Search PubMed⌕ Search

Biomedical subjects

M J Solomon

Publications and source records attributed to M J Solomon.

At least 19 recordsLinked to original sources
PubMed2003

Assessment of the accuracy of transrectal ultrasonography in anorectal neoplasia.

BACKGROUND: Accurate preoperative staging of anorectal neoplasia is required to identify patients for whom local excision or adjuvant therapy may be appropriate. The objectives of this study were to review the accuracy of endoluminal transrectal ultrasonography (TRUS) in the staging of rectal cancers and to determine the learning curve before optimal staging accuracy can be achieved. METHODS: The results of all TRUS examinations for the assessment of anorectal neoplasia performed by two colorectal surgeons at two teaching hospitals of the University of Sydney from 1991 to 2001 were collected prospectively. RESULTS: Of the 433 patients examined by TRUS, 356 were included, of whom 263 (73.9 per cent) had nodal status assessed histologically. Of the 77 patients excluded, 50 had undergone radiotherapy before operation. TRUS achieved excellent accuracy when compared with histopathology reports using kappa statistics for standard Union Internacional Contra la Cancrum (UICC) staging (kappa = 0.89), tumour wall penetration (kappa = 0.70), lymph node detection (kappa = 0.66) and a proposed new staging system (kappa = 0.94). In addition, the increase in TRUS accuracy with operator experience demonstrates the need to perform 50 or more procedures before optimal accuracy is achieved. CONCLUSION: TRUS provides an appropriate investigation with which to select patients with T1 tumours for local excision, and patients with T3 or T4 tumours for preoperative radiotherapy. The relative inaccuracy of staging T2 tumours by TRUS has led to a proposed alternative ultrasonographic staging system.

Anus Neoplasms↗
PubMed2002

Randomized clinical trial of laparoscopic versus open abdominal rectopexy for rectal prolapse.

BACKGROUND: The objectives of this study were to compare both subjective clinical outcomes and the objective stress response of laparoscopic and open abdominal rectopexy in patients with full-thickness rectal prolapse. Abdominal rectopexy for patients with rectal prolapse is well suited for a laparoscopic approach as no resection or anastomosis is necessary. METHODS: Forty patients with a full-thickness rectal prolapse were randomized before operation to a laparoscopic group and an open group. They agreed to conform to a clinical pathway (CP) of liquid diet (CP1) and full mobility (CP2) on day 1, solid diet (CP3) on day 2 and discharge (CP4) before day 5. Their compliance was monitored by an assessor blinded to the operative group, who also rated pain and mobility. Patient-controlled morphine use was documented. Neuroendocrine and immune stress response and respiratory function were measured. RESULTS: Some 75 per cent of all clinical pathway objectives of early recovery were achieved in the laparoscopic group compared with 37 per cent in the open group (P < 0.01). Significant differences in favour of laparoscopy were noted with regard to narcotic requirements, and pain and mobility scores. Differences in objective measures of stress response favouring laparoscopy were found for urinary catecholamines, interleukin 6, serum cortisol and C-reactive protein. No differences were noted in respiratory function but significant respiratory morbidity was greater in the open group (P < 0.05). None of the measured outcomes, subjective or objective, favoured the open group apart from operating time, which was significantly shorter (153 versus 102 min; P < 0.01). CONCLUSION: This study has demonstrated significant subjective and objective differences in favour of a laparoscopic technique for abdominal rectopexy. The advantages were all short term but no evidence of any adverse effect on longer-term outcomes was observed.

Analgesia, Patient-Controlled↗
PubMed2002

p53, DCC and thymidylate synthase as predictors of survival after resection of hepatic metastases from colorectal cancer.

