Biomedical subjects

A C Nirkko

Publications and source records attributed to A C Nirkko.

22 records · Page 2Linked to original sources

PubMed1991

Molecular and functional analysis of tumor-suppressor genes by transfection.

The transformed and tumorigenic phenotype of H-ras transfected rat FE-8 cells can be suppressed by cell fusion with normal rat embryo fibroblasts. Transfection into FE-8 cells of DNA prepared from normal human placenta followed by selective elimination of tumorigenic transfected cell clones resulted in the isolation of phenotypically normal revertants. These cells exhibited a fibroblastlike, normal morphology; were anchorage-dependent; and were unable to proliferate in medium with reduced serum concentrations. Their tumorigenicity was also reduced. The suppressed phenotype has been transferred in a second transfection cycle. Human repetitive DNA sequences were detected in secondary transfectant DNA. A putative human suppressor gene, designated NTS-1, has been molecularly cloned. Reintroduction of cloned NTS-1 sequences into FE-8 cells resulted in suppression of the neoplastic phenotype in spite of a high ras expression.

Animals↗

PubMed1991

Evidence for human DNA-mediated transfer of the suppressed phenotype into malignant Chinese hamster cells.

Genetic suppression of the neoplastic phenotype has been demonstrated in somatic cell hybrids between tumor and normal cells. Suppression in whole-cell and microcell hybrids cannot, as yet, be attributed to specific elements defined at the molecular level. To identify a gene capable of suppressing the neoplastic phenotype, we have introduced DNA of normal human cells into tumorigenic Chinese hamster Wg3-h-o cells. Primary and secondary transfectants which exhibit the suppressed phenotype similar to Wg3-h-o x embryonic fibroblast hybrids were selected. The cells require serum growth factors and anchorage for proliferation in vitro and show a reduced tumorigenicity in nude mice. Transferred human DNA segments were molecularly cloned from a secondary transfectant. Indirect evidence suggests that the cloned human DNA is associated with the expression of the suppressed phenotype.

3T3 Cells↗

PubMed1990

Effect of nimodipine on cerebrovascular response to CO2 in asymptomatic individuals and patients with subarachnoid hemorrhage: a transcranial Doppler ultrasound study.

The cerebrovascular response to CO2 was evaluated by measuring relative changes in blood flow velocity within the middle cerebral artery by transcranial Doppler ultrasonography during normo-, hypo-, and hypercapnia. In seven patients without subarachnoid hemorrhage (five with unruptured arteriovenous malformations and two with aneurysms), the CO2 vasoreactivity was tested on the side of the middle cerebral artery with normal flow velocities opposite the lesion. A baseline CO2 reactivity test was obtained in each patient and then repeated under constant intravenous infusion of nimodipine, 2 mg/hr. Nine patients with ruptured aneurysms who were rated at Hunt and Hess Grades 1 or 2 were operated on within 1 to 3 days after the hemorrhage and treated with nimodipine, 2 mg/hr, given intravenously. In these patients, CO2 vasoreactivity was tested during the second week after the hemorrhage, when the middle cerebral artery velocity was increased by at least 50% of the initial value or more. Nimodipine was then discontinued and, 48 hours later, when the middle cerebral artery velocity was still in the same range, CO2 vasoreactivity was tested again. Two months later, after full recovery from the subarachnoid hemorrhage and normalization of the velocities, a third measurement of CO2 reactivity was obtained as a baseline control. No significant effect of nimodipine on CO2 vasoreactivity could be demonstrated in any of the test periods. In the second week after a subarachnoid hemorrhage, a significant reduction of the cerebrovascular response to CO2 was found (P less than 0.005).

Adolescent↗

PubMed1988

Partial reversion of the transformed phenotype in HRAS-transfected tumorigenic cells by transfer of a human gene.

The transformed phenotype of rat FE-8 cells transfected by an activated human HRAS gene was suppressed upon fusion with normal cells. An experimental approach was developed to identify and isolate a human gene capable of suppressing the transforming activity of the HRAS oncogene in FE-8 cells. Genomic DNA from human placenta was introduced into FE-8 cells by cotransfection with the plasmid pY3 conferring hygromycin B resistance. Transfectants were selected in medium containing hygromycin B. HRAS-transformed FE-8 cells showed an increased sensitivity toward ouabain when compared to their normal counterparts. Therefore, the population of transfected hygromycin B-resistant cells was treated with ouabain to eliminate cells with a transformed phenotype. Ouabain selection resulted in a small number of cell clones exhibiting a more normal phenotype. The clones had lost the morphology of transformed cells and required anchorage for growth. The tumorigenicity of transfectants in nude mice was reduced but not completely abolished. FE-8 revertants continued to express the p21 RAS protein. Human repetitive sequences contained in the DNA of a secondary transfectant were used for isolation of the suppressor gene from reverted FE-8 cells. The cloned DNA fragment was transfected into tumorigenic FE-8 cells and conferred a partial reversion of the transformed phenotype.

Animals↗