Is the c-Cbl proto-oncogene involved in chronic lymphocytic leukemia?
ABSTRACT Chronic lymphocytic leukemia (CLL) is characterized by survival advantage and accumulation of CD5+ mature B lymphocytes. Expression of zeta-chain-associated protein-70 (ZAP-70), normally present in T lymphocytes or immature B cells, is associated with disease aggressiveness, as IgVH mutational status, and some proteins implicated in survival signal pathways are found to be constitutively activated in CLL cells. ZAP-70 signaling is regulated through molecular adaptors, such as the proto-oncogene product c-Casitas B lineage lymphoma (c-Cbl). The aim of this study was to determine the implication of this proto-oncogene product in CLL in survival signals. It appeared that expression of c-Cbl was increased in CLL and not correlated to that of B cell linker protein or ZAP-70. Furthermore, c-Cbl was significantly hypophosphorylated in progressive disease, so that hypophosphorylated form of c-Cbl (c-Cbl.P) along with ZAP-70, set a cutoff ratio distributing patients with stable situation below 1, and those with progressive disease equal or above 1. Given that phospholipase gamma 2 (PLC gamma 2) function is also influenced by c-Cbl hypophosphorylation, the ratio of PLC gamma 2 to c-Cbl.P was measured in CLL B cells and consistently found to be >or= 1 in Binet stage B CLL patients, as opposed to stage A CLL patients. These findings invite analysis of the role of c-Cbl in CLL.
- SourceAvailable from: Takahiko Horiuchi[Show abstract] [Hide abstract]
ABSTRACT: The aberrant regulation of B-cell receptor (BCR) signaling allows unwanted B cells to persist, thereby potentially leading to autoimmunity and B-cell malignancies. Casitas B-lineage lymphoma (Cbl) proteins suppress BCR signaling; however, the molecular mechanisms that control Cbl function in human B cells remain unclear. Here, we demonstrate that CIN85 (c-Cbl interacting protein of 85 kDa) is constitutively associated with c-Cbl, Cbl-b, and B-cell linker in B cells. Experiments using CIN85-overexpressing and CIN85-knockdown B-cell lines revealed that CIN85 increased c-Cbl phosphorylation and inhibited BCR-induced calcium flux and phosphorylation of Syk and PLCγ2, whereas it did not affect BCR internalization. The Syk phosphorylation in CIN85-overexpressing and CIN85-knockdown cells was inversely correlated with the ubiquitination and degradation of Syk. Moreover, CIN85 knockdown in primary B cells enhanced BCR-induced survival and growth, and increased the expression of BcLxL, A1, cyclin D2, and myc. Following the stimulation of BCR and Toll-like receptor 9, B-cell differentiation- associated molecules were up-regulated in CIN85-knockdown cells. Together, these results suggest that CIN85 is required for Cbl-mediated regulation of BCR signaling and for downstream events such as survival, growth, and differentiation of human B cells.Blood 03/2012; 119(10):2263-73. · 9.78 Impact Factor