STAT3 Regulates the Growth and Immunoglobulin Production of BCL1 B Cell Lymphoma through Control of Cell Cycle Progression

STAT3 is constitutively phosphorylated on tyrosine705 in self-renewing, CD5+ murine B-1 lymphocytes. Nuclear extracts from untreated primary B-1 or CD5+ BCL1 B lymphoma cells were found to contain immunoreactive STAT3 protein that binds to a sis-inducible element present in the promoter of the p21waf1/cip1 tumor suppressor gene and is constitutively phosphorylated on serine727. To determine the functional significance of constitutive STAT3 activation in B lymphoma cells, a specific STAT3 antisense oligonucleotide was developed and used to examine basal BCL1 cell growth and IgM production. Abrogating STAT3 expression in BCL1 cells inhibited their proliferative capacity and induced a corresponding decrease in secretion of IgM. Cell cycle analysis showed a block in progression through G1 in BCL1 cells treated with the STAT3 antisense oligonucleotide. These results indicate that STAT3 controls cell growth and immunoglobulin secretion by enhancing progression through the G1 phase of the cell cycle in BCL1 B cell lymphoma.