Constitutive and inducible levels of egr-1 and c-myc early growth response gene expression in self-renewing B-1 lymphocytes.

B-1 lymphocytes constitute a mature B cell population that differs from conventional B cells in signaling requirements for cell cycle progression, being unusually responsive to PKC agonism but refractory to antigen receptor stimulation. Further, B-1 cells are self-renewing and derive from surface immunoglobulin-positive precursors. A previous report on clonally derived B-1 cells suggested that increased levels of expression of c-myc might underlie these unusual growth characteristics. This issue has now been reexamined using primary B-1 cells. The possible role of egr-1, in addition to c-myc, in specifying the responsiveness of B-1 cells was evaluated by determining levels of gene expression at baseline and after mitogenic treatment. Expression of the two genes was similar in B-1 and B-2 cells prior to stimulation. Subsequently, B-1 cells responded with higher levels of gene expression than B-2 cells regardless of ultimate cell cycle progression, with the exception of stimulation by anti-Ig. Overall, there was no apparent direct correlation between stimulated levels of expression of egr-1 or c-myc and mitogen-induced S phase entry, nor were B-1 cells characterized by constitutively elevated levels of either proto-oncogene that might explain their capacity for self-renewal.