Investigation and response to an outbreak of Neisseria meningitidis serogroup Y ST-1466 urogenital infections, Australia

Abstract

In 2023, an increased number of urogenital and anorectal infections with Neisseria meningitis serogroup Y (MenY) were reported in New South Wales (NSW). Whole genome sequencing (WGS) found a common sequence type (ST-1466), with limited sequence diversity. Confirmed outbreak cases were NSW residents with a N. meningitidis isolate matching the cluster sequence type; probable cases were NSW residents with MenY isolated from a urogenital or anorectal site from 1 July 2023 without WGS testing. Of the 41 cases, most were men (n = 27), of whom six reported recent contact with a female sex worker. Five cases were men who have sex with men and two were female sex workers. Laboratory alerts regarding the outbreak were sent to all Australian jurisdictions through the laboratories in the National Neisseria Network. Two additional states identified urogenital MenY ST-1466 infections detected in late 2023. Genomic analysis showed all MenY ST-1466 sequences were interspersed, suggestive of an Australia-wide outbreak. The incidence of these infections remains unknown, due to varied testing and reporting practices both within and across jurisdictions. Isolates causing invasive meningococcal disease (IMD) in Australia are typed, and there has been no MenY ST-1466 IMD recorded in Australia to end of March 2024. Concerns remain regarding the risk of IMD, given the similarity of these sequences with a MenY ST-1466 IMD strain causing a concurrent outbreak in the United States of America.

The challenge of providing medical follow-up for sexual assault victims: can we predict who will attend? A retrospective cross-sectional study

This study examined the impact of a pathway between a sexual assault service and a public sexual health service developed to improve rates of post-sexual assault medical follow-up. Follow-up attendances improved in the first 12months of the pathway (2014) compared with attendances in 2013 (17.8%vs 9.6%, P =0.01). Factors independently associated with attendance at follow-up were being prescribed HIV post-exposure prophylaxis and knowing the assailant. Those with physical injuries were less likely to attend. The prevalence of sexually transmissible infections in this cohort, 8% at the acute presentation and 5% at follow-up, suggests a need for alternatives to clinic-based follow-up.

Characteristics of heterosexually-acquired compared to homosexually-acquired HIV and implications for clinical practice: results from the Australian HIV Observational Database

Heterosexuals living with HIV report feeling additional HIV stigma compared to homosexual men, which may affect clinical outcomes. Yet, beyond routinely collected surveillance data, little is known about the characteristics of individuals who acquire HIV heterosexually and clinical outcomes by mode of sexual acquisition have not been directly compared. Using data from the Australian HIV Observational Database, we compared clinical characteristics of those with heterosexually-acquired (Het-HIV) to homosexually-acquired HIV (Hom-HIV) to investigate any differences and their implications for clinical management. 513 Het-HIV and 1467 Hom-HIV patients were included and contributed 3,127 and 9,457 person-years of follow-up, respectively. Compared with Hom-HIV, Het-HIV were more often born outside Australia (62.5% vs 39.9%, p<0.001), less likely to have Hepatitis C (4.8% vs 7.8%, p=0.029) and had lower median CD4 counts at diagnosis (292 vs 450 cells/µL, p<0.001) and cART initiation (270 vs 340 cells/µL, p<0.001). Despite these lower CD4 counts, there were no significant differences between groups for time to the major clinical endpoints of cART initiation, viral suppression, virological failure or all-cause mortality. Het-HIV had a lower risk of loss-to-follow-up than Hom-HIV (aHR 0.78; 95% CI 0.64-0.95). Further studies examining factors associated with, and interventions to inform retention in care are required.

Prevalence and associations of larger burden of intra-anal high-grade squamous intraepithelial lesions at baseline in an Australian cohort of gay and bisexual men: The Study of the Prevention of Anal Cancer

OBJECTIVES

To investigate factors associated with larger burden of intra-anal high-grade squamous intraepithelial lesions (HSIL) in a natural history study of HSIL.

METHODS

617 gay and bisexual men (GBM) attended a baseline visit. High-resolution anoscopy-directed biopsy was performed of suspected HSIL. GBM with biopsy-confirmed HSIL (bHSIL) affecting a single-octant were compared with those who had bHSIL affecting a larger area.

RESULTS

Of 196 men with bHSIL at baseline, 73 (37.2 %) had larger bHSIL burden. Larger burden was independently associated with anal HPV16 detection (aOR 2.06, 95 % CI 1.09-3.89, p = 0.026) and infection with a greater number of high-risk HPV types (aOR per type increase 1.25, 95 % CI 1.05-1.49, p-trend = 0.010).

CONCLUSION

The observation that men with a larger burden of HSIL also had more risk factors for anal cancer suggests this group may warrant closer observation to ensure earlier detection, and thus improved prognosis, of individuals whose HSIL may progress to anal cancer.

Cardiovascular disease and diabetes in HIV-positive and HIV-negative gay and bisexual men over the age of 55 years in Australia: insights from the Australian Positive & Peers Longevity Evaluation Study

OBJECTIVES

As HIV-positive people age, diagnosis and management of comorbidities associated with ageing are of increasing concern. In this study, we aimed to compare the self-reported prevalences of heart disease, stroke, thrombosis and diabetes in older Australian HIV-positive and HIV-negative gay and bisexual men (GBM).

METHODS

We analysed data from the Australian Positive & Peers Longevity Evaluation Study (APPLES), a study of a prospectively recruited cross-sectional sample of 228 (51.1%) HIV-positive and 218 (48.9%) HIV-negative GBM, aged ≥ 55 years. Regression methods were used to assess the association of HIV status with self-reported comorbidities.

RESULTS

Of 446 patients, 389 [200 (51.4%) HIV-positive] reported their disease history. The reported prevalence of comorbidities was higher in the HIV-positive group than in the HIV-negative group: heart disease, 19.5 versus 12.2%; stroke, 7.5 versus 4.2%; thrombosis, 10.5 versus 4.2%; and diabetes, 15.0 versus 9.0%, respectively. In adjusted analyses, HIV-positive GBM had significantly increased odds of reporting heart disease [adjusted odds ratio (aOR) 1.99; P = 0.03] and thrombosis (aOR 2.87; P = 0.01). In our analysis, HIV status was not significantly associated with either age at diagnosis of heart disease (median 53 years for HIV-positive GBM versus 55 years for HIV-negative GBM; P = 0.64) or 5-year cardiovascular disease (CVD) risk estimated using the Framingham risk score.

CONCLUSIONS

HIV-positive GBM more commonly reported heart disease and thrombosis compared with their HIV-negative peers. These results further highlight the need to understand the impact of HIV on age-related comorbidities in GBM, to guide optimal screening and treatment strategies to reduce the risk of these comorbidities among the HIV-positive population.

Association of anal symptoms with anal high grade squamous intraepithelial lesions (HSIL) among men who have sex with men: Baseline data from the study of the prevention of anal cancer (SPANC)

BACKGROUND

The association between anal high-grade squamous intraepithelial lesion (HSIL) and anal symptoms has not been systematically investigated.

