Second generation HIV surveillance in Pakistan: policy challenges and opportunities

From 2004 to 2011, the Canada-Pakistan HIV/AIDS Surveillance Project (HASP) worked with government and non-government partners in Pakistan to design and implement an HIV second generation surveillance (SGS) system. Insights into the development of scalable cost effective surveillance methodologies, implementation, use of data for HIV prevention and human rights were gained over the course of HASP. An ideal SGS system would be affordable, able to be implemented independently by local partners and produce data that could be readily applied in policy and programmes. Flexibility in design and implementation is important to ensure that any SGS system is responsive to information needs, political changes and changes in key population dynamics and HIV epidemics. HASP's mapping methodology is innovative and widely accepted as best practice, but sustainability of the SGS system it developed is a challenge.

Patterns and trends in Pakistan's heterogeneous HIV epidemic

BACKGROUND

Considerable HIV transmission occurs among injection drug users (IDUs) in Pakistan and recently the HIV prevalence has been increasing among male (MSW), hijra (transgender; HSW) and female (FSW) sex workers. We describe past and estimate future patterns of HIV emergence among these populations in several cities in Pakistan.

METHODS

The density of these key populations per 1000 adult men was calculated using 2011 mapping data from Karachi, Lahore, Faisalabad, Larkana, Peshawar and Quetta, and surveillance data were used to assess bridging between these key populations. We used the UNAIDS Estimation and Projection Package model to estimate and project HIV epidemics among these key populations in Karachi, Lahore, Faisalabad and Larkana.

RESULTS

The density and bridging of key populations varied across cities. Lahore had the largest FSW population (11.5/1000 adult men) and the smallest IDU population (1.7/1000 adult men). Quetta had the most sexual and drug injection bridging between sex workers and IDUs (6.7%, 7.0% and 3.8% of FSW, MSW and HSW, respectively, reported injecting drugs). Model evidence suggests that by 2015 HIV prevalence is likely to reach 17-22% among MSWs/HSWs in Karachi, 44-49% among IDUs in Lahore and 46-66% among IDUs in Karachi. Projection suggests the prevalence may reach as high as 65-75% among IDUs in Faisalabad by 2025. HIV prevalence is also estimated to increase among FSWs, particularly in Karachi and Larkana.

CONCLUSIONS

There is a need to closely monitor regional and subpopulation epidemic patterns and implement prevention programmes customised to local epidemics.

Beyond internalised stigma: daily moralities and subjectivity among self-identified kothis in Karnataka, South India

The Bill and Melinda Gates Foundation has poured a tremendous amount of resources into epidemic prevention in India's high HIV prevalence zones, through their Avahan initiative. These community-centred programmes operate under the assumption that fostering community-based organisational development and empowering the community to take charge of HIV prevention and education will help to transform the wider social inequalities that inhibit access to health services. Focusing on the South Indian state of Karnataka, this paper explores a troubling set of local narratives that, we contend, hold broader implications for future programme planning and implementation. Although confronting stigma and discrimination has become a hallmark in community mobilisation discourse, communities of self-identified kothis (feminine men) who were involved in Avahan programme activities continued to articulate highly negative attitudes about their own sexualities in relation to various spheres of social life. Rather than framing an understanding of these narratives in psychological terms of 'internalized stigma', we draw upon medical anthropological approaches to the study of stigma that emphasise how social, cultural and moral processes create stigmatising conditions in the everyday lives of people. The way stigma continues to manifest itself in the self-perceptions of participants points to an area that warrants critical public health attention.

The size and distribution of key populations at greater risk of HIV in Pakistan: implications for resource allocation for scaling up HIV prevention programmes

Background

With competing interests, limited funding and a socially conservative context, there are many barriers to implementing evidence-informed HIV prevention programmes for sex workers and injection drug users in Pakistan. Meanwhile, the HIV prevalence is increasing among these populations across Pakistan. We sought to propose and describe an approach to resource allocation which would maximise the impact and allocative efficiency of HIV prevention programmes.