BACKGROUND: Hepatic metastasis from colorectal cancer is a common problem. Hepatic resection offers the only chance of cure. Prognosis of patients following hepatic resection is currently based on clinicopathological factors (of both the primary cancer and the hepatic metastasis), which do not accurately predict the subsequent behaviour of the tumour. The aim of this study was to evaluate three molecular genetic markers - p53, DCC (deleted in colonic cancer) and thymidylate synthase - in both the primary colorectal tumour and the resected hepatic metastases, and to determine their correlation, if any, with survival in patients with resected hepatic metastases from colorectal cancer. METHODS: Sixty-three patients with hepatic metastases and 40 corresponding colorectal primary tumours were studied using immunohistochemical staining for p53, DCC and thymidylate synthase, as well as p53 gene mutations using polymerase chain reaction-single-stranded conformational polymorphism (PCR-SSCP) analysis. The results were correlated with survival. RESULTS: There was no correlation between p53, DCC or thymidylate synthase immunohistochemical staining, or between p53 PCR-SSCP analysis, and survival for either hepatic metastases or the colorectal primary tumour. CONCLUSION: Prediction of prognosis in patients having resection of hepatic metastases from colorectal cancer continues to be problematic. Other genetic markers or combination of markers need to be evaluated.

Adult↗
PubMed2001

D box and KEN box motifs in budding yeast Hsl1p are required for APC-mediated degradation and direct binding to Cdc20p and Cdh1p.

The precise order of molecular events during cell cycle progression depends upon ubiquitin-mediated proteolysis of cell cycle regulators. We demonstrated previously that Hsl1p, a protein kinase that inhibits the Swe1p protein kinase in a bud morphogenesis checkpoint, is targeted for ubiquitin-mediated turnover by the anaphase-promoting complex (APC). Here, we investigate regions of Hsl1p that are critical both for binding to the APC machinery and for APC-mediated degradation. We demonstrate that Hsl1p contains both a destruction box (D box) and a KEN box motif that are necessary for Hsl1p turnover with either APC(Cdc20) or APC(Cdh1). In coimmunoprecipitation studies, the D box of full-length Hsl1p was critical for association with Cdc20p, whereas the KEN box was important for association with Cdh1p. Fusion of a 206-amino-acid fragment of Hsl1p containing these motifs to a heterologous protein resulted in APC-dependent degradation of the fusion protein that required intact D box and KEN box motifs. Finally, this bacterially expressed Hsl1p fusion protein interacted with Cdc20p and Cdh1p either translated in vitro or expressed in and purified from insect cells. Binding to Cdc20p and Cdh1p was disrupted completely by a D box/KEN box double mutant. These results indicate that D box and KEN box motifs are important for direct binding to the APC machinery, leading to ubiquitination and subsequent protein degradation.

Amino Acid Motifs↗
PubMed2001

Dynamic structure of thermoreversible colloidal gels of adhesive spheres.

The dynamic structure factor f(q,t) of suspensions of adhesive colloidal spheres has been characterized as a function of temperature over the volume fraction range 0.010<phi<0.075. Below a critical temperature that is volume fraction dependent, the suspensions underwent an abrupt, reversible transition in dynamic structure. Below their gel points suspensions became nonergodic, and the time decay of f(q,t) was arrested by as many as five decades. Static light scattering demonstrated that the adhesive spheres formed a fractal cluster gel structure. A recent model of the dynamics of fractal clusters [A. H. Krall and D. A. Weitz, Phys. Rev. Lett. 80, 778 (1998)] was applied to extract the temperature and volume fraction dependence of the characteristic decay times of f(q,t). Immediately above the gel temperature a single stretched exponential decay of f(q,t) was observed. The temperature dependence of the decay time was taualpha approximately epsilon(-1.15+/-0.06), where epsilon=(T-Tgel)/Tgel, and Tgel is the gelation temperature. The argument of the stretched exponential decay p decreased monotonically as the temperature was lowered toward the gel point, until, at gelation, p approximately 0.5. Below the gel temperature, an initial stretched exponential decay of f(q,t) was followed by a plateau. Finally, at long times, an additional exponential decay of the gel f(q,t) was observed. By applying the fractal cluster dynamics model, it was found that the initial decay time, taubeta approximately epsilon(-1.00+/-0.07). The plateau in f(q,t) was due to an upper bound of the mean-squared displacement of gel segments, denoted delta2. The typical magnitude of delta2 was not much greater than the square of the particle radius. The data showed delta2 approximately epsilon(-1.05+/-0.07). The additional exponential decay at long times, taugamma, depended only weakly on epsilon. Its dependence on the scattering vector was taugamma approximately q(-0.53+/-0.06). The argument of the stretched exponential decay of the gel f(q,t) and volume fraction dependence of taubeta and delta2 indicate that the spatial scaling of the gel compliance is consistent with the gel network bonds possessing angular rigidity. The epsilon dependence of the characteristic times taualpha and taubeta could not be fully explained by the fractal cluster dynamics model. The long time decay of f(q,t) exhibited behavior that differed from that recently reported for dilute gels of aqueous colloidal polystyrene [Cipelletti et al., Phys. Rev. Lett. 84, 2275 (2000)]. We hypothesize that the long-time decay in f(q,t) of the gels studied here is due to rare bond disaggregation processes that occur because of the relatively weak interaction between the adhesive spheres (deltaEmin/kT approximately 10) of the thermoreversible gel.

