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V B Morhenn

Publications and source records attributed to V B Morhenn.

61 records · Page 4Linked to original sources
PubMed1982

Separation of human skin cells by velocity sedimentation into functionally distinct fractions.

The epidermis consists of a heterogeneous population of cells including Langerhans cells, Merkel cells, melanocytes, and keratinocytes in various stages of differentiation. The current study was undertaken to determine if skin cell suspensions can be separated into morphologically and/or functionally distinct fractions. Skin cells were suspended by trypsinization and separated into multiple fractions by velocity sedimentation. Certain fractions reproducibly stimulated proliferation of allogeneic lymphocytes in the skin cell lymphocyte reaction, whereas other fractions, containing larger cells, supported growth of keratinocyte colonies in cell cultures. These results indicate that stimulation in the skin cell lymphocyte reaction and growth of keratinocyte colonies are mediated by distinct cells, separable by velocity sedimentation.

Cell Division↗
PubMed1981

The effect of polyoma virus, serum factors, and dibutyryl cyclic AMP on dihydrofolate reductase synthesis, and the entry of quiescent cells into S phase.

Three procedures were used to induced dihydrofolate reductase synthesis in quiescent cultures of methotrexate resistant mouse fibroblasts: 1) lytic infection with polyoma virus, 2) growth stimulation by replating cells at lower density in fresh cell culture medium, and 3) the addition of fresh medium to confluent cells. Following polyoma infection, an increase in the percentage of S-phase cells began at approximately 20 hours; dihydrofolate reductase synthesis also increased following a lag of 20 hours or more, and continued to increase throughout the late phase of lytic infection, reaching values nearly fivefold greater than that originally present in the quiescent cells. When quiescent cells received fresh medium (with or without replating), the percentage of cells in S phage began to increase by 10 hours and was accompanied by an increase in dihydrofolate reductase synthesis which reached a maximum by approximately 25 hours. These observations show that the initial entry of cells into S phase following mitogenic stimulation is associated with an induction of dihydrofolate reductase synthesis. Dibutyryl cyclic AMP blocked the stimulation of dihydrofolate reductase synthesis and the increase in the percentage of S-phase cells that resulted from the addition of fresh medium to confluent cells. When dibutyryl cyclic AMP was added at various times following the addition of fresh medium, the block in the induction of dihydrofolate reductase synthesis was correlated with a corresponding block in the increase in S-phase cells. These results suggest that dibutyryl cyclic AMP blocks cells at a point in G1 prior to either the induction of dihydrofolate reductase synthesis of the beginning of S phase. The relationship between the control of dihydrofolate reductase synthesis and entry into S phase suggests some form of coordinate control over these two parameters.

Animals↗
PubMed1980

Inhibition of cell mediated immune responses by 8-methoxypsoralen and long-wave ultraviolet light: a possible explanation for the clinical effects of photoactivated psoralen.

Human thymus-derived lymphocytes proliferate when cultured with lymphocyes or epidermal cells from unrelated individuals because such cells express HLA-D antigens, which are recognized as foreign by thymus-derived lymphocytes. The current study demonstrates that these responses are inhibited if either the stimulator cells or responder cells are pretreated with the combination of 8-methoxypsoralen and long-wave ultraviolet light. Additional studies revealed that photoactivated 8-methoxypsoralen has a lethal effect on lymphocytes and monocytes but not on the majority of epidermal cells. These obervations suggest that the dramatic beneficial effect of PUVA on patients with psoriasis and other skin disorders may be due to a toxic effect on immunocompetent cells in the epidermis, which results in inhibition of cell mediated immune responses.

Epidermis↗
PubMed1979

Polyoma virus and cyclic AMP-mediated control of dihydrofolate reductase mRNA abundance in methotrexate-resistant mouse fibroblasts.

As a model cell culture system for studying polyoma-mediated control of host gene expression, we isolated methotrexate-resistant 3T6 cells in which one of the virus-induced enzymes, dihydrofolate reductase, is a major cellular protein. In highly methotrexate-resistant cell lines dihydrofolate reductase synthesis accounts for over 10% that of soluble portein, corresponding to an increase of approximately 100-fold over the level in parental cells. This increase in dihydrofolate reductase synthesis is due to a corresponding increase in the abundance of dihydrofolate reductase mRNA and gene sequences. We have used these cells to show that infection with polyoma virus results in a 4- to 5-fold increase in the relative rate of dihydrofolate reductase synthesis and a corresponding increase in dihydrofolate reductase mRNA abundance. The increase in dihydrofolate reductase synthesis begins 15 to 20 h after infection and continues to increase until cell lysis. These observations represent the first direct evidence that viral infection of eukaryotic cells results in the increased synthesis of a specific cellular enzyme and an increase in the abundance of a specific cellular mRNA. In order to gain additional insight into the control of dihydrofolate reductase synthesis we examined other parameters affecting dihydrofolate reductase synthesis. We found that the addition of fresh serum to stationary phase cells results in a 2-fold stimulation of dihydrofolate reductase synthesis, beginning 10 to 12 h after serum addition. Serum stimulation of dihydrofolate reductase synthesis is completely inhibited by the presence of dibutyryl cyclic AMP as well as by theophylline or prostaglandin E1, compounds which cause an increase in intracellular cyclic AMP levels. In fact, the presence of dibutyryl cyclic AMP and theophylline results in a 2- to 3-fold decrease in the rate of dihydrofolate reductase synthesis and the abundance of dihydrofolate reductase mRNA. However, in contrast to the effect on serum stimulation, dibutyryl cyclic AMP and theophylline do not inhibit polyoma virus induction of dihydrofolate reductase synthesis or dihydrofolate reductase mRNA levels. These observations suggest that dihydrofolate reductase gene expression is controlled by at least two regulatory pathways: one involving serum that is blocked by high levels of cyclic AMP and another involving polyoma induction that is not inhibited by cyclic AMP.

Bucladesine↗
PubMed1979

The effect of 8-methoxypsoralen-plus ultraviolet light on cell-virus interaction: the transforming infection; effect of PUVA on the transformation of baby hamster kidney cells by polyoma virus.

Pre-treatment of baby hamster kidney (BHK) cells with 8-methoxypsoralen (8-MOP) plus ultraviolet (UV) light enhances the frequency of their transformation by polyoma (Py) virus. Of the doses tested, 0.5 microgram/ml 8-MOP plus 0.3 J/cm2 UV-light results in maximal (30-fold) stimulation of viral transformation. 8-MOP alone does not affect viral transformation and UV-light alone causes only a slight increase in the transformation frequency. Thus the drug and light act synergistically in promoting the effect. Treatment of BHK cells with drug plus light without Py infection does not lead to a transformed morphology. A drug-light combination (0.01 microgram/ml 8-MOP plus 1.2 J/cm2 UV) that inhibits cellular DNA synthesis to 75% of control at 28 hr after treatment results in a 6-fold stimulation of the transformation frequency.

Animals↗