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.

Regulation of telomerase by human papillomaviruses.

The E6 oncoprotein of human papillomaviruses (HPVs) induces telomerase activity in primary human epithelial cells. This activity is dependent on association of E6 with E6AP, a cellular ubiquitin ligase. E6 activates the transcription of hTERT, the catalytic subunit of telomerase. E boxes near the start of hTERT transcription are required for E6; however, acetylated histones are only present in the E6 cells. We identified two isoforms of NFX1, a new binding partner of E6/E6AP. The NFX1- 91 isoform binds to an X-box motif located adjacent to the proximal E box, binds Sin3A and HDACs, repressing hTERT transcription. It preferentially binds E6/E6AP and is targeted for ubiquitin-mediated degradation. The NFX1-123 isoform has the opposite activity, increasing hTERT transcription or translation. This is the first example of viral oncoproteins disrupting regulation of telomerase, a critical event in tumorigenesis.

Hypermethylation of the DAP-kinase CpG island is a common alteration in B-cell malignancies.

Death-associated protein kinase (DAP-Kinase) is a novel serine/threonine kinase whose expression is required for gamma interferon-induced apoptosis. A previous study suggested that DAP-Kinase expression may be lost epigenetically in cancer cell lines, because treatment of several nonexpressing cell lines with 5-aza-2'-deoxycytidine resulted in the expression of DAP-Kinase. Using methylation-specific polymerase chain reaction (MSP), we examined the DAP-Kinase CpG island for hypermethylation in cancer. Normal lymphocytes and lymphoblastoid cell lines are unmethylated in the 5' CpG island of DAP-Kinase. However, in primary tumor samples, all Burkitt's lymphomas and 84% of the B-cell non-Hodgkin's lymphomas were hypermethylated in the DAP-Kinase CpG island. In contrast, none of the T-cell non-Hodgkin's lymphoma samples and 15% or less of leukemia samples examined had hypermethylated DAP-Kinase alleles. U937, an unmethylated, DAP-Kinase-expressing leukemia cell line, was treated with gamma interferon and underwent apoptosis; however, Raji, a fully methylated, DAP-Kinase nonexpressing Burkitt's lymphoma cell line, only did so when treated with 5-aza-2'-deoxycytidine followed by gamma interferon. Our findings in cell lines and primary tumors suggest that hypermethylation of the DAP-Kinase gene and loss of gamma interferon-mediated apoptosis may be important in the development of B-cell malignancies and may provide a promising biomarker for B-cell-lineage lymphomas.

A mechanism for the differential regulation of gonadotropin subunit gene expression by gonadotropin-releasing hormone.

The hypothalamic hormone gonadotropin-releasing hormone (GnRH) is released in a pulsatile fashion, with its frequency varying throughout the reproductive cycle. Varying pulse frequencies and amplitudes differentially regulate the biosynthesis and secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by pituitary gonadotropes. The mechanism by which this occurs remains a major question in reproductive physiology. Previous studies have been limited by lack of available cell lines that express the LH and FSH subunit genes and respond to GnRH. We have overcome this limitation by transfecting the rat pituitary GH3 cell line with rat GnRH receptor (GnRHR) cDNA driven by a heterologous promoter. These cells, when cotransfected with regulatory regions of the common alpha, LH beta, or FSH beta subunit gene fused to a luciferase reporter gene, respond to GnRH with an increase in luciferase activity. Using this model, we demonstrate that different cell surface densities of the GnRHR result in the differential regulation of LH and FSH subunit gene expression by GnRH. This suggests that the differential regulation of gonadotropin subunit gene expression by GnRH observed in vivo in rats may, in turn, be mediated by varying gonadotrope cell surface GnRHR concentrations. This provides a physiologic mechanism by which a single ligand can act through a single receptor to regulate differentially the production of two hormones in the same cell.

Evidence that signalling pathways by which thyrotropin-releasing hormone and gonadotropin-releasing hormone act are both common and distinct.

TRH and GnRH receptors are each coupled to G proteins of the Gq/11 family. Activation of each of these receptors by their respective ligands results in the stimulation of phospholipase C activity, leading to calcium mobilization and protein kinase C activation. Thus, the effects of TRH and GnRH may be mediated through the same intracellular signal transduction pathway. To compare responses to TRH and GnRH directly within one cell type, we have stably transfected the rat pituitary GH3 lactotrope cell line, which expresses the endogenous TRH receptor, with an expression vector containing rat GnRH receptor cDNA. Transfected cells specifically bound GnRH with high affinity and responded to GnRH stimulation with an increase in PRL mRNA levels, analogous to their response to TRH stimulation. Stably transfected GH3 cells, which were then transiently transfected with luciferase reporter constructs containing either the PRL or the glycoprotein hormone alpha-subunit promoter, responded to either GnRH or TRH stimulation with an increase in luciferase activity in a time- and dose-dependent fashion. The stimulatory effects of maximally effective concentrations of TRH and GnRH were additive on PRL, but not alpha-subunit, gene expression. These data, coupled with evidence of cross-desensitization of alpha-subunit, but not PRL, promoter activity stimulation by TRH and GnRH, suggest that there may be differences in the signal transduction pathways activated by TRH and GnRH receptors in the regulation of PRL and alpha-subunit gene expression.