Detection of human papillomavirus in the oral cavities of persons with Fanconi anemia.

OBJECTIVE: We conducted a cross-sectional study to describe the prevalence and correlates of type-specific human papillomavirus (HPV) DNA in the oral cavities of persons with Fanconi anemia. MATERIALS AND METHODS: Oral swabs were collected from 67 participants with Fanconi anemia and tested for 27 HPV genotypes using polymerase chain reaction-based methods. RESULTS: Participants were a mean of 18.6 (standard deviation, 10.0) years of age (range 4-47 years). The prevalence of oral HPV infection was 7.5%, and the prevalence of high-risk HPV infection was 6.0%. HPV type 16 was not detected in any samples. Prevalence was higher in adults than in children (13.3% vs 2.7% in those ≥18 vs <18 years of age). Among adults, prevalence was higher in males than in females (25.0% vs 9.1%, respectively). CONCLUSIONS: Prevalence of oral HPV infection in persons with Fanconi anemia was comparable to estimates from other studies in the general population. However, in contrast to previous studies, we did not identify HPV type 16 (the type found in most HPV-related head and neck cancers) in any participants.

Loss of normal p53 function confers sensitization to Taxol by increasing G2/M arrest and apoptosis.

The anticancer agent paclitaxel (Taxol) stabilizes tubulin polymerization resulting in arrest in mitosis and apoptotic cell death. Normal human fibroblasts depleted of functional p53 by SV40 T antigen or HPV-16 E6, and primary embryo fibroblasts from p53 null mice showed seven- to ninefold increased cytotoxicity by paclitaxel. Reduced levels of p53 correlated with increased G2/M phase arrest, micronucleation, and p53-independent paclitaxel-induced apoptosis. Surviving cells with intact p53 progressed through mitosis and transiently accumulated in the subsequent G1 phase, coincident with increased p53 and p21cip1,waf1 protein levels. These results are in contrast to studies linking p53 loss with resistance to DNA damaging anticancer agents.

Inhibiting CDK inhibitors: new lessons from DNA tumor viruses.

The ability of viral oncoproteins to inactivate the retinoblastoma and p53 tumor suppressors provides mechanisms for bypassing the normal inhibitory activities of cyclin-dependent-kinase inhibitors (CKIs). Recent studies point to novel mechanisms for inhibiting the activities of the CKIs p21CIP1 and p27KIP1 activity. Such mechanisms involve the binding of viral oncoproteins or other proteins to these CKIs and suggest a model in which the cell-cycle activities of p21CIP1 are coordinated through protein-protein interactions.

Sequence and structural requirements of a herpes simplex viral DNA replication origin.

Herpes simplex virus (HSV) types 1 and 2 contain two classes of origins of DNA replication, oriS and oriL, which are closely related. A series of plasmids was constructed which contained specifically altered versions of the HSV type 2 oriS replication origin. Their ability to replicate in an in vivo replicon assay allowed a core origin of 75 base pairs (bp) to be defined. It included both arms of a 56-bp palindrome and from 13 to 20 bp of sequence leftward of the palindrome. The AT-rich sequence at the center of the palindrome was essential. Sequences on either side of the core origin enhanced replication. When additional copies of the -AT-dinucleotide were introduced progressively into the center of the palindrome, an oscillating effect on origin function was observed. These and other data implicate a linear rather than a cruciform conformation of the oriS palindrome in the initiation of HSV replication.

The G(2) checkpoint is maintained by redundant pathways.

While p53 activity is critical for a DNA damage-induced G(1) checkpoint, its role in the G(2) checkpoint has not been compelling because cells lacking p53 retain the ability to arrest in G(2) following DNA damage. Comparison between normal human foreskin fibroblasts (HFFs) and HFFs in which p53 was eliminated by transduction with human papillomavirus type 16 E6 showed that treatment with adriamycin initiated arrest in G(2) with active cyclin B/CDC2 kinase, regardless of p53 status. Both E6-transduced HFFs and control (LXSN)-transduced cells maintained a prolonged arrest in G(2); however cells with functional p53 extinguished cyclin B-associated kinase activity. Down regulation was mediated by p53-dependent transcriptional repression of the CDC2 and cyclin B promoters. In contrast, cells lacking p53 showed a prolonged G(2) arrest despite high levels of cyclin B/CDC2 kinase activity, at least some of which translocated into the nucleus. Furthermore, the G(2) checkpoint became attenuated as p53-deficient cells aged in culture. Thus, at late passage, E6-transduced HFFs entered mitosis following DNA damage, whereas the age-matched parental HFFs sustained a G(2) arrest. These results indicate that normal cells have p53-independent pathways to maintain DNA damage-induced G(2) arrest, which may be augmented by p53-dependent functions, and that cells lacking p53 are at greater risk of losing the pathway that protects against aneuploidy.

