Efficacy of immune checkpoint inhibition in metastatic uveal melanoma: a systematic review and meta-analysis

Metastatic uveal melanoma (mUM) has historically been associated with short survival and limited effective treatments. Immune checkpoint inhibitors (ICIs) have been trialed in mUM; however, robust conclusions regarding their efficacy are difficult to draw given small study sizes and heterogeneous patient populations. Five databases were searched using a combination of 'ICI' and 'mUM' headings, and data on patient demographics, objective response rate (ORR), overall survival (OS) and progression-free survival (PFS) were extracted. Pooled ORR was calculated using a random effects model and the inverse variance method. Available Kaplan-Meier OS and PFS curves were used to construct summary OS and PFS plots, from which median values were derived. Pooled ORR was 9.2% overall (95% CI 7.2-11.8) [4.1% for anti-CTLA4 (95% CI 2.1-7.7), 7.1% for anti-PD(L)1 (95% CI 4.5-10.9) and 13.5% for anti-CTLA4 plus anti-PD1 (95% CI 10.0-18.0)]. Median OS was 11.5 months overall (95% CI 9.5-13.8) [8.0 months for anti-CTLA4 (95% CI 5.5-9.9), 11.7 months for anti-PD(L)1 (95% CI 9.0-14.0) and 16.0 months for ipilimumab plus anti-PD1 (95% CI 11.5-17.7) ( P < 0.001)]. Median PFS was 3.0 months overall (95% CI 2.9-3.1). ICIs have limited efficacy in mUM and a recommendation for their use must consider the balance of benefit and risk for individual patients if no other options are available. Further biomarker profiling studies may be helpful in assessing which patients will benefit from ICIs, in particular the addition of ipilimumab to anti-PD1 therapy.

Antibody-Drug Conjugates: Ushering in a New Era of Cancer Therapy

Antibody-drug conjugates (ADCs) have provided new therapeutic options and significant promise for patients with cancer, particularly where existing treatments are limited. Substantial effort in ADC development is underway globally, with 13 ADCs currently approved and many more in development. The therapeutic benefits of ADCs leverage the ability to selectively target cancer cells through antibody binding, resultant relative sparing of non-malignant tissues, and the targeted delivery of a cytotoxic payload. Consequently, this drug class has demonstrated activity in multiple malignancies refractory to standard therapeutic options. Despite this, limitations exist, including narrow therapeutic windows, unique toxicity profiles, development of therapeutic resistance, and appropriate biomarker selection. This review will describe the development of ADCs, their mechanisms of action, pivotal trials, and approved indications and identify common themes. Current challenges and opportunities will be discussed for this drug class in cancer therapeutics at a time when significant developments in antibody therapies, immunotherapy, and targeted agents are occurring.

CDK4/6 inhibitor resistance in estrogen receptor positive breast cancer, a 2023 perspective

CDK4/6 inhibitors have become game-changers in the treatment of estrogen receptor-positive (ER+) breast cancer, and in combination with endocrine therapy are the standard of care first-line treatment for ER+/HER2-negative advanced breast cancer. Although CDK4/6 inhibitors prolong survival for these patients, resistance is inevitable and there is currently no clear standard next-line treatment. There is an urgent unmet need to dissect the mechanisms which drive intrinsic and acquired resistance to CDK4/6 inhibitors and endocrine therapy to guide the subsequent therapeutic decisions. We will review the insights gained from preclinical studies and clinical cohorts into the diverse mechanisms of CDK4/6 inhibitor action and resistance, and highlight potential therapeutic strategies in the context of CDK4/6 inhibitor resistance.

A systematic review of neoadjuvant and definitive immunotherapy in locally advanced head and neck squamous cell carcinoma

BACKGROUND

Patients with locally advanced head and neck squamous cell carcinoma (HNSCC) require multi-modality treatment. Immune checkpoint inhibitors (ICIs) are now standard of care in management of recurrent/metastatic HNSCC. However, its role in the definitive and neoadjuvant setting remains unclear.

METHODS

A literature search was conducted that included all articles investigating ICI in untreated locally advanced (LA) HNSCC. Data was extracted and summarised and rated for quality using the Cochrane risk of bias tool.

RESULTS

Of 1086 records, 29 met the final inclusion criteria. In both concurrent and neoadjuvant settings, the addition of ICI was safe and did not delay surgery or reduce chemoradiotherapy completion. In the concurrent setting, although ICI use demonstrates objective responses in all published trials, there has not yet been published data to with PFS or OS benefit. In the neoadjuvant setting, combination ICI resulted in superior major pathological response rates compared to ICI monotherapy without a significant increase adverse event profiles, but its value in improving survival is not clear. ICI efficacy appears to be affected by tumour characteristics, in particular PD-L1 combined positive score, HPV status and the tumour microenvironment.

CONCLUSIONS

There is significant heterogeneity of ICI use in untreated LA HNSCC with multiple definitive concurrent and neoadjuvant protocols used. Resultantly, conclusions regarding the survival benefits of adding ICI to standard-of-care regimens cannot be made. Further trials and translational studies are required to elucidate optimal ICI sequencing in the definitive setting as well as better define populations more suited for neoadjuvant protocols.

Recurrent cervical cancer after trachelectomy diagnosed by hysteroscopy: A case report

Surveillance for cervical cancer recurrence after radical trachelectomy is challenging and warrants additional research to establish evidence-based screening guidelines. Papanicolaou (Pap smear) with HPV testing, physical exam, and symptom reporting remain the standard of care despite high false positive rates. In this patient with a history of early-stage cervical adenocarcinoma status post radical trachelectomy, a diagnosis of recurrence was made hysteroscopically, prompting evaluation of the utility of this technique for screening and management of patients with suspected recurrent cervical cancer after trachelectomy.

Multicentric, prospective observational data show sperm capacitation predicts male fertility, and cohort comparison reveals a high prevalence of impaired capacitation in men questioning their fertility

RESEARCH QUESTIONS

Can a previously defined relationship between sperm capacitation and the probability of a man generating pregnancy within three cycles, prospectively predict male fertility in diverse clinical settings? A second study asked, what is the prevalence of impaired sperm fertilizing ability in men questioning their fertility (MQF), and does this relate to traditional semen analysis metrics?