Methods

Programme performance reports were used to assess current resource allocation. Population size estimates derived from mapping conducted in 2011 among injection drug users and hijra, male and female sex workers and programme costs per person documented from programmes in the province of Sindh and also in India were used to estimate the cost to deliver services to 80% of these key population members across Pakistan. Cities were prioritised according to key population size.

Results

To achieve 80% population coverage, HIV prevention programmes should be implemented in 10 major cities across Pakistan for a total annual operating cost of approximately US$3.5 million, which is much less than current annual expenditures. The total cost varies according to the local needs and the purchasing power of the local currency.

Conclusions

By prioritising key populations at greatest risk of HIV in cities with the largest populations and limited resources, may be most effectively harnessed to quell the spread of HIV in Pakistan.

The organisation, operational dynamics and structure of female sex work in Pakistan

Background

Pakistan is known to have large populations of female sex workers (FSWs) with considerable geographic heterogeneity in their characteristics. In this paper, we describe the social organisation and structural patterns of female sex work in different geographic regions of Pakistan.

Methods

We report geographic and network mapping data collected among FSWs in 15 cities across Pakistan in 2011 as part of the Canada-Pakistan HIV/AIDS Surveillance Project.

Results

A total number of 89 178 FSWs were estimated in the target cities for an average of 7.2 FSWs per 1000 adult males. 55% of the estimated number of FSWs concentrated in Karachi and Lahore. Based on the operations of female sex work, two major typologies of FSWs were identified: establishment-based and non-establishment-based. FSWs were further subtyped into those operating through brothels, homes, kothikhanas, streets and by cell phone. Cities varied considerably in terms of predominance of different FSW typologies.

Conclusions

There is considerable heterogeneity among FSWs in Pakistan, geographically and in terms of operational typology. Understanding the social organisation of sex work and the influence of social-cultural and legal factors in Pakistan is essential for the design of HIV prevention programmes and other services for FSWs.

Heterogeneity of characteristics, structure, and dynamics of male and hijra sex workers in selected cities of Pakistan

BACKGROUND

We sought to describe the characteristics and operational dynamics of male sex workers (MSW) and hijra sex workers (HSWs) in 11 cities across Pakistan in 2011.

METHODS

We report descriptive statistics of self-reported sexual behaviour data from cross-sectional mapping and biological and behavioural surveys conducted among 1431 MSWs and 1415 HSWs in four cities across Pakistan in 2011.

RESULTS

While Karachi had the largest numbers of MSWs and HSWs, Quetta had the largest relative population sizes, with 3.6 MSWs per 1000 male adults and 3.3 HSWs per 1000 male adults. There was considerable variability in the proportion of HSWs who operate through deras, ranging from 2.2% in Peshawar to 62.7% in Karachi. The number of HSWs per guru varies by city, from 1.5 in Quetta to 16.5 HSWs per guru in Karachi. Among HSWs, the use of mobile phones for solicitation ranged from 37.6% in Quetta to 83% in Peshawar and among MSWs the use of mobile phones ranged from 27% in Karachi to 52% in Quetta. In Quetta, a large proportion of HSWs (41%) find clients through gurus. Client volume tended to be higher among HSWs and among both MSWs and HSWs in Quetta and Peshawar. Condom use with clients was most consistent in Quetta, with 31% of MSWs and 41% of HSWs reporting always using condoms with clients. Peshawar had the greatest proportion reporting never using condoms.

CONCLUSIONS

There is considerable geographic heterogeneity in the characteristics and operational dynamics of MSWs and HSWs across Pakistan.

Sexual behaviour, structural vulnerabilities and HIV prevalence among female sex workers in Pakistan

Background

We sought to describe differences in individual and structural vulnerabilities faced by female sex workers (FSWs) in Pakistan between 2006 and 2011, and to characterise risk factors for inconsistent condom use and HIV prevalence in this population.