Progressive region-specific de novo methylation of the p16 CpG island in primary human mammary epithelial cell strains during escape from M(0) growth arrest.

CpG island methylation plays an important role in normal cellular processes, such as genomic imprinting and X-chromosome inactivation, as well as in abnormal processes, such as neoplasia. However, the dynamics of de novo CpG island methylation, during which a CpG island is converted from an unmethylated, active state to a densely methylated, inactive state, are largely unknown. It is unclear whether the development of de novo CpG island methylation is a progressive process, in which a subset of CpG sites are initially methylated with a subsequent increase in methylation density, or a single event, in which the initial methylation event encompasses the entire CpG island. The tumor suppressor gene p16/CDKN2a/INK4a (p16) is inactivated by CpG island methylation during neoplastic progression in a variety of human cancers. We investigated the development of methylation in the p16 CpG island in primary human mammary epithelial cell strains during escape from mortality stage 0 (M(0)) growth arrest. The methylation status of 47 CpG sites in the p16 CpG island on individual DNA molecules was determined by sequencing PCR clones of bisulfite-treated genomic DNA. The p16 CpG island was initially methylated at a subset of sites in three discrete regions in association with p16 transcriptional repression and escape from M(0) growth arrest. With continued passage, methylation gradually increased in density and methylation expanded to sites in adjacent regions. Thus, de novo methylation in the p16 CpG island is a progressive process that is neither site specific nor completely random but instead is region specific. Our results suggest that early detection of methylation in the CpG island of the p16 gene will require methylation analysis of the three regions and that the identification of region-specific methylation patterns in other genes may be essential for an accurate assessment of methylation-mediated transcriptional silencing.

Inactivation of p16 in human mammary epithelial cells by CpG island methylation.

Proliferation of human mammary epithelial cells (HMEC) is limited to a few passages in culture due to an arrest in G1 termed selection or mortality stage 0, M0. A small number of cells spontaneously escape M0, continue to proliferate in culture, and then enter a second mortality stage, M1, at which they senesce. Evidence that M0 involves the Rb pathway comes from the observation that expression of human papillomavirus type 16 E7 alleviates the M0 proliferation block, and we further show that the Rb-binding region of E7 is required to allow cells to bypass M0. In contrast, E6 does not prevent HMEC from entering M0 but, rather, is involved in M1 bypass. Here we show that inactivation of the D-type cyclin-dependent kinase inhibitor p16INK4A is associated with escape from the M0 proliferation block. Early-passage HMEC express readily detectable amounts of p16 protein, whereas normal or E6-expressing HMEC that escaped M0 expressed markedly reduced amounts of p16 mRNA and protein. This initial reduction of p16 expression was associated with limited methylation of the p16 promoter region CpG island. At later passages, a further reduction in p16 expression occurred, accompanied by increased CpG island methylation. In contrast, reduction of p16 expression did not occur in E7-expressing HMEC that bypassed M0, due to inactivation of Rb. These observations in the E6-expressing HMEC correlate well with the finding that CpG island methylation is a mechanism of p16 inactivation in the development of human tumors, including breast cancer.

Quality of life and alteration in comorbidity following laparoscopic adjustable gastric banding.

OBJECTIVES: Obesity is an increasing problem in the UK and bariatric surgery is likely to increase in volume in the future. While substantial weight loss is the primary outcome following bariatric surgery, the effect on obesity-related morbidity, mortality and quality of life (QOL) is equally important. This study reports on weight loss, QOL, and health outcomes following laparoscopic adjustable gastric banding (LAGB) in a low volume bariatric centre (<20 cases/year) and presents the first assessment of factors relating to the QOL which has been produced from a UK based surgical practice. STUDY DESIGN: Questionnaire based study of patients who had LAGB. Each patients' initial body mass index (BMI), QOL, and comorbidities were recorded. Change in these parameters was measured including excess weight loss, and output from both the Moorehead-Ardelt QOL questionnaire, and the Bariatric Analysis and Reporting Outcome System (BAROS). RESULTS: Eighty-one patients (14 males, 67 females) answered the questionnaire. More than 50% excess weight loss was recorded in 52/81 patients (64%). Sixty-four patients (79%) reported improvement in their QOL including self-esteem, physical activity, social involvement, and ability to work. Seventy-one patients had initial obesity related comorbidity. In 61 of these patients (86%) their comorbidities resolved or improved. Minor port site related complications were recorded in nine patients while two patients had removal of the band because of infection. CONCLUSION: LAGB is a safe method of bariatric surgery. It can achieve satisfactory weight loss with significant improvement in QOL and comorbidity.