DESIGN

In the multicentric, prospective observational study, data (n = 128; six clinics) were analysed to test a published relationship between the percentage of fertilization-competent, capacitated spermatozoa (Cap-Score) and probability of generating pregnancy (PGP) within three cycles of intrauterine insemination. Logistic regression of total pregnancy outcomes (n = 252) assessed fit. In the cohort comparison, Cap-Scores of MQF (n = 2155; 22 clinics) were compared with those of 76 fertile men.

RESULTS

New outcomes (n = 128) were rank-ordered by Cap-Score and divided into quintiles (25-26 per group); chi-squared testing revealed no difference between predicted and observed pregnancies (P = 0.809). Total outcomes (n = 252; 128 new + 124 previous) were pooled and the model recalculated, yielding an improved fit (P < 0.001). Applying the Akaike information criterion found that the optimal model used Cap-Score alone. Cap-Scores were performed on 2155 men (with semen analysis data available for 1948). To compare fertilizing ability, men were binned by PGP (≤19%, 20-29%, 30-39%, 40-49%, 50-59%, ≥60%). Distributions of PGP and the corresponding Cap-Scores were significantly lower in MQF versus fertile men (P < 0.001). Notably, 64% of MQF with normal volume, concentration and motility (757/1183) had PGP of 39% or less (Cap-Scores ≤31), versus 25% of fertile men.

CONCLUSIONS

Sperm capacitation prospectively predicted male fertility. Impaired capacitation affects many MQF with normal semen analysis results, informing diagnosis versus idiopathic infertility.

Endometrial Ablation for Aplastic Anemia-Associated Menorrhagia

Aplastic anemia is characterized by bone marrow failure and pancytopenia. In women, this can lead to menorrhagia secondary to thrombocytopenia which may require treatment depending on its severity. We report a patient with aplastic anemia-associated menorrhagia requiring emergency inpatient endometrial ablation due to transfusion dependence. A 42-year-old G3P3003 female presented with severe anemia, thrombocytopenia, and metrorrhagia. Her subsequent bone marrow biopsy revealed aplastic anemia. Her menometrorrhagia progressively worsened and she remained transfusion dependent. In the hospital, the patient underwent an uneventful endometrial ablation to control her vaginal bleeding. Patient reports only minor spotting after the procedure. Endometrial ablation is a safe and effective technique of treating acute menorrhagia in patients with aplastic anemia. It can reduce vaginal bleeding and decrease transfusion dependence.

Liquidity in Retirement Savings Systems: An International Comparison

We compare the liquidity that six developed countries have built into their employer-based defined contribution (DC) retirement schemes. In Germany, Singapore, and the UK, withdrawals are essentially banned no matter what kind of transitory income shock the household realizes. By contrast, in Canada and Australia, liquidity is state-contingent. For a middle-income household, DC accounts are completely illiquid unless annual income falls substantially, in which case DC assets become highly liquid. The US stands alone in the universally high liquidity of its DC system: whether or not income falls, the penalties for early withdrawal are low or non-existent.

Differential granulosa cell gene expression in young women with diminished ovarian reserve

OBJECTIVE

To investigate if a diagnosis of diminished ovarian reserve (DOR) is associated with a differential gene profile of ovarian granulosa cells (GCs) in infertile women undergoing in vitro fertilization (IVF).

DESIGN

Prospective Cohort Study.

SETTING

Academic IVF Program.

PATIENTS

Infertile women <38 years were prospectively enrolled into 2 groups: normal ovarian reserve (NOR, follicle-stimulating hormone [FSH] < 10 mIU/mL, n = 4) and DOR (FSH ≥ 10.0 mIU/mL, n = 4).

INTERVENTIONS

Cumulus (C) and mural (M) GCs were isolated at egg retrieval; messenger RNA was extracted and transcribed.

MAIN OUTCOME MEASURE(S)

Differential gene expression in cerebellar granule cells (CGCs) in the 2 groups was assessed by cDNA microarray. Microarray findings were validated by quantitative real-time polymerase chain reaction (qRTPCR) in CGCs and explored in multinucleated giant cells (MGCs).

RESULTS

Of the 1256 differentially regulated genes identified in CGCs of women with DOR, the insulin-like growth factor (IGF) family was a biologically relevant gene family of a priori interest. Downregulation of IGF1 and IGF2 ligands (-3.28- and -2.54-fold, respectively), and their receptors, (-3.53- and -1.32-fold downregulation of IGF1R and IGF2R, respectively) was identified in luteinized CGCs in women with DOR compared to those with NOR. Downregulation of both IGF1 and IGF 2 ligands (-4.35- and 3.89-fold, respectively) was furthermore observed in MGCs in women with DOR compared to those with NOR; no differences in the expression of respective receptors were however observed in MGCs in the 2 groups.

CONCLUSIONS

Components of the IGF gene family are downregulated in GCs of women with DOR. These findings maybe contributory to the reproductive compromise observed in women with DOR, and merit further exploration.

Obatoclax induces Atg7-dependent autophagy independent of beclin-1 and BAX/BAK

Direct pharmacological targeting of the anti-apoptotic B-cell lymphoma-2 (BCL-2) family is an attractive therapeutic strategy for treating cancer. Obatoclax is a pan-BCL-2 family inhibitor currently in clinical development. Here we show that, although obatoclax can induce mitochondrial apoptosis dependent on BCL-2 associated x protein/BCL-2 antagonist killer (BAX/BAK) consistent with its on-target pharmacodynamics, simultaneous silencing of both BAX and BAK did not abolish acute toxicity or loss of clonogenicity. This is despite complete inhibition of apoptosis. Obatoclax dramatically reduced viability without inducing loss of plasma membrane integrity. This was associated with rapid processing of light chain-3 (LC3) and reduction of S6 kinase phosphorylation, consistent with autophagy. Dramatic ultrastructural vacuolation, not typical of autophagy, was also induced. Silencing of beclin-1 failed to prevent LC3 processing, whereas knockout of autophagy-related (Atg)7 abolished LC3 processing but failed to prevent obatoclax-induced loss of clonogenicity or ultrastructural changes. siRNA silencing of Atg7 in BAX/BAK knockout mouse embryonic fibroblasts did not prevent obatoclax-induced loss of viability. Cells selected for obatoclax resistance evaded apoptosis independent of changes in BCL-2 family expression and displayed reduced LC3 processing. In summary, obatoclax exhibits BAX- and BAK-dependent and -independent mechanisms of toxicity and activation of autophagy. Mechanisms other than autophagy and apoptosis are blocked in obatoclax resistant cells and contribute significantly to obatoclax's anticancer efficacy.

