- Volume 80, Issue 11, 1999

Papovavirus tumour antigens have been widely used to study cell growth regulation in cultured cells. We investigated the role of mouse polyomavirus T antigens, small-, middle- and large-T, in stimulating growth-arrested REF52 fibroblasts to enter the S phase. Microinjecting cells with cDNAs encoding the various T antigens showed: first, that middle-T expression blocked cell cycle stimulation by serum; second, that middle-T-arrested cells were released into the S phase upon coexpression of small-T; third, that expression of middle-T together with large-T committed resting cells to enter the cell cycle even in the absence of serum. Our data indicate that extensive cooperation among polyomavirus T antigens is essential for T antigen-mediated cell cycle stimulation in growth-arrested cells. In addition, the data suggest a new role for small-T in signalling to mitogenic pathways.

A novel human papillomavirus (HPV) type, HLT7474-S, was isolated from a cervical scraping of a female sex worker with a wart virus infection. The complete DNA sequence of 7812 bp was derived from four overlapping PCR products and authenticated by RFLP analysis. The L1 gene exhibited 78% identity to those of its most closely related known HPV types in group A7, comprising HPV types 18, 39, 45, 59, 68 and 70. The genomic organization and phylogenetic analysis of HLT7474-S and group A7 HPVs reiterated their relatedness. Of significance were the strong sequence similarity, phylogenetic relationship and conservation of critical motifs between the transforming E6 and E7 of HLT7474-S and E6 of HPV-18 and E7 of HPV-59, respectively. These features clearly suggest that HLT7474-S is a high-risk genital HPV isolate, closely related to HPV-18 and other members of the A7 group of genital HPVs.

Human papillomavirus (HPV) exists as more than 100 genotypes. It is not well-established whether the different HPV types interfere with infection or pathogenesis by each other. Possible interactions in cervical carcinogenesis between infection with the most common HPV types (6, 11, 16, 18 and 33) were studied in a seroepidemiological case- control study of 218 women with primary untreated cervical cancer and 219 healthy age-matched control women. As previously shown, HPV-16 seropositivity was associated with cervical cancer risk [odds ratio (OR), 2·39], but HPV-16 was not associated with cervical cancer risk among HPV-6 seropositive women (OR, 1·0). The relative excess risk due to interaction between HPV-6 and -16 was −2·35 (95% confidence interval, −0·04 to −4·65), indicating significant antagonism. The results suggest that infection with HPV-6 may interfere with HPV-16-associated cervical carcinogenesis.

Human papillomavirus (HPV) infections are prevalent in human immunodeficiency virus (HIV)-positive individuals. To highlight the effect of HIV on HPV expression, HPV-18-positive HIV-permissive HeLa-T4 cells were either infected with HIV-1 or treated with Tat or with the cytokines IL-1α, IL-1β, IL-6 and TNF-α . The presence of HPV-18 E1 (early) and L1 (late) transcripts was then determined by dot-blot or Northern blot hybridization with E1 and L1 or with genomic HPV-18 DNA probes, respectively. Protein extracts from parallel cultures were challenged by Western blotting with an antiserum raised against an L1–β-galactosidase hybrid protein. Results indicated that HeLa-T4 cells constitutively express E1 and L1 transcripts. When cells were infected with HIV, the amounts of E1 and L1 RNAs increased with time, followed by the de novo appearance of L1 protein. E1 and L1 transcripts were also increased, in a dose-dependent manner, by treatment of uninfected cultures with Tat or with IL-6, but were not affected by IL-1α, IL-1β and TNF- α. Neither Tat nor IL-6 could induce L1 translation. These findings raise the hypothesis that the increase of HPV shedding and of HPV-associated diseases in HIV-infected individuals could be due in part to a direct or cytokine-mediated action of HIV, in addition to the HIV-induced immunodeficiency.