METHODS

The Study of Prevention of Anal Cancer is a prospective cohort study of men who have sex with men (MSM) ≥ 35 years old in Sydney, Australia. Self-reported symptoms were collected. Anal cytology and high-resolution anoscopy were undertaken. Using baseline visit data, men negative for squamous intra-epithelial lesion (SIL) were compared with men diagnosed with composite-HSIL (cytology and/or histology). Logistic regression analyses were performed to assess the association of symptoms with HSIL.

RESULTS

Among 414 MSM included (composite-HSIL (n = 231); negative for SIL (n = 183)), 306 (73.9%) reported symptom(s) within the last 6 months. There was no association between any symptom and composite-HSIL. A significant association between anal lump and a larger burden of HSIL (at least 2 intra-anal octants) (anal lump within last month: p = 0.014; anal lump within last 6 months: p = 0.010) became non-significant after adjusting for HIV-status and recent anal warts (anal lump within last month: p = 0.057; anal lump within last 6 months: p = 0.182).

CONCLUSIONS

Among MSM age 35 years and older, most anal symptoms are not a useful marker of anal HSIL.

Comparison of Kaposi Sarcoma Risk in Human Immunodeficiency Virus-Positive Adults Across 5 Continents: A Multiregional Multicohort Study

BACKGROUND

We compared Kaposi sarcoma (KS) risk in adults who started antiretroviral therapy (ART) across the Asia-Pacific, South Africa, Europe, Latin, and North America.

METHODS

We included cohort data of human immunodeficiency virus (HIV)-positive adults who started ART after 1995 within the framework of 2 large collaborations of observational HIV cohorts. We present incidence rates and adjusted hazard ratios (aHRs).

RESULTS

We included 208140 patients from 57 countries. Over a period of 1066572 person-years, 2046 KS cases were diagnosed. KS incidence rates per 100000 person-years were 52 in the Asia-Pacific and ranged between 180 and 280 in the other regions. KS risk was 5 times higher in South African women (aHR, 4.56; 95% confidence intervals [CI], 2.73-7.62) than in their European counterparts, and 2 times higher in South African men (2.21; 1.34-3.63). In Europe, Latin, and North America KS risk was 6 times higher in men who have sex with men (aHR, 5.95; 95% CI, 5.09-6.96) than in women. Comparing patients with current CD4 cell counts ≥700 cells/µL with those whose counts were <50 cells/µL, the KS risk was halved in South Africa (aHR, 0.53; 95% CI, .17-1.63) but reduced by ≥95% in other regions.

CONCLUSIONS

Despite important ART-related declines in KS incidence, men and women in South Africa and men who have sex with men remain at increased KS risk, likely due to high human herpesvirus 8 coinfection rates. Early ART initiation and maintenance of high CD4 cell counts are essential to further reducing KS incidence worldwide, but additional measures might be needed, especially in Southern Africa.

Experience and psychological impact of anal cancer screening in gay, bisexual and other men who have sex with men: a qualitative study

OBJECTIVE

Human papillomavirus-related anal cancer rates are increasing and are particularly high in gay, bisexual and other men who have sex with men (GBM/MSM), especially HIV-positive individuals. Although screening programs for high-risk populations have been advocated, concerns about possible adverse psychological consequences exist. This study aimed to investigate GBM/MSM's experience, understanding and emotional response to screening techniques for anal cancer to determine how best to minimise psychological distress in future programs.

METHODS

In-depth qualitative face-to-face interviews were conducted with 21 GBM/MSM participating in the "Study of the Prevention of Anal Cancer" in Sydney, Australia, between June 2013 and June 2014. Nonrandom, purposive sampling was used to ensure heterogeneity with respect to HIV status and screening test results. Framework analysis method was used to organise the data and identify emerging themes.

RESULTS

Knowledge about anal cancer, human papillomavirus and the link between them was limited. Abnormal screening results affected participants' sense of well-being and were associated with anxiety and concern about developing anal cancer. HIV-negative men receiving abnormal results showed higher levels of distress compared to their HIV-positive counterparts. Consultations with general practitioners about abnormal results had an important role in increasing participants' understanding and in moderating their anxiety.

CONCLUSION

Anal cancer screening should be accompanied by health education around anal cancer, its aetiology and the meaning of associated test results. Simple and effective communication strategies should be encouraged. Collaboration with general practitioners could assist the process of education and reporting test results.

A longitudinal cohort study of HIV 'treatment as prevention' in gay, bisexual and other men who have sex with men: the Treatment with Antiretrovirals and their Impact on Positive And Negative men (TAIPAN) study protocol

BACKGROUND

Australia has increased coverage of antiretroviral treatment (ART) over the past decade, reaching 73% uptake in 2014. While ART reduces AIDS-related deaths, accumulating evidence suggests that it could also bolster prevention efforts by reducing the risk of HIV transmission ('treatment as prevention'). While promising, evidence of community-level impact of treatment as prevention on reducing HIV incidence among gay and bisexual men is limited. We describe a study protocol that aims to determine if scale up of testing and treatment for HIV leads to a reduction in community viraemia and, in turn, if this reduction is temporally associated with a reduction in HIV incidence among gay and bisexual men in Australia's two most populous states.

METHODS

Over the period 2009 to 2017, we will establish two cohorts making use of clinical and laboratory data electronically extracted retrospectively and prospectively from 73 health services and laboratories in the states of New South Wales and Victoria. The 'positive cohort' will consist of approximately 13,000 gay and bisexual men (>90% of all people living with HIV). The 'negative cohort' will consist of at least 40,000 HIV-negative gay and bisexual men (approximately half of the total population). Within the negative cohort we will use standard repeat-testing methods to calculate annual HIV incidence. Community prevalence of viraemia will be defined as the proportion of men with a viral load ≥200RNA copies/mm³, which will combine viral load data from the positive cohort and viraemia estimates among those with an undiagnosed HIV infection. Using regression analyses and adjusting for behavioural and demographic factors associated with infection, we will assess the temporal association between the community prevalence of viraemia and the incidence of HIV infection. Further analyses will make use of these cohorts to assess incidence and predictors of treatment initiation, repeat HIV testing, and viral suppression.

DISCUSSION

This study will provide important information on whether 'treatment as prevention' is associated with a reduction in HIV incidence at a community level among gay and bisexual men.

Protocol for an open-label, single-arm trial of HIV pre-exposure prophylaxis (PrEP) among people at high risk of HIV infection: the NSW Demonstration Project PRELUDE

INTRODUCTION

Despite a number of HIV prevention strategies, the number of new HIV infections remains high. In Australia, over three-quarters of new HIV diagnoses are in gay and bisexual men (GBM). Pre-exposure prophylaxis (PrEP) has been shown to be effective at preventing new HIV infections in several randomised trials. The PRELUDE study aims to evaluate the implementation of PrEP in healthcare settings in New South Wales (NSW), Australia, among a sample of high-risk adults.

