Cell signaling through membrane mucins

MUC1 and MUC4 are the two membrane mucins that have been best characterized. Although they have superficially similar structures and have both been shown to provide steric protection of epithelial surfaces, recent studies have also implicated them in cellular signaling. They act by substantially different mechanisms, MUC4 as a receptor ligand and MUC1 as a docking protein for signaling molecules. MUC4 is a novel intramembrane ligand for the receptor tyrosine kinase ErbB2/HER2/Neu, triggering a specific phosphorylation of the ErbB2 in the absence of other ErbB ligands and potentiating phosphorylation and signaling through the ErbB2/ErbB3 heterodimeric receptor complex formed in the presence of neuregulin. In contrast, MUC1 has a highly conserved cytoplasmic tail, which binds beta-catenin, a key component of adherens junctions and a regulator of transcription, in a process that is tightly regulated by MUC1 phosphorylation. The specific localization of these membrane mucins to the apical surfaces of epithelial cells suggests that their signaling functions may be important as sensor mechanisms in response to invasion or damage of epithelia.

Muc4/sialomucin complex, the intramembrane ErbB2 ligand, induces specific phosphorylation of ErbB2 and enhances expression of p27(kip), but does not activate mitogen-activated kinase or protein kinaseB/Akt pathways

Muc4/sialomucin complex (SMC) is a multifunctional glycoprotein complex which can repress apoptosis in transfected tumor cells. Its transmembrane subunit acts as an intramembrane ligand for the receptor tyrosine kinase ErbB2 to induce the phosphorylation of ErbB2 and, by acting synergistically with the ErbB3 ligand neuregulin, can potentiate the phosphorylation of ErbB2 and ErbB3. In the present study we show that Muc4/SMC alone robustly induces the phosphorylation of ErbB2 to enhance the tyrosine phosphate epitope (Tyr1248) recognized by anti-phospho-ErbB2. Although this tyrosine phosphorylation has been implicated in cell transformation, it does not activate any of the three mitogen-activated protein kinases (MAPKs) or protein kinase B/Akt of the phosphatidyl inositol 3-kinase pathway. Instead, Muc4/SMC expression induces up-regulation of the cell cycle inhibitor p27(kip), consistent with the expression of Muc4/SMC in differentiated, rather than proliferative, epithelial cells. Interestingly, a combination of Muc4/SMC and neuregulin down-regulate p27(kip) and activate protein kinase B/Akt. These observations suggest that Muc4/SMC acts as a regulator of differentiation by inducing a limited phosphorylation of ErbB2 and a modulator of proliferation when acting synergistically with neuregulin to induce a more extensive phosphorylation on both ErbB2 and ErbB3.

Muc4/sialomucin complex, the intramembrane ErbB2 ligand, in cancer and epithelia: to protect and to survive

The membrane mucin Muc4, also called sialomucin complex (SMC), is a heterodimeric complex of two subunits, ASGP-1 and ASGP-2, derived from a single gene. It is produced by multiple epithelia in both membrane and soluble forms and serves as a protective agent for the epithelia. The membrane form of Muc4 acts as a steric barrier to the apical cell surface of epithelial or tumor cells. An important example is the uterus of the rat, in which Muc4 expression is downregulated for blastocyst implantation. The soluble form facilitates the protection and lubrication of epithelia by mucous gels composed of gel-forming mucins, as in the airway, where Muc4 is proposed to participate in mucociliary transport as a constituent of the periciliary fluid. The soluble form is also found in body fluids, such as milk, tears, and saliva. The transmembrane subunit ASGP-2 acts as an intramembrane ligand and activator for the receptor tyrosine kinase ErbB2. Formation of this ligand-receptor complex is proposed to repress apopotosis in epithelial and cancer cells in which the ligand-receptor complex is formed, providing a second type of cell protective mechanism. Muc4 expression is regulated in epithelial tissues in a cell- and tissue-specific manner during epithelial differentiation. In stratified epithelia, it is predominantly in the most superficial, differentiated layers, often coincident with ErbB2. Dysregulation of Muc4 expression may contribute to cell and tissue dysfunction, such as the proposed contribution of Muc4 to mammary tumor progression. These observations clearly show that Muc4 has multiple roles in epithelia, which may provide insights into aberrant behaviors of these tissues and their derivative carcinomas.