A full-length cDNA copy of the genome of Potato leafroll virus (PLRV) was introduced into the genome of tobacco and potato plants by Agrobacterium tumefaciens-mediated transformation. Transgenic lines were obtained in which the transgene was readily detected by PCR with DNA extracted from T1 tobacco seedlings and clonally multiplied potato plants. PLRV-specific genomic and sub- genomic RNAs, coat protein antigen and virus particles were detected in transgenic plants. Aphids fed on the transgenic tobacco plants readily transmitted PLRV to test plants. Infected transgenic tobacco plants, like non-transgenic (WT) PLRV-infected plants, displayed no symptoms of the infection but transgenic plants of potato were severely stunted. In parallel tests, the mean PLRV titres in WT tobacco plants and transgenic tobacco plants were 600 and 630 ng virus/g leaf, respectively, although differences in PLRV titres among transgenic plants were much greater than those among infected WT plants. In similar tests with potato, the mean PLRV titre of WT plants was 50 ng virus/g leaf whereas higher concentrations (up to 3400 ng virus/g leaf) accumulated in transgenic potato plants. In tissue prints of stems, PLRV was detected in similar proportions of phloem cells in transgenic and infected WT plants. In transgenic tobacco and potato plants, but not in infected WT plants, a few stem epidermal cells also contained virus. From tissue prints of transgenic tobacco leaves, it was estimated that about one in 40000 mesophyll cells contained virus, but in transgenic potato, a greater proportion of mesophyll cells was infected.

Over 40 isolates of potato spindle tuber viroid (PSTVd) have been reported from potato, other Solanum species and greenhouse tomato. These isolates have sequence similarities in the range 95–99%. A viroid which caused chlorotic leaves and severe dwarfing of plants in greenhouse tomato crops was detected. The viroid was found to hybridize readily with PSTVd probes. It migrated faster than PSTVd in return-polyacrylamide gel electrophoresis and was not amplified in RT–PCR by a primer pair based on the lower strand of the central conserved region of PSTVd. Nucleotide sequencing of the viroid indicated that it is a circular RNA of 360 nt, with less than 90% sequence similarities with PSTVd isolates. The Variable domain (V) has less than 60% and the Terminal Right domain less than 90% sequence similarity, while the remainder of the molecule has greater than 97% similarity with PSTVd. Because of its less-than 90% sequence similarities, unique V domain, lack of seed-transmission and lack of cross-protection by PSTVd, the viroid from tomato is proposed to be a distinct viroid species (tomato chlorotic dwarf viroid; TCDVd) which also differs from two viroids infecting tomato in nature. TCDVd may be an evolutionary link in the development of crop viroids, with Mexican papita viroid as the ancestral viroid.

Apart from a few cases of iatrogenic and familial human transmissible spongiform encephalopathies (TSEs) or prion diseases, the cause of Creutzfeldt–Jakob disease (CJD) remains unknown. In this paper we investigated the possibility that dental procedures may represent a potential route of infection. This was assessed by using the experimental model of scrapie in hamster. In the first part of this study we found that after intraperitoneal inoculation, oral tissues commonly involved in dental procedures (gingival and pulp tissues) bore a substantial level of infectivity. We also found high scrapie infectivity in the trigeminal ganglia, suggesting that the scrapie agent had reached the oral tissues through the sensitive terminal endings of the trigeminal nerves. In the second part of the study we inoculated a group of hamsters in the tooth pulp and showed that all of them developed scrapie disease. In these animals, we detected both infectivity and the pathological prion protein (PrPsc) in the trigeminal ganglion homolateral to the site of injection but not in the controlateral one. This finding suggests that the scrapie agent, and likely other TSE agents as well, spreads from the buccal tissues to the central nervous system through trigeminal nerves. Although these findings may not apply to humans affected by TSEs, they do raise concerns about the possible risk of transmitting these disorders through dental procedures. Particular consideration should be taken in regard to new variant CJD patients because they may harbour more infectivity in peripheral tissues than sporadic CJD patients.