METHODS AND ANALYSIS

PRELUDE is an ongoing open-label, single-arm demonstration project, conducted in public and private clinics across NSW, Australia. Enrolment began in November 2014. The study is designed for 300 high-risk participants-mainly GBM and heterosexual women. Participants receive daily oral PrEP, composed of emtricitabine (FTC) and tenofovir disoproxil fumarate (TDF), for up to 2.5 years. Quarterly study visits include testing for HIV and sexually transmitted infections (STIs), assessment of ongoing eligibility and side effects, and self-reported adherence. Following each study visit, online behavioural surveys are administered to collect information on medication adherence, risk behaviours and attitudes. Blood samples will be collected in a subset of patients 1, 6 and 12 months after PrEP initiation to measure FTC/TDF concentrations. Analyses using longitudinal regression models will focus on feasibility, adherence, safety, tolerability and effects of PrEP on behaviour. This study will inform PrEP policy and guide the implementation of PrEP in Australia in people at high risk of HIV.

ETHICS AND DISSEMINATION

The study will be conducted in accordance with the Declaration of Helsinki. All patients will provide written informed consent prior to participation in the study. Publications relating to each of the primary end points will be gradually released after 12 months of follow-up is complete.

TRIAL REGISTRATION NUMBER

NCT02206555; Pre-results.

Risk factors associated with incident sexually transmitted infections in HIV-positive patients in the Australian HIV Observational Database: a prospective cohort study

OBJECTIVES

We established a subcohort of HIV-positive individuals from 10 sexual health clinics within the Australian HIV Observational Database (AHOD). The aim of this study was to assess demographic and other factors that might be associated with an incident sexually transmitted infection (STI).

METHODS

The cohort follow-up was from March 2010 to March 2013, and included patients screened at least once for an STI. We used survival methods to determine time to first new and confirmed incident STI infection (chlamydia, gonorrhoea, syphilis or genital warts). Factors evaluated included sex, age, mode of HIV exposure, year of AHOD enrolment, hepatitis B or C coinfection, time-updated CD4 cell count, time-updated HIV RNA viral load, and prior STI diagnosis.

RESULTS

There were 110 first incident STI diagnoses observed over 1015 person-years of follow-up, a crude rate of 10.8 [95% confidence interval (CI) 9.0-13.0] per 100 person-years. Factors independently associated with increased risk of incident STI included younger age [≥ 50 vs. 30-39 years old, adjusted hazards ratio (aHR) 0.4; 95% CI 0.2-0.8; P < 0.0001]; prior STI infection (aHR 2.5; 95% CI 1.6-3.8; P < 0.001), and heterosexual vs. men who have sex with men (MSM) as the likely route of exposure (aHR 0.2; 95% CI 0.1-0.6; P < 0.001).

CONCLUSIONS

In this cohort of individualsbeing treated with antiretroviral drugs, those who were MSM, who were 30-39 years old, and who had a prior history of STI, were at highest risk of a further STI diagnosis.

Cervical cancer screening and abnormalities among women in a residential drug-rehabilitation program

Women in a residential drug-rehabilitation program had lower rates of cervical screening attendance and higher rates ofdetected abnormalities than women attending a local Well Women's Clinic. As a result ofthis study we plan to include a more comprehensive sexual health history into routine women's health consultations.

Cancer, immunodeficiency and antiretroviral treatment: results from the Australian HIV Observational Database (AHOD)

OBJECTIVES

The objective of the study was to conduct a within-cohort assessment of risk factors for incident AIDS-defining cancers (ADCs) and non-ADCs (NADCs) within the Australian HIV Observational Database (AHOD).

METHODS

A total of 2181 AHOD registrants were linked to the National AIDS Registry/National HIV Database (NAR/NHD) and the Australian Cancer Registry to identify those with a notified cancer diagnosis. Included in the current analyses were cancers diagnosed after HIV infection. Risk factors for cancers were also assessed using logistic regression methods.

RESULTS

One hundred and thirty-nine cancer cases were diagnosed after HIV infection among 129 patients. More than half the diagnoses (n = 68; 60%) were ADCs, of which 69% were Kaposi's sarcoma and 31% non-Hodgkin's lymphoma. Among the NADCs, the most common cancers were melanoma (n = 10), lung cancer (n = 6), Hodgkin's lymphoma (n = 5) and anal cancer (n = 5). Over a total of 21021 person-years (PY) of follow-up since HIV diagnosis, the overall crude cancer incidence rate for any cancer was 5.09/1000 PY. The overall rate of cancers decreased from 15.9/1000 PY [95% confidence interval (CI) 9.25-25.40/1000 PY] for CD4 counts < 100 cells/μL to 2.4/1000 PY (95% CI 1.62-3.39/1000 PY) for CD4 counts > 350 cells/μL. Lower CD4 cell count and prior AIDS diagnoses were significant predictors for both ADCs and NADCs.

CONCLUSIONS

ADCs remain the predominant cancers in this population, although NADC rates have increased in the more recent time period. Immune deficiency is a risk factor for both ADCs and NADCs.

Self-report is a valid measure of circumcision status in homosexual men

OBJECTIVE

Misreporting of circumcision status may affect observed relationships between circumcision status and HIV or other sexually transmissible infections. As no data exist on the validity of self-reported circumcision status among homosexual men, we investigated the agreement between self-report and examination findings in a subgroup of participants in the Health in Men (HIM) study in Sydney, Australia.

METHODS

A subgroup of 240 participants in the community based HIM cohort study attending annual interview agreed to a brief genital examination by a trained study nurse who was unaware of their previous self-reported circumcision status.

RESULTS

Five participants reported being uncircumcised at baseline but were classified as circumcised on examination. All participants who self-reported being circumcised were found on examination to be circumcised. Three cases in which the examining study nurse was unsure of participants' circumcision status were excluded. Of the remaining 237 participants, 155 (65.4%) were classified as circumcised on examination, including five men who self identified as uncircumcised. Compared with examination, self-reported circumcision status resulted in a sensitivity of 96.8%, specificity of 100%, positive predictive value of 100% and negative predictive value of 94.3%. The overall agreement between circumcision status on examination and self-report was 97.9% (kappa score, 0.95; p<0.001)

CONCLUSION

Self-report was a valid measure of circumcision status in this group of predominantly Anglo gay-community-attached men. We believe our findings can be generalised to similarly aged gay-community-attached men in other developed countries.

Incidence and risk factors for urethral and anal gonorrhoea and chlamydia in a cohort of HIV-negative homosexual men: the Health in Men Study

BACKGROUND

Early detection and treatment of bacterial sexually transmitted infections has been advocated as an HIV prevention strategy.

AIM

To inform screening guidelines, the incidence and risk factors for urethral and anal gonorrhoea and chlamydia were studied in a prospective cohort of community-based HIV negative homosexual men in Sydney, New South Wales, Australia.

METHODS

All participants were offered annual screening for gonorrhoea and chlamydia (study-visit diagnoses) on urine and anal swabs using nucleic acid amplification. Participants also reported diagnoses of gonorrhoea and chlamydia made elsewhere between interviews (interval diagnoses). All diagnoses were summed to create a combined incidence rate, and detailed data on specific sexual practices with casual and regular partners were collected.