Fetal-maternal microchimerism in normal parous females and parous female cancer patients

OBJECTIVE

The prevalence of male microchimerism (MC) in parous females, nonparous females, and parous female cancer patients was examined.

MATERIALS AND METHODS

DNA extracted from peripheral blood leukocytes and male Y-chromosomal DNA was amplified using a sensitive two-stage polymerase chain reaction technique. Controls prepared by mixing human male and female cell lines demonstrated the sensitivity of the technique to be in the range of 1 male cell per 1 million female cells.

RESULTS

Findings of this study showed that the percentage of MC-positive females was highly dependent on the amount of DNA analyzed; 57% of normal parous females who bore at least one son were found to have male cells in their blood when 25 mug DNA or more from the samples was analyzed. This frequency is much higher than previous reports indicating a prevalence of 33% for normal parous females. Analysis of samples obtained from 200 parous female cancer patients revealed an incidence of 34% MC(+); 7.4% of normal nonparous female controls had evidence of MC.

CONCLUSION

The long-term persistence of male cells in the maternal circulation could indicate maternal immune tolerance of paternally inherited fetal antigens. This maternal tolerance might be exploited in female patients with malignant disease to deliver immune cellular therapy from their sons.

Multidrug resistance correlates with overexpression of Muc4 but inversely with P-glycoprotein and multidrug resistance related protein in transfected human melanoma cells

Due to the size, glycosylation, and location in the plasma membrane of the sialomucin complex Muc4, which has been implicated in ErbB2 signaling, in the repression of apoptosis and cell adhesion, and in tumor metastasis, studies were initiated to determine whether its presence could influence cell sensitivity to anticancer drugs. Growth inhibition assays using melanoma cell lines that either express the glycoprotein (Muc4(+)) or do not (Muc4(-)) showed that Muc4 renders cells resistant to taxol, doxorubicin, vinblastine, rhodamine 123, and 2-deoxyglucose. When treated with various concentrations of doxorubicin, Muc4(+) cells were blocked less frequently in G(2) and underwent less DNA fragmentation (apoptosis and/or necrosis) than Muc4(-) cells. All of the drugs tested (except for 2-deoxyglucose) are well recognized by P-glycoprotein-mediated multidrug resistance 1 (MDR1) and to a lesser degree by multidrug resistance related protein 1 (MRP1) transporters. Therefore, transporter gene expression in these cells was assayed. Surprisingly, Muc4(+) cells expressed lower levels of both transporter genes than Muc4(-) cells. Moreover, rhodamine 123 was retained more highly in the Muc4(+) than in the Muc4(-) cells, demonstrating that these transporters are functional. Overall, these results indicate that although Muc4(+) cells express less MDR1 and MRP1, they are more resistant to drugs recognized by these transporters.

Recent advances in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal bone marrow disorders characterized by both bone marrow failure and a propensity for development of acute myeloid leukemia. The incidence of these conditions has risen sharply over the past several years, making them the most common malignant bone marrow disorders. While the majority of patients are diagnosed with low-grade disease, approximately two-thirds will succumb to complications of peripheral blood cytopenias or progression to acute leukemia. In recent years, there has been striking progress in our understanding of the pathogenesis of these disorders. For example, the recognition of the roles of angiogenesis and cytokine abnormalities in the development of these diseases led to clinical trials with agents such as thalidomide, which yielded encouraging erythroid responses. Subsequent work with the thalidomide derivative lenalidomide resulted in marked erythroid and cytogenetic responses in individuals with the 5q- abnormality. Additionally, the identification of hypermethylation as an important aspect in the pathogenesis of these and other hematological diseases led to clinical trials utilizing the demethylating agents azacitidine and decitibine. These agents are now known to result in trilineage responses in 30% to 50% of patients with MDS with as many as 20% achieving partial or complete remissions. These results have altered the natural history of these diseases in a significant number of patients. Investigators anticipate that further studies with tyrosine kinase, histone deacetylase, and farnesyl transferase inhibitors will contribute to already promising attempts to reverse or block the pathogenesis of these diseases. Other novel agents are being evaluated as investigators continue to make progress for patients affected by these disorders.