Methods

To describe differences in vulnerabilities, we analysed behavioural data from serial cross-sectional surveys conducted across nine cities in 2006 and 2011. Using data from 12 cities in 2011, we used logistic regression to characterise risk factors for (a) inconsistent condom use in the past month (N=6987), and (b) HIV (N=4301).

Results

Compared to FSWs in 2006, FSWs in 2011 were significantly more likely to solicit clients via cell phones, and to report a larger client volume and anal sex with clients, but also consistent condom use with clients (30.0% vs 23.6% in 2006). In 2011, independent risk factors for inconsistent condom use with clients included: recent sexual violence, recent sex with a person who injects drugs, and absence of programme exposure. HIV prevalence was 0.63% (95% CI 0.43% to 0.92%) in 2011, and was associated with a recent history of injection drug use and absence of programme exposure.

Conclusions

While condom use with clients was higher in 2011, protective behaviours remained low and vulnerabilities related to sex work may have risen. HIV is emerging in this population and an adaptive HIV prevention programme that addresses different vulnerabilities and the intersection of sexual networks with injection drug use is needed.

Geographical and temporal variation of injection drug users in Pakistan

Objectives

We describe the characteristics of injecting drug users (IDU) in Pakistan in 2006 and 2011, and assess the heterogeneity of IDU characteristics across different cities and years as well as factors associated with HIV infection.

Methods

Cross-sectional, integrated behavioural-biological surveys of IDU were conducted in 10 cities across Pakistan in 2006 and 2011. Univariate and multivariable analyses were used to describe the differences in HIV prevalence and risk behaviours between cities and over time.

Results

Large increases in HIV prevalence among injection drug users in Pakistan were observed, with overall HIV prevalence increasing from 16.2% in 2006 to 31.0% in 2011; an increase in HIV prevalence was also seen in all geographic areas except one. There was an increase in risk behaviours between 2006 and 2011, anecdotally related to a reduction in the availability of services for IDU. In 2011, larger proportions of IDU reported injecting several times a day and using professional injectors, and fewer reported always using clean syringes. An increase in the proportion living on the street was also observed and this was associated with HIV infection. Cities differ in terms of HIV prevalence, risk profiles, and healthcare seeking behaviours.

Conclusions

There is a high prevalence of HIV among injection drug users in Pakistan and considerable potential for further transmission through risk behaviours. HIV prevention programs may be improved through geographic targeting of services within a city and for involving groups that interact with IDU (such as pharmacy staff and professional injectors) in harm reduction initiatives.

Translating knowledge from Pakistan's second generation surveillance system to other global contexts

Background

From 2004 to 2011, a collaborative project was undertaken to enhance the capacity of the Government of Pakistan to implement an effective second-generation surveillance system for HIV/AIDS, known as the HIV/AIDS Surveillance Project (HASP). In four separate rounds, behavioural questionnaires were administered among injection drug users, and female, male and hijra (transgender) sex workers. Dried blood spots were collected for HIV testing.

Methods

Through interviews with project staff in Pakistan and Canada, we have undertaken a critical review of the role of HASP in generating, using and translating knowledge, with an emphasis on capacity building within both the donor and recipient countries. We also documented ongoing and future opportunities for the translation of knowledge produced through HASP.

Results

Knowledge translation activities have included educational workshops and consultations held in places as diverse as Colombia and Cairo, and the implementation of HASP methodologies in Asia, the Middle East and sub-Saharan Africa. HASP methodologies have been incorporated in multiple WHO reports. Importantly, the donor country, Canada, has benefited in significant ways from this partnership. Operational and logistical lessons from HASP have, in turn, improved how surveillance is performed in Canada. Through this project, significant capacity was built among the staff of HASP, non-governmental organisations which were engaged as implementation partners, data coordination units which were established in each province, and in the laboratory. As is to be expected, different organisations have different agendas and priorities, requiring negotiation, at times, to ensure the success of collaborative activities. Overall, there has been considerable interest in and opportunities made for learning about the methodologies and approaches employed by HASP.

Conclusions

Generally, the recognition of the strengths of the approaches and methodologies used by HASP has ensured an appetite for opportunities of mutual learning.