RESULTS

Among 1427 men enrolled, the combined incidence rates were 3.49 and 2.96 per 100 person-years for urethral and anal gonorrhoea, respectively; and 7.43 and 4.98 per 100 person-years for urethral and anal chlamydia, respectively. Urethral infections were associated with unprotected anal intercourse (UAI) with HIV-positive partners (hazard ratio (HR) = 2.58, 95% CI 1.10 to 6.05 for urethral gonorrhoea) and with frequent insertive oral sex (p for trend 0.007 for urethral chlamydia). Anal infections were associated with receptive UAI (p for trend 0.001 for both anal gonorrhoea and chlamydia) and other receptive anal sexual practices. Stratified analyses showed the independence of the associations of insertive oral sex with urethral infections and of non-intercourse receptive anal practices with anal infections.

CONCLUSION

Incident gonorrhoea and chlamydia were common. Risk behaviours for both urethral and anal infections were not restricted to UAI. Screening that includes tests for anal and urethral infections should be considered for all sexually active homosexual men, not just for those who report UAI.

65. CIRCUMCISION STATUS AND RISK OF SEXUALLY TRANSMITTED INFECTIONS IN THE HIM COHORT OF HOMOSEXUAL MEN IN SYDNEY, AUSTRALIA

Objectives: To examine circumcision status as an independent risk factor for prevalent and incident sexually transmitted infections (STIs) in the community-based Health in Men (HIM) cohort of homosexual men. Methods: Between 2001 and 2004, 1427 initially HIV-negative men were enrolled. Circumcision status was self-reported at baseline and was validated by clinical examination in a sub-sample of participants. All participants were tested annually for HIV and offered testing for other STIs including nucleic acid amplification tests (NAAT) for urethral gonorrhoea and chlamydia, and serology for syphilis and herpes simplex virus (HSV). Demographic information and past history of STIs was collected at baseline and detailed information on sexual risk behaviours was collected every 6 months. At annual face-to-face visits, participants reported diagnoses of STIs made in the previous 12 months. Results: At baseline, 66% of participants reported being circumcised; mostly as infants. Uptake of STI testing was high with over 90% of participants tested each year. On multivariate analysis, controlling for age and sexual risk behaviour, circumcision was not associated with baseline seropositivity to syphilis (p�=�0.34), HSV1 (p�=�0.33) or HSV2 (p�=�0.92), nor with a history of self-reported genital warts (p�=�0.18). There was also no association with incident bacterial urethral infections (p�=�0.67 & p�=�0.89 for gonorrhoea and chlamydia, respectively), self-reported incident genital warts (p�=�0.35), incident HSV1 (p�=�0.70) or incident HSV2 (p�=�0.36). However, circumcision was associated with a significantly reduced risk of incident syphilis after controlling for age, number of casual partners in the previous 6 months and unprotected anal intercourse according to partners' HIV status (HR�=�0.35, 95% CI 0.14-0.87, p�=�0.024). Conclusion: Circumcised men had a reduced risk of incident syphilis in this cohort. Although most STIs were not associated with circumcision, these data suggest that circumcision may have an effect on syphilis acquisition in homosexual men.

41. CIRCUMCISION AND RISK OF HIV SEROCONVERSION IN THE HIM COHORT OF HOMOSEXUAL MEN IN SYDNEY

Objectives: We examined circumcision as a risk factor for HIV seroconversion in a community-based cohort of homosexual men in Sydney. Methods: Between 2001 and 2004, 1427 initially HIV-negative men were enrolled. Circumcision status was self-reported at baseline, and self-report was validated by clinical examination during study visits in a sub-sample of approximately 300 participants. All participants were tested annually for HIV and offered testing for other sexually transmitted infections (STIs). Detailed information on sexual risk behaviours was collected every 6 months. Results: At baseline, 66% of participants reported being circumcised; mostly as infants. The proportion circumcised ranged from 83% in those aged 45 or more to only 50% in those aged less than 25 (p�<�0.0001). There were 49 HIV seroconversions through 2006, an incidence of 0.80 per 100 person years (PY). Anorectal gonorrhoea and anal warts were independent risk factors for HIV infection. Overall, being circumcised was not related to HIV infection (relative risk (RR) 1.07, 95% CI 0.56-2.06). After controlling for non-concordant unprotected anal intercourse (UAI), anorectal STIs and age, there remained no association with circumcision (RR�=�0.88, 95% CI 0.45-1.74). Only nine of the 49 seroconversions occurred among men who reported no receptive UAI, an incidence of 0.35 per 100PY. In this group, circumcision was also not associated with HIV seroconversion (RR�=�0.99, 95% CI 0.25-3.96). Conclusion: Overall, circumcision status was not associated with HIV seroconversion. In addition, analyses limited to those men who reported no receptive UAI, who are more likely to have been infected through insertive sex, suggest that circumcision may not reduce HIV risk even for insertive anal intercourse. Other preventive strategies are required to reduce HIV incidence in homosexual men.

25. ANAL SEXUALLY TRANSMISSIBLE INFECTIONS AS RISK FACTORS FOR HIV SEROCONVERSION

Objectives: Sexually transmitted infections (STIs) are believed to increase the risk of HIV acquisition, but few studies have focused on homosexual men. We examined sexual behaviour and common STIs as independent risk factors for HIV seroconversion in a community-based cohort of homosexual men in Sydney. Methods: Between 2001 and 2004, 1427 initially HIV-negative men were enrolled. They were tested annually for HIV, for gonorrhoea and chlamydia in the urethra and anus (strand displacement amplification, BDProbeTec), and for herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) using type specific ELISA. Participants also reported diagnoses of STIs since their last interview. Detailed information on sexual risk behaviours was collected every 6 months. Results: There were 49 HIV seroconversions through 2006, an incidence of 0.80 per 100PY. A higher number of episodes of insertive and receptive unprotected anal intercourse (UAI) with HIV positive or HIV status unknown partners was each significantly associated with HIV seroconversion. In multivariate analysis of behavioural risk factors, HIV seroconversion was significantly associated with a higher number of episodes of receptive UAI with a partner of unknown HIV status (p trend <0.001) or with a partner known to be HIV positive (p trend <0.001). After controlling for these sexual behaviours, a study diagnosis of anal gonorrhoea remained strongly related to HIV seroconversion (RR�=�7.41, 95% CI 1.75-31.75). Most cases of anal gonorrhoea diagnosed were asymptomatic. In addition, there was an independent association with anal warts (RR�=�3.43, 95% CI 1.43-8.19), and prevalent HSV-1 infection was of borderline significance (RR�=�2.78, 95% CI 0.99-7.80). Conclusion: Certain anal STIs were associated with HIV seroconversion, even after adjustment for UAI. For some anal conditions, in particular gonorrhoea, infection was frequently asymptomatic. Screening for anal STIs should be investigated as a potential HIV prevention intervention.

