RESUMO
The hallmark of chronic lymphocytic leukemia (CLL) is the relentless accumulation of mature lymphocytes, mostly due to their decreased apoptosis. CD74 was recently shown to serve as a survival receptor on CLL cells. In this study, we show that stimulation of CD74 with its natural ligand, migration inhibitory factor, initiates a signaling cascade that results in upregulation of TAp63, which directly regulates CLL survival. In addition, TAp63 expression elevates the expression of the integrin VLA-4, particularly during the advanced stage of the disease. Blocking of CD74, TAp63, or VLA-4 inhibits the in vivo homing of CLL cells to the bone marrow (BM). Thus, CD74 and its target genes TAp63 and VLA-4 facilitate migration of CLL cells back to the BM, where they interact with the supportive BM environment that rescues them from apoptosis. These results could form the basis of novel therapeutic strategies aimed at blocking homing of CLL cells in their return to the BM and attenuating their survival.
Assuntos
Antígenos de Diferenciação de Linfócitos B/fisiologia , Células da Medula Óssea/imunologia , Células da Medula Óssea/patologia , Regulação Neoplásica da Expressão Gênica/imunologia , Antígenos de Histocompatibilidade Classe II/fisiologia , Integrina alfa4beta1/genética , Leucemia Linfocítica Crônica de Células B/imunologia , Leucemia Linfocítica Crônica de Células B/patologia , Transativadores/fisiologia , Proteínas Supressoras de Tumor/fisiologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Animais , Anticorpos Bloqueadores/farmacologia , Antígenos de Diferenciação de Linfócitos B/imunologia , Antígenos de Diferenciação de Linfócitos B/metabolismo , Antígenos de Neoplasias/biossíntese , Antígenos de Neoplasias/genética , Antígenos de Neoplasias/fisiologia , Proteínas Reguladoras de Apoptose/biossíntese , Proteínas Reguladoras de Apoptose/genética , Proteínas Reguladoras de Apoptose/fisiologia , Inibição de Migração Celular/imunologia , Movimento Celular/genética , Movimento Celular/imunologia , Sobrevivência Celular/genética , Sobrevivência Celular/imunologia , Feminino , Antígenos de Histocompatibilidade Classe II/imunologia , Antígenos de Histocompatibilidade Classe II/metabolismo , Humanos , Integrina alfa4beta1/biossíntese , Oxirredutases Intramoleculares/antagonistas & inibidores , Oxirredutases Intramoleculares/fisiologia , Leucemia Linfocítica Crônica de Células B/genética , Fatores Inibidores da Migração de Macrófagos/antagonistas & inibidores , Fatores Inibidores da Migração de Macrófagos/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Pessoa de Meia-Idade , Transdução de Sinais/imunologia , Transativadores/biossíntese , Transativadores/genética , Fatores de Transcrição , Proteínas Supressoras de Tumor/biossíntese , Proteínas Supressoras de Tumor/genética , Regulação para Cima/imunologiaRESUMO
Homing to secondary lymphoid organs and bone marrow (BM) is a central aspect of leukemic pathophysiology. We investigated the roles of the two major lymphocyte integrins LFA-1 and VLA-4 on B-cell chronic lymphocytic leukemia (CLL) cells in these processes. We found that the majority of CLL cells expressed significantly reduced LFA-1 due to low beta2 integrin transcripts. VLA-4 expression was heterogeneous but underwent rapid activation by the BM chemokine CXCL12. CLL cells failed to transmigrate across VCAM-1-expressing, ICAM-1-expressing, and CXCL12-expressing endothelium, whereas when LFA-1 expression was regained in subsets of CLL cells, these lymphocytes rapidly transmigrated the endothelium. Furthermore, when injected into tail veins of immunodeficient mice, normal B cells rapidly homed to lymph nodes (LN) in a LFA-1-dependent manner, whereas CLL cells did not. Nevertheless, only residual CLL subsets could reenter BM, whereas both normal and CLL cells homed to the mice spleen in an LFA-1-independent and VLA-4-independent manner. Our results suggest that CLL cells have a reduced capacity to adhere and transmigrate through multiple vascular endothelial beds and poorly home to lymphoid organs other than spleen. Integrin blocking could thus be an efficient strategy to prevent circulating CLL cells from reaching prosurvival niches in LNs and BM but not in spleen.
Assuntos
Medula Óssea/imunologia , Movimento Celular/imunologia , Leucemia Linfocítica Crônica de Células B/imunologia , Linfonodos/imunologia , Células Neoplásicas Circulantes/imunologia , Animais , Medula Óssea/patologia , Quimiocinas/imunologia , Células Endoteliais/imunologia , Células Endoteliais/patologia , Humanos , Integrina alfa4beta1/imunologia , Leucemia Linfocítica Crônica de Células B/sangue , Leucemia Linfocítica Crônica de Células B/patologia , Linfonodos/patologia , Antígeno-1 Associado à Função Linfocitária/biossíntese , Antígeno-1 Associado à Função Linfocitária/imunologia , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Células Neoplásicas Circulantes/patologia , Baço/imunologiaRESUMO
Chronic lymphocytic leukemia (CLL) is a malignant disease of small mature lymphocytes. Previous studies have shown that CLL B lymphocytes express relatively large amounts of CD74 mRNA relative to normal B cells. In the present study, we analyzed the molecular mechanism regulated by CD74 in B-CLL cells. The results presented here show that activation of cell-surface CD74, expressed at high levels from an early stage of the disease by its natural ligand, macrophage migration-inhibition factor (MIF), initiates a signaling cascade that contributes to tumor progression. This pathway induces NF-kappaB activation, resulting in the secretion of IL-8 which, in turn, promotes cell survival. Inhibition of this pathway leads to decreased cell survival. These findings could form the basis of unique therapeutic strategies aimed at blocking the CD74-induced, IL-8- dependent survival pathway.
Assuntos
Antígenos de Diferenciação de Linfócitos B/fisiologia , Sobrevivência Celular , Antígenos de Histocompatibilidade Classe II/fisiologia , Interleucina-8/metabolismo , Leucemia Linfocítica Crônica de Células B/patologia , Western Blotting , Citometria de Fluxo , Humanos , Interleucina-8/genética , Interleucina-8/fisiologia , Leucemia Linfocítica Crônica de Células B/imunologia , Transdução de SinaisRESUMO
CD74 is an integral membrane protein that was thought to function mainly as an MHC class II chaperone. However, CD74 was recently shown to have a role as an accessory-signaling molecule. Our studies demonstrated that CD74 regulates B-cell differentiation by inducing a pathway leading to the activation of transcription mediated by the NF-kappaB p65/RelA homodimer and its coactivator, TAF(II)105. Here, we show that CD74 stimulation with anti-CD74 antibody leads to an induction of a signaling cascade resulting in NF-kappaB activation, entry of the stimulated cells into the S phase, elevation of DNA synthesis, cell division, and augmented expression of BCL-X(L). These studies therefore demonstrate that surface CD74 functions as a survival receptor.