RESUMEN
Small Cell Lung Cancer (SCLC) is a specific subtype of lung cancer presenting as highly metastatic disease with extremely poor prognosis. Despite responding initially well to chemo- or radiotherapy, SCLC almost invariably relapses and develops resistance to chemotherapy. This is suspected to be related to tumor cell subpopulations with different characteristics resembling stem cells. Epithelial-Mesenchymal Transition (EMT) is known to play a key role in metastatic processes and in developing drug resistance. This is also true for NSCLC, but there is very little information on EMT processes in SCLC so far. SCLC, in contrast to NSCLC cell lines, grow mainly in floating cell clusters and a minor part as adherent cells. We compared these morphologically different subpopulations of SCLC cell lines for EMT and epigenetic features, detecting significant differences in the adherent subpopulations with high levels of mesenchymal markers such as Vimentin and Fibronectin and very low levels of epithelial markers like E-cadherin and Zona Occludens 1. In addition, expression of EMT-related transcription factors such as Snail/Snai1, Slug/Snai2, and Zeb1, DNA methylation patterns of the EMT hallmark genes, functional responses like migration, invasion, matrix metalloproteases secretion, and resistance to chemotherapeutic drug treatment all differed significantly between the sublines. This phenotypic variability might reflect tumor cell heterogeneity and EