexes with the free binding energy of -12.95 for HSA and -11.55 for BSA and -8.92kcal/mol for b-LG conjugates. Steroid conjugation induced major perturbations of serum protein conformations. Serum proteins can transport steroids to the target molecules.

The function of CUX1 in oxidative DNA damage repair is needed to prevent premature senescence of mouse embryo fibroblasts

Despite having long telomeres, mouse embryo fibroblasts (MEFs) senesce more rapidly than human diploid fibroblasts because of the accumulation of oxidative DNA damage. The CUX1 homeodomain protein was recently found to prevent senescence in RAS-driven cancer cells that produce elevated levels of reactive-oxygen species. Here we show that Cux1-/- MEFs are unable to proliferate in atmospheric (20%) oxygen although they can proliferate normally in physiological (3%) oxygen levels. CUX1 contains three domains called Cut repeats. Structure/function analysis established that a single Cut repeat domain can stimulate the DNA binding, Schiff-base formation, glycosylase and AP-lyase activities of 8-oxoguanine DNA glycosylase 1, OGG1. Strikingly and in contrast to previous reports, OGG1 exhibits efficient AP-lyase activity in the presence of a Cut repeat. Repair of oxidative DNA damage and proliferation in 20% oxygen were both rescued in Cux1-/- MEFs by ectopic expression of CUX1 or of a recombinant Cut repeat protein that stimulates OGG1 but is devoid of transcription activation potential. These findings reinforce the causal link between oxidative DNA damage and cellular senescence and suggest that the role of CUX1 as an accessory factor in DNA repair will be critical in physiological situations that generate higher levels of reactive oxygen species.

Transporting testosterone and its dimers by serum proteins

A substantial part of steroids is bound to serum proteins in vivo. We report the association of testosterone and it aliphatic dimer (alip) and aromatic dimer (arom) with human serum albumin (HSA) and bovine serum albumin (BSA) in aqueous solution at physiological pH. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize steroid-protein binding and protein aggregation process. Spectroscopic analysis showed that steroids bind protein via hydrophobic, hydrophilic and H-bonding interactions. HSA forms more stable complexes than BSA. The binding affinity of steroid-protein adducts is testosterone>dimer-aromatic>dimer-aliphatic. Transmission electron microscopy showed major changes in protein morphology as steroid-protein complexation occurred with increase in the diameter of the protein aggregate indicating encapsulation of steroids by serum proteins. Modeling showed the presence of H-bonding stabilized testosterone-protein complexes with the free binding energy of -12.95 for HSA and -11.55 kcal/mol for BSA, indicating that the interaction process is spontaneous at room temperature. Steroid complexation induced more perturbations of BSA conformation than HSA.

Encapsulation of testosterone and its aliphatic and aromatic dimers by milk beta-lactoglobulin

The encapsulation of testosterone and it aliphatic dimer (alip) and aromatic dimer (arom) with milk β-lactoglobulin (β-LG) was studied in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize testosterone-β-LG binding and protein aggregation process. Spectroscopic analysis showed that steroids bind β-LG via hydrophobic and H-bonding interactions with overall binding constants K test-β-LG = 5.6 (± 0.6) × 10(4)M(-1), K test-dimeralip-β-LG = 4.8 (± 0.5) × 10(3)M(-1) and K test-dimer-arom-β-LG = 2.9 (± 0.4) × 10(4)M(-1). The binding affinity was testosterone > testosterone dimer-aromatic > testosterone dimer-aliphatic. Transmission electron microscopy showed major changes in protein morphology as testosterone-protein complexation occurred with increase in the diameter of the protein aggregate indicating encapsulation of steroids by β-LG. Modeling showed the presence of H-bonding stabilized testosterone-β-LG complexes with the free binding energy of -9.82 Kcal/mol indicating that the interaction process is spontaneous at room temperature.

ERα-targeted therapy in ovarian cancer cells by a novel estradiol-platinum(II) hybrid

