Cyclin-Dependent Kinases Regulate Ig Class Switching by Controlling Access of AID to the Switch Region

Abstract

Ig class switching requires cell proliferation and is division linked, but the detailed mechanism is unknown. By analyzing the first switching cells early in the kinetics, our analysis suggested that proliferating B cells had a very short G1 phase (<3.5 h), a total cell cycle time of ∼11 h, and that Ig class switching preferentially occurred in the late G1 or early S phase. Inhibition of cyclin-dependent kinases (CDKs) caused dramatic reduction of switching rate within 6 h. This was associated with less targeting of activation-induced cytidine deaminase (AID) to the Igh locus. Interestingly, ectopically expressed nuclear AID in HeLa cells was preferentially found in the early S phase. Furthermore, in CDK2 hypomorphic cells there was reduced nuclear AID accumulation. Thus, our data are compatible with the idea that division-linked Ig class switching is in part due to CDK2-regulated AID nuclear access at the G1/S border.

Deletion of Dock10 in B Cells Results in Normal Development but a Mild Deficiency upon In Vivo and In Vitro Stimulations

“…Together, these data indicate that Dock10 acts as a GEF for Cdc42 in a receptor-selective manner. We next examined if the decreased proliferative response to LPS and anti-CD40 + IL-4 was associated with altered Ig class switching, known to be dependent on cell proliferation ( 31 , 32 ). The production of IgM, IgG1, IgG2b, IgG3, or IgE responses were similar in Dock10 knockout and control B cells after in vitro activation with LPS or anti-CD40 + IL-4 (Figures 5 C–E).…”

“…These two responses are most likely linked. A lower capacity of B cells to proliferate would be expected to have a reducing effect on the IgG response, since switching is linked to the capacity of cells to enter into S-phase and is occurring only after B cells have proliferated several times ( 31 , 32 ). The puzzle is why lower proliferation capacity did not change the affinity of the response.…”

Mutations, kataegis and translocations in B cells: understanding AID promiscuous activity

“…B cells lacking factors necessary for NHEJ or homologous recombination accumulate AID-mediated breaks in S and G2/M 26, 135 , These lesions might represent delayed repair or in some cases active deamination at S and G2M. Some mechanisms that might restrict AID activity to G1 include stage-specific regulation of AID protein localization and/or stability 136, 137 , phosphorylation, availability of co-factors, or the regulation of nuclear AID stability by cyclins, as has been recently proposed 138 . To date, this topic remains largely unexplored.…”

DNA Replication Origins in Immunoglobulin Switch Regions Regulate Class Switch Recombination in an R-Loop-Dependent Manner

“…Therefore, CSR requires S phase entry, but not proliferation per se (Hasham et al, 2012). Furthermore, a recent study measuring the kinetics of the cell cycle in switching B cells revealed that switching occurs in the early S phase and involves DNA synthesis (He et al, 2015). Finally, it appears that the G1/S phase cell-cycle checkpoint in switching B cells is not responsive to AID-mediated DSBs and that cells with unrepaired DSBs can enter S phase (Hasham et al, 2012;Yamane et al, 2013).…”