Mechanisms involved in stimulation of human immunodeficiency virus type 1 replication by aminooxypentane RANTES

Aminooxypentane (AOP)-RANTES is a potent inhibitor of nonsyncytium-inducing (NSI), CCR5-tropic (R5) human immunodeficiency virus type 1 (HIV-1) isolates. Although classical chemotactic responses are not induced in primary leukocytes by AOP-RANTES, recent studies suggest that a remnant of cell signaling occurs upon binding of receptor to this compound. We have detected a breakthrough of NSI/R5 replication from the inhibitory effects of high AOP-RANTES concentrations (<100 nM). A stimulation of different primary syncytium-inducing (SI), CXCR4-tropic (X4) HIV-1 isolates was also observed in the presence of AOP-RANTES. This stimulation was also observed after 110 h in PCR and RT-PCR for minus-strand strong-stop DNA and unspliced and multiply spliced RNA, respectively. However, there was significant variability between different SI/X4 or NSI/R5 HIV-1 isolates with regard to this AOP-RANTES-mediated stimulation or breakthrough, respectively. To further define the mechanism(s) responsible for this AOP-RANTES effect, we performed detailed retroviral replication studies with an NSI/R5 (B-92BR021) and SI/X4 (D-92UG021) HIV-1 isolate in the presence of the drug. Treatment of peripheral blood mononuclear cells with 125 nM AOP-RANTES and virus did not alter coreceptor expression, HIV-1 entry, reverse transcription, or mRNA transcription from the long terminal repeat, but it did result in increased HIV-1 integration. This AOP-RANTES-mediated increase in HIV-1 integration was diminished by treatment with pertussis toxin. Phosphorylation of the mitogen-activated protein kinase (MAPK) isoforms, extracellular signal-regulated kinase 1 (ERK1) and ERK2, was increased in a CD4(+) CCR5(+) U87 cell line treated with AOP-RANTES or with an NSI/R5 HIV-1 isolate. These findings suggest that AOP-RANTES may induce a MAPK/ERK signal transduction pathway upon binding to a G-protein-coupled receptor. MAPK/ERK1 and -2 appear to phosphorylate the HIV-1 preintegration complex, a step necessary for nuclear translocation and successful integration.

Protein kinases: getting NEKed for S6K activation

The 70/85 kDa ribosomal protein S6 kinase is regulated through the concerted actions of multiple phosphatases and kinases. A newly identified S6 kinase kinase, NEK6, appears to provide the penultimate activation step.

Cell cycle-dependent localization of the CDK2-cyclin E complex in Cajal (coiled) bodies

We have found that CDK2 and cyclin E, but not cyclin A, accumulates within Cajal bodies (CBs) in a cell cycle-dependent fashion. In the absence of cyclin E, CDK2 is not enriched in the CB compartment, suggesting that the translocation of CDK2 to CBs is dependent on cyclin E. CDK2 and cyclin E could be recruited to CBs as a functional complex or CBs may serve as ‘docking stations’ for CDK2-cyclin E activation by CAKs during the G(1)/S transition. Notably, CDK7-cyclin H-Mat1 complexes are known to accumulate in CBs. Treatment of cells with inhibitors of either CDKs (olomoucine, 200 microM) or RNA polymerase I (actinomycin D, 0.05 microgram/ml), results in a striking reorganization of CDK2 and p80 coilin to the nucleolar periphery. Furthermore, we demonstrate that p80 coilin can be phosphorylated by purified CDK2-cyclin E complexes in vitro. Thus coilin and other CB proteins appear to be downstream targets of CDK2-cyclin E complex-mediated signaling pathways regulating cell cycle progression and controlling aspects of CB function. Possible roles for CDK2 and cyclin E in the well-documented association of CBs, histone gene clusters and RNA 3′ end processing factors are discussed.

Quinone reductase (NQO1), a sensitive redox indicator, is increased in Alzheimer's disease

NAD(P)H:quinone oxidoreductase 1 (NQO1), a redox-regulated flavoenzyme, plays a central role in monitoring cellular redox state. NQO1 acts to protect against oxidative stress induced by a variety of metabolic situations, including metabolism of quinones and other xenobiotics, by: (i) functioning as a two electron donor to provide a shunt that competes with the formation of reactive oxygen species; (ii) maintaining reduced coenzyme Q; and (iii) regulating the stress activated kinase pathway. In Alzheimer's disease, while there is abundant evidence for the involvement of oxidative stress, the cause or the consequences are largely unresolved. We suspected that increased NQO1 could signal a major shift in redox balance in Alzheimer's disease and, in this study, found that NQO1 is localized not only to neurofibrillary tangles but also the cytoplasm of hippocampal neurons. By marked contrast, there is very little NQO1 in the same neuronal populations in young and age-matched controls. This novel association of NQO1 further buttresses the nexus of oxidative stress, via free radicals, with selective neuronal vulnerability and also supports a fundamental abnormality in redox balance in Alzheimer's disease.

Quinone reductase inhibitors block SAPK/JNK and NFkappaB pathways and potentiate apoptosis

A variety of environmental stresses stimulate the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEKK) > stress-activated protein kinase (SAPK)-ERK kinase (SEK) > SAPK/c-Jun NH(2)-terminal kinase (JNK) stress-activated protein kinase cascade and coordinately activate the transcription factor NFkappaB. Mechanisms of stress activation upstream of MEKK1 have not been precisely determined. Redox mechanisms involving sulfhydryls are likely because N-acetyl-cysteine at millimolar concentrations blocks stress signals. Because intracellular sulfhydryl concentrations can be regulated through redox cycling involving reactive quinones (1), we tested the ability of quinone reductase inhibitors to alter stress signaling. Several quinone reductases are inhibited by dicoumarol, a coumarin derivative. Dicoumarol prevented SAPK activation in vivo by chemical cell stressors and also prevented SAPK activation induced by expression of the tumor necrosis factor alpha (TNFalpha) receptor-associated protein TRAF2 but not by expression of truncated active MEKK1. Other coumarin derivatives failed to block SAPK activation, but other inhibitors of quinone reductases, particularly menadione, similarly blocked SAPK activation. Cells deficient in a major quinone reductase, NQO1, displayed hypersensitivity to dicoumarol stress inhibition, whereas SAPK in cells reconstituted with the NQO1 gene displayed relative dicoumarol resistance. Consistent with the proposed role of overlapping upstream signaling cascades in activation of NFkappaB, dicoumarol also blocked NFkappaB activation in primary macrophages stimulated with either lipopolysaccharide or TNFalpha. In addition, dicoumarol strongly potentiated TNFalpha-induced apoptosis in HeLa cells, probably by blocking the anti-apoptotic effect of NFkappaB. The ability of dicoumarol to simultaneously inhibit SAPK and NFkappaB activation and to potentiate apoptotic cell death suggests that SAPK is not an obligate participant in apoptosis. Dicoumarol, currently in clinical use as an oral anticoagulant, represents a potential therapeutic inhibitor of the SAPK and NFkappaB response.