As we previously showed, we have synthesized a new family of 17β-estradiol-platinum(II) hybrids. Earlier studies revealed the VP-128 hybrid to show high efficiency compared with cisplatin toward hormone-dependent breast cancer cells. In the present research, we have studied the antitumor activity of VP-128 in vitro and in vivo against ovarian cancer. In nude mice with ovarian xenografts, VP-128 displayed selective activity toward hormone-dependent tumors and showed higher efficiency than cisplatin to inhibit tumor growth. Similarly, in vitro, transient transfection of estrogen receptor (ER)-α in ERα-negative A2780 cells increased their sensitivity to VP-128-induced apoptosis, confirming the selectivity of VP-128 toward hormone-dependent tumor cells. In agreement, Western blot analysis revealed that VP-128 induced higher caspase-9, caspase-3, and poly (ADP-ribose) polymerase cleavage compared with cisplatin. The activation of caspase-independent apoptosis was also observed in ERα-negative A2780 cells, in which VP-128 rapidly induced the translocation of apoptosis-inducing factor to the nucleus. Conversely, subcellular localization of apoptosis-inducing factor was not modified in ERα-positive Ovcar-3 cells. We also discovered that VP-128 induces autophagy in ovarian cancer cells because of the formation of acidic vesicular organelles (AVOs) and increase of Light Chain 3B-II protein responsible for the formation of autophagosomes; pathways related to autophagy (AKT and mammalian target of rapamycin) were also down-regulated, supporting this mechanism. Finally, the inhibition of autophagy using chloroquine increased VP-128 efficiency, indicating a possible combination therapy. Altogether these results highlight the beneficial value of VP-128 for the treatment of hormone-dependent ovarian cancers and provide preliminary proof of concept for the efficient targeting of ERα- by 17β-estradiol-Pt(II)-linked chemotherapeutic hybrids in these tumors.

Long-range transcriptional regulation by the p110 CUX1 homeodomain protein on the ENCODE array

Background

Overexpression of the Cut homeobox 1 gene, CUX1, inversely correlates with patient survival in breast cancers. Cell-based assays and molecular studies have revealed that transcriptional regulation by CUX1 involves mostly the proteolytically processed p110 isoform. As there is no antibody specific to p110 CUX1 only, an alternate strategy must be employed to identify its targets.

Results

We expressed physiological levels of a tagged-p110 CUX1 protein and performed chromatin affinity purification followed by hybridization on ENCODE and promoter arrays. Targets were validated by chromatin immunoprecipitation and transcriptional regulation by CUX1 was analyzed in expression profiling and RT-qPCR assays following CUX1 knockdown or p110 CUX1 overexpression. Approximately 47% and 14% of CUX1 binding sites were respectively mapped less than 4 Kbp, or more than 40 Kbp, away from a transcription start site. More genes exhibited changes in expression following CUX1 knockdown than p110 CUX1 overexpression. CUX1 directly activated or repressed 7.4% and 8.4% of putative targets identified on the ENCODE and promoter arrays respectively. This proportion increased to 11.2% for targets with 2 binding sites or more. Transcriptional repression was observed in a slightly higher proportion of target genes. The CUX1 consensus binding motif, ATCRAT, was found at 47.2% of the CUX1 binding sites, yet only 8.3% of the CUX1 consensus motifs present on the array were bound in vivo. The presence of a consensus binding motif did not have an impact on whether a target gene was repressed or activated. Interestingly, the distance between a binding site and a transcription start site did not significantly reduced the ability of CUX1 to regulate a target gene. Moreover, CUX1 not only was able to regulate the next adjacent gene, but also regulated the gene located beyond this one as well as the gene located further away in the opposite direction.

Conclusion

Our results demonstrate that p110 CUX1 can activate or repress transcription when bound at a distance and can regulate more than one gene on certain genomic loci.

Genome-wide location analysis and expression studies reveal a role for p110 CUX1 in the activation of DNA replication genes

Proteolytic processing of the CUX1 transcription factor generates an isoform, p110 that accelerates entry into S phase. To identify targets of p110 CUX1 that are involved in cell cycle progression, we performed genome-wide location analysis using a promoter microarray. Since there are no antibodies that specifically recognize p110, but not the full-length protein, we expressed physiological levels of a p110 isoform with two tags and purified chromatin by tandem affinity purification (ChAP). Conventional ChIP performed on synchronized populations of cells confirmed that p110 CUX1 is recruited to the promoter of cell cycle-related targets preferentially during S phase. Multiple approaches including silencing RNA (siRNA), transient infection with retroviral vectors, constitutive expression and reporter assays demonstrated that most cell cycle targets are activated whereas a few are repressed or not affected by p110 CUX1. Functional classes that were over-represented among targets included DNA replication initiation. Consistent with this finding, constitutive expression of p110 CUX1 led to a premature and more robust induction of replication genes during cell cycle progression, and stimulated the long-term replication of a plasmid bearing the oriP replicator of Epstein Barr virus (EBV).