Journal Article↗
PubMed2001

Randomized, controlled trials in surgery: perceived barriers and attitudes of Australian colorectal surgeons.

PURPOSE: Although the randomized, controlled trial has gained preeminence as the criterion standard for evaluating pharmaceutical treatments, randomized controlled trials in surgery have been perceived as difficult to surmount. Furthermore, attitudes of surgeons toward randomized, controlled trials are not well understood. We determined the views of Australian surgeons about feasibility of and barriers to surgical randomized trials. METHODS: All members of the Section of Colon and Rectal Surgery of the Royal Australasian College of Surgeons (n = 147) and all Australian colorectal subspecialist surgeons (n = 72) were mailed a questionnaire that included questions about surgical randomized, controlled trials. RESULTS: A total of 195 surgeons responded (89 percent). Two-thirds (66.7 percent; 95 percent confidence interval 59.5-73.1) of respondents agreed that "Randomized controlled trials should be the study design of choice" to evaluate new surgical procedures. Only 19 percent (95 percent confidence interval 13.9-25.3) endorsed the statement that "too much emphasis is placed on results of randomized controlled trials." Barriers to conducting surgical randomized, controlled trials identified by the majority included insufficient funding (74.4 percent; 95 percent confidence interval 67.5-80.2), a lack of support from the wider surgical community (55.9 percent; 95 percent confidence interval 48.6-62.9), and difficulties in convincing patients to accept random allocation to treatment (62.6 percent; 95 percent confidence interval 55.3-69.3). CONCLUSION: These results reveal positive attitudes among Australian surgeons toward randomized, controlled trials, although concerns about the feasibility of randomized, controlled trials have been reinforced.

Adult↗
PubMed2001

Is there an association between fecal incontinence and lower urinary dysfunction?

BACKGROUND: Urinary and fecal incontinence in females are both common and distressing conditions. Because common pathophysiologic mechanisms have been described, an association between the two would be expected. The aim of this study was to determine whether patients with lower urinary tract dysfunction have concomitant fecal incontinence when compared with age and gender matched community controls and, second, to determine whether they have predisposing factors that have led to lower urinary tract symptoms and concomitant fecal incontinence. METHODS: A case-control study was performed by means of detailed questionnaire and review of investigation results. One thousand consecutive females presenting for urodynamic investigation of lower urinary tract dysfunction, were compared with 148 age and gender matched community controls. RESULTS: Frequent fecal incontinence was significantly more prevalent among all cases than among community controls (5 vs. 0.72 percent, P = 0.023). Occasional fecal incontinence was also more prevalent (24.6 vs. 8.4 percent, P < 0.001). Fecal incontinence was not significantly more prevalent among females with genuine stress incontinence (5.1 percent) when compared with females with detrusor instability (3.8 percent) or any other urodynamic diagnosis. Symptoms of fecal urgency and fecal urge incontinence were significantly more prevalent among those with a urodynamic diagnosis of detrusor instability or sensory urgency than among females with other urodynamic diagnoses or community controls. Multivariate analysis comparing cases with fecal incontinence with other cases and also with community controls did not indicate that individual obstetric factors contributed significantly to the occurrence of fecal incontinence in these patients. CONCLUSIONS: There is an association between genuine stress incontinence, lower urinary tract dysfunction, and symptoms of fecal incontinence, but the exact mechanism of injury related to childbirth trauma is questioned.

Adult↗
PubMed2001

The role of Thr160 phosphorylation of Cdk2 in substrate recognition.