Declining ovarian reserve adversely influences granulosa cell viability

OBJECTIVE

To identify if declining ovarian reserve adversely influences granulosa cell (GC) parameters in patients undergoing IVF.

DESIGN

Prospective study.

SETTING

Academic IVF Center.

PATIENT(S)

Twenty-four women undergoing IVF.

INTERVENTION(S)

Mural and cumulus GCs were harvested (at time of egg retrieval).

MAIN OUTCOME MEASURE(S)

Influence of ovarian reserve, reflected by maximal basal FSH levels, on GC (cumulative, mural, and cumulus) counts and viability were investigated.

RESULT(S)

The FSH levels demonstrated an inverse correlation with cumulative and mural, but not cumulus, GC viability. Adverse influence of increasing FSH on cumulative GC viability was independent of patient's age. The GC counts were uninfluenced by ovarian reserve status. Neither GC count nor viability demonstrated any relationship with clinical pregnancy after IVF.

CONCLUSION(S)

We observed an adverse association between declining ovarian reserve and GC parameters. We believe these findings may partly explain the suboptimal reproductive performance in these women.

Targeting of human DNA polymerase iota to the replication machinery via interaction with PCNA

Human DNA polymerase iota (hPoliota) promotes translesion synthesis by inserting nucleotides opposite highly distorting or noninstructional DNA lesions. Here, we provide evidence for the physical interaction of hPoliota with proliferating cell nuclear antigen (PCNA), and show that PCNA, together with replication factor C (RFC) and replication protein A (RPA), stimulates the DNA synthetic activity of hPoliota. In the presence of these protein factors, on undamaged DNA, the efficiency (V(max)/K(m)) of correct nucleotide incorporation by hPoliota is increased approximately 80-150-fold, and this increase in efficiency results from a reduction in the apparent K(m) for the nucleotide. PCNA, RFC, and RPA also stimulate nucleotide incorporation opposite the 3'-T of the (6) thymine-thymine (T-T) photoproduct and opposite an abasic site. The interaction of hPoliota with PCNA implies that the targeting of this polymerase to the replication machinery stalled at a lesion site is achieved via this association.

The Schizosaccharomyces pombe origin recognition complex interacts with multiple AT-rich regions of the replication origin DNA by means of the AT-hook domains of the spOrc4 protein

The interaction between an origin sequence and the origin recognition complex (ORC), which is highly conserved in eukaryotes, is critical for the initiation of DNA replication. In this report, we have examined the interaction between the Schizosaccharomyces pombe (sp) autonomously replicating sequence 1 (ars1) and the spORC. For this purpose, we have purified the spORC containing all six subunits, a six-subunit complex containing the N-terminal-deleted spOrc4 subunit (spORC(Delta N-Orc4)), and the spOrc4 subunit by using the baculovirus expression system. Wild-type spORC showed sequence-specific binding to ars1, and the spOrc4 protein alone showed the same DNA-binding properties as wild-type spORC. In contrast, the spORC(Delta N-Orc4) and the Delta N-spOrc4p alone did not bind significantly to ars1. These findings indicate that the N-terminal domain of the spOrc4 protein that contains multiple AT-hook motifs is essential for the ars1-binding activity. DNA-binding competition assays with fragments of ars1 and DNase I footprinting studies with full-length ars1 revealed that the spORC interacted with several AT-rich sequence regions of ars1. These DNA-binding properties of spORC correlate with the previously determined sequence requirements of the S. pombe ars1. These studies indicate that because of its unique Orc4 subunit, S. pombe uses a mechanism to recognize its origins different from that used by Saccharomyces cerevisiae.

Physical and functional interactions of human DNA polymerase eta with PCNA

Human DNA polymerase eta (hPoleta) functions in the error-free replication of UV-damaged DNA, and mutations in hPoleta cause cancer-prone syndrome, the variant form of xeroderma pigmentosum. However, in spite of its key role in promoting replication through a variety of distorting DNA lesions, the manner by which hPoleta is targeted to the replication machinery stalled at a lesion site remains unknown. Here, we provide evidence for the physical interaction of hPoleta with proliferating cell nuclear antigen (PCNA) and show that mutations in the PCNA binding motif of hPoleta inactivate this interaction. PCNA, together with replication factor C and replication protein A, stimulates the DNA synthetic activity of hPoleta, and steady-state kinetic studies indicate that this stimulation accrues from an increase in the efficiency of nucleotide insertion resulting from a reduction in the apparent K(m) for the incoming nucleotide.

Purification and characterization of human DNA damage checkpoint Rad complexes

Checkpoint Rad proteins function early in the DNA damage checkpoint signaling cascade to arrest cell cycle progression in response to DNA damage. This checkpoint ensures the transmission of an intact genetic complement to daughter cells. To learn about the damage sensor function of the human checkpoint Rad proteins, we purified a heteropentameric complex composed of hRad17-RFCp36-RFCp37-RFCp38-RFCp40 (hRad17-RFC) and a heterotrimeric complex composed of hRad9-hHus1-hRad1 (checkpoint 9-1-1 complex). hRad17-RFC binds to DNA, with a preference for primed DNA and possesses weak ATPase activity that is stimulated by primed DNA and single-stranded DNA. hRad17-RFC forms a complex with the 9-1-1 heterotrimer reminiscent of the replication factor C/proliferating cell nuclear antigen clamp loader/sliding clamp complex of the replication machinery. These findings constitute biochemical support for models regarding the roles of checkpoint Rads as damage sensors in the DNA damage checkpoint response of human cells.