Biochemical characterization of the mammalian Cux2 protein

The CCAAT displacement protein (CDP) and cux (Cut homeobox) genes were originally identified as the human and mouse orthologs of Drosophila melanogaster cut. More recently, vertebrates were found to possess a second cut orthologs that was generated by gene duplication: Cux2. We report the initial biochemical characterization of the Cux2 protein in tissue culture and in vitro. We generated four polyclonal antibodies that were able to recognize the human and mouse Cux2 protein but displayed little or no cross-reactivity towards CDP1 and Cux1. The expression of the Cux2 protein was convincingly detected in only one among 19 neuronal cell lines: the SH-SY5Y human neuroblastoma cell line. CDP/Cux proteins contain four DNA binding domains, three Cut repeat (CR1, CR2 and CR3) and one Cut homeodomain (HD). Purified fusion proteins containing either CR1CR2, CR2CR3HD or CR3HD exhibited similar DNA binding specificities as the corresponding domains of Cux1, but their DNA binding kinetics were much more rapid. Similarly, the full-length Cux2 protein made rapid but transient interactions with DNA. We did not observe an N-terminally processed Cux2 isoform equivalent to the Cux1 p110 isoform. Whereas Cux1 can function as a repressor or activator in a promoter-specific manner, Cux2 functioned exclusively as a transcriptional repressor in NIH3T3 cells. Overall, our results suggest that the Cux1 and Cux2 proteins carry distinct biochemical functions. Cux2 is able, like Cux1, to perform the CCAAT-displacement activity. However, Cux2 is unlikely to execute transcriptional regulatory functions that require stable interaction with DNA.

The N-terminal Region of the CCAAT Displacement Protein (CDP)/Cux Transcription Factor Functions as an Autoinhibitory Domain that Modulates DNA Binding

The CCAAT displacement protein/Cut homeobox (CDP/Cux) transcription factor is expressed as multiple isoforms that may contain up to four DNA-binding domains: Cut repeats 1, 2, and 3 (CR1, CR2, CR3) and the Cut homeodomain (HD). The full-length protein, which contains all four DNA-binding domains, is surprisingly less efficient than the shorter isoforms in DNA binding. Using a panel of recombinant proteins expressed in mammalian or bacterial cells, we have identified a domain at the extreme N terminus of the protein that can inhibit DNA binding. This domain was able to inhibit the activity of full-length CDP/Cux and of proteins containing various combinations of DNA-binding domains: CR1CR2, CR3HD, or CR2CR3HD. Since inhibition of DNA binding was also observed with purified proteins obtained from bacteria, we conclude that autoinhibition does not require post-translational modification or interaction with an interacting protein but instead functions through an intramolecular mechanism. Antibodies directed against the N-terminal region were able to partially relieve inhibition. In vivo, the transition between the inactive and active states for DNA binding is likely to be governed by posttranslational modifications and/or interaction with one or more protein partners. In addition, we show that the relief of autoinhibition can be accomplished via the proteolytic processing of CDP/Cux. Altogether, these results reveal a novel mode of regulation that serves to modulate the DNA binding activity of CDP/Cux.

Development of an in vitro assay for the proteolytic processing of the CDP/Cux transcription factor

The CDP/Cux transcription factor was previously shown to be proteolytically processed at the G1/S transition. In view of characterizing and eventually identifying the protease responsible for CDP/Cux processing, we have established an in vitro proteolytic processing assay. CDP/Cux recombinant proteins expressed in mammalian or bacterial cells were efficiently processed in vitro using as a source of protease either whole cell extracts, the nuclear or the cytoplasmic fraction. Processing was found to take place optimally at a lower pH, to be insensitive to variations in salt concentration, and to be inhibited by the protease inhibitors MG132 and E64D. Interestingly, the bacterially-produced substrate was more efficiently processed than the substrate purified from mammalian cells. Moreover, processing in vitro was more efficient when CDP/Cux substrates were purified from populations of cells enriched in the S phase than in the G1 phase of the cell cycle. Altogether, these results suggest that posttranslational modifications of CDP/Cux in mammalian cells inhibits processing and contributes to the cell cycle-dependent regulation of processing. The in vitro processing assay described in this study will provide a useful tool for the purification and identification of the protease responsible for the processing of CDP/Cux.

