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Biomedical subjects

C L Friedman

Publications and source records attributed to C L Friedman.

18 recordsLinked to original sources
PubMed2000

Amplification of the human dihydrofolate reductase gene via double minutes is initiated by chromosome breaks.

DNA sequence amplification is one of the most frequent manifestations of genomic instability in human tumors. We have shown previously that amplification of the dihydrofolate reductase (DHFR) gene in Chinese hamster cells is initiated by chromosome breaks, followed by bridge-breakage-fusion cycles that generate large intrachromosomal repeats; these are ultimately trimmed by an unknown process to smaller, more homogenous units manifested as homogenously staining chromosome regions (HSRs). However, in most human tumor cells, amplified DNA sequences are borne on unstable, extrachromosomal double minutes (DMs), which suggests the operation of a different amplification mechanism. In this study, we have isolated a large number of independent methotrexate-resistant human cell lines, all of which contained DHFR-bearing DMs. Surprisingly, all but one of these also had suffered partial or complete loss of one of the parental DHFR-bearing chromosomes. Cells in a few populations displayed what could be transient intermediates in the amplification process, including an initial HSR, its subsequent breakage, the appearance of DHFR-containing fragments, and, finally, DMs. Our studies suggest that HSRs and DMs both are initiated by chromosome breaks, but that cell types differ in how the extra sequences ultimately are processed and/or maintained.

Chromosome Aberrations↗
PubMed1992

Viral integration and fragile sites in human papillomavirus-immortalized human keratinocyte cell lines.

Human papillomavirus (HPV) types 16 and 18 integration sites were mapped in six HPV-immortalized human keratinocyte cell lines by fluorescence in situ hybridization (FISH). Mapping of HPV sequences in these cell lines revealed that HPV integration varied in copy number and location but that integration sites were stable over extended passages in culture. Integration occurred at different sites throughout the genome and did not correspond to the location of specific cellular genes. However, integration sites were consistent with integration near or within known fragile sites in five of the six cell lines. Induction of aphidicolin-sensitive fragile sites in one cell line prior to in situ hybridization revealed that integrated HPV DNA was disrupted by fragile-site expression, suggesting that integration occurred within a fragile site.

Cell Line, Transformed↗
PubMed1976

Increased erythrocyte permeability to Li and Na in the spontaneously hypertensive rat.

Red blood cells incubated in a physiological medium in which Li replaces Na (LiPSS) gain Li in exchange for Na and K. The rate of Li uptake is modestly but significantly increased in the spontaneously hypertensive rat (SHR) at 37 degrees C and at 22 degrees C. The slow rate of Na gain and K loss during cooling at 2 degrees C was about doubled in unmodified whole blood samples from the SHR.

Animals↗
PubMed1976

Cell permeability, sodium transport, and the hypertensive process in the rat.

The tail artery of the spontaneously hypertensive rat (SHR) (Carworth Farms), excised rapidly and immersed immediately in cold (2 degrees C) Li-substituted physiologic salt solution (LiPSS), continues to exchange cell Na+ and K+ for Li+, this exchange is negligible to the control (Carworth Farms normotensive) CFN). In the incubated artery at 37 degrees C, when the vascular smooth muscle cell is slack, the leakiness of the cell membrane in the SHR is more than offset by increased Na+ pumping activity, so that cell Na+ is subnormal. A high precision technique with ion-specific electrodes was developed to follow the passive downhill and active uphill phases of Na+-K+ exchange in the perfused artery exposed to K+-free physiologic salt solution (K+-free PSS) followed by physiological salt solution (PSS). The exchange was found to be fully reversible and sufficiently equimolar to be definable in terms of movements of K+ alone. The rates of ionic movement across the vascular smooth muscle cell were found to be about 6 times faster for the vessel perfused at low pressure (less than 3 mm Hg) than for the slack incubated artery. The rate of passive downhill movement was significantly accelerated in the mature SHR compared with CFN, and the net active transport activity much enhanced. Similar changes were seen as early as 3 weeks after treatment with DOCA and were pronounced at 8 weeks. It is proposed that conditions favoring a sustained accumulation of Na+ in the vascular smooth muscle cell are countered by an enhanced synthesis of transport protein, of contractile protein, and of paracellular matrix protein which progressively restructure the wall.

Animals↗
PubMed1975

Cell Na and K in the rat tail artery during the development of hypertension induced by desoxycorticosterone acetate.

An increase in total Na, due in large part to an increase in cell Na, was measured in the freshly excised rat tail artery during the course of DOCA-saline treatment. Since this change was associated with a fall in cell K, was first observed at 2 weeks, coincident with the rise in blood pressure, and was not sustained during subsequent immersion of the artery at zero pressure, it probably reflects the high in vivo intravascular pressure. In the incubated artery, cell Na is significantly reduced early in the course of treatment, while cell K falls late. Thus, Na transport in the artery is under direct attack from the start, but it is suggested that this leads to hypertrophy rather than to vasoconstriction.

Animals↗