Increase in the 64-kDa subunit of the polyadenylation/cleavage stimulatory factor during the G0 to S phase transition.
The amount of the 64-kDa subunit of polyadenylation/cleavage stimulatory factor (CstF-64) increases 5-fold during the G0 to S phase transition and concomitant proliferation induced by serum in 3T6 fibroblasts. Higher levels of CstF-64 result in an increase in CstF trimer. The rise in CstF-64 occurs at a time when the amount of poly(A)-containing RNA rose at least 5-8 fold in the cytoplasm. Primary human splenic B cells, resting in G0, show a similar 5-fold increase in CstF-64 when cultured under conditions inducing proliferation (CD40 ligand exposure). Therefore, the increase in CstF-64 is associated with the G0 to S phase transition. As B cell development progresses, RNA processing changes occur at the Ig heavy chain locus resulting in a switch from the membrane- to the upstream secretory-specific poly(A) site. Treating resting B cells with agents triggering this switch in Ig mRNA production along with proliferation (CD40 ligand plus lymphokines or Staphylococcus aureus protein A) induces no further increase in CstF-64 above that seen for proliferation alone. The rise in CstF-64 is therefore insufficient to induce secretion. After stimulation of a continuously growing B cell line with lymphokines, a switch to Ig micrometer secretory mRNA and protein occurs but without a change in the CstF-64 level. Therefore, an increase in CstF-64 levels is not necessary to mediate the differentiation-induced switch to secreted forms of Ig-micrometer heavy chain. Because augmentation of CstF-64 levels is neither necessary nor sufficient for Ig secretory mRNA production, we conclude that other lymphokine-induced factors play a role.
Martincic
K
K
Department of Molecular Genetics and Biochemistry, University of Pittsburgh, School of Medicine, Pittsburgh, PA 15261, USA.
Campbell
R
R
Edwalds-Gilbert
G
G
Souan
L
L
Lotze
M T
MT
Milcarek
C
C
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D023201:CD40 Ligand; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D007134:Immunoglobulin Switch Region / Q000235:genetics; D015850:Interleukin-6 / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D011061:Poly A / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D016192:Resting Phase, Cell Cycle / Q000502:physiology*; D016196:S Phase / Q000502:physiology*; D013154:Spleen / Q000378:metabolism; D039221:mRNA Cleavage and Polyadenylation Factors
D007075:Immunoglobulin M; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D039221:mRNA Cleavage and Polyadenylation Factors; D023201:CD40 Ligand; D011061:Poly A