The role of bacteriologic infection in the etiology of nasolacrimal duct obstruction

BACKGROUND

In patients with nasolacrimal duct obstruction, the inflammation and fibrosis may be secondary to coexisting infectious colonization within the lumen of the lacrimal sac. We examined the bacterial flora within the lacrimal sac at the sac-duct junction to explore the possibility of a primary bacteriologic etiology of the inflammatory response.

METHODS

The study included 114 consecutive patients (132 sides) with epiphora undergoing routine external dacryocystorhinostomy (DCR) at a tertiary care hospital in Toronto between November 1999 and April 2000. A lacrimal sac tissue biopsy specimen was acquired intraoperatively from the inferior posterior lacrimal sac near the sac-duct junction. Microbiologic analysis was carried out to determine the presence and identification of infectious organisms.

RESULTS

Culture gave positive results in 51 patients (44.7%) (41.7% of specimens). A total of 65 isolates were cultured, of which 78.5% were gram-positive bacteria and 21.5% gram-negative bacteria. Of the gram-positive organisms 76.5% were Staphylococcus sp. The presence of a positive culture result was independent of a history of dacryocystitis or the presence of a mucocele.

INTERPRETATION

Using direct biopsy methods, we found culture-positive lacrimal sac specimens in a large proportion of patients undergoing DCR surgery. These organisms were found to be present in patients with and without a history of infection.

Processive DNA helicase activity of the minichromosome maintenance proteins 4, 6, and 7 complex requires forked DNA structures

The minichromosome maintenance (Mcm) proteins 2-7 are required for both the initiation and elongation steps of chromosomal DNA replication. Previous studies have shown that the Mcm complex consisting of the Mcm 4, 6, and 7 proteins contains 3' to 5' DNA helicase activity with limited processivity (displacing duplex DNA regions up to 30 nt). In this report, we show that the presence of both 5' and 3' single-stranded tails in DNA helicase substrates is essential for the processive helicase activity of the Mcm complex. The presence of both 5' and 3' tails facilitated the formation of double heterohexameric complexes of Mcm4/6/7 on substrate DNA, which appeared to be essential for the processive helicase activity. The double heterohexameric complex of Mcm4/6/7, in the presence of a single-strand DNA binding protein, is capable of unwinding duplex DNA region of about 600 bp in length. These results support the hypothesis that the Mcm4/6/7 complex can function as a replication helicase.

The human homolog of Saccharomyces cerevisiae Mcm10 interacts with replication factors and dissociates from nuclease-resistant nuclear structures in G(2) phase

Mcm10 (Dna43), first identified in Saccharomyces cerevisiae, is an essential protein which functions in the initiation of DNA synthesis. Mcm10 is a nuclear protein that is localized to replication origins and mediates the interaction of the Mcm2-7 complex with replication origins. We identified and cloned a human cDNA whose product was structurally homologous to the yeast Mcm10 protein. Human Mcm10 (HsMcm10) is a 98-kDa protein of 874 amino acids which shows 23 and 21% overall similarity to Schizosaccharomyces pombe Cdc23 and S. cerevisiae Mcm10, respectively. The messenger RNA level of HsMcm10 increased at the G(1)/S-boundary when quiescent human NB1-RGB cells were induced to proliferate as is the case of many replication factors. HsMcm10 associated with nuclease-resistant nuclear structures throughout S phase and dissociated from it in G(2) phase. HsMcm10 associated with human Orc2 protein when overexpressed in COS-1 cells. HsMcm10 also interacted with Orc2, Mcm2 and Mcm6 proteins in the yeast two-hybrid system. These results suggest that HsMcm10 may function in DNA replication through the interaction with Orc and Mcm2-7 complexes.

Species specificity of human RPA in simian virus 40 DNA replication lies in T-antigen-dependent RNA primer synthesis

Replication protein A (RPA) is a three-subunit protein complex with multiple functions in DNA replication. Previous study indicated that human RPA (h-RPA) could not be replaced by Schizosaccharomyces pombe RPA (sp-RPA) in simian virus 40 (SV40) replication, suggesting that h-RPA may have a specific function in SV40 DNA replication. To understand the specificity of h-RPA in replication, we prepared heterologous RPAs containing the mixture of human and S.pombe subunits and compared these preparations for various enzymatic activities. Heterologous RPAs containing two human subunits supported SV40 DNA replication, whereas those containing only one human subunit poorly supported DNA replication, suggesting that RPA complex requires at least two human subunits to support its function in SV40 DNA replication. All heterologous RPAs effectively supported single-stranded (ss)DNA binding activity and an elongation of a primed DNA template catalyzed by DNA polymerase (pol) alpha and delta. A strong correlation between SV40 DNA replication activity and large tumor antigen (T-ag)-dependent RNA primer synthesis by pol alpha-primase complex was observed among the heterologous RPAs. Furthermore, T-ag showed a strong interaction with 70- and 34-kDa subunits from human, but poorly interacted with their S.pombe counterparts, indicating that the specificity of h-RPA is due to its role in RNA primer synthesis. In the SV40 replication reaction, the addition of increasing amounts of sp-RPA in the presence of fixed amount of h-RPA significantly reduced overall DNA synthesis, but increased the size of lagging strand, supporting a specific role for h-RPA in RNA primer synthesis. Together, these results suggest that the specificity of h-RPA in SV40 replication lies in T-ag-dependent RNA primer synthesis.