Modulation of the herpes simplex virus type-1 UL9 DNA helicase by its cognate single-strand DNA-binding protein, ICP8

The mechanism of stimulation of a DNA helicase by its cognate single-strand DNA-binding protein was examined using herpes simplex virus type-1 UL9 DNA helicase and ICP8. UL9 and ICP8 are two essential components of the viral replisome that associate into a complex to unwind the origins of replication. The helicase and DNA-stimulated ATPase activities of UL9 are greatly elevated as a consequence of this association. Given that ICP8 acts as a single-strand DNA-binding protein, the simplest model that can account for its stimulatory effect predicts that it tethers UL9 to the DNA template, thereby increasing its processivity. In contrast to the prediction, data presented here show that the stimulatory activity of ICP8 does not depend on its single-strand DNA binding activity. Our data support an alternative hypothesis in which ICP8 modulates the activity of UL9. Accordingly, the data show that the ICP8-binding site of UL9 constitutes an inhibitory region that maintains the helicase in an inefficient ground state. ICP8 acts as a positive regulator by neutralizing this region. ICP8 does not affect substrate binding, ATP hydrolysis, or the efficiency of translocation/DNA unwinding. Rather, we propose that ICP8 increases the efficiency with which substrate binding and ATP hydrolysis are coupled to translocation/DNA unwinding.

Extensive uterovaginal prolapse during labor

Uterovaginal prolapse complicating pregnancy is an extremely rare event. Obstetricians should be familiar with the condition as early recognition and close follow up is essential in order to avoid possible fetomaternal risks. We report a case of 35-year-old lady who presented to the emergency with complaints of labor pains, absent fetal movements and huge uterine cervical prolapse in active phase of labor. She was conservatively treated with bedrest, blood transfusions and irrigation of prolapsed cervix. A dead female fetus was delivered vaginally. Ring pessary was placed postnatally. We believe that an extensive uterovaginal prolapse needs close surveillance and can be managed conservatively.

Endometrial stromal sarcoma in a 20-year-old woman

Endometrial stromal sarcoma (ESS) is an uncommon and challenging condition comprising 10% of all uterine sarcomas and found in women 42-58 years of age. ESS is difficult to diagnose in young women as it masquerades as a leiomyoma. We report this tumour in a 20-year-old woman presenting with heavy and prolonged menses and urinary retention. She was not sexually active and did not give consent for pelvic examination. A preoperative diagnosis of a submucous leiomyoma with an adnexal mass was made. At laparotomy, the leiomyoma was found to be wedged between the cervix and the vagina, and was removed vaginally. A 5-6 cm retroperitoneal mass was adherent to the right pelvic wall, which was also removed. Histopathology of both specimens revealed ESS. The final diagnosis according to the International Federation of Gynaecology and Obstetrics classification was stage IV ESS. After oncology consult, she was referred for chemotherapy. She is now on follow-up.

Response and tolerability of a 5-day azacytidine schedule in pateints with myelodysplastic syndromes

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Background: Azacitidine (AZA) is a DNA methyltransferase inhibitor with activity in patients with myelodysplastic syndrome (MDS). The current approved schedule of AZA is 75 mg/m2/d for 7 days every 28 days. This schedule is inconvenient for patients and providers because of the need for weekend administration. Methods: The records of 9 patients who received AZA 100 mg/m2/d for 5 days with an anticipated 28 day cycle between 10/04 to 1/06 were reviewed to determine response, duration of response and tolerability. A minimum of two cycles were required for response evaluation (n = 8). All patients were assessed for tolerability. The International Working Group response criteria for MDS was utilized for evaluation. Results: Patients had secondary MDS (n = 4), chronic myelomonocytic leukemia (n = 2), refractory anemia (n = 2) and refractory anemia with ringed sideroblasts (n = 1). Of the 8 patients who received at least 2 cycles of therapy, 5 responded: 1 achieved partial response, 3 achieved hematologic improvement in at least one cell line and 1 remained in a stable disease state. The overall response rate was 63%. Average response duration was 6.2 months. The longest response duration was 10 months. Myelosuppression was seen in 2 of the 9 patients treated, one of whom continued treatment with growth factor support; therapy is currently on hold for the other patient. Injection site reaction was seen in 2 patients, resulting in discontinuation of treatment in one. One patient experienced severe malaise after 2 cycles and was given the standard dose for further therapy with a major hematologic improvement. Other isolated events included mouth ulcers, mild nausea and flare of erythema nodosum. Of the 5 responders, 1 later died of disease progression (after 7 cycles), 1 died of a complication of comorbidity (after 5 cycles), 1 is alive with disease progression (after 10 cycles) and 2 are continuing therapy with AZA (after 4 and 5 cycles, respectively). Conclusions: AZA 100 mg/m2/day for 5 days every 28 days seems to be tolerated as well as the 7-day treatment schedule. It also appears to have efficacy similar to the standard dose and schedule. If larger studies are confirmatory, this 5-day schedule may be more convenient for patients and providers.

