Sortilin (approximately 95 kDa) is a member of the recently discovered family of Vps10p-domain receptors, and is expressed in a variety of tissues, notably brain, spinal cord and muscle. It acts as a receptor for neurotensin, but predominates in regions of the nervous system that neither synthesize nor respond to this neuropeptide, suggesting that sortilin has additional roles. Sortilin is expressed during embryogenesis in areas where nerve growth factor (NGF) and its precursor, proNGF, have well-characterized effects. These neurotrophins can be released by neuronal tissues, and they regulate neuronal development through cell survival and cell death signalling. NGF regulates cell survival and cell death via binding to two different receptors, TrkA and p75NTR (ref. 10). In contrast, proNGF selectively induces apoptosis through p75NTR but not TrkA. However, not all p75NTR-expressing cells respond to proNGF, suggesting that additional membrane proteins are required for the induction of cell death. Here we report that proNGF creates a signalling complex by simultaneously binding to p75NTR and sortilin. Thus sortilin acts as a co-receptor and molecular switch governing the p75NTR-mediated pro-apoptotic signal induced by proNGF.

DNA of human papillomavirus (HPV) types 16 and 18 has been found closely associated with human genital cancer, supporting the concept that members of this virus group are key factors in the aetiology of genital cancer. HPV 18 DNA sequences were also detected in cell lines derived from cervical cancer. We have now analysed these cell lines, HeLa, C4-1 and 756, for the structural organization and transcription of the HPV 18 genome and we find that the HPV 18 DNA is integrated into the cellular genome and is amplified in HeLa and 756 cells. Almost the complete HPV 18 genome seems to be present in 756 cells, with the early region being disrupted into two portions in each integrated copy. In HeLa and C4-1 cells, a 2-3 kilobase (kb) segment of HPV 18-specific sequences is missing from the E2 to L2 region. HPV 18 sequences are specifically transcribed from the E6-E7-E1 region into poly(A)+ RNAs of 1.5-6.5 kb. Hybridization analysis of cDNA clones indicated that some of the transcripts are composed of HPV 18 and cellular sequences. In addition, poly(A)+ RNA hybridizing with HPV 16 DNA was found in two out of three cervical carcinoma biopsies.

Neuenheimer Feld 280, 6900 Heidelberg, FRG Communicated by H.zur Hausen Transcription of human papillomavirus type 18 (HPV18) DNA in the human cervical carcinoma cell lines HeLa, C41 and SW756 was studied by nucleotide sequence analysis of HPV18-positive cDNA clones isolated from a HeLa, C41 and SW756 cDNA library, respectively, and the cDNA sequences were used to predict the potential encoded proteins. The cDNA clones from all three cell lines were found to be derived from virus-cell fusion transcripts in which 3'-terminal host cell sequences (different for each cell line) were spliced to 5'-tenminal exon sequences from the HPV18 E6-E7-E1 region.Three different types of cDNA clones can be distinguished according to the splicing patterns observed in the 5' tenminal HPV18 sequences. They carry as potential protein-coding regions the HPV18 specific open reading frames E6 and E6* (generated by splicing and identical with E6 up to the E6* splice junction), E7 and El (only in HeLa). Translation of specific cellular genes from the chimeric viral-cellular transcripts seems to be unlikely. The mapping of the 5'-ends of the virus-cell fusion transcripts indicates that transcription is initiated at a viral promoter. The similar patterns of HPV18 transcription in the three different cervical carcinoma cell lines suggest a functional role of HPV18 early genes for the malignant phenotype of these cells.

We have identi®ed parameters which de®ne a causal role of HPV16 in head and neck cancer. Twenty-eight tumours which were typed positive for HPV16 DNA, were comprehensively analysed for expression of the viral oncogenes E6 and E7, the status of the p53 gene, and the protein status of pRb and p16 INK4a. In a subset of cases, we have searched for integrated viral DNA, and have determined the genomic status of the E6 gene. Expression of E6/E7 was found in 12 tumours most of which were derived from the oropharynx, whereas p53 mutations were present in 13 tumours from various sites. The tumours either carried p53 mutations but did not express E6/E7, or they did express E6/E7 but were p53-wild-type. Coexistence of E6/E7 expression with a mutated p53 was found in only one case. Strikingly, in most p53-mutated tumours without E6/E7 expression, we found the E6 gene to be disrupted. E6/E7 expression was associated with reduced pRb and overexpressed p16INK4a . Viral-cellular fusion transcripts were found in two cases. Our data demonstrate that HPV16 DNA-positivity in head and neck cancers is not indicative of a causal role. A causal role of HPV16 in head and neck cancer is de®ned by: E6/E7 expression, viral integration with an intact E6 gene, and perturbation of pRb cell cycle control. Mostly, the p53 gene is wild-type.

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During polyadenylation of mRNA precursors in metazoan cells, poly(A) polymerase is stimulated by the nuclear poly(A) binding protein PABPN1. We report that stimulation depends on binding of PABPN1 to the substrate RNA directly adjacent to poly(A) polymerase and results in an~80-fold increase in the apparent af®nity of poly(A) polymerase for RNA without signi®cant effect on catalytic ef®ciency. PABPN1 associates directly with poly(A) polymerase either upon allosteric activation by oligo(A) or, in the absence of RNA, upon deletion of its N-terminal domain. The N-terminal domain of PABPN1 may function to inhibit undesirable interactions of the protein; the inhibition is relieved upon RNA binding. Tethering of poly(A) polymerase is mediated largely by the C-terminal domain of PABPN1 and is necessary but not suf®cient for stimulation of the enzyme; an additional interaction dependent on a coiled-coil structure located within the N-terminal domain of PABPN1 is required for a productive interaction.

The chromosomal locations of cellular sequences flanking integrated papillomavirws DNA in four cervical carcinoma cell lines and a primary cervical carcinoma have been determined. The two human papillomavirus (HPV) 16 flanking sequences derived from the tumor were localized to chromosome regions 20pter-*20ql3 and 3p25-+3qter, regions that also contain the protooncogenes c-src-l and c-raf-1, respectively. The HPV 16 integration site in the SiHa cervical carcinoma-derived cell line is in chromosome region 13ql4-+ 13q32. The HPV 18 integration site in SW756 cervical carcinoma cells is in chromosome 12 but is not closely linked to the Ki-ras2 gene. (8,10). We have therefore used the cloned cellular sequences that flank HPV DNA or the 3' terminal cellular sequences of cDNA clones to determine, by analysis of rodent-human hybrids retaining defined subsets of human chromosomes, the location of the integration sites on the human gene map.We have found integration sites on chromosomes 3 and 20 in a tumor that harbored multiple HPV 16 integration sites. Integration sites in four cervical carcinoma-derived cell lines were in three different chromosomes, 8, 12, and 13.