Isolation and characterization of various complexes of the minichromosome maintenance proteins of Schizosaccharomyces pombe

Minichromosome maintenance (Mcm) proteins 2-7 are highly conserved in eukaryotes and play an essential role in DNA replication. Here, we describe the reconstitution of the various complexes of the Mcm proteins of Schizosaccharomyces pombe using the baculovirus expression system. The simultaneous expression of all six of the Mcm proteins, as well as different combinations of these proteins, yielded several stable complexes that included the heterohexamer of Mcm2/3/4/5/6/7, the Mcm2/4/6/7 heterotetramer, the dimer of the Mcm4/6/7 heterotrimer, and the Mcm3/5 heterodimer. The purification and characterization of the biochemical properties of these complexes showed that only the dimeric complex of the Mcm4/6/7 heterotrimer possessed single stranded DNA-dependent ATPase, ATP-dependent single stranded DNA binding, and 3' to 5' DNA helicase activities. Consistent with these results, the interaction of either Mcm2 or Mcm3/5 with the Mcm4/6/7 complex resulted in the disassembly of the dimeric complex of Mcm4/6/7 and the loss of DNA helicase activity. These results suggest that the Mcm4/6/7 complex is a catalytic core of the Mcm complex and that Mcm2 and Mcm3/5 may be involved in the regulation of the activity of this complex.

Proliferating cell nuclear antigen as the cell cycle sensor for an HLA-derived peptide blocking T cell proliferation

Synthetic peptides corresponding to structural regions of HLA molecules are novel immunosuppressive agents. A peptide corresponding to residues 65-79 of the alpha-chain of HLA-DQA03011 (DQ65-79) blocks cell cycle progression from early G1 to the G1 restriction point, which inhibits cyclin-dependent kinase-2 activity and phosphorylation of the retinoblastoma protein. A yeast two-hybrid screen identified proliferating cell nuclear Ag (PCNA) as a cellular ligand for this peptide, whose interaction with PCNA was further confirmed by in vitro biochemistry. Electron microscopy demonstrates that the DQ65-79 peptide enters the cell and colocalizes with PCNA in the T cell nucleus in vivo. Binding of the DQ65-79 peptide to PCNA did not block polymerase delta (pol delta)-dependent DNA replication in vitro. These findings support a key role for PCNA as a sensor of cell cycle progression and reveal an unanticipated function for conserved regions of HLA molecules.

Fidelity of eucaryotic DNA polymerase delta holoenzyme from Schizosaccharomyces pombe

The fidelity of Schizosaccharomyces pombe DNA polymerase delta was measured in the presence or absence of its processivity subunits, proliferating cell nuclear antigen (PCNA) sliding clamp and replication factor C (RFC) clamp-loading complex, using a synthetic 30-mer primer/100-mer template. Synthesis by pol delta alone was distributive. Processive synthesis occurred in the presence of PCNA, RFC, and Escherichia coli single strand DNA-binding protein (SSB) and required the presence of ATP. "Passive" self-loading of PCNA onto DNA takes place in the absence of RFC, in an ATP-independent reaction, which was strongly inhibited by SSB. The nucleotide substitution error rate for pol delta holoenzyme (HE) (pol delta + PCNA + RFC) was 4.6 x 10(-4) for T.G mispairs, 5.3 x 10(-5) for G.G mispairs, and 4.5 x 10(-6) for A.G mispairs. The T.G misincorporation frequency for pol delta without the accessory proteins was unchanged. The fidelity of pol delta HE was between 1 and 2 orders of magnitude lower than that measured for the E. coli pol III HE at the same template position. This relatively low fidelity was caused by inefficient proofreading by the S. pombe polymerase-associated proofreading exonuclease. The S. pombe 3'-exonuclease activity was also extremely inefficient in excising primer-3'-terminal mismatches in the absence of dNTP substrates and in hydrolyzing single-stranded DNA. A comparison of pol delta HE with E. coli pol IIIalpha HE (lacking the proofreading exonuclease subunit) showed that both holoenzymes exhibit similar error rates for each mispair.

Characterization of an ATP-dependent DNA ligase from the thermophilic archaeon Methanobacterium thermoautotrophicum

We report the production, purification and characterization of a DNA ligase encoded by the thermophilic archaeon Methanobacterium thermoautotrophicum. The 561 amino acid MTH: ligase catalyzed strand-joining on a singly nicked DNA in the presence of a divalent cation (magnesium, manganese or cobalt) and ATP (K(m) 1.1 microM). dATP can substitute for ATP, but CTP, GTP, UTP and NAD(+) cannot. MTH: ligase activity is thermophilic in vitro, with optimal nick-joining at 60 degrees C. Mutational analysis of the conserved active site motif I (KxDG) illuminated essential roles for Lys251 and Asp253 at different steps of the ligation reaction. Mutant K251A is unable to form the covalent ligase-adenylate intermediate (step 1) and hence cannot seal a 3'-OH/5'-PO(4) nick. Yet, K251A catalyzes phosphodiester bond formation at a pre-adenylated nick (step 3). Mutant D253A is active in ligase-adenylate formation, but defective in activating the nick via formation of the DNA-adenylate intermediate (step 2). D253A is also impaired in phosphodiester bond formation at a pre-adenylated nick. A profound step 3 arrest, with accumulation of high levels of DNA-adenylate, could be elicited for the wild-type MTH: ligase by inclusion of calcium as the divalent cation cofactor. MTH: ligase sediments as a monomer in a glycerol gradient. Structure probing by limited proteolysis suggested that MTH: ligase is a tightly folded protein punctuated by a surface-accessible loop between nucleotidyl transferase motifs III and IIIa.

In vitro reconstitution of the Schizosaccharomyces pombe alternative excision repair pathway

Schizosaccharomyces pombe alternative excision repair has been shown genetically and biochemically to be involved in the repair of a wide variety of DNA lesions. AER is initiated by a damage-specific endonuclease (Uve1p) that recognizes UV-induced photoproducts, base mispairs, abasic sites, and platinum G-G diadducts and cleaves the DNA phosphodiester backbone 5' to a lesion. Several models exist that employ various mechanisms for damage removal based on the activities of Rad2p, a nuclease thought to be responsible for damage excision in AER. This study represents the first report of the biochemical reconstitution of the AER pathway. A base mispair-containing substrate is repaired in a reaction requiring S. pombe Uve1p, Rad2p, DNA polymerase delta, replication factor C, proliferating cell nuclear antigen, and T4 DNA ligase. Surprisingly, damage is removed exclusively by the 5' to 3' exonuclease activity of Rad2p and not its "flap endonuclease" activity and is absolutely dependent upon the presence of the 5'-phosphoryl moiety at the Uve1p cleavage site.