[Table: see text]

Role of Trastuzumab in the Adjuvant Treatment of HER2-Positive Early Breast Cancer

Amplification of the human epidermal growth factor receptor 2 ( HER2) gene occurs in 18–23% of invasive breast carcinomas and is associated with a worse prognosis. This novel transforming gene was identified in 1985, and in 1987 HER2 amplification was demonstrated to be central to the aggressive, malignant phenotype of these cancers and a significant predictor of both time to relapse and overall survival. These observations led to the development of the first monoclonal antibody targeting the extracellular domain of HER2, trastuzumab (Herceptin®, Genentech and Hoffman LaRoche, Switzerland), which was approved by the US FDA for metastatic breast cancer in 1998. In 2005, results from four major trastuzumab adjuvant trials demonstrated a marked reduction in risk of recurrence, and trastuzumab is now an essential component of the adjuvant treatment of H ER2-positive early breast cancer. Concerns regarding cardiac safety and mechanisms of resistance to trastuzumab remain important issues and are being addressed in ongoing research efforts.

A Patient With Regressed Diffuse Large B-Cell Lymphoma and Aggressive Follicular Lymphoma

Diffuse large B‐cell lymphoma (DLBCL) and follicular lymphoma (FL) are the two most aggressive forms of non‐Hodgkin lymphomas (NHLs). Spontaneous remission of DLBCL is a rare phenomenon. Immune system activation has been observed to play a significant role in the regression of untreated disease on some occasions. We present a case of DLBCL in a 75-year-old male patient who has been free of disease for two months without any treatment due to possible immune-related mechanism, but later he presented with FL.

Response to azacitidine (AZA) in patients with secondary myelodysplastic syndrome

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Background: Myelodysplastic syndrome (MDS) is characterized by maturation defects in hematopoietic progenitor cells that result in ineffective hematopoiesis, various cytopenias and risk of progression to acute myeloid leukemia. MDS can arise de novo or secondary to exposure to myelotoxic drugs or ionizing radiation. Secondary MDS (t-MDS) tends to have more aggressive behavior than de novo MDS. Azacitidine (AZA), a DNA methyl transferase inhibitor has activity in MDS. To date there is little data in patients with t-MDS Methods: The records of 21 patients with t-MDS treated with AZA between 05/96 and 01/06 were reviewed to determine response, duration of response and tolerability in these high-risk patients. 15 of the 21 patients received AZA as part of a National Cancer Institute special exception program (75mg/m2 subcutaneously for seven days every four weeks). Patients who received at least 2 cycles were considered evaluable for response (N=16). All patients were evaluated for toxicity. The International working group standardized response criteria for MDS were used for evaluation. Results: Patients had a median age of 68 years; male: female ratio was 3:1. 11 patients had refractory anemia, 6 had refractory anemia with excess blasts, 3 had chronic myelomonocytic leukemia, 1 had refractory anemia with ringed sideroblasts. Response was seen in 8 (50%) of 16 patients, with 2 (12.5%) partial remissions, 6 (37.5%) showed major hematological response. The median duration of response was 12.3 months (range 4–38). Stable disease was seen in 5 patients (31%), with an average duration of 6.5 months (range 2–15). 3 patients failed therapy due to disease progression or death. Treatment was well tolerated in general, with the most side effects being nausea, vomiting, diarrhea and cytopenias. Febrile neutropenia was seen in 5 patients. Conclusions: Azacitidine appears to be effective and well tolerated in patients with t-MDS.