In vitro maturation and intracytoplasmic sperm injection of oocytes collected from hormonally stimulated common wombats, Vombatus ursinus.

Porcine FSH/LH stimulation successfully induced development of multiple large (>or=4mm) antral follicles in 10 of 11 common wombats. A mean of 5.5 metaphase II (MII) oocytes were aspirated from wombats that were stimulated during the follicular phase of the oestrous cycle (n=3) or after pouch young removal (n=3). Three subadults (n=3) and two anoestrus adults did not produce MII oocytes despite pFSH/pLH administration. In vitro maturation of immature oocytes at the time of aspiration doubled the number of MII oocytes that could be collected from pFSH/pLH stimulated wombats. Immature oocytes with cumulus attached, matured more readily to the MII stage than immature oocytes without cumulus. Following intracytoplasmic sperm injection (ICSI), approximately 5% of the oocytes that were MII at the time of collection cleaved. Approximately 5% of those that were matured by in vitro maturation (IVM) formed two polar bodies following ICSI, although they not cleave. Parthenogenesis cannot be excluded. This demonstrates that assisted reproductive technologies may be applicable to the common wombat.

Injection of conjugated linoleic acid into beef strip loins.

Beef strip loins (IMPS 180; n=15) were sectioned in thirds and sections (n=45) were left untreated (CNT) or injected with either a commercial powder conjugated linoleic acid (CLA) source (Powder) or a commercial oil CLA source (Oil), whose major isomers were 18:2cis-9, trans-11 and 18:2trans-10, cis-12 CLA isomers. Fresh Oil steaks had 3.20 and 3.15, Powder steaks had 4.67 and 4.62, and CNT steaks had 0.19 and 0.02mg/g muscle tissue (wet basis) of the cis-9, trans-11 and trans-10, cis-12 CLA isomers, respectively. TBARS were similar (Oil) and lower (Powder), compared to CNT. Powder steaks had similar instrumental color, and beef and off flavor characteristics as CNT. Artificial marbling was created with Oil steaks having USDA Small(79) and Powder steaks having USDA Modest(86) marbling scores, while CNT steaks had USDA Slight(94) marbling scores. Injection of CLA can be effective in significantly increasing CLA and potentially creating artificial marbling.

Stiffness of modified Type 1a linear external skeletal fixators.

Modifications of a Type 1a external skeletal fixator (ESF) frame were evaluated by alternately placing transfixation pins on opposite sides of the connecting rod (Type 1a-MOD) or by placing additional connecting rods on either of the two inside (Type 1a-INSIDE) or two outside (Type 1a-OUTSIDE) transfixation pins. The objective of this study was to evaluate the stiffness of these modifications in terms of axial compression (AC), cranial-caudal bending (CCB), and medial-lateral bending (MLB). We hypothesized that these designs would allow significant increase in unilateral frame stiffness, over Type 1a, without proportional increase in frame complexity or technical difficulty of application. All of the ESF frames were constructed using large IMEX SKtrade mark clamps, 3.2 mm threaded fixation pins, 9.5 mm carbon fibre connecting rods and Delrin rods as bone models. Nine, eight pin frames of each design were constructed, and subjected to repetitive non-destructive loading forces (AC, CCB, MLB) using a materials testing machine. Frame construct stiffness for each force (AC, CCB, MLB) was derived from load-deformation curve analysis and displayed in N/mm. Data revealed the 1a-MOD and 1a-OUTSIDE constructs had significantly increased stiffness in CCB and AC as compared to the Type 1a constructs while all of the modified constructs were significantly stiffer in MLB than the Type 1a constructs.

Small bowel infarction in a patient with coeliac disease.