A unique organization of the protein subunits of the DNA polymerase clamp loader in the archaeon Methanobacterium thermoautotrophicum deltaH

Replication factor C (RFC, also called activator 1), in conjunction with proliferating cell nuclear antigen (PCNA), is responsible for processive DNA synthesis catalyzed by the eukaryotic replicative DNA polymerases delta and epsilon. Here we report the isolation and characterization of homologues of RFC and PCNA from the archaeon, Methanobacterium thermoautotrophicum DeltaH. In contrast to the five subunit RFC complex isolated from eukaryotic cells, the mthRFC contains only two subunits. The two genes encoding the RFC subunits called, mthRFC1 and mthRFC3, were cloned, and the proteins (54.4 and 36.8 kDa, respectively) were overexpressed in Escherichia coli and purified individually and as a complex. The gene encoding PCNA was also cloned, and the protein was purified after overexpression in E. coli. Based on sizing column elution and subunit composition, the mthRFC complex appears to be a hexamer consisting of two mthRFC1 protomers and four mthRFC3 protomers. Although mthRFC differs in organization from its eukaryotic counterpart, it was shown to be functionally similar to eukaryotic RFC in: (i) catalyzing DNA-dependent ATP hydrolysis; (ii) binding preferentially to DNA primer ends; (iii) loading mthPCNA onto singly nicked circular DNA; and (iv) supporting mthPolB-catalyzed PCNA-dependent DNA chain elongation. The importance and roles of RFC and PCNA in M. thermoautotrophicum DeltaH replication are discussed.

Structure and activity associated with multiple forms of Schizosaccharomyces pombe DNA polymerase delta

DNA polymerase delta (Pol delta) isolated from Schizosaccharomyces pombe (sp) consists of at least four subunits, Pol3, Cdc1, Cdc27, and Cdm1. We have reconstituted the four-subunit complex by simultaneously expressing these polypeptides in baculovirus-infected insect cells. The properties of the purified cloned spPol delta were identical to the native spPol delta isolated from S. pombe cells. In addition, we also isolated a three-subunit complex containing Pol3, Cdc1, and Cdm1. Both three- and four-subunit complexes required replication factor C and proliferating cell nuclear antigen for DNA replication. However, in the presence of low levels of polymerase complexes, the three-subunit complex was less efficient than the four-subunit complex in supporting DNA replication. The inefficient synthesis of DNA by the three-subunit complex can be remedied by the addition of Cdc27, the subunit missing in the three-subunit complex. Gel filtration analysis demonstrated that the three-subunit complex is a monomer of the heterotrimer (Pol3, Cdc1, and Cdm1) and that the four-subunit complex is a dimer of the heterotetramer (Pol3, Cdc1, Cdc27, and Cdm1), similar to the structure of native spPol delta. We have further shown that Cdc1 and Cdc27 interact to form a heterodimeric complex. Gel filtration studies indicate that the structure of this complex is dimeric. These observations suggest that the Cdc27 subunit may play an important role contributing to the dimerization of Pol delta.

Dynamics of beta and proliferating cell nuclear antigen sliding clamps in traversing DNA secondary structure

Chromosomal replicases of cellular organisms utilize a ring shaped protein that encircles DNA as a mobile tether for high processivity in DNA synthesis. These "sliding clamps" have sufficiently large linear diameters to encircle duplex DNA and are perhaps even large enough to slide over certain DNA secondary structural elements. This report examines the Escherichia coli beta and human proliferating cell nuclear antigen clamps for their ability to slide over various DNA secondary structures. The results show that these clamps are capable of traversing a 13-nucleotide ssDNA loop, a 4-base pair stem-loop, a 4-nucleotide 5' tail, and a 15-mer bubble within the duplex. However, upon increasing the size of these structures (20-nucleotide loop, 12-base pair stem-loop, 28-nucleotide 5' tail, and 20-nucleotide bubble) the sliding motion of the beta and proliferating cell nuclear antigen over these elements is halted. Studies of the E. coli replicase, DNA polymerase III holoenzyme, in chain elongation with the beta clamp demonstrate that upon encounter with an oligonucleotide annealed in its path, it traverses the duplex and resumes synthesis on the 3' terminus of the oligonucleotide. This sliding and resumption of synthesis occurs even when the oligonucleotide contains a secondary structure element, provided the beta clamp can traverse the structure. However, upon encounter with a downstream oligonucleotide containing a large internal secondary structure, the holoenzyme clears the obstacle by strand displacing the oligonucleotide from the template. Implications of these protein dynamics to DNA transactions are discussed.

The single minichromosome maintenance protein of Methanobacterium thermoautotrophicum DeltaH contains DNA helicase activity

Previous studies have identified an ATP-dependent DNA helicase activity intrinsic to the human minichromosome maintenance (MCM) complex, composed of MCM subunits 4, 6, and 7 [Ishimi, Y. (1997) J. Biol. Chem. 272, 24508-24513]. In contrast to the presence of multiple MCM genes (at least six) in eukaryotes, the archaeon Methanobacterium thermoautotrophicum DeltaH (mth) genome contains a single open reading frame coding for an MCM protein. In this study we report the isolation of the mthMCM protein overexpressed in Escherichia coli. The purified recombinant protein was found to exist in both multimeric ( approximately 10(3) kDa) and monomeric (76 kDa) forms. Both forms of the protein bind to single-stranded DNA, hydrolyze ATP in the presence of DNA, and possess 3'-to-5' ATP-dependent DNA helicase activities. Thus, a single mthMCM protein contains biochemical properties identical to those associated with the eukaryotic MCM4, -6, and -7 complex. These results suggest that the characterization of the mthMCM protein and its multiple forms may contribute to our understanding of the role of MCM helicase activity in eukaryotic chromosomal DNA replication.

