Signaling regulation of transitional immature to mature B cell development

Abstract

The immature B cell compartment in the spleen comprises of two subsets termed Transitional Type 1 (T1) and Transitional Type 2 (T2). Our laboratory has shown that T1 and T2 B cell subsets respond differently to crosslinking of the BCR; T1 cells die upon BCR stimulation whereas T2 cells proliferate and differentiate into a mature B cell phenotype. The signaling mechanisms that control these disparate biological outcomes in T1 versus T2 cells remain elusive. I hypothesize that the composition of the BCR signalosome is altered during T1 to T2 B cell development. This in turn activates distinct signaling pathways in response to BCR crosslinking. I performed cDNA microarrays and proteomic approaches to define the global genetic and biochemical signaling programs that control the differential BCR responses of T1, T2 and mature B cells. Through proteomics I identified the serine/threonine phosphatase PP2A, CD45 associated protein (CD45-AP) and a never before identified protein in B cells, Src Kinase Associated Phosphoprotein (SKAP55) specifically in T1 but not T2 or mature B cells. Through microarray analysis we found that pro-apoptotic genes did not show any significant difference among T1, T2 and mature B cells, but T1 cells did have lower levels of two anti-apoptotic genes, A1 and Bcl-2. This suggests that the effect in B cell survival of T1 cells may be due to lower expression of anti-apoptotic genes. In addition I found that T1 B cells had lower levels of NF-kappaB1 and NF-kappaB2. Thus, global genomics and proteomics are feasible approaches to help define the unique characteristics of the transitional B cell subsets that underlie their differentiation.