Deficiency of Transporter for Antigen Presentation (TAP) in Tumor Cells Allows Evasion of Immune Surveillance and Increases Tumorigenesis

Proteins involved in class I MHC (MHC-I) Ag processing, such as the TAP, are deficient in some human tumor cells. This suggests that antitumor responses by CD8 T cells provide selection pressure to favor outgrowth of cells with defective processing of tumor Ags. Nonetheless, this evidence is only correlative, and controlled in vivo experiments have been lacking to demonstrate that TAP deficiency promotes survival of tumor cells. To explore the role of Ag processing defects in tumor progression, matched panels of TAP1-positive and TAP1-negative tumor cell lines were generated from a parental transformed murine fibroblast line. Inoculation of C57BL/6 mice with TAP1-negative cells produced large and persistent tumors. In contrast, TAP1-positive cells did not generate lasting tumors, although small tumors were detected transiently and regressed spontaneously. Both TAP1-positive and TAP1-negative cells produced tumors in athymic mice, confirming that TAP-dependent differences in tumorigenicity were due to T cell-dependent immune responses. Inoculation of C57BL/6 mice with mixtures of TAP1-positive and TAP1-negative cells produced tumors composed exclusively of TAP1-negative cells, indicating in vivo selection for cells with TAP deficiency. Thus, loss of TAP function allows some tumor cells to avoid T cell-dependent elimination, resulting in selection for tumor cells with deficient Ag processing.

Deficiency of transporter for antigen presentation (TAP) in tumor cells allows evasion of immune surveillance and increases tumorigenesis

Proteins involved in class I MHC (MHC-I) Ag processing, such as the TAP, are deficient in some human tumor cells. This suggests that antitumor responses by CD8 T cells provide selection pressure to favor outgrowth of cells with defective processing of tumor Ags. Nonetheless, this evidence is only correlative, and controlled in vivo experiments have been lacking to demonstrate that TAP deficiency promotes survival of tumor cells. To explore the role of Ag processing defects in tumor progression, matched panels of TAP1-positive and TAP1-negative tumor cell lines were generated from a parental transformed murine fibroblast line. Inoculation of C57BL/6 mice with TAP1-negative cells produced large and persistent tumors. In contrast, TAP1-positive cells did not generate lasting tumors, although small tumors were detected transiently and regressed spontaneously. Both TAP1-positive and TAP1-negative cells produced tumors in athymic mice, confirming that TAP-dependent differences in tumorigenicity were due to T cell-dependent immune responses. Inoculation of C57BL/6 mice with mixtures of TAP1-positive and TAP1-negative cells produced tumors composed exclusively of TAP1-negative cells, indicating in vivo selection for cells with TAP deficiency. Thus, loss of TAP function allows some tumor cells to avoid T cell-dependent elimination, resulting in selection for tumor cells with deficient Ag processing.

Osmotic stress inhibits p70/85 S6 kinase through activation of a protein phosphatase

While studying the stress regulation of p70/85 S6 kinase (S6K), we observed that anisomycin and UV light stimulated S6K activity, but that sorbitol inactivated S6K. Pretreatment with hyperosmotic stress also prevented the activation of S6K by both 12-O-tetradecanoylphorbol-13-acetate and anisomycin. Comparison of sorbitol and rapamycin revealed that both agents inactivated S6K and caused dephosphorylation of Ser/Thr-Pro sites in the COOH terminus of S6K, including Thr(412), a residue essential to S6K regulation, as determined by phospho-specific antibodies. Rapamycin-resistant S6K truncation mutants were similarly resistant to deactivation by sorbitol. Additionally, the PHAS-1 mobility shift, which is sensitive to rapamycin, was also found to be sensitive to osmotic stress. Experiments using the p38 inhibitor SB203580 and dominant negative mutants involving both stress-activated protein kinase/c-Jun NH(2)-terminal kinase and p38 stress pathways indicated that these pathways are probably not involved in osmotic stress inhibition of S6K. Examining the potential involvement of a phosphatase, we found that sodium pyrophosphate, sodium vanadate, cyclosporin A, tautomycin, and okadaic acid had no effect on osmotic stress inhibition of S6K. However, calyculin A prevented both rapamycin- and sorbitol-mediated deactivation of S6K. Our results suggest that osmotic stress and rapamycin act through a calyculin A-sensitive phosphatase to cause dephosphorylation and deactivation of S6K.

Functional interactions between herpesvirus oncoprotein MEQ and cell cycle regulator CDK2

Marek's disease virus, an avian alphaherpesvirus, has been used as an excellent model to study herpesvirus oncogenesis. One of its potential oncogenes, MEQ, has been demonstrated to transform a rodent fibroblast cell line, Rat-2, in vitro by inducing morphological transformation and anchorage- and serum-independent growth and by protecting cells from apoptosis induced by tumor necrosis factor alpha, C2-ceramide, UV irradiation, or serum deprivation. In this report, we show that there is a cell cycle-dependent colocalization of MEQ protein and cyclin-dependent kinase 2 (CDK2) in coiled bodies and the nucleolar periphery during the G1/S boundary and early S phase. To our knowledge, this is the first demonstration that CDK2 is found to localize to coiled bodies. Such an in vivo association and possibly subsequent phosphorylation may result in the cytoplasmic translocation of MEQ protein. Indeed, MEQ is expressed in both the nucleus and the cytoplasm during the G1/S boundary and early S phase. In addition, we were able to show in vitro phosphorylation of MEQ by CDKs. We have mapped the CDK phosphorylation site of MEQ to be serine 42, a residue in the proximity of the bZIP domain. An indirect-immunofluorescence study of the MEQ S42D mutant, in which the CDK phosphorylation site was mutated to a charged residue, reveals more prominent cytoplasmic localization. This lends further support to the notion that the translocation of MEQ is regulated by phosphorylation. Furthermore, phosphorylation of MEQ by CDKs drastically reduces the DNA binding activity of MEQ, which may in part account for the lack of retention of MEQ oncoprotein in the nucleus. Interestingly, the localization of CDK2 in coiled bodies and the nucleolar periphery is observed only in MEQ-transformed Rat-2 cells, implicating MEQ in modifying the subcellular localization of CDK2. Taken together, our data suggest that there is a novel reciprocal modulation between the herpesvirus oncoprotein MEQ and CDK2.

Paclitaxel (Taxol)-induced gene expression and cell death are both mediated by the activation of c-Jun NH2-terminal kinase (JNK/SAPK)

Paclitaxel (Taxol) is a novel anti-cancer drug that has shown efficacy toward several malignant tumors, particularly ovarian tumors. We reported previously that paclitaxel can induce interleukin (IL)-8 promoter activation in subgroups of ovarian cancer through the activation of both AP-1 and nuclear factor kappaB. Further analysis of paclitaxel analogs indicates that the degree of IL-8 induction by analysis correlates with the extent of cell death; however, IL-8 itself is not the cause of cell death. This suggests that pathways that lead to IL-8 and cell death may overlap, although IL-8 per se does not kill tumor cells. To decipher the upstream signals for paclitaxel-induced transcriptional activation and cell death, we studied the involvement of protein kinases that lead to the activation of AP-1, specifically the c-Jun NH2-terminal kinase (JNK1), p38, and the extracellular signal-regulated kinase 1 (ERK1). The role of IkappaB in paclitaxel-induced cell death was also analyzed. Paclitaxel activated JNK, and to a lesser degree p38, but not ERK1. Paclitaxel-induced IL-8 promoter activation was inhibited by dominant-inhibitory mutants of JNK, p38, and the super-repressor form of IkappaBalpha, but not by dominant-inhibitory forms of ERK1. Dominant-inhibitory mutants of JNK1 also greatly reduced paclitaxel-induced cell death, and the kinetics of JNK induction was closely followed by DNA fragmentation. These results indicate (i) that paclitaxel activates the JNK signaling pathway and (ii) that JNK activation is a common point of paclitaxel-induced gene induction and cell death.