A 40 year old man was admitted with a four week history of intractable diarrhoea and abdominal pain. A clinical diagnosis of inflammatory bowel disease was supported by biopsies of colonic mucosa. There was no response to Mesalazine and over 12 days the patient became critically ill with diarrhoea, hypovolaemia, and peritonism. A laparotomy was performed and 130 cm of infarcted ileum was resected. Extensive investigations excluded thrombophilia and echocardiography excluded intracardiac thrombus. Postoperatively the patient continued to have diarrhoea and he was diagnosed with coeliac disease on the basis of positive antiendomysial and antitissue transglutaminase autoantibodies and duodenal histology. Although there is no proof that mesenteric infarction occurred as a direct consequence of coeliac disease, clinicians should be aware of this possibility.

Lack of association of serologically detectable human melanoma-associated antigens with beta 2 microglobulin: serologic and immunochemical evidence.

Serologic and immunochemical assays showed that human melanoma-associated antigens (MAA) identified with operationally specific xenoantisera were neither spatially nor structurally associated with beta 2-microglobulin (beta 2-mu), the light chain of the HLA-A,B antigen molecular complex; i.e., cultured melanoma cells coated with a specific anti-beta 2-mu xenoantiserum maintained their reactivity with anti-MAA xenoantisera. Furthermore, soluble MAA were not bound by a beta 2-mu immunoadsorbent. Finally, MAA were shed into the culture medium of melanoma cells and then were immunoprecipitated with specific anti-MAA xenoantisera, analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, they appeared as two distinct structures with molecular weights of 240,000 and 94,000 but comprised no structure with the characteristic 12,000 molecular weight of beta 2-mu. Conversely immunoprecipitates obtained by the reaction of spent culture medium of [3H]valine-labeled melanoma cells with anti-beta 2-mu xenoantiserum had the 12,000-molecular-weight component but no structures with the molecular weights established for MAA. Thus the data refute the contention that serologically detectable MAA have a molecular structure similar to that of HLA antigens.

Genomic variation of human papillomavirus type 16 and risk for high grade cervical intraepithelial neoplasia.

BACKGROUND: Epidemiologic studies have demonstrated strong and consistent associations between the detection of human papillomavirus (HPV) type 16 DNA and the risk of cervical intraepithelial neoplasia (CIN) and cervical cancer. However, HPV16 is also the most common type of HPV in the normal population, and only a minority of women with HPV16 infection develop cervical cancer. Studies of genomic heterogeneity in HPV16 have demonstrated the presence of multiple variant forms in all human populations examined to date. It is conceivable that the natural variants of HPV16 in a given population may not have the same biologic behavior. PURPOSE: This study was designed to determine the association between natural variants of HPV16 and the risk of biopsy-confirmed CIN 2 or 3, the most important precancerous lesions of the uterine cervix. METHODS: Prospective studies were conducted among 1) women attending a university and 2) women presenting to a sexually transmitted disease clinic. Subjects were eligible for inclusion in this investigation if the initial cytologic findings did not reveal CIN 2-3 and HPV16 DNA was detected by means of a polymerase chain reaction (PCR)-based method in one or more cervical or vulvovaginal samples. Eligible subjects were followed every 4 months with cervical Pap smears and colposcopic examinations. Women were referred for biopsy if cytology or colposcopy suggested CIN 2-3. Two groups of HPV16 variants, prototype-like and nonprototype-like, were determined by means of single-strand conformation polymorphism (SSCP) analysis of PCR products from the noncoding region of the viral genome. Representative SSCP patterns from HPV16 variants were further characterized by direct DNA sequencing of the PCR products. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated by Cox regression analysis. RESULTS: Prototype-like variants accounted for 79% of the HPV16 detected in university students and 86% of the virus detected in patients presenting to the sexually transmitted disease clinic. CIN 2-3 was confirmed by biopsy in nine of 57 HPV16-positive women attending the university and in 10 of 66 HPV16-positive women presenting to the sexually transmitted disease clinic. Among university students, those with HPV16 nonprototype-like variants were 6.5 (95% CI = 1.6-27.2) times more likely to develop CIN 2-3 than those with prototype-like variants. A similar association was observed among women presenting to the sexually transmitted disease clinic (RR = 4.5; 95% CI = 0.9-23.8). CONCLUSIONS: This study suggests that the risk of developing CIN 2-3 is not the same with all variants of HPV16 and that nonprototype-like variants confer a greater risk compared with prototype-like variants. The important genomic differences underlying this increased risk of CIN 2-3 remain to be determined.

Oral cancer risk in relation to sexual history and evidence of human papillomavirus infection.