Outbreaks of influenza-like illness in long-term care facilities in Winnipeg, Canada

Please cite this paper as: Mahmud et al. (2012) Outbreaks of influenza‐like illness in long‐term care facilities in Winnipeg, Canada. Influenza and Other Respiratory Viruses 10.1111/irv.12052

Background  Outbreaks of influenza‐like illness (ILI) are common in long‐term care facilities (LTCFs) and result in significant morbidity and mortality among residents.

Objectives  We describe patterns of reported ILI outbreaks in LTCFs in Winnipeg, Canada, and examine LTCF and outbreak characteristics that influence the clinical outcomes of these outbreaks.

Methods  We analyzed the electronic records of all ILI outbreaks reported by LTCFs in Winnipeg from 2003 to 2011. Outbreak duration, ILI attack rates among staff and residents, and residents’ death rates were calculated by presumed viral etiology, staff vaccination rates, type of influenza chemoprophylaxis used, and time to notification to public health.

Results  Of a total of 154 reported outbreaks, most (N = 80) were attributed to influenza, and these outbreaks tended to have higher attack and death rates among LTCF residents compared with outbreaks caused by other respiratory viruses (12) or those of unknown etiology (62). About 92% of residents and 38% of staff of the average LTCFs were vaccinated. Chemoprophylaxis was used in 57·5% of influenza outbreaks. Regardless of presumed viral etiology, outbreaks reported within 3 days of onset ended sooner and had lower attack and mortality rates among residents.

Conclusions  Influenza‐like illness outbreaks still occur among highly immunized LTCF residents, so in addition to vaccination of staff and residents, it is important to maintain competent infection control practices. Early identification and notification to public health authorities and possibly early initiation of control measures could improve clinical outcomes of ILI outbreaks.

A Kenyan newspaper analysis of the limitations of voluntary medical male circumcision and the importance of sustained condom use

BACKGROUND

Since the completion of three clinical trials indicating that voluntary medical male circumcision (VMMC) is an effective method to reduce men's chances of acquiring HIV, use of the procedure has been advocated in Kenya. Media messages shape popular understandings of the benefits and limitations of male circumcision. The objectives of this study were to (1) investigate promotion messages in a popular online newspaper to determine how the limitations of male circumcision are represented, and whether condom use is still being promoted; and (2) gain insight into popular understandings of the limitations of this new procedure through newspaper reader comments.

METHODS

A content analysis was conducted on 34 online media articles published by the Daily Nation between January 1, 2008 and December 31, 2010. Information about condom promotion, partial immunity, limitations and complications of the procedure, as well as emergent themes, were analyzed.

RESULTS

Results demonstrated an irregular and occasionally misleading presentation of these topics and a perceived lack of objective information about the risks and limitations of VMMC.

CONCLUSIONS

There is a need for governmental and non-governmental public health organizations to engage with the media to improve risk messaging.

Medical ward admissions among HIV-positive patients in Winnipeg, Canada, 2003–10

Canadian data regarding the characteristics of HIV-positive patients admitted to hospital as well as the causes and patterns of admissions remain limited. Chart reviews were performed to ascertain admission diagnosis, co-morbidities and CD4 counts among this sub-population, which had an over-representation of Aboriginal persons. Infectious diseases, particularly pneumonia, represent the most common admission diagnosis for HIV-positive persons in Winnipeg. Further, individuals presenting to hospital often have very low CD4 counts, representing significant immune suppression. Earlier HIV diagnosis and treatment in an effort to delay the onset of advanced disease and hospitalization is needed.

HIV epidemic appraisals for assisting in the design of effective prevention programmes: shifting the paradigm back to basics

BACKGROUND

To design HIV prevention programmes, it is critical to understand the temporal and geographic aspects of the local epidemic and to address the key behaviours that drive HIV transmission. Two methods have been developed to appraise HIV epidemics and guide prevention strategies. The numerical proxy method classifies epidemics based on current HIV prevalence thresholds. The Modes of Transmission (MOT) model estimates the distribution of incidence over one year among risk-groups. Both methods focus on the current state of an epidemic and provide short-term metrics which may not capture the epidemiologic drivers. Through a detailed analysis of country and sub-national data, we explore the limitations of the two traditional methods and propose an alternative approach.

