Microinjection of ADP-ribosylated actin inhibits actin synthesis in hepatocyte-hepatoma hybrid cells.
Treatment of hepatocyte-hepatoma hybrid cells with Clostridium botulinum C2 toxin led to a 167% increase in monomeric globular actin (G-actin) and to a 57% decrease in filamentous actin (F-actin) within 2 h. Simultaneously, the level of actin mRNA was specifically decreased to 49% and actin synthesis was significantly diminished. In contrast, treatment of hybrid cells with phalloidin led to a decrease in G-actin to 55% and to a reciprocal increase in actin mRNA to 244% and an increase in actin synthesis. These alterations of actin synthesis depending on the G-actin/F-actin ratio corresponded to the autoregulation of actin synthesis observed in primary cultures of rat hepatocytes. Microinjection of C2 toxin or of phalloidin into hepatocyte-hepatoma hybrid cells had the same effects on actin synthesis as incubation with either toxin in the culture medium. Microinjection of nonpolymerizable ADP-ribosylated G-actin into hepatocyte-hepatoma hybrid cells specifically decreased the incorporation of [35S]methionine into newly synthesized actin within 1 h. This decrease continued for at least 19 h. Microinjection of ADP-ribosylated actin led to rounding of cells and obvious disaggregation of actin filaments, which might be due to capping of actin filaments by the ADP-ribosylated actin. Because stabilization of actin filaments by phalloidin before microinjection of ADP-ribosylated actin also resulted in decreased actin synthesis, the concentration of monomeric G-actin seems to be responsible for the regulation of actin synthesis in hepatocyte-hepatoma hybrid cells, which can be regarded as immortalized hepatocytes.
Reuner
K H
KH
Institut für Klinische Chemie und Pathobiochemie der Universität Giessen, Federal Republic of Germany.
van der Does
A
A
Dunker
P
P
Just
I
I
Aktories
K
K
Katz
N
N
D000199:Actins / Q000096:biosynthesis* / Q000302:isolation & purification / Q000494:pharmacology*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology*; D002478:Cells, Cultured; D006706:Homeostasis; D006822:Hybrid Cells / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D010590:Phalloidine / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012709:Serum Albumin / Q000096:biosynthesis; D014158:Transcription, Genetic
D000199:Actins; D012333:RNA, Messenger; D012709:Serum Albumin; D010590:Phalloidine; D000246:Adenosine Diphosphate Ribose; D001905:Botulinum Toxins; C096324:botulinum toxin type C