BACKGROUND: Experimental models and analyses of human tumors suggest that oncogenic, sexually transmittable human papillomaviruses (HPVs) are etiologic factors in the development of oral squamous cell carcinoma (SCC). We conducted a population-based, case-control study to determine whether the risk of this cancer is related to HPV infection and sexual history factors. METHODS: Case subjects (n = 284) were 18-65-year-old residents of three counties in western Washington State who were newly diagnosed with oral SCC from 1990 through 1995. Control subjects (n = 477) similar in age and sex were selected from the general population. Serum samples were tested for HPV type 16 capsid antibodies. Exfoliated oral tissue collected from case and control subjects and tumor tissue from case subjects were tested for HPV DNA. Odds ratios (ORs) were calculated after adjusting for age, sex, cigarette smoking, and alcohol consumption. RESULTS: Among males only, oral SCC risk increased with self-reported decreasing age at first intercourse, increasing number of sex partners, and a history of genital warts. Approximately 26% of the tumors in case subjects contained HPV DNA; 16.5% of the tumors contained HPV type 16 DNA. The prevalence of oncogenic HPV types in exfoliated oral tissue was similar in case and control subjects. The ORs for HPV type 16 capsid seropositivity were 2.3 (95% confidence interval [CI] = 1.6-3.3) for all oral SCCs and 6.8 (95% CI = 3.0-15.2) for oral SCCs containing HPV type 16 DNA. The joint association of cigarette smoking and HPV type 16 capsid seropositivity with oral SCC (OR = 8.5; 95% CI = 5.1-14.4) was stronger than predicted from the sum of individual associations with current smoking (OR = 3.2; 95% CI = 2.0-5.2) and seropositivity (OR = 1.7; 95% CI = 1.1-2.6). CONCLUSIONS: HPV type 16 infection may contribute to the development of a small proportion of oral SCCs in this population, most likely in combination with cigarette smoking.

Cofactors with human papillomavirus in a population-based study of vulvar cancer.

BACKGROUND: Human papillomavirus (HPV) has been previously associated with vulvar cancer. In a population-based study, we examined whether exposure to HPV, cigarette smoking, or herpes simplex virus 2 (HSV2) increases the risk of this cancer. METHODS: Incident cases of in situ (n = 400) and invasive (n = 110) squamous cell vulvar cancer diagnosed among women living in the Seattle area from 1980 through 1994 were identified. Serum samples were analyzed for antibodies against specific HPV types and HSV2. HPV DNA in tumor tissue was detected by means of the polymerase chain reaction. In most analyses, case subjects were compared with population-based control subjects (n = 1403). Relative risks of developing vulvar cancer were estimated by use of adjusted odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: Increased risks of in situ or invasive vulvar cancer were associated with HPV16 seropositivity (ORs = 3.6 [95% CI = 2.6-4.8] and 2.8 [95% CI = 1.7-4.7], respectively), current cigarette smoking (ORs = 6.4 [95% CI = 4.4-9.3] and 3.0 [95% CI = 1.7-5.3], respectively), and HSV2 seropositivity (ORs = 1.9 [95% CI = 1.4-2.6] and 1.5 [95% CI = 0.9-2.6], respectively). When the analysis was restricted to HPV16 DNA-positive tumors (in situ or invasive), the OR associated with HPV16 seropositivity was 4.5 (95% CI = 3.0-6.8). The OR for vulvar cancer was 18.8 (95% CI = 11.9-29.8) among current smokers who were HPV16 seropositive in comparison with never smokers who were HPV16 seronegative. CONCLUSIONS: Current smoking, infection with HPV16, and infection with HSV2 are risk factors for vulvar cancer. Risk appears particularly strong among women who are both current smokers and HPV16 seropositive.

Prospective study of laparoscopic adjustable gastric banding in the west of Scotland.

UNLABELLED: Obesity is an increasing problem in Scotland and Laparoscopic Adjustable Gastric Bands (LAGB) are an effective method of weight reduction. Most outcome data are reported from high volume units with extensive experience or dedicated bariatric practice. We aimed to assess an experienced laparoscopic surgeon's outcome working outwith a dedicated bariatric practice in the west of Scotland. METHODS: All LAGB procedures performed by a single surgeon were prospectively assessed from 1997 to 2004. LAGB were inserted using pars flaccida approach. Patient selection was based on BMI >35 or significant obesity related co-morbidities. Outcomes included percentage excess weight loss (%EWL) and excess BMI loss (EBL). We assessed total operating time to assess the learning curve for LAGB placement. RESULTS: 125 patients were assessed (107 F:18 M). 123 patients were in regular follow-up (98%). Median age was 44 years (range 25-63). Mean follow-up was 34 months (range 11-91). Median initial BMI was 49 (range 37-73). 31% were BMI 35-45, 36% were BMI 45-50 and 33% were BMI>50. %EWL at 1,3 and 5 years was 45, 58 and 74, respectively. EBL at 1, 3 and 5 years was 11.7, 16.1, and 21.7, respectively. Complications included 4 converted procedures, 1 failed band insertion after conversion and re-operation for removal in five. Eight patients had tubing access port problems requiring intervention. The median overall total operation time was 80 minutes (range 50 - 160). CONCLUSIONS: In this cohort LAGB insertion by an experienced laparoscopic surgeon is safe with few re-operations. Satisfactory weight loss is obtained and patient compliance with follow-up is high.