Full activation of cyclin-dependent kinases (Cdks) requires binding to a cyclin and phosphorylation on an activating site equivalent to Thr160 in Cdk2 by the Cdk-activating kinase. Much is known about the effects of cyclin binding, but the role of the activating phosphorylation is less well understood. We have characterized the effects of Thr160 phosphorylation of Cdk2 on its interactions with substrates, particularly with the P + 3 position. We find that an ionic interaction participates in the recognition of the P + 3 position of the substrate and confirms an observation from structural studies indicating that a key element of this recognition is an interaction between the lysine at the P + 3 position and the Thr160 phosphate of Cdk2. The major effect of disrupting the lysine-phosphate interaction was on kcat values rather than Km values, suggesting that the energy from this interaction is used to align the substrate for efficient catalysis. A lack of effect of Thr160 phosphorylation on the ATPase activity of Cdk2 supported this interpretation.

Binding Sites↗
PubMed2001

Island flap perineoplasty for coverage of perineal skin defects after repair of cloacal deformity.

BACKGROUND: Traumatic cloacal defect is an injury sustained during childbirth in which the anovaginal septum is completely disrupted and the anus and vagina open as a common channel. Such injuries result in complete faecal incontinence and are difficult to repair both in terms of improving function and obtaining skin closure. METHODS: Four cases of traumatic cloacal defect with a delayed presentation are illustrated here. All were treated with an overlapping anterior sphincter repair in combination with island flap perineoplasty to achieve skin closure. Anorectal function before and after surgery and the success of achieving primary wound healing were evaluated. RESULTS: In all four cases profound incontinence was found preoperatively; all patients returned to normal or near normal continence following overlapping anterior sphincter repair. Island flap perineoplasty was successful in achieving primary healing in all cases and no flaps were lost to necrosis. CONCLUSIONS: Island flap perineoplasty is an effective method of achieving skin closure after anterior sphincter repair of traumatic cloacal defects.

Adult↗
PubMed2001

Does type of surgeon matter in rectal cancer surgery? Evidence, guideline consensus and surgeons' views.

One of the most obvious but controversial trends in contemporary surgical practice is that of subspecialization. There is a lack of definitive evidence that subspecialization improves cancer outcomes largely because previous research is compromised by confounding variables of referral practice, lack of standardized definitions of surgical skills and selection bias. Randomized controlled trials of generalized versus subspecialist surgical care are unlikely ever to be performed. The present study of surgeons' views about the role of subspecialization in the care of colorectal cancer patients demonstrates partisan reactions among surgeons themselves (89% response rate). Results of national audits will contribute to wider debate about surgical subspecialization in colorectal cancer.

Attitude of Health Personnel↗
PubMed2001

CAK-independent activation of CDK6 by a viral cyclin.

In normal cells, activation of cyclin-dependent kinases (cdks) requires binding to a cyclin and phosphorylation by the cdk-activating kinase (CAK). The Kaposi's sarcoma-associated herpesvirus encodes a protein with similarity to D-type cyclins. This KSHV-cyclin activates CDK6, alters its substrate specificity, and renders CDK6 insensitive to inhibition by the cdk inhibitor p16(INK4a). Here we investigate the regulation of the CDK6/KSHV-cyclin kinase with the use of purified proteins and a cell-based assay. We find that KSHV-cyclin can activate CDK6 independent of phosphorylation by CAK in vitro. In addition, CAK phosphorylation decreased the p16(INK4a) sensitivity of CDK6/KSHV-cyclin complexes. In cells, expression of CDK6 or to a lesser degree of a nonphosphorylatable CDK6(T177A) together with KSHV-cyclin induced apoptosis, indicating that CDK6 activation by KSHV-cyclin can proceed in the absence of phosphorylation by CAK in vivo. Coexpression of p16 partially protected cells from cell death. p16 and KSHV-cyclin can form a ternary complex with CDK6 that can be detected by binding assays as well as by conformational changes in CDK6. The Kaposi's sarcoma-associated herpesvirus has adopted a clever strategy to render cell cycle progression independent of mitogenic signals, cdk inhibition, or phosphorylation by CAK.