CDP/Cux stimulates transcription from the DNA polymerase alpha gene promoter

CDP/Cux (CCAAT-displacement protein/cut homeobox) contains four DNA binding domains, namely, three Cut repeats (CR1, CR2, and CR3) and a Cut homeodomain. CCAAT-displacement activity involves rapid but transient interaction with DNA. More stable DNA binding activity is up-regulated at the G(1)/S transition and was previously shown to involve an N-terminally truncated isoform, CDP/Cux p110, that is generated by proteolytic processing. CDP/Cux has been previously characterized as a transcriptional repressor. However, here we show that expression of reporter plasmids containing promoter sequences from the human DNA polymerase alpha (pol alpha), CAD, and cyclin A genes is stimulated in cotransfections with N-terminally truncated CDP/Cux proteins but not with full-length CDP/Cux. Moreover, expression of the endogenous DNA pol alpha gene was stimulated following the infection of cells with a retrovirus expressing a truncated CDP/Cux protein. Chromatin immunoprecipitation (ChIP) assays revealed that CDP/Cux was associated with the DNA pol alpha gene promoter specifically in the S phase. Using linker scanning analyses, in vitro DNA binding, and ChIP assays, we established a correlation between binding of CDP/Cux to the DNA pol alpha promoter and the stimulation of gene expression. Although we cannot exclude the possibility that stimulation of gene expression by CDP/Cux involved the repression of a repressor, our data support the notion that CDP/Cux participates in transcriptional activation. Notwithstanding its mechanism of action, these results establish CDP/Cux as an important transcriptional regulator in the S phase.

Characterization of a tissue-specific CDP/Cux isoform, p75, activated in breast tumor cells

Two isoforms of the CCAAT-displacement protein/cut homeobox (CDP/Cux) transcription factor have been characterized thus far. The full length protein, p200, which contains four DNA binding domains, transiently binds to DNA and carries the CCAAT-displacement activity. The p110 isoform is generated by proteolytic processing at the G1-S transition and is capable of stable interaction with DNA. Here we demonstrate the existence of a shorter CDP/Cux isoform, p75, which contains only two DNA binding domains, Cut repeat 3 and the Cut homeodomain, and binds more stably to DNA. CDP/Cux p75 was able to repress a reporter carrying the promoter for the cyclin-dependent kinase inhibitor p21 gene and to activate a DNA polymerase alpha gene reporter. Expression of CDP/Cux p75 involved a novel mechanism: transcription initiation within intron 20. The intron 20-initiated mRNA (I20-mRNA) was expressed at higher level in the thymus and in CD4+/CD8+ and CD4+ T cells. I20-mRNA was expressed only weakly or not at all in normal human mammary epithelial cells and normal breast tissues but was detected in many breast tumor cells lines and breast tumors. In invasive tumors a significant association was established between higher I20-mRNA expression and a diffuse infiltrative growth pattern (n = 41, P = 0.0137). In agreement with these findings, T47D breast cancer cells stably expressing p75 could not form tubule structures in collagen but rather developed as solid undifferentiated aggregates of cells. Taken together, these results suggest that aberrant expression of the CDP/Cux p75 isoform in mammary epithelial cells may be associated with the process of tumorigenesis in breast cancer.

Expression of N-terminally truncated isoforms of CDP/CUX is increased in human uterine leiomyomas

Genetic analyses and mRNA expression studies have implicated CUTL1 as a candidate tumor-suppressor gene in uterine leiomyomas and breast cancers. However, modulation of CDP/Cux, the protein encoded by CUTL1, does not agree with this notion. The activity of CDP/Cux, which is the DNA binding subunit of HiNF-D, was upregulated as normal cells progressed into S phase and constitutively elevated in several tumor cell lines. Activation of CDP/Cux at the G(1)/S transition involved the proteolytic processing of the protein to generate a shorter isoform. Uterine leiomyomas represent a unique reagent for molecular analysis because they are resected as homogeneous tumor tissue together with the adjacent normal myometrium and they are often very large. In the present study, proteins were isolated from 16 pairs of matched tumors and adjacent myometrium and analyzed by Western blot and electrophoretic mobility shift assays. Strikingly, in 11/16 tumors, the steady-state level of small CDP/Cux isoforms was increased compared to normal control tissue. Where tested, a corresponding increase in CDP/Cux stable DNA binding activity was observed. DNA sequencing analysis of CUTL1 cDNAs from 6 leiomyomas, including 4 with LOH of CUTL1, did not reveal any gross rearrangement or point mutations. Altogether these findings suggest that CUTL1 is probably not the tumor suppressor on 7q22. Moreover, the frequent increase in smaller CDP/Cux isoforms indicates that molecular events associated with the truncation of CDP/Cux proteins may be selected in uterine leiomyomas.