Serological and immunochemical analysis of the specificity of xenoantiserum 8986 elicited with hybrids between human melanoma cells and murine fibroblasts.

Antisera were elicited in rabbits with hybrids derived from the fusion of human melanoma cells with murine fibroblasts. Following absorption with cultured human lymphoid cells, Xenoantiserum 8986 reacts with cultured human melanoma cells and other tumors of nonlymphoid origin. Rosette inhibition assays showed that the xenoantiserum reacts with structures which carry the determinants recognized by the monoclonal antibodies 165.28T and 653.25N and which are recognized by a xenoantiserum elicited with cultured human melanoma cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the immune complexes formed by reacting spent medium of cultured melanoma cells with Xenoantiserum 8986 showed that the antiserum contains antibodies reacting with a M.W. 240,000 melanoma-associated antigen and a M.W. 94,000 melanoma-associated antigen.

Inactivation of p53 enhances sensitivity to multiple chemotherapeutic agents.

Many tumor types have p53 and/or RB mutations, and it is unclear what role the mutations of these tumor suppressor genes have on the efficacy of chemotherapeutic agents. The effect of p53 and RB inactivation on sensitivity to chemotherapeutic drugs was examined using a model system in which p53 or RB was inactivated in normal human foreskin fibroblasts (HFFs) by acute expression of human papillomavirus (HPV) 16E6 or 16E7. Cytotoxicity assays showed that HFFs expressing HPV 16E6 were 6- to 9-fold more sensitive to the DNA crosslinkers cisplatin and carboplatin and 7.8- to 11.5-fold more sensitive to the tubulin polymerizing agent paclitaxel than were LXSN-expressing cells. Analysis of mouse embryonal fibroblasts lacking p53 (p53-/-) compared with mouse embryonal fibroblasts homozygous (p53+/+) and heterozygous (p53+/-) for wild-type p53 confirmed the role of p53 in the enhanced sensitivity to cisplatin. Treatment with the alkylating agents melphalan and nitrogen mustard resulted in 3.8- to 7.3-fold greater sensitivity in HPV 16E6- or 16E7-expressing cells compared with LXSN-expressing cells. Enhanced sensitivity to cisplatin in cells lacking p53 function was explored by examination of its effects on cell cycle progression after exposure. When treated with cisplatin, HFFs expressing 16E6 showed delayed progression through S phase relative to HFFs expressing LXSN. The delay in S phase progression was coincident with the induction of p53 protein levels in LXSN-containing HFFs, suggesting a role for p53 in DNA repair of cisplatin-induced damage. These results indicate that the inactivation of p53 in the absence of other genetic alterations leads to enhanced sensitivity to multiple chemotherapeutic agents rather than to increased resistance.

Abrogation of the G2 checkpoint results in differential radiosensitization of G1 checkpoint-deficient and G1 checkpoint-competent cells.

We have examined the effect of abrogation of the G2 checkpoint on the radiosensitivity of G1 checkpoint-proficient and G1 checkpoint-deficient cells. A549 human lung adenocarcinoma cells were transduced with the E6 oncogene of the human papillomavirus type 16 to eliminate their radiation-induced G1 arrest. These E6+ cells exhibited a dose-dependent increase in radiation resistance compared to control A549 cells transduced with the vector alone. Treatment (96 h) with 2 mM caffeine resulted in an abrogation of the cellular G2 checkpoint in both E6+ and control cells and a differential radiosensitizing effect on the two cell lines such that the E6+ clones and the vector controls became equally radiosensitive. These data show that human tumors which are radioresistant due to the loss of the p53-mediated G1 checkpoint can be made radiosensitive by abrogation of the G2 checkpoint. The implications of these results for cancer therapy are discussed.