Control of profilin and actin expression in muscle and nonmuscle cells.
Profilin is a small G-actin binding protein implicated in sequestering actin monomers in vivo. We have quantitated profilin and actin expression in human hepatoma HepG-2 cells and in two mouse myogenic cell lines, BC3H1 and C2C12, to determine whether the expression of profilin and the expression of nonmuscle isoactin or total actin are co-regulated. During differentiation of both muscle cell types, profilin and nonmuscle actin expression decrease in a coordinate manner as shown by measurements of steady state mRNA and newly synthesized protein. In human hepatoma HepG-2 cells, the twofold increase in actin synthesis observed after 24 hours of exposure to cytochalasin D did not result in an increase in profilin synthesis. Thus, profilin and actin expression are not co-regulated in all cells. To determine if there is sufficient profilin to sequester a large portion of cellular G-actin, we measured total profilin and G-actin levels in the three cell types. In each case, profilin accounted for less than 10% of the total G-actin on a molar basis. Thus, profilin is not responsible for total G-actin sequestration in these cells. Finally, using poly-L-proline affinity chromatography, we showed that, in the cell types tested, less than 20% of the poly-L-proline purified profilin existed as a complex with G-actin. The profilin in these cells may be interacting with cellular components other than actin.
Babcock
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Department of Biochemistry, University of Iowa College of Medicine, Iowa City 52242-1109.
Rubenstein
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PA
D000199:Actins / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002460:Cell Line; D003285:Contractile Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism*; D051379:Mice; D008840:Microfilament Proteins / Q000096:biosynthesis* / Q000235:genetics; D009132:Muscles / Q000378:metabolism*; D051304:Profilins; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000199:Actins; D003285:Contractile Proteins; D008840:Microfilament Proteins; C495738:PFN1 protein, human; C495739:Pfn1 protein, mouse; D051304:Profilins; D012333:RNA, Messenger