Phosphorylation of the CCAAT displacement protein (CDP)/Cux transcription factor by cyclin A-Cdk1 modulates its DNA binding activity in G(2)

Stable DNA binding by the mammalian CCAAT displacement protein (CDP)/Cux transcription factor was previously found to be up-regulated at the G(1)/S transition as the result of two events, dephosphorylation by the Cdc25A phosphatase and proteolytic processing, to generate an amino-truncated isoform of 110 kDa. In S phase, CDP/Cux was shown to interact with and repress the core promoter of the p21(WAF1) gene. Here we demonstrate that DNA binding by p110 CDP/Cux is down-modulated as cells progress into G(2). Accordingly, cyclin A-Cdk1 was found to bind to CDP/Cux and modulate its DNA binding activity in vitro and in vivo. Interaction with CDP/Cux required the presence of both cyclin A and a cyclin-dependent kinase (Cdk)-activating kinase-activated Cdk1 and involved the Cut homeodomain and a downstream Cy motif. Phosphorylation of serines 1237 and 1270 caused inhibition of DNA binding in vitro. In cotransfection studies, cyclin A-Cdk1 inhibited CDP/Cux stable DNA binding and prevented repression of the p21(WAF1) reporter. In contrast, mutant CDP/Cux proteins in which serines 1237 and 1270 were replaced with alanines were not affected by cyclin A-Cdk1. In summary, our results suggest that the phosphorylation of CDP/Cux by cyclin A-Cdk1 contributes to down-modulate CDP/Cux activity as cells progress into the G(2) phase of the cell cycle.

S phase-specific proteolytic cleavage is required to activate stable DNA binding by the CDP/Cut homeodomain protein

The CCAAT displacement protein (CDP), the homologue of the Drosophila melanogaster Cut protein, contains four DNA binding domains that function in pairs. Cooperation between Cut repeat 3 and the Cut homeodomain allows stable DNA binding to the ATCGAT motif, an activity previously shown to be upregulated in S phase. Here we showed that the full-length CDP/Cut protein is incapable of stable DNA binding and that the ATCGAT binding activity present in cells involves a 110-kDa carboxy-terminal peptide of CDP/Cut. A vector expressing CDP/Cut with Myc and hemagglutinin epitope tags at either end generated N- and C-terminal products of 90 and 110 kDa, suggesting that proteolytic cleavage was involved. In vivo pulse/chase labeling experiments confirmed that the 110-kDa protein was derived from the full-length CDP/Cut protein. Proteolytic processing was weak or not detectable in G(0) and G(1) but increased in populations of cells enriched in S phase, and the appearance of the 110-kDa protein coincided with the increase in ATCGAT DNA binding. Interestingly, the amino-truncated and the full-length CDP/Cut isoforms exhibited different transcriptional properties in a reporter assay. We conclude that proteolytic processing of CDP/Cut at the G(1)/S transition generates a CDP/Cut isoform with distinct DNA binding and transcriptional activities. These findings, together with the cleavage of the Scc1 protein at mitosis, suggest that site-specific proteolysis may play an important role in the regulation of cell cycle progression.

p62dok negatively regulates CD2 signaling in Jurkat cells

p62(dok) belongs to a newly identified family of adaptor proteins. In T cells, the two members that are predominantly expressed, p56(dok) and p62(dok), are tyrosine phosphorylated upon CD2 or CD28 stimulation, but not upon CD3 ligation. Little is known about the biological role of Dok proteins in T cells. In this study, to evaluate the importance of p62(dok) in T cell function, we generated Jurkat clones overexpressing p62(dok). Our results demonstrate that overexpression of p62(dok) in Jurkat cells has a dramatic negative effect on CD2-mediated signaling. The p62(dok)-mediated inhibition affects several biochemical events initiated by CD2 ligation, such as the increase of intracellular Ca(2+), phospholipase C gamma 1 activation, and extracellular signal-regulated kinase 1/2 activation. Importantly, these cellular events are not affected in the signaling cascade induced by engagement of the CD3/TCR complex. However, both CD3- and CD2-induced NF-AT activation and IL-2 secretion are impaired in p62(dok)-overexpressing cells. In addition, we show that CD2 but not CD3 stimulation induces p62(dok) and Ras GTPase-activating protein recruitment to the plasma membrane. These results suggest that p62(dok) plays a negative role at multiple steps in the CD2 signaling pathway. We propose that p62(dok) may represent an important negative regulator in the modulation of the response mediated by the TCR.

CCAAT displacement activity involves CUT repeats 1 and 2, not the CUT homeodomain

The CCAAT displacement protein, the homolog of the Drosophila melanogaster CUT protein, contains four DNA-binding domains: three CUT repeats (CR1, CR2, and CR3) and the CUT homeodomain (HD). Using a panel of fusion proteins, we found that a CUT repeat cannot bind to DNA as a monomer, but that certain combinations of domains exhibit high DNA-binding affinity: CR1+2, CR3HD, CR1HD, and CR2HD. One combination (CR1+2) exhibited strikingly different DNA-binding kinetics and specificities. CR1+2 displayed rapid on and off rates and bound preferably to two C(A/G)AT sites, organized as direct or inverted repeats. Accordingly, only CR1+2 was able to bind to the CCAAT sequence, and its affinity was increased by the presence of a C(A/G)AT site at close proximity. A purified CCAAT displacement protein/CUT protein exhibited DNA-binding properties similar to those of CR1+2; and in nuclear extracts, the CCAAT displacement activity also required the simultaneous presence of a C(A/G)AT site. Moreover, CR1+2, but not CR3HD, was able to displace nuclear factor Y. Thus, the CCAAT displacement activity requires the presence of an additional sequence (CAAT or CGAT) and involves CR1 and CR2, but not the CUT homeodomain.

