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S Harper

Publications and source records attributed to S Harper.

8 recordsLinked to original sources
PubMed1992

Interaction of Epstein-Barr virus nuclear antigen 1 with the viral latent origin of replication.

The Epstein-Barr virus latent origin of replication (oriP) requires only one viral protein, the Epstein-Barr virus nuclear antigen 1 (EBNA-1), for activity. oriP consists of two spatially separated, essential sequence elements, regions I and II, both of which contain multiple EBNA-1-binding sites. Region II contains, or is close to, the site at which DNA synthesis initiates. The role of region I, a transcriptional enhancer in cells that express EBNA-1, in replication is not understood. To determine how the binding of EBNA-1 to sites in region II leads to the initiation of DNA synthesis and to investigate the role of region I, EBNA-1 has been overproduced in insect cells by using a baculovirus vector and purified to homogeneity, and the interaction of EBNA-1 with oriP has been examined. Footprinting experiments demonstrated that EBNA-1 binds to oriP in a sequence-specific manner and bends or untwists the DNA at two symmetry-related sites in region II. Distortion of region I by EBNA-1 was not detected, suggesting that differences in the spacing of binding sites in regions I and II and resulting protein-protein interactions underlie differences in their biological properties. KMnO4 footprinting experiments did not reveal significant single-stranded structures in region II, suggesting that cellular proteins may recognize the EBNA--region II complex and unwind the DNA duplex. Region I did not quantitatively or qualitatively alter the interaction of EBNA-1 with region II. The contribution of an A + T-rich sequence in region II to replication was investigated by a mutational analysis. The results indicated that the overall A + T-rich nature of this sequence is not essential for replication of oriP-bearing plasmids. Nuclease protection experiments performed with these mutagenized plasmids provided additional evidence for protein-protein interactions in region II.

Animals↗
PubMed1990

NGF mRNA expression in developing cutaneous epithelium related to innervation density.

To determine if the initial level of NGF mRNA in developing cutaneous epithelium is correlated with its final innervation density, we measured the concentration of NGF mRNA in the epithelia of the maxillary, mandibular and ophthalmic territories of trigeminal ganglion in the embryonic mouse. At the onset of neuronal death in the ganglion there were marked differences in the concentration of NGF mRNA in these epithelia: the level was highest in the epithelium of the densely innervated maxillary territory, it was lower in the epithelium of the moderately innervated mandibular territory and was lowest in the epithelium of the sparsely innervated ophthalmic territory. These regional differences in the level of NGF mRNA during the early stages of target field innervation suggest that the level of NGF production in target field cells, rather than regional differences in the access of innervating neurons to NGF, governs the number of neurons that survive. Because the same percentage cell death occurs in each of the subsets of trigeminal neurons that innervate the maxillary, mandibular and ophthalmic territories, regional differences in NGF synthesis are not responsible for establishing differences in innervation density, rather they maintain differences that arise earlier in development.

Animals↗
PubMed1990

Wives, husbands, and daughters caring for institutionalized and noninstitutionalized dementia patients: toward a model of caregiver burden.

The primary purposes of this article are to clarify some of the inconsistencies in the previous research studies done on factors associated with caregiver burden; to identify specific sets of variables that best explain the differential burden levels among caregivers; and to provide a substantial foundation for developing a model of caregiver burden useful for both research and clinical interventions. The caregiver's gender, relationship to the patient, and the residential location of the patient (same house, community, or institution) are major considerations in our analyses. This study is also unique, because it uses a relatively large national sample of caregivers, which is necessary to accomplish the study's objectives. Mailed questionnaires were completed by 409 caregivers identified by fifty local support groups in sixteen different states in the United States. Generally, the primary correlates of burden were factors related to the levels and types of impairment in patient functioning, caregiver life satisfaction, and social support. Each category of caregiver circumstances had a unique set of three to five correlates with the total amount of variance explained in burden ranging from 25 percent (husbands living with the patients) to 68 percent (husbands with spouses in nursing homes). Implications for future research and interventions are discussed.

Alzheimer Disease↗
PubMedDate not supplied

Colorectal carcinogenesis: sequential steps in the in vitro immortalization and transformation of human colonic epithelial cells (review).

The development of colorectal cancer is an excellent example of the complex multistage nature of carcinogenesis and most colorectal cancers are thought to develop from adenomas. In this paper we have reviewed in vitro models developed in our laboratory for the study of human colorectal carcinogenesis. For these studies epithelial cell lines have been isolated from hereditary and sporadic colorectal adenomas representing different stages in tumour progression. Karyotypic analysis has shown specific abnormalities of chromosomes 1, 7, 14, 17, 18 and 22 to occur in these premalignant adenoma cell lines. The majority of cell cultures derived from small adenomas (less than 1 cm in diameter) senesced whereas the larger adenomas (greater than 2 cm in diameter) were more likely to give rise to immortal cell lines indicating that the acquisition of in vitro immortality occurs at a relatively late stage of colorectal carcinogenesis. Abnormalities of chromosome I have been implicated in tumour progression and in the in vitro immortalization of colorectal adenomas. Furthermore, several stages have been described in the transformation of an adenoma cell line PC/AA to a tumorigenic phenotype. Sodium butyrate and the potent carcinogen N-methyl-N-nitro-nitrosoguanidine (MNNG) were used in this transformation. Sodium butyrate is proposed to act as a possible promoter of colorectal carcinogenesis, and MNNG to cause the further genetic changes required for the conversion of the premalignant cells to a carcinoma. Markers to study the progression of an adenoma cell line to a tumorigenic phenotype in vitro include in vitro immortalization, aneuploidy, clonogenicity, resistance to the inhibitory effects of sodium butyrate, anchorage independent growth, ras gene activation, production of active proteinases and tumorigenicity in athymic nude mice. A role for a constitutively produced tumour promoter in colorectal carcinogenesis is discussed together with the possibility that different events are involved in the development of sporadic versus hereditary tumours due to the importance of the microenvironment in hereditary cancer. Our in vitro progression provides the first experimental evidence for the adenoma to carcinoma sequence and the cytogenetic evidence suggests that it is relevant to in vivo carcinogenesis.

Adenoma↗