METHODS AND FINDINGS

We compared outputs of the traditional methods in five countries for which results were published, and applied the numeric and MOT model to India and six districts within India. We discovered three limitations of the current methods for epidemic appraisal: (1) their results failed to identify the key behaviours that drive the epidemic; (2) they were difficult to apply to local epidemics with heterogeneity across district-level administrative units; and (3) the MOT model was highly sensitive to input parameters, many of which required extraction from non-regional sources. We developed an alternative decision-tree framework for HIV epidemic appraisals, based on a qualitative understanding of epidemiologic drivers, and demonstrated its applicability in India. The alternative framework offered a logical algorithm to characterize epidemics; it required minimal but key data.

CONCLUSIONS

Traditional appraisals that utilize the distribution of prevalent and incident HIV infections in the short-term could misguide prevention priorities and potentially impede efforts to halt the trajectory of the HIV epidemic. An approach that characterizes local transmission dynamics provides a potentially more effective tool with which policy makers can design intervention programmes.

"Google flu trends" and emergency department triage data predicted the 2009 pandemic H1N1 waves in Manitoba

OBJECTIVES

We assessed the performance of syndromic indicators based on Google Flu Trends (GFT) and emergency department (ED) data for the early detection and monitoring of the 2009 H1N1 pandemic waves in Manitoba.

METHODS

Time-series curves for the weekly counts of laboratory-confirmed H1N1 cases in Manitoba during the 2009 pandemic were plotted against the three syndromic indicators: 1) GFT data, based on flu-related Internet search queries, 2) weekly count of all ED visits triaged as influenza-like illness (ED ILI volume), and 3) percentage of all ED visits that were triaged as an ILI (ED ILI percent). A linear regression model was fitted separately for each indicator and correlations with weekly virologic data were calculated for different lag periods for each pandemic wave.

RESULTS

All three indicators peaked 1-2 weeks earlier than the epidemic curve of laboratory-confirmed cases. For GFT data, the best-fitting model had about a 2-week lag period in relation to the epidemic curve. Similarly, the best-fitting models for both ED indicators were observed for a time lag of 1-2 weeks. All three indicators performed better as predictors of the virologic time trends during the second wave as compared to the first. There was strong congruence between the time series of the GFT and both the ED ILI volume and the ED ILI percent indicators.

CONCLUSION

During an influenza season characterized by high levels of disease activity, GFT and ED indicators provided a good indication of weekly counts of laboratory-confirmed influenza cases in Manitoba 1-2 weeks in advance.

Estimated cumulative incidence of pandemic (H1N1) influenza among pregnant women during the first wave of the 2009 pandemic

BACKGROUND

Hospitalization and lab confirmed cases of H1N1 have been reported during the first wave of the 2009 pandemic but these are not accurate measures of influenza incidence in the population. We estimated the cumulative incidence of pandemic (H1N1) influenza among pregnant women in the province of Manitoba during the first wave of the 2009 pandemic.

METHODS

Two panels of stored frozen serum specimens collected for routine prenatal screening were randomly selected for testing before (March 2009, n = 252) and after (August 2009, n = 296) the first wave of the pandemic. A standard hemagglutination inhibition assay was used to detect the presence of IgG antibodies against the pandemic (H1N1) 2009 virus. The cumulative incidence of pandemic (H1N1) influenza was calculated as the difference between the point prevalence rates in the first and second panels.

RESULTS

Of the specimens collected in March, 7.1% were positive for the IgG antibodies (serum antibody titre ≥ 1:40). The corresponding prevalence was 15.7% among the specimens collected in August. The difference indicated a cumulative incidence of 8.6% (95% confidence interval [CI] 3.2%-13.7%). The rate differed geographically, the highest being in the northern regions (20.8%, 95% CI 7.9%-31.8%), as compared with 4.0% (95% CI 0.0%-11.9%) in Winnipeg and 8.9% (95% CI 0.0%-18.8%) in the rest of the province.