Apoptosis↗
PubMed2000

Dephosphorylation of human cyclin-dependent kinases by protein phosphatase type 2C alpha and beta 2 isoforms.

We previously reported that the activating phosphorylation on cyclin-dependent kinases in yeast (Cdc28p) and in humans (Cdk2) is removed by type 2C protein phosphatases. In this study, we characterize this PP2C-like activity in HeLa cell extract and determine that it is due to PP2C beta 2, a novel PP2C beta isoform, and to PP2C alpha. PP2C alpha and PP2C beta 2 co-purified with Mg(2+)-dependent Cdk2/Cdk6 phosphatase activity in DEAE-Sepharose, Superdex-200, and Mono Q chromatographies. Moreover, purified recombinant PP2C alpha and PP2C beta 2 proteins efficiently dephosphorylated monomeric Cdk2/Cdk6 in vitro. The dephosphorylation of Cdk2 and Cdk6 by PP2C isoforms was inhibited by the binding of cyclins. We found that the PP2C-like activity in HeLa cell extract, partially purified HeLa PP2C alpha and PP2C beta 2 isoforms, and the recombinant PP2Cs exhibited a comparable substrate preference for a phosphothreonine containing substrate, consistent with the conservation of threonine residues at the site of activating phosphorylation in CDKs.

Amino Acid Sequence↗
PubMed2000

Kinetic analysis of the cyclin-dependent kinase-activating kinase (Cak1p) from budding yeast.

Cak1p, the Cyclin-dependent kinase-activating kinase from budding yeast, is an unusual protein kinase that lacks many of the highly conserved motifs observed among members of the protein kinase superfamily. Cak1p phosphorylates and activates Cdc28p, the major cyclin-dependent kinase (CDK) in yeast, and is thereby required for passage through the yeast cell cycle. In this paper, we explore the kinetics of CDK phosphorylation by Cak1p, and we examine the role of the catalytic step in the reaction mechanism. Cak1p proceeds by a sequential reaction mechanism, binding to both ATP and CDK2 with reasonable affinities, exhibiting K(d) values of 7.2 and 0.6 microm, respectively. Interestingly, these values are approximately the same as the K(M) values, indicating that the binding of substrates is fast with respect to catalysis and that the most likely reaction mechanism is rapid equilibrium random. Cak1p is a slow enzyme, with a catalytic rate of only 4.3 min(-)(1). The absence of a burst phase indicates that product release is not rate-limiting. This result, and a solvent isotope effect, suggests that a catalytic step is rate-limiting.

Adenosine Triphosphate↗
PubMed2000

The effects of changing the site of activating phosphorylation in CDK2 from threonine to serine.

Cyclin-dependent kinases (CDKs) that control cell cycle progression are regulated in many ways, including activating phosphorylation of a conserved threonine residue. This essential phosphorylation is carried out by the CDK-activating kinase (CAK). Here we examine the effects of replacing this threonine residue in human CDK2 by serine. We found that cyclin A bound equally well to wild-type CDK2 (CDK2(Thr-160)) or to the mutant CDK2 (CDK2(Ser-160)). In the absence of activating phosphorylation, CDK2(Ser-160)-cyclin A complexes were more active than wild-type CDK2(Thr-160)-cyclin A complexes. In contrast, following activating phosphorylation, CDK2(Ser-160)-cyclin A complexes were less active than phosphorylated CDK2(Thr-160)-cyclin A complexes, reflecting a much smaller effect of activating phosphorylation on CDK2(Ser-160). The kinetic parameters for phosphorylating histone H1 were similar for mutant and wild-type CDK2, ruling out a general defect in catalytic activity. Interestingly, the CDK2(Ser-160) mutant was selectively defective in phosphorylating a peptide derived from the C-terminal domain of RNA polymerase II. CDK2(Ser-160) was efficiently phosphorylated by CAKs, both human p40(MO15)(CDK7)-cyclin H and budding yeast Cak1p. In fact, the k(cat) values for phosphorylation of CDK2(Ser-160) were significantly higher than for phosphorylation of CDK2(Thr-160), indicating that CDK2(Ser-160) is actually phosphorylated more efficiently than wild-type CDK2. In contrast, dephosphorylation proceeded more slowly with CDK2(Ser-160) than with wild-type CDK2, either in HeLa cell extract or by purified PP2Cbeta. Combined with the more efficient phosphorylation of CDK2(Ser-160) by CAK, we suggest that one reason for the conservation of threonine as the site of activating phosphorylation may be to favor unphosphorylated CDKs following the degradation of cyclins.

