Biomedical subjects

K P Lu

Publications and source records attributed to K P Lu.

5 recordsLinked to original sources

PubMed1992

Calmodulin and cell cycle control.

Previous studies have indicated a role for the calcium receptor calmodulin in the control of eukaryotic cell proliferation. Using a molecular genetic approach in the filamentous fungus Aspergillus nidulans we have shown that CaM is required for cell cycle progression at multiple points in the cell cycle. Construction of an A nidulans strain conditional for calmodulin expression reveals that this protein is required during G1/S and for the initiation of mitosis. A lack of calmodulin results in cell cycle arrest, and a failure in polar growth that accompanies germination of A nidulans spores. In addition, increased expression of calmodulin in this organism permits growth at suboptimal calcium concentrations, indicating that cell growth is coordinately regulated by calcium and calmodulin. Together these results indicate that calmodulin-dependent processes may be conserved between A nidulans and vertebrate cells, and suggest that this approach may allow us to elucidate the molecular mechanism underlying calmodulin-regulated control of cell proliferation.

Aspergillus nidulans↗

PubMed1992

Cooperative regulation of cell proliferation by calcium and calmodulin in Aspergillus nidulans.

Calcium and calmodulin have been widely implicated in the control of cell proliferation. We have created a strain of the genetically tractable filamentous fungus, Aspergillus nidulans, that is conditional for calmodulin expression. This was accomplished by replacing the unique endogenous calmodulin gene with one regulated by the inducible alcohol dehydrogenase (alcA) gene promoter by homologous recombination. This strain cannot grow when the cells are incubated in medium containing a carbon source that represses the alcA promoter. Characterization of the arrested cells shows that 83% are blocked in the G2 phase of the cell cycle. The block is due to very low levels of calmodulin and is fully reversible upon changing to medium that contains an inducer of the alcA promoter. The rate of cell proliferation in this strain is dependent upon both the intracellular calmodulin and extracellular Ca2+ concentrations. Raising the calmodulin concentration by inducing the alcA promoter not only causes the cells to enter the proliferative cycle more quickly and to grow faster, but also decreases the concentration of extracellular Ca2+ required to support growth by 10-fold, as compared with cells grown in noninducing medium. Thus both the intracellular calmodulin and extracellular Ca2+ concentrations are important and interactive factors in regulating the nuclear division cycle of Aspergillus nidulans.

Aspergillus nidulans↗

PubMed1991

Regulatory functions of calmodulin.

Calmodulin is a Ca2+ binding protein present in all eukaryotic cells that serves as the primary intracellular receptor for Ca2+. This 148 amino acid protein is involved in activation of more than 20 enzymes which mediate a wide variety of physiological processes. Many of these enzymes are inhibited in an intramolecular manner and the Ca(2+)-calmodulin complex relieves this inhibition. Calmodulin is essential for life as disruption of the gene in genetically tractable organisms is lethal. This protein plays important regulatory roles in cell proliferation and is required at multiple points in the cell cycle. The mechanism of enzyme activation by calmodulin and its importance in cell growth regulation are reviewed.

Animals↗

PubMed1990

Characterization and expression of the unique calmodulin gene of Aspergillus nidulans.

Complete cDNA and genomic clones for the unique calmodulin (CaM) gene of the filamentous fungus Aspergillus nidulans have been isolated and characterized. The gene contains five introns, of which three are at unique positions relative to other CaM genes. The A. nidulans CaM gene is transcribed as a single, 0.85-kilobase mRNA species that encodes a predicted protein 84% identical (93% similar if conservative changes are considered) to vertebrate CaM. The complete cDNA was ligated into a lambda PL promoter-regulated bacterial expression vector to allow expression of A. nidulans CaM in Escherichia coli. The expressed protein was purified from bacterial lysates by phenyl-Sepharose chromatography and migrated as a single species on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the presence of Ca2+, A. nidulans CaM exhibited a shift in apparent Mr identical to vertebrate CaM. The bacterially synthesized protein activated vertebrate CaM-dependent phosphodiesterase, CaM-dependent protein kinase II, and myosin light chain kinase with kinetics similar to vertebrate CaM. Isolated conidia (G0 spores) were germinated to induce synchronous cell cycle re-entry and the levels of CaM mRNA and protein determined. Both CaM and its mRNA were regulated during cell cycle re-entry. Calmodulin mRNA levels increased 20-fold as germlings progressed through the G1 phase, while CaM levels increased 2-fold prior to the initiation of DNA synthesis. Messenger RNA levels decreased during S-phase while protein levels increased an additional 2-fold, peaking at the onset of mitosis followed by a subsequent decrease as cells completed mitosis. Disruption of the CaM gene by site-specific homologous recombination was lethal, indicating that CaM is essential for cell cycle progression.

Amino Acid Sequence↗

PubMed1990

The stimulatory effect of heavy metal cations on proliferation of aortic smooth muscle cells.

Heavy metal cations Cd2+, Pb2+, and Hg2+ were added to substitute for Ca2+ in culture media to study their effect on the relationship between CaM and the proliferation of cultured rabbit aortic smooth muscle cells (ASMC). It was found that all the heavy metal cations studied stimulated the proliferation of ASMC in varying degrees, increased the CaM content in cells at late G1 stage and decreased the activity of cAMP PDE. These results suggest that the adverse effect of heavy metals may be related to the pathogenesis of atherosclerosis and hypertensive disease.

3',5'-Cyclic-AMP Phosphodiesterases↗