Exon/intron structure and alternative transcripts of the CUTL1 gene

The human CUTL1 gene (Cut-like 1) is a candidate tumor suppressor gene located on chromosome 7 at band 22, a region that is frequently deleted in several human cancers. The gene spans at least 340kb and contains 33 exons. Synthesis of five different transcripts involves two promoter regions, two polyadenylation sites and seven alternative splicing events. The two polyadenylation sites are located at the ends of exons 24 and 33 and are separated by approximately 40kb. Transcription is initiated in two genomic regions, giving rise to alternate first exons which are spliced to a common exon 2. All transcripts contain exons 2 to 14, but differ in their 3' regions. Exon 14 can be spliced alternatively to the beginning or the middle of exon 15, or to exon 25, generating transcripts with exons 15 to 24 or exons 25 to 33. Moreover, exon 16 can be spliced out from the mature transcripts that contain exons 15 to 24. Overall, five distinct transcripts are generated as a result of alternative transcription initiation, splicing and polyadenylation. We discuss potential mechanisms by which alternate polyadenylation site usage may affect alternative splicing events and vice versa.

Synthesis and preliminary in vitro cytotoxic activity of novel cisplatin and carboplatin analogues

Six new platinum(II) complexes were synthesized from a common triphenylethylene precursor using various diamines. The cytotoxicity of the compounds, evaluated on human breast cancer cell lines (MCF-7 and MDA-MB-231), was greatly influenced by the nature of the diamine ligand. Two derivatives presented cytotoxic activity greater than tamoxifen and, for the first time, as potent as cisplatin.

Effects of new triphenylethylene platinum(II) complexes on the interaction with phosphatidylcholine liposomes

In a previous work we synthesized a class of new antineoplastic drugs by coupling a cisplatin derivative to a triphenylethylene moiety similar to the antiestrogen, tamoxifen. These drugs differ in the number of hydroxy functions on the triphenylethylene rings and in the length of the linking arm. To gain more insight into the cellular mechanism by which these new drugs act on cells, we studied, using differential scanning calorimetry, the effects of these compounds on the phase transition of membrane phospholipid (distearoyl phosphatidyl choline (DSPC)), and correlated these effects to drug cytotoxicity. The drugs without hydroxy function showed the highest cytotoxicity and induced little change on the thermogram of DSPC. Contrarily, the drugs bearing two or three hydroxy groups were less toxic, but induced important modifications of the thermogram. We suggest that the drugs with no hydroxy group enter the membrane, with the triphenylethylene moiety localized deep within the hydrophobic core of the bilayer and do not affect the cooperativity region (C2-C8). In contrast, drugs which bear hydroxy groups on the triphenylethylene rings system perturb the phospholipid molecular arrangement; this may be due either to the additional steric hindrance of the hydroxy functions in the core of the bilayer, or to their hydrophilic effect on the polar head of the lipid. In vitro, the cytotoxic effect of these drugs seems not to be related to their affinity for the estrogen receptor. We suggest that the addition of a triphenylethylene moiety to the platinum(II) complexes increases the hydrophobicity, and consequently the resulting drugs become more permeable to the membrane, particularly the non-hydroxylated triphenylethylene derivatives.

The mammalian Cut homeodomain protein functions as a cell-cycle-dependent transcriptional repressor which downmodulates p21WAF1/CIP1/SDI1 in S phase

Cut is a homeodomain transcription factor which has the unusual property of containing several DNA-binding domains: three regions called Cut repeats and the Cut homeodomain. Genetic studies in Drosophila melanogaster indicate that cut plays important roles in the determination and maintenance of cell-type specificity. In the present study, we show that mammalian Cut proteins may yet play another biological role, specifically in proliferating cells. We found that the binding of Cut to a consensus binding site varies during the cell cycle. Binding was virtually undetectable in G0 and early G1, but became very strong as cells reached S phase. This was shown to result both from an increase in Cut expression and dephosphorylation of the Cut homeodomain by the Cdc25A phosphatase. We also show that the increase in Cut activity coincides with a decrease in p21WAF1/CIP1/SDI1 mRNAs. In co-transfection experiments, Cut proteins repressed p21WAF1/CIP1/SDI1 gene expression through binding to a sequence that overlaps the TATA box. Moreover, p21WAF1/CIP1/SDI1 expression was repressed equally well by either Cdc25A or Cut. Altogether, these results suggest a model by which Cdc25A activates the Cut repressor which then downregulates transcription of p21WAF1/CIP1/SDI1 in S phase. Thus, in addition to their role during cellular differentiation, Cut proteins also serve as cell-cycle-dependent transcriptional factors in proliferating cells.