INTERPRETATION

We estimated that the cumulative incidence of pandemic (H1N1) influenza among pregnant women in Manitoba during the first wave of the 2009 pandemic was 8.6%. It was 20.8% in the northern regions of the province.

Effects of Ape1 overexpression on cellular resistance to DNA-damaging and anticancer agents

In vitro biochemical studies indicate that Ape1 is the major mammalian enzyme responsible for repairing abasic lesions in DNA and a significant factor in the processing of specific 3'-replication-blocking termini. Toward addressing the role of Ape1 in cellular resistance to specific DNA-damaging and anticancer agents, we constructed a chinese hamster ovary (CHO) cell line, AA8-Ape1, that exhibits a 7-fold higher Ape1-dependent nuclease activity; this overexpression is abolished upon exposure to tetracycline (Tc). In comparison to the AA8 parental control, our data indicates that Ape1 activity is not rate-limiting for the repair of cytotoxic damages induced by the alkylating agent methyl methanesulfonate (MMS), the oxidizing agent hydrogen peroxide (H2O2), or ionizing radiation (IR). AA8-Ape1 cells did exhibit increased resistance to bleomycin following a chronic 3-day exposure, but not to more acute challenges of 1 h. Most notably, the AA8-Ape1 line displayed approximately 1.7-fold elevated resistance to the replication-blocking nucleoside analog dioxolane cytidine (L-OddC); this improved resistance was abrogated by the addition of Tc to the medium. These studies demonstrate that Ape1 is not rate-limiting in the repair of MMS- or H2O2-induced DNA damage, that Ape1 may dictate the sensitivity of bleomycin, depending on dosing scheme, and for the first time, that Ape1 can influence cellular resistance to the anticancer/antiviral antimetabolite L-OddC.

Restoration of nucleotide excision repair in a helicase-deficient XPD mutant from intragenic suppression by a trichothiodystrophy mutation

The UV-sensitive V-H1 cell line has a T46I substitution mutation in the Walker A box in both alleles of XPD and lacks DNA helicase activity. We characterized three partial revertants that curiously display intermediate UV cytotoxicity (2- to 2.5-fold) but normal levels of UV-induced hprt mutations. In revertant RH1-26, the efficient removal of pyrimidine (6-4) pyrimidone photoproducts from both strands of hprt suggests that global-genomic nucleotide excision repair is normal, but the pattern of cyclobutane pyrimidine dimer removal suggests that transcription-coupled repair (TCR) is impaired. To explain the intermediate UV survival and lack of RNA synthesis recovery in RH1-26 after 10 J of UV/m(2), we propose a defect in repair-transcription coupling, i.e., the inability of the cells to resume or reinitiate transcription after the first TCR event within a transcript. All three revertants carry an R658H suppressor mutation, in one allele of revertants RH1-26 and RH1-53 and in both alleles of revertant RH1-3. Remarkably, the R658H mutation produces the clinical phenotype of trichothiodystrophy (TTD) in several patients who display intermediate UV sensitivity. The XPD(R658H) TTD protein, like XPD(T46I/R658H), is codominant when overexpressed in V-H1 cells and partially complements their UV sensitivity. Thus, the suppressing R658H substitution must restore helicase activity to the inactive XPD(T46I) protein. Based on current knowledge of helicase structure, the intragenic reversion mutation may partially compensate for the T46I mutation by perturbing the XPD structure in a way that counteracts the effect of this mutation. These findings have implications for understanding the differences between xeroderma pigmentosum and TTD and illustrate the value of suppressor genetics for studying helicase structure-function relationships.