Amino Acid Substitution↗
PubMed2000

Biofeedback for fecal incontinence using transanal ultrasonography: novel approach.

PURPOSE: Neosphincter procedures may prove to be the treatment of choice for patients with neuropathic fecal incontinence but are rarely proposed for milder forms of the disease. Biofeedback may prove beneficial to these patients but is yet unproven. The objectives of this study were to develop a method of performing biofeedback using transanal ultrasound to teach the patient to contract repetitively and to determine biologic measures of sphincter function using transanal ultrasound in healthy and incontinent patients. METHODS: Initial uncontrolled studies were performed to determine the compliance, normal values, biologic measures of external sphincter strength (isotonic and isometric fatigue times), and early efficacy data using continence scores and visual analog scale scores. RESULTS: Forty-four patients were assessed during three months, with relative improvements in continence scores (St. Mark's Hospital, 40 percent; Pescatori, 20 percent) and patient and investigator visual analog scale scores (38 percent for both) and measurable increase in biologic fatigue times measured by transanal ultrasound. CONCLUSIONS: Transanal ultrasound seems to be a method of teaching external sphincter contraction and measuring sphincter strength with good initial compliance. Clinically and statistically significant improvements in incontinence scores, visual analog scale scores, and biologic strength of the external sphincter were detected in the short-term follow-up with uncontrolled data. The randomized, controlled trial that we have begun will either confirm or refute these results.

Adult↗
PubMed2000

Analysis of CAK activities from human cells.

The cdk-activating kinase (CAK) activates cyclin-dependent kinases (cdks) that control cell-cycle progression by phosphorylating a threonine residue conserved in cdks. CAK from humans contains p40MO15 (cdk7), cyclin H and MAT1, which are also subunits of transcription factor IIH where they phosphorylate the C-terminal domain of the large subunit of RNA polymerase II. In contrast, budding yeast Cak1p is a monomeric enzyme without C-terminal domain kinase activity. Here, we analyze CAK activities in HeLa cells using cdk2-affinity chromatography. In addition to MO15, a second CAK activity was detected that runs on gel filtration at 30-40 kDa. This activity phosphorylated and activated cdk2 and cdk6. Furthermore, this 'small CAK' activity resembled Cak1p rather than MO15 in terms of substrate specificity, reactivity to antibodies against MO15 and Cak1p, and sensitivity to 5'-fluorosulfonylbenzoyladenosine, an irreversible inhibitory ATP analog. Our findings suggest the presence of at least two different CAK activities in human cells.

CDC2-CDC28 Kinases↗
PubMed2000

Activating phosphorylation of the Saccharomyces cerevisiae cyclin-dependent kinase, cdc28p, precedes cyclin binding.

Eukaryotic cell cycle progression is controlled by a family of protein kinases known as cyclin-dependent kinases (Cdks). Two steps are essential for Cdk activation: binding of a cyclin and phosphorylation on a conserved threonine residue by the Cdk-activating kinase (CAK). We have studied the interplay between these regulatory mechanisms during the activation of the major Saccharomyces cerevisiae Cdk, Cdc28p. We found that the majority of Cdc28p was phosphorylated on its activating threonine (Thr-169) throughout the cell cycle. The extent of Thr-169 phosphorylation was similar for monomeric Cdc28p and Cdc28p bound to cyclin. By varying the order of the addition of cyclin and Cak1p, we determined that Cdc28p was activated most efficiently when it was phosphorylated before cyclin binding. Furthermore, we found that a Cdc28p(T169A) mutant, which cannot be phosphorylated, bound cyclin less well than wild-type Cdc28p in vivo. These results suggest that unphosphorylated Cdc28p may be unable to bind tightly to cyclin. We propose that Cdc28p is normally phosphorylated by Cak1p before it binds cyclin. This activation pathway contrasts with that in higher eukaryotes, in which cyclin binding appears to precede activating phosphorylation.

Antibody Specificity↗