Reconstitution of proliferating cell nuclear antigen-dependent repair of apurinic/apyrimidinic sites with purified human proteins

An apurinic/apyrimidinic (AP) site is one of the most abundant lesions spontaneously generated in living cells and is also a reaction intermediate in base excision repair. In higher eukaryotes, there are two alternative pathways for base excision repair: a DNA polymerase beta-dependent pathway and a proliferating cell nuclear antigen (PCNA)-dependent pathway. Here we have reconstituted PCNA-dependent repair of AP sites with six purified human proteins: AP endonuclease, replication factor C, PCNA, flap endonuclease 1 (FEN1), DNA polymerase delta, and DNA ligase I. The length of nucleotides replaced during the repair reaction (patch size) was predominantly two nucleotides, although longer patches of up to seven nucleotides could be detected. Neither replication protein A nor Ku70/80 enhanced the repair activity in this system. Disruption of the PCNA-binding site of either FEN1 or DNA ligase I significantly reduced efficiency of AP site repair but did not affect repair patch size.

Multiple competition reactions for RPA order the assembly of the DNA polymerase delta holoenzyme

Processive extension of DNA in eukaryotes requires three factors to coordinate their actions. First, DNA polymerase alpha-primase synthesizes the primed site. Then replication factor C loads a proliferating cell nuclear antigen (PCNA) clamp onto the primer. Following this, DNA polymerase delta assembles with PCNA for processive extension. This report shows that these proteins each bind the primed site tightly and trade places in a highly coordinated fashion such that the primer terminus is never left free of protein. Replication protein A (RPA), the single-stranded DNA-binding protein, forms a common touchpoint for each of these proteins and they compete with one another for it. Thus these protein exchanges are driven by competition-based protein switches in which two proteins vie for contact with RPA.

Identification and reconstitution of the origin recognition complex from Schizosaccharomyces pombe

The origin recognition complex (ORC), first identified in Saccharomyces cerevisiae (sc), is a six-subunit protein complex that binds to DNA origins. Here, we report the identification and cloning of cDNAs encoding the six subunits of the ORC of Schizosaccharomyces pombe (sp). Sequence analyses revealed that spOrc1, 2, and 5 subunits are highly conserved compared with their counterparts from S. cerevisiae, Xenopus, Drosophila, and human. In contrast, both spOrc3 and spOrc6 subunits are poorly conserved. As reported by Chuang and Kelly [(1999) Proc. Natl. Acad. Sci. USA 96, 2656-2661], the C-terminal region of spOrc4 is also conserved whereas the N terminus uniquely contains repeats of a sequence that binds strongly to AT-rich DNA regions. Consistent with this, extraction of S. pombe chromatin with 1 M NaCl, or after DNase I treatment, yielded the six-subunit ORC, whereas extraction with 0.3 M resulted in five-subunit ORC lacking spOrc4p. The spORC can be reconstituted in vitro with all six recombinant subunits expressed in the rabbit reticulocyte system. The association of spOrc4p with the other subunits required the removal of DNA from reaction mixture by DNase I. This suggests that a strong interaction between spOrc4p and DNA can prevent the isolation of the six-subunit ORC. The unique DNA-binding properties of the spORC may contribute to our understanding of the sequence-specific recognition required for the initiation of DNA replication in S. pombe.

Isolation and characterization of a split B-type DNA polymerase from the archaeon Methanobacterium thermoautotrophicum deltaH

We describe here the isolation and characterization of a B-type DNA polymerase (PolB) from the archaeon Methanobacterium thermoautotrophicum DeltaH. Uniquely, the catalytic domains of M. thermoautotrophicum PolB are encoded from two different genes, a feature that has not been observed as yet in other polymerases. The two genes were cloned, and the proteins were overexpressed in Escherichia coli and purified individually and as a complex. We demonstrate that both polypeptides are needed to form the active polymerase. Similar to other polymerases constituting the B-type family, PolB possesses both polymerase and 3'-5' exonuclease activities. We found that a homolog of replication protein A from M. thermoautotrophicum inhibits the PolB activity. The inhibition of DNA synthesis by replication protein A from M. thermoautotrophicum can be relieved by the addition of M. thermoautotrophicum homologs of replication factor C and proliferating cell nuclear antigen. The possible roles of PolB in M. thermoautotrophicum replication are discussed.

The C-terminal region of Schizosaccaromyces pombe proliferating cell nuclear antigen is essential for DNA polymerase activity

Proliferating cell nuclear antigen (PCNA), the processivity factor (sliding clamp) of DNA polymerases (Pols), plays essential roles in DNA metabolism. In this report, we examined the functional role of the C-terminal region of Schizosaccaromyces pombe PCNA both in vitro and in vivo. The deletion or Ala substitution of the last 9 aa (252-260A), as well as Ala replacement of only 4 aa (252-255A) at the C terminus, failed to substitute for the wild-type PCNA protein for cell growth in S. pombe. Two other PCNA mutant proteins, A251V and K253E, exhibited cold-sensitive phenotypes. Several yeast strains harboring mutations, including those at the acidic C-terminal region, showed elevated sensitivity to DNA damage. The ability of the mutant PCNA proteins to stimulate DNA synthesis by Poldelta and Polepsilon also was studied in vitro. The mutant proteins that did not support cell growth and a mutant protein containing a single amino acid substitution at position 252, where Pro is replaced by Ala, stimulated Poldelta and Polepsilon activities poorly. All mutant PCNA proteins, however, were assembled around DNA by the clamp loader, replication factor C, efficiently. Thus, the C-terminal region of PCNA is important for interactions with both Poldelta and Polepsilon and for cell survival after DNA damage. The C terminus of sliding clamps from other organisms has been shown to be important for clamp loading as well as polymerase interactions. The relationship between the conserved sequence in this region in different organisms is discussed.