Induction of cyclooxygenase-2 by the activated MEKK1 --> SEK1/MKK4 --> p38 mitogen-activated protein kinase pathway

The mitogen-activated protein kinase (MAPK) cascade is believed to function as an important regulator of prostaglandin biosynthesis. Previously we reported that interleukin-1beta induces activation of JNK/SAPK and p38 MAPK with concomitant up-regulation of cyclooxygenase (Cox)-2 expression and prostaglandin E2 (PGE2) synthesis. Our experiments demonstrate that overexpression of DeltaMEKK1 (a constitutively active truncation mutant of MEKK1 containing the C-terminal 324 amino acids) increases Cox-2 expression and PGE2 production which is completely blocked by SC68376, a pharmacologic inhibitor of p38 MAPK. DeltaMEKK1 overexpression results in activation of both c-Jun N-terminal kinases/extracellular signal-regulated kinases (JNK/SAPK) and p38 MAPK. Furthermore, activation of MEKK1 increases SEK1/MKK4 but not MKK3 or MKK6 activity. These findings suggest that MEKK1 --> SEK1/MKK4 may function as an upstream kinase capable of activating both p38 MAPK and JNK/SAPK with subsequent induction of Cox-2 expression and PGE2 production. We also found that overexpression of the constitutively active form of SEK1 (SEK1-ED) increases both p38 MAPK and JNK/SAPK phosphorylation, and increases PGE2 production and Cox-2 expression. By comparison, overexpression of the dominant negative form of SEK1 (SEK1-AL) decreases the phosphorylation of both p38 MAPK and JNK/SAPK and reduces Cox-2 expression. Together, this data suggests a potential role for the MEKK1 --> SEK1/MKK4 --> p38 MAPK -->--> Cox-2 cascade linking members of the MAPK pathway with prostaglandin biosynthesis.

Fas-induced proteolytic activation and intracellular redistribution of the stress-signaling kinase MEKK1

The stress-activated protein kinase (SAPK, alternatively JNK) is activated rapidly by cell stress stimuli such as inflammatory cytokines and oxidative stress, and more slowly by the initiation of the apoptotic cell death response by events such as ligation of the Fas protein. Mitogen-activated protein kinase/Erk kinase kinase-1 (MEKK1) is an activator of SAPK, serving as a SAPK-kinase-kinase through intermediate phosphorylation of the SAPK kinase SEK1. By sequencing proteolytic cleavage products of MEKK1, we found that the proapoptotic protease caspase 3 (CPP32) cleaves MEKK1 after residue D68 both in vivo and in vitro. Cleavage of MEKK1 after D68 is blocked by viral and chemical protease inhibitors. Cleavage of MEKK1 at D68 changes the intracellular distribution of the protein from a Triton-insoluble compartment to a Triton-soluble compartment, reflected in a redistribution from a particulate to a diffuse cytoplasmic staining seen by immunofluorescence. Activation of both SAPK and MEKK1 after Fas ligation is prevented by both viral and chemical caspase 3 inhibitors, which in contrast fail to block activation of SAPK by rapidly acting cell stresses. Stress factor-induced SAPK signaling is not dependent on caspase 3 function. We propose that two mechanisms of stress signaling through MEKK1 exist. One is rapid, independent of proteases, and occurs in the particulate Triton-insoluble compartment. The other is more slowly activated and involves liberation of particulate MEKK1 by proteolytic cleavage and activation by caspase 3.

Regulation of the activity of MEK kinase 1 (MEKK1) by autophosphorylation within the kinase activation domain

MEK kinase 1 (MEKK1) shares sequence identity with the yeast kinases Ste11 and Byr2, and is capable of phosphorylation and activation of both mitogen-activated protein/extracellular signal-related protein kinase (MAP/ERK) kinase (MEK) and stress-activated protein kinase (SAPK)/ERK kinase (SEK) in vitro. In vivo, however, MEKK1 predominantly activates the SEK/SAPK kinase cascade. Mechanisms of activation of MEKK1 are unclear. We have identified a major site of autophosphorylation (Thr-575) within the 'activation loop' of MEKK1 between the kinase subdomains VII and VIII. Phosphatase treatment of a constitutively active MEKK1 decreased kinase activity by 59%. Dephosphorylated T575 was rapidly re-(auto)phosphorylated by MEKK1. Mutation of T575 to alanine decreased MEKK1 transphosphorylation activity with a SEK substrate to approx. 30% of wild-type. Mutation of a second threonine residue (Thr-587) to alanine eliminated the phosphorylation of MEK or SEK substrate but not autophosphorylation. MEKK1 autophosphorylation is an intramolecular reaction because active MEKK1 cannot transphosphorylate a kinase-inactive MEKK1. Inactive MEKK1 was not phosphorylated on Thr-575 within cells, suggesting that the phosphorylation of Thr-575 in vivo results from autophosphorylation rather than phosphorylation by an upstream kinase. Autoactivation of MEKK1 via autophosphorylation of Thr-575 might be an immediate response to initial kinase activation through non-phosphorylation mechanisms.

The cyclin box and C-terminus of cyclins A and E specify CDK activation and substrate specificity

The cyclins and their catalytic partners, the Cyclin Dependent Kinases (CDKs), are essential for progression through the cell cycle. Cyclin/kinase complexes containing cyclins A or E are active primarily in late G1 to S phase and both have been shown to phosphorylate histone H1 and the retinoblastoma gene product (pRb) in vitro. Despite these similarities, cyclins A and E display differences in CDK activation and substrate specificity. We find that in vitro, cyclin E/CDK2 and cyclin A/CDK2 phosphorylate histone H1 similarly but only cyclin A/CDK2 phosphorylates lamin B. While both cyclin A and cyclin E bind CDK1 efficiently, only cyclin A activates CDK1 kinase activity. Using chimeric proteins between cyclins A and E we find that both the cyclin box and C-terminus of cyclins A and E are required for CDK binding, activation and targeting of substrate specificity.

Activation of SAPK/JNK by TNF receptor 1 through a noncytotoxic TRAF2-dependent pathway

Interaction of the p55 tumor necrosis factor receptor 1 (TNF-R1)-associated signal transducer TRADD with FADD signals apoptosis, whereas the TNF receptor-associated factor 2 protein (TRAF2) is required for activation of the nuclear transcription factor nuclear factor kappa B. TNF-induced activation of the stress-activated protein kinase (SAPK) was shown to occur through a noncytotoxic TRAF2-dependent pathway. TRAF2 was both sufficient and necessary for activation of SAPK by TNF-R1; conversely, expression of a dominant-negative FADD mutant, which blocks apoptosis, did not interfere with SAPK activation. Therefore, SAPK activation occurs through a pathway that is not required for TNF-R1-induced apoptosis.