DNA binding by cut homeodomain proteins is down-modulated by casein kinase II

The Drosophila and mammalian Cut homeodomain proteins contain, in addition to the homeodomain, three other DNA binding regions called Cut repeats. Cut-related proteins thus belong to a distinct class of homeodomain proteins with multiple DNA binding domains. Using nuclear extracts from mammalian cells, Cut-specific DNA binding was increased following phosphatase treatment, suggesting that endogenous Cut proteins are phosphorylated in vivo. Sequence analysis of Cut repeats revealed the presence of sequences that match the consensus phosphorylation site for casein kinase II (CKII). Therefore, we investigated whether CKII can modulate the activity of mammalian Cut proteins. In vitro, a purified preparation of CKII efficiently phosphorylated Cut repeats causing an inhibition of DNA binding. In vivo, overexpression of the CKII alpha and beta caused a decrease in DNA binding by Cut. The CKII phosphorylation sites within the murine Cut (mCut) protein were identified by in vitro mutagenesis as residues Ser400, Ser789, and Ser972 within Cut repeat 1, 2, and 3, respectively. Cut homeodomain proteins were previously shown to function as transcriptional repressors. Overexpression of CKII reduced transcriptional repression by mCut, whereas a mutant mCut protein containing alanine substitutions at these sites was not affected. Altogether our results indicate that the transcriptional activity of Cut proteins is modulated by CKII.

DNA binding by cut homeodomain proteins is down-modulated by protein kinase C

The Drosophila and mammalian Cut homeodomain proteins contain, in addition to the homeodomain, three other DNA binding regions called Cut repeats. Cut-related proteins thus belong to a distinct class of homeodomain proteins with multiple DNA binding domains. Using nuclear extracts from mammalian cells, Cut-specific DNA binding was increased following phosphatase treatment, suggesting that endogenous Cut proteins are phosphorylated in vivo. Sequence analysis of Cut repeats revealed the presence of sequences that match the consensus phosphorylation site for protein kinase C (PKC). Therefore, we investigated whether PKC can modulate the activity of mammalian Cut proteins. In vitro, a purified preparation of PKC efficiently phosphorylated Cut repeats, which inhibited DNA binding. In vivo, a brief treatment of cells with calphostin C, a specific inhibitor of PKC, led to an increase in Cut-specific DNA binding, whereas phorbol 12-myristate 13-acetate, a specific activator of PKC, caused a decrease in DNA binding. The PKC phosphorylation sites within the murine Cut (mCut) protein were identified by in vitro mutagenesis as residues Thr415, Thr804, and Ser987 within Cut repeats 1-3, respectively. Cut homeodomain proteins were previously shown to function as transcriptional repressors. Activation of PKC by phorbol 12-myristate 13-acetate reduced transcriptional repression by mCut, whereas a mutant mCut protein containing alanine substitutions at these sites was not affected. Altogether, our results indicate that the transcriptional activity of Cut proteins is modulated by PKC.

The human cut homeodomain protein can repress gene expression by two distinct mechanisms: active repression and competition for binding site occupancy

By analogy with other homeodomain proteins conserved in evolution, mammalian Cut proteins are believed, as in Drosophila melanogaster, to play an important role in determining cell type specificity in several tissues. At the molecular level, Cut proteins appear to serve as transcriptional repressors. In this study, we have examined the mechanism by which the human Cut (hCut) protein down-regulates gene expression. The homeodomain and the three regions called Cut repeats are evolutionarily conserved and were previously shown to function as DNA binding domains. The carboxy-terminal region, although it does not show amino acid sequence homology per se, in all cases is enriched in alanine and proline residues, a distinctive feature of some transcriptional repression domains. Our results reveal two distinct modes of repression: competition for binding site occupancy and active repression. On one hand, the composite DNA binding domain formed by Cut repeat 3 and the Cut homeodomain was shown to bind to CCAAT and Sp1 sites within the tk gene promoter and to reduce gene expression, presumably by preventing activation by the corresponding transcription factors. On the other hand, the carboxy-terminal region of mammalian Cut proteins was found to function as an active repression domain in a distance-independent manner. We have further narrowed this activity to two subdomains that can independently repress activated transcription. Finally, we present a model to illustrate the two mechanisms by which Cut proteins repress gene expression.