Homologous recombinational repair of DNA ensures mammalian chromosome stability

The process of homologous recombinational repair (HRR) is a major DNA repair pathway that acts on double-strand breaks and interstrand crosslinks, and probably to a lesser extent on other kinds of DNA damage. HRR provides a mechanism for the error-free removal of damage present in DNA that has replicated (S and G2 phases). Thus, HRR acts in a critical way, in coordination with the S and G2 checkpoint machinery, to eliminate chromosomal breaks before the cell division occurs. Many of the human HRR genes, including five Rad51 paralogs, have been identified, and knockout mutants for most of these genes are available in chicken DT40 cells. In the mouse, most of the knockout mutations cause embryonic lethality. The Brca1 and Brca2 breast cancer susceptibility genes appear to be intimately involved in HRR, but the mechanistic basis is unknown. Biochemical studies with purified proteins and cell extracts, combined with cytological studies of nuclear foci, have begun to establish an outline of the steps in mammalian HRR. This pathway is subject to complex regulatory controls from the checkpoint machinery and other processes, and there is increasing evidence that loss of HRR gene function can contribute to tumor development. This review article is meant to be an update of our previous review [Biochimie 81 (1999) 87].

Chromosome instability and defective recombinational repair in knockout mutants of the five Rad51 paralogs

The Rad51 protein, a eukaryotic homologue of Escherichia coli RecA, plays a central role in both mitotic and meiotic homologous DNA recombination (HR) in Saccharomyces cerevisiae and is essential for the proliferation of vertebrate cells. Five vertebrate genes, RAD51B, -C, and -D and XRCC2 and -3, are implicated in HR on the basis of their sequence similarity to Rad51 (Rad51 paralogs). We generated mutants deficient in each of these proteins in the chicken B-lymphocyte DT40 cell line and report here the comparison of four new mutants and their complemented derivatives with our previously reported rad51b mutant. The Rad51 paralog mutations all impair HR, as measured by targeted integration and sister chromatid exchange. Remarkably, the mutant cell lines all exhibit very similar phenotypes: spontaneous chromosomal aberrations, high sensitivity to killing by cross-linking agents (mitomycin C and cisplatin), mild sensitivity to gamma rays, and significantly attenuated Rad51 focus formation during recombinational repair after exposure to gamma rays. Moreover, all mutants show partial correction of resistance to DNA damage by overexpression of human Rad51. We conclude that the Rad51 paralogs participate in repair as a functional unit that facilitates the action of Rad51 in HR.

Codominance associated with overexpression of certain XPD mutations

Mutations in the XPD gene are associated with three complex clinical phenotypes, namely xeroderma pigmentosum (XP), XP in combination with Cockayne syndrome (XP-CS), and trichothiodystrophy (TTD). XP is caused by a deficiency in nucleotide excision repair (NER) that results in a high risk of skin cancer. TTD is characterized by severe developmental and neurological defects, with hallmark features of brittle hair and scaly skin, and sometimes has defective NER. We used CHO cells as a system to study how specific mutations alter the dominant/recessive behavior of XPD protein. Previously we identified the T46I and R75W mutations in two highly UV-sensitive hamster cell lines that were reported to have paradoxically high levels of unscheduled DNA synthesis. Here we report that these mutants have greatly reduced XPD helicase activity and fully defective NER in a cell-extract excision assay. We conclude that the unscheduled DNA synthesis seen in these mutants is caused by abortive "repair" that does not contribute to cell survival. These mutations, as well as the K48R canonical helicase-domain mutation, each produced codominant negative phenotypes when overexpressed in wild-type CHO cells. The common XP-specific R683W mutation also behaved in a codominant manner when overexpressed, which is consistent with the idea that this mutation may affect primarily the enzymatic activity of the protein rather than impairing protein interactions, which may underlie TTD. A C-terminal mutation uniquely found in TTD (R722W) was overexpressed but not to levels sufficiently high to rigorously test for a codominant phenotype. Overexpression of mutant XPD alleles may provide a simple means of producing NER deficiency in other cell lines.