Mammalian mitogen-activated protein kinase pathways are regulated through formation of specific kinase-activator complexes

Mammalian cells contain at least three signaling systems which are structurally related to the mitogen-activated protein kinase (MAPK) pathway. Growth factors acting through Ras primarily stimulate the Raf/MEK/MAPK cascade of protein kinases. In contrast, many stress-related signals such as heat shock, inflammatory cytokines, and hyperosmolarity induce the MEKK/SEK(MKK4)/SAPK(JNK) and/or the MKK3 or MKK6/p38(hog) pathways. Physiological agonists of these pathway types are either qualitatively or quantitatively distinct, suggesting few common proximal signaling elements, although past studies performed in vitro, or in cells using transient over-expression, reveal interaction between the components of all three pathways. These studies suggest a high degree of cross-talk apparently not seen in vivo. We have examined the possible molecular basis of the differing agonist profiles of these three MAPK pathways. We report preferential association between MAP kinases and their activators in eukaryotic cells. Furthermore, using the yeast 2-hybrid system, we show that association between these components can occur independent of additional eukaryotic proteins. We show that SAPK(JNK) or p38(hog) activation is specifically impaired by co-expression of cognate dominant negative MAP kinase kinase mutants, demonstrating functional specificity at this level. Further divergence and insulation of the stress pathways occurs proximal to the MAPK kinases since activation of the MAPK kinase kinase MEKK results in SAPK(JNK) activation but does not cause p38(hog) phosphorylation. Therefore, in intact cells, the three MAPK pathways may be independently regulated and their components show specificity in their interaction with cognate cascade members. The degree of intermolecular specificity suggests that mammalian MAPK signaling pathways may remain distinct without the need for specific scaffolding proteins to sequester components of individual pathways.

Sphingolipid metabolites differentially regulate extracellular signal-regulated kinase and stress-activated protein kinase cascades

The mitogen-activated protein kinase (MAPK) signalling pathway serves to translocate information from activated plasma-membrane receptors to initiate nuclear transcriptional events. This cascade has recently been subdivided into two analogous pathways: the extracellular signal-regulated kinase (ERK) cascade, which preferentially signals mitogenesis, and the stress-activated protein kinase (SAPK) cascade, which is linked to growth arrest and/or cellular inflammation. In concurrent experiments utilizing rat glomerular mesangial cells (MCs), we demonstrate that growth factors or sphingosine activate ERK but not SAPK. In contrast, inflammatory cytokines or cell-permeable ceramide analogues activate SAPK but not ERK. Ceramide, but not sphingosine, induces interleukin-6 secretion, a marker of an inflamed phenotype. Moreover, ceramide can suppress growth factor- or sphingosine-induced ERK activation as well as proliferation. These studies implicate sphingolipid metabolites as opposing regulators of cell proliferation and inflammation through activation of separate kinase cascades.

Raf, but not MEK or ERK, is sufficient for differentiation of hippocampal neuronal cells

To elucidate signal transduction pathways leading to neuronal differentiation, we have investigated a conditionally immortalized cell line from rat hippocampal neurons (H19-7) that express a temperature sensitive simian virus 40 large T antigen. Treatment of H19-7 cells with the differentiating agent basic fibroblast growth factor at 39 degrees C, the nonpermissive temperature for T function, resulted in the activation of c-Raf-1, MEK, and mitogen-activated protein (MAP) kinases (ERK1 and -2). To evaluate the role of Raf-1 in neuronal cell differentiation, we stably transfected H19-7 cells with v-raf or an oncogenic human Raf-1-estrogen receptor fusion gene (deltaRaf-1:ER). deltaRaf-1:ER transfectants in the presence of estradiol for 1 to 2 days expressed a differentiation phenotype only at the nonpermissive temperature. However, extended exposure of the deltaRaf-1:ER transfectants to estradiol or stable expression of the v-raf construct yielded cells that extended processes at the permissive as well as the nonpermissive temperature, suggesting that cells expressing the large T antigen are capable of responding to the Raf differentiation signal. deltaRaf-1:ER, MEK, and MAP kinase activities in the deltaRaf-1:ER cells were elevated constitutively for up to 36 h of estradiol treatment at the permissive temperature. At the nonpermissive temperature, MEK and ERKs were activated to a significantly lesser extent, suggesting that prolonged MAP kinase activation may not be sufficient for differentiation. To test this possibility, H19-7 cells were transfected or microinjected with constitutively activated MEK. The results indicate that prolonged activation of MEK or MAP kinases (ERK1 and -2) is not sufficient for differentiation of H19-7 neuronal cells and raise the possibility that an alternative signaling pathway is required for differentiation of H19-7 cells by Raf.

Reconstitution of novel signalling cascades responding to cellular stresses

Mammalian cells respond to their immediate environment by inducing signal transduction cascades that regulate metabolism, secretion and gene expression. Several of these signalling pathways are structurally and organizationally related insofar as they require activation of a protein-serine kinase via it's phosphorylation on tyrosine and threonine; the archetype being mitogen-activated protein kinase (MAPK) which responds primarily to mitogenic stimuli via Ras. In contrast, two more recently identified cascades are responsive to cellular stresses such as heat, inflammatory cytokines, ischaemia and metabolic poisons. The recent identification of the components of these pathways has allowed manipulation of the stress-responsive pathways and evaluation of their physiological roles. These studies reveal a high degree of independence between the pathways not apparent from in vitro studies. Manipulation of the pathways in vivo will likely result in novel therapies for inflammatory disease and reperfusion injury.

Induction of mitogen-activated protein kinase phosphatase 1 by the stress-activated protein kinase signaling pathway but not by extracellular signal-regulated kinase in fibroblasts

The intracellular mechanisms involved in the activation of extracellular signal-regulated kinase (ERK) are relatively well understood. However, the intracellular signaling pathways which regulate the termination of ERK activity remain to be elucidated. Mitogen-activated protein kinase phosphatase 1 (MKP-1) has been shown to dephosphorylate and inactivate ERK in vitro and in vivo. In the present study, we show in NIH3T3 fibroblasts that activation of the stress-activated protein kinase (SAPK) pathway by either specific extracellular stress stimuli or via induction of MEKK, an upstream kinase of SAPK, results in MKP-1 gene expression. In contrast, selective stimulation of the ERK pathway by 12-O-tetradecanoylphorbol-13-acetate or following expression of constitutively active MEK, the upstream dual specificity kinase of ERK did not induce the transcription of MKP-1. Hence, these findings demonstrate the existence of cross-talk between the ERK and SAPK signaling cascades since activation of SAPK induced the expression of MKP-1 that can inactivate ERK. This mechanism may modulate the cellular response to stimuli which employ the SAPK signal transduction pathway.