Conjugation of doxorubicin to monoclonal anti-carcinoembryonic antigen antibody via novel thiol-directed cross-linking reagents

In order to improve the available methods to produce an immunoconjugate the use of longer heterobifunctional cross-linking reagents were investigated. Two new maleimidobenzoyl spacers have been synthesized in a one step process from 4-maleimidobenzoic acid. The new heterobifunctional cross-linking reagents were fully characterized by their IR, 1H NMR, 13C NMR and mass spectra. These spacers are selectively attached to NH2-3' of the daunosamine moiety of doxorubicin. The spacer-doxorubicin derivatives were also characterized by 1H NMR spectrometry before coupling to thiol groups of thiolated anti-carcinoembryonic antigen (CEA) monoclonal antibody (11-285-14). These conjugates contain 1.51-3.44 molecules of drug for each molecule of monoclonal antibody (MAb).

Novel doxorubicin-monoclonal anti-carcinoembryonic antigen antibody immunoconjugate activity in vitro

Doxorubicin was modified with five different heterobifunctional reagents to produce drug analogs containing 3'-N-amide or C-13 hydrazone linkage with maleimide. Synthesis and characterization of two new reagents, 4-maleimidobenzohydrazide trifluoroacetate salt (13) and N-(4-maleimidobenzoyl)-6-aminocaprohydrazide trifluoroacetate salt (14) are described here. All Dox maleimido derivatives were conjugated to thiolated anti-carcinoembryonic antigen monoclonal antibody, 11-285-14, via a Michael addition reaction. Antibody-directed cytotoxicity was demonstrated with the MTT assay using combinations of antigen-positive and antigen-negative cell lines. The immunoconjugates prepared from Dox 3'-N-amide analogs are not active in vitro, however, Dox(hydrazone-linked) immunoconjugates are selectively toxic to the CEA positive cell line.

DNA-binding specificity of the cut repeats from the human cut-like protein

The Drosophila Cut and mammalian Cut-like proteins contain, in addition to the homeodomain, three other DNA-binding regions called Cut repeats. Cut-like proteins, therefore, belong to a distinct class of homeodomain proteins with multiple DNA-binding domains. In this study, we assessed the DNA-binding specificity of the human Cut repeats by performing PCR-mediated random oligonucleotide selection with glutathione S-transferase fusion proteins. Cut repeat 1, Cut repeat 3, and Cut repeat 3 plus the homeodomain selected related yet distinct sequences. Therefore, sequences selected by one of the fusion proteins were often, but not always, recognized by the other proteins. Consensus binding sites were derived for each fusion protein. In each case, however, some selected sequences diverged from the consensus but were confirmed to be high-affinity recognition sites by electrophoretic mobility shift assay. We conclude that Cut DNA-binding domains have broad, overlapping DNA-binding specificities. Determination of dissociation constants indicated that in addition to the core consensus, flanking sequences have a moderate but significant effect on sequence recognition. Evidence from electrophoretic mobility shift assay, DNase footprinting, and dissociation constant analyses strongly suggested that glutathione S-transferase/Cut fusion proteins bind to DNA as dimers. The implications of these findings are discussed in relation to the DNA-binding capabilities of Cut repeats. In contrast to other studies, we found that the human Cut-like protein does not preferably bind to a site that includes an ATTA homeodomain-binding motif. Here we demonstrate that the native human Cut-like protein recognizes more efficiently a site containing an ATCGAT core consensus flanked with G/C-rich sequences.

Synthesis and preliminary in vitro biological activity of non-steroidal cytotoxic estrogens designed for the treatment of breast cancer

The development of resistance to endocrine therapy as well as chemotherapy is presently a major problem in the treatment of breast cancer. To minimize this obstacle, new, more selective and potent, chemotherapeutic agents should be designed. One way to improve selectivity is to link a cytotoxic moiety to a molecule possessing an affinity to the estrogen receptor (ER). The latter would be used to direct the cytotoxic portion of the molecule towards the target cells. Our initial approach led us to the synthesis of new triphenylethylene–platinum(II) complexes 1a–c. The commercially available desoxyanisoin (10) was efficiently transformed in seven steps into the platinum(II) complexes 1a–c with an overall yield exceeding 30%. The biological activity of compounds 1a–c was evaluated in vitro on ER+ and ER− human breast tumor cell lines: MCF-7 and MDA-MD-231.