Identification of ICR170-induced XPD mutations in UV-sensitive CHO cells

We highlight selected contributions of Dr. Richard Setlow that contributed to our earlier understanding of excision repair processes and set the stage for dissecting nucleotide excision repair (NER) in mammalian cells through molecular genetics. More than 20 years ago, large-scale screens for UV-sensitive mutants of hamster CHO cells isolated approximately 200 mutants, many of which were assigned to the XPD/ERCC2 complementation group, but the nature of the mutations was not determined. The XPD protein performs not only an essential viability function as a structural component of transcription initiation factor TFIIH, but also an NER function as a 5' to 3' DNA helicase within TFIIH that unwinds DNA on the 3' side of bulky lesions. Alterations in these XPD functions are responsible for three UV-sensitivity genetic disorders that have distinguishable clinical features. In this study, we sequenced six UV-sensitive ICR170-induced Chinese hamster ovary (CHO) cell mutants that previously were assigned to the XPD complementation group to determine whether they carry frameshift mutations. All six mutants show 3- to 5-fold increased hypersensitivity to UV irradiation, similar to the XPD mutant prototype UV5. Even though ICR170 is a strong frameshift mutagen, all six cell lines contain base substitution mutations, five of which are unique among all mutations identified so far in human and rodent cells. The sixth mutation was identical to the R75W mutation previously found in CHO UVL-1. The results presented here contribute to a mutation database that should prove useful in structure-function studies of this unique DNA-structure-specific helicase and its complex mutant phenotypes.

The Rad51 paralog Rad51B promotes homologous recombinational repair

The highly conserved Saccharomyces cerevisiae Rad51 protein plays a central role in both mitotic and meiotic homologous DNA recombination. Seven members of the Rad51 family have been identified in vertebrate cells, including Rad51, Dmc1, and five Rad51-related proteins referred to as Rad51 paralogs, which share 20 to 30% sequence identity with Rad51. In chicken B lymphocyte DT40 cells, we generated a mutant with RAD51B/RAD51L1, a member of the Rad51 family, knocked out. RAD51B(-/-) cells are viable, although spontaneous chromosomal aberrations kill about 20% of the cells in each cell cycle. Rad51B deficiency impairs homologous recombinational repair (HRR), as measured by targeted integration, sister chromatid exchange, and intragenic recombination at the immunoglobulin locus. RAD51B(-/-) cells are quite sensitive to the cross-linking agents cisplatin and mitomycin C and mildly sensitive to gamma-rays. The formation of damage-induced Rad51 nuclear foci is much reduced in RAD51B(-/-) cells, suggesting that Rad51B promotes the assembly of Rad51 nucleoprotein filaments during HRR. These findings show that Rad51B is important for repairing various types of DNA lesions and maintaining chromosome integrity.

Efficient repair of 8-oxo-7,8-dihydrodeoxyguanosine in human and hamster xeroderma pigmentosum D cells

The repair of the endogenous lesion 8-oxo-7,8-dihydrodeoxyguanosine (8-oxodG) was investigated in the nucleotide excision repair mutant xeroderma pigmentosum D (XPD), using human normal or transformed XPD fibroblasts and the Chinese hamster XPD cell line UV5. In vivo repair of 8-oxodG induced by hydrogen peroxide treatment and analyzed by high-performance liquid chromatography/electrochemical detection was normal in the XPD mutant fibroblasts XP15PV and GM434, as compared to normal human fibroblasts GM970, GM5757, and GM6114. Similar results were obtained with the human SV40-transformed XPD mutant cell line GM8207 in comparison to the control cell line GM637. Repair of 8-oxodG was even slightly (2-3-fold) but reproducibly increased in Chinese hamster XPD mutant UV5 cells, as compared to parental AA8 cells. This unexpected effect was reversed by transfection in UV5 cells of a wild-type XPD cDNA and confirmed in in vitro experiments in which a plasmid substrate containing a single 8-oxoG was repaired by UV5 cell extracts. The data show that repair of 8-oxodG is normal in XPD cells, thus indicating that the neurological complications of XPD patients may not be linked to in vivo accumulation of this lesion.