Regulation of Casein Kinase 2 by Direct Interaction with Cell Surface Receptor CD5

Abstract

The transmembrane protein CD5, expressed on all T cells and the B1 subset of B cells, modulates antigen receptor-mediated activation. We used the yeast twohybrid system to identify proteins that interact with its cytoplasmic domain and play a role in CD5 proximal signaling events. We found that the ␤ subunit of the serine/threonine kinase casein kinase 2 (CK2) interacts specifically with the cytoplasmic domain of CD5. Coimmunoprecipitation experiments showed activationindependent association of CK2 with CD5 in human and murine B and T cell lines and murine splenocytes. The interaction of CK2 holoenzyme with CD5 is mediated by the amino terminus of the regulatory subunit ␤. CK2 binds and phosphorylates CD5 at the CK2 motifs flanked by Ser 459 and Ser 461 . Cross-linking of CD5 leads to the activation of CD5-associated CK2 in a murine B-lymphoma cell line and a human T-leukemia cell line and is independent of net recruitment of CK2 to CD5. In contrast, CK2 is not activated following cross-linking of the B cell receptor complex or the T cell receptor complex. This direct regulation of CK2 by a cell surface receptor provides a novel pathway for control of cell activation that could play a significant role in regulation of CD5-dependent antigen receptor activation in T and B cells.CD5 is a 67-kDa glycoprotein that belongs to the cysteinerich macrophage scavenger receptor family of proteins expressed on all thymocytes and T cells and a subset of B cells, described as B1a B cells (CD5 B cells) (1-4). It is expressed on T cells very early in development, before the expression of the TCR-CD3 1 complex, and during progressive stages of thymocyte development, the level of CD5 expression increases, suggesting a role in thymocyte biology (5). In cells of B-lineage, the onset of CD5 expression is not well defined, but it is expressed in all Ableson transformed lines, which represent the pre-B stage (6, 7). Proposed counter-receptors for CD5 include the B cell-specific CD72, gp35-37, which is expressed on activated splenocytes and activated T cell clones, and the Ig V H framework region (8 -11). The functional significance of these candidates in context with CD5 activation has not been been established.CD5 is physically associated with the antigen receptor complex in both T and B cells and modulates intracellular signals initiated by both . The conserved cytoplasmic domain of CD5 contains four tyrosines and several sites for serine and threonine phosphorylation (15)(16)(17)(18)(19)(20). Two of the tyrosines form an imperfect immunoreceptor tyrosine activation motif (21, 22). The serine/threonine sites include four CK2-dependent serine phosphorylation sites and a protein kinase C-dependent threonine phosphorylation site. TCR crosslinking leads to rapid tyrosine phosphorylation followed by serine/threonine phosphorylation of CD5 (14,23,24). In contrast, CD5 ligation leads to tyrosine kinase activation and tyrosine phosphorylation of several substrates but only to serine phosphorylation of its own cytoplasmic domain (25,26). CD5 ...

Protein kinase CK2 regulates CDC25B phosphatase activity

“…This interaction is mediated by the b regulatory subunit of CK2. Similar interactions with the b subunit have been reported for CK2-specific substrates: p53 (Filhol et al, 1992), FGF2 (Bonnet et al, 1996), DNA Topoisomerase IIa , CD5 (Raman et al, 1998), Nopp 140 (Li et al, 1997a) and the p21 protein (a CDK inhibitor) (Gotz et al, 2000;Romero-Oliva and Allende, 2001). It is clearly established that on binding to CK2b, CK2a changes activity and substrate specificity.…”

Increased numbers of thymic and peripheral CD4+ CD25+Foxp3+ cells in the absence of CD5 signaling

“…Upon CD3 ligation, the CD5 cytoplasmic tail becomes phosphorylated leading to the likely recruitment of p56 lck [33], PI3K [34], proto-oncoprotein c-Cbl, ras GTPase-activating protein [35] and SHP-1 [36]. In addition, CD5 ligation allows the activation of casein kinase II, which is constitutively associated to its cytoplasmic tail [37][38][39], as well as the activation of protein kinase C by a phosphatidylcholine-specific phospholipase C-dependent pathway [40]. Early in vitro studies indicated that CD5 acts as a costimulatory molecule for T-cell activation [41,42].…”

“…In addition, CD5 ligation allows the activation of casein kinase II, which is constitutively associated to its cytoplasmic tail [37][38][39], as well as the activation of protein kinase C by a phosphatidylcholine-specific phospholipase C-dependent pathway [40]. Early in vitro studies indicated that CD5 acts as a costimulatory molecule for T-cell activation [41,42].…”

High Mda-7 expression promotes malignant cell survival and p38 MAP kinase activation in chronic lymphocytic leukemia

“…We have however observed that, contrary to the majority of CD5 À B cells, normal CD5 þ blood B cells displayed a low Ca 2 þ response following anti-IgM stimulation, 15 confirming the role of CD5 as a negative regulator of BCR signaling. 16,17 Even though BCR-mediated activation is often deficient in CLL, CD5 may act independently of the BCR by recruiting signaling molecules, 18,19 and eliciting the production of B-cell survival factors such as interleukin (IL)-10. 15 IL-10 is indeed produced by most CLL B-cells, 20 improves the survival of malignant CLL B-cells, 21 and IL-10 serum levels in CLL correlated with the severity of the disease.…”