Studies on the interactions between human replication factor C and human proliferating cell nuclear antigen

Proliferating cell nuclear antigen (PCNA) is a processivity factor required for DNA polymerase delta (or epsilon)-catalyzed DNA synthesis. When loaded onto primed DNA templates by replication factor C (RFC), PCNA acts to tether the polymerase to DNA, resulting in processive DNA chain elongation. In this report, we describe the identification of two separate peptide regions of human PCNA spanning amino acids 36-55 and 196-215 that bind RFC by using the surface plasmon resonance technique. Site-directed mutagenesis of residues within these regions in human PCNA identified two specific sites that affected the biological activity of PCNA. Replacement of the aspartate 41 residue by an alanine, serine, or asparagine significantly impaired the ability of PCNA to (i) support the RFC/PCNA-dependent polymerase delta-catalyzed elongation of a singly primed DNA template; (ii) stimulate RFC-catalyzed DNA-dependent hydrolysis of ATP; (iii) be loaded onto DNA by RFC; and (iv) activate RFC-independent polymerase delta-catalyzed synthesis of poly dT. Introduction of an alanine at position 210 in place of an arginine also reduced the efficiency of PCNA in supporting RFC-dependent polymerase delta-catalyzed elongation of a singly primed DNA template. However, this mutation did not significantly alter the ability of PCNA to stimulate DNA polymerase delta in the absence of RFC but substantially lowered the efficiency of RFC-catalyzed reactions. These results are in keeping with a model in which surface exposed regions of PCNA interact with RFC and the subsequent loading of PCNA onto DNA orients the elongation complex in a manner essential for processive DNA synthesis.

Androgens in preeclampsia

OBJECTIVE

The purpose of the study was to determine whether maternal serum levels of androgens, especially testosterone, are higher in patients with preeclampsia than in matched normotensive control subjects.

STUDY DESIGN

Serum testosterone, dehydroepiandrosterone sulfate, sex hormone binding globulin, and estradiol levels were measured in 16 subjects in the third trimester of pregnancy with documented preeclampsia and 26 healthy, normotensive women with similar maternal and gestational ages. All subjects were primigravid women with singleton pregnancies who were seen in the labor and delivery department at North Oakland Medical Centers in Pontiac, Mich.

RESULTS

Total testosterone and free testosterone levels were significantly higher in patients with preeclampsia (213.6 +/- 25.9 ng/dL and 0.5 +/- 0.1 ng/dL, respectively) than in the control group (154.5 +/- 14.8 ng/dL and 0. 3 +/- 0.03 ng/dL, respectively). There were no significant differences in sex hormone binding globulin, dehydroepiandrosterone sulfate, and estradiol concentrations. There were also no significant differences in maternal age, gestational age, body mass index, and neonatal sex.

CONCLUSION

Levels of the potent androgen testosterone were significantly higher in primigravid women with preeclampsia than in normotensive women with similar gestational and maternal ages. This difference may indicate a role for testosterone in the pathogenesis of preeclampsia.

The human RNA helicase A (DDX9) gene maps to the prostate cancer susceptibility locus at chromosome band 1q25 and its pseudogene (DDX9P) to 13q22, respectively

RNA helicase A is the homolog of the Drosophila maleless protein, an essential factor involved in dosage compensation, and plays a crucial role in early development in mammals. Here, we have mapped the human RNA helicase A (DDX9) gene to the major susceptibility locus for prostate cancer at chromosome band 1q25, and its pseudogene (DDX9P) to the band 13q22 by fluorescence in situ hybridization, somatic cell hybrid analysis, and assignment of YAC clones, respectively.

RNA helicase A is essential for normal gastrulation

RNA helicase A (RHA) is the human homologue of the Drosophila maleless protein, an essential factor for the development of male flies. Recently, it was shown that RHA cooperates with the cAMP-responsive element in mediating the cAMP-dependent transcriptional activation of a number of genes. Due to the participation of cAMP as a second messenger in a number of signaling pathways, we examined the function of RHA during mammalian embryogenesis. To examine the role(s) of RHA in mammalian development, RHA knockout mice were generated by homologous recombination. Homozygosity for the mutant RHA allele led to early embryonic lethality. Histological analysis, combined with terminal deoxynucleotidyltransferase-mediated UTP end labeling (TUNEL) reactions of RHA-null embryos, revealed marked apoptotic cell death specifically in embryonic ectodermal cells during gastrulation. RNA in situ analyses of the expression of HNF-3beta and Brachyury, two molecular markers for gastrulation, showed that RHA-null embryos at days 7.5 and 8.5 expressed both HNF-3beta and Brachyury in a pattern similar to those of pre- and early streak stages of embryos, respectively. These observations indicate that RHA is necessary for early embryonic development and suggest the requirement of RHA for the survival and differentiation of embryonic ectoderm.

ATP hydrolysis catalyzed by human replication factor C requires participation of multiple subunits

Human replication factor C (hRFC) is a five-subunit protein complex (p140, p40, p38, p37, and p36) that acts to catalytically load proliferating cell nuclear antigen onto DNA, where it recruits DNA polymerase delta or epsilon to the primer terminus at the expense of ATP, leading to processive DNA synthesis. We have previously shown that a subcomplex of hRFC consisting of three subunits (p40, p37, and p36) contained DNA-dependent ATPase activity. However, it is not clear which subunit(s) hydrolyzes ATP, as all five subunits include potential ATP binding sites. In this report, we introduced point mutations in the putative ATP-binding sequences of each hRFC subunit and examined the properties of the resulting mutant hRFC complex and the ATPase activity of the hRFC or the p40.p37.p36 complex. A mutation in any one of the ATP binding sites of the p36, p37, p40, or p140 subunits markedly reduced replication activity of the hRFC complex and the ATPase activity of the hRFC or the p40.p37.p36 complex. A mutation in the ATP binding site of the p38 subunit did not alter the replication activity of hRFC. These findings indicate that the replication activity of hRFC is dependent on efficient ATP hydrolysis contributed to by the action of four hRFC subunits.

Protein-PCNA interactions: a DNA-scanning mechanism?

Proliferating-cell nuclear antigen (PCNA) plays an essential role in nucleic-acid metabolism in all eukaryotes. The PCNA protein interacts with a large number of proteins. These proteins can be divided into two groups: the first contains proteins that have a known enzymatic activity; the second contains regulatory proteins that are involved in cell-cycle progression, checkpoint control and cellular differentiation. Interestingly, all of the enzymes known to interact with PCNA either recognize specific structures on DNA or have limited DNA-sequence specificity. Proteins that have low sequence specificities could utilize PCNA as an adapter in order to interact with their DNA substrates.