[Table: see text]

Yttrium-90 (90Y) ibritumomab tiuxetan for treatment of relapsed or refractory non-hodgkin’s lymphoma: The Western Pennsylvania Cancer Institute experience

12511

Background: Yttrium-90 (90Y) ibritumomab tiuxetan (Zevalin) radioimmunotherapy is an effective agent for treatment of CD20+ B-cell lymphoma (NHL).It is approved for treatment of relapsed or refractory, follicular or transformed B cell lymphoma. An overall response rate ranging from 74% to 82% has been reported. Median response duration of 11.5 to 28.1 months has been reported. Methods: We identified, retrospectively, 37 patients treated at our institution with relapsed or refractory NHL who were treated with 90Y ibritumomab tiuxetan at a dose of 0.3mCi/kg or 0.4mCi/kg. Response rate and survival were assessed. Median age was 60 years (range 28–82 years) of which 65% were male. Follicular lymphoma was present in 57% (n = 21) and diffuse large B-cell lymphoma in 22% (n = 8) of patients. Advanced disease (stage III or IV) was present in 84% (n = 31) of patients. All of the patients had received at least one prior regimen and 68% (n = 25) had received ≥ 3 regimens before 90Y ibritumomab tiuxetan. Results: Overall response rate was 65% (24/37); CR 43% (16/37); PR 19% (7/37); SD 3% (1/37). Duration of response was 13.3 months (range 4 to 48 months) with response duration greater than 12 months in 35% (n = 13) of the patients. Of responders, 67% (16/23) had failed to respond to prior immediate therapy. The only toxic event was pancytopenia, which predictably occurred after treatment. No patients died of toxicity and all toxicity was reversible. Conclusions: 90Y ibritumomab tiuxetan was well tolerated and effective for our patients.We document durable response in our patients with relapsed or refractory NHL and with advanced stage disease. Further study of ibritumomab tiuxetan using different doses and in combination with chemotherapy is warranted.

No significant financial relationships to disclose.

Medical intervention in adolescent menorrhagia

Objectives: To find out causative factors of adolescent menorrhagia and success of various treatments. Design: Descriptive cross sectional study Place & duration of study: Lady Willingdon Hospital, Lahore from May 2004 to April 2005. Subject and methods: Fifty unmarried patients at 12-19 years with menorrhagia selected by non-probability convenience sampling. Blood loss was determined by duration of bleeding extending beyond seven days, passage of clots and presence of anaemia. Results: The most common cause of menorrhagia was DUB (92%) followed by bleeding and endocrinal disorder. Non-steroidal anti-inflammatory drug and antifibrinolytic agent produced 75% subjective improvement in complaints. However, combined oral contraceptive produced 66% improvement. Conclusion: NSAIDS and antifibrinolytic drugs were found to be effective in reducing menstrual loss and should be used as first line of treatment.

Preparing health professionals to practice environmentally sustainable healthcare

Background

In 2019 the WHO identified climate change and air pollution as the top global threat to health. This was illustrated by the health consequences of the catastrophic 2019-20 Australian bushfire season. Health-care systems also contribute to climate change and environmental degradation. For Australia, health care contributes 7% of total carbon emissions and produces considerable clinical and non-clinical waste which is either incinerated or sent to landfill. Despite these threats to health there is a limited response by health professions education to include climate change and environmentally sustainable healthcare in curricula.

Methods

Medical Deans of Australia and New Zealand (MDANZ) is the peak body for professional medical education in Australasia. MDANZ formed a Climate Change and Health Working Group to develop curriculum and learning resources. The Group comprises representatives of Australasian medical schools and student representative organisations. The scope for curriculum was defined by searching the literature, reviewing teaching experience, and benchmarking against relevant courses developed for medical students by peers.

Results

Five broad areas of learning were identified; graduate outcome statements and learning objectives were developed aligned with these. Once endorsed by MDANZ these were circulated to all medical schools to inform curriculum review. A resource repository is being developed to support curriculum change. Ways to measure and monitor inclusion in medical programs are being researched.

Conclusions

We must prepare future practitioners for their role in transforming health care to become carbon neutral. Using a public health approach, system level change in medical education is being supported in Australasia. All health professions have a role in providing environmentally sustainable health care. The Group provides a model that can be used by other health professions to create change at the necessary pace and scale.

Key messages

The health education sector must prepare graduates for climate change and environmentally sustainable healthcare. By working collaboratively at a systems level, change can occur at pace and scale.