Mechanism of actin polymerization in cellular ATP depletion.
Cellular ATP depletion in diverse cell types results in the net conversion of monomeric G-actin to polymeric F-actin and is an important aspect of cellular injury in tissue ischemia. We propose that this conversion results from altering the ratio of ATP-G-actin and ADP-G-actin, causing a net decrease in the concentration of thymosinactin complexes as a consequence of the differential affinity of thymosin beta4 for ATP- and ADP-G-actin. To test this hypothesis we examined the effect of ATP depletion induced by antimycin A and substrate depletion on actin polymerization, the nucleotide state of the monomer pool, and the association of actin monomers with thymosin and profilin in the kidney epithelial cell line LLC-PK1. ATP depletion for 30 min increased F-actin content to 145% of the levels under physiological conditions, accompanied by a corresponding decrease in G-actin content. Cytochalasin D treatment did not reduce F-actin formation during ATP depletion, indicating that it was predominantly not because of barbed end monomer addition. ATP-G-actin levels decreased rapidly during depletion, but there was no change in the concentration of ADP-G-actin monomers. The decrease in ATP-G-actin levels could be accounted for by dissociation of the thymosin-G-actin binary complex, resulting in a rise in the concentration of free thymosin beta4 from 4 to 11 microm. Increased detection of profilin-actin complexes during depletion indicated that profilin may participate in catalyzing nucleotide exchange during depletion. This mechanism provides a biochemical basis for the accumulation of F-actin aggregates in ischemic cells.
Atkinson
Simon J
SJ
Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA. satkinso@iupui.edu
Hosford
Melanie A
MA
Molitoris
Bruce A
BA
D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000968:Antimycin A / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D015638:Cytochalasin D / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007511:Ischemia; D007668:Kidney / Q000378:metabolism; D008954:Models, Biological; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D017830:Octoxynol / Q000494:pharmacology; D051381:Rats; D013552:Swine; D013947:Thymosin / Q000378:metabolism; D013997:Time Factors; D000099201:Thymosin beta(4)
D000199:Actins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000900:Anti-Bacterial Agents; D000968:Antimycin A; D015638:Cytochalasin D; D003902:Detergents; D019384:Nucleic Acid Synthesis Inhibitors; D017830:Octoxynol; D013947:Thymosin; D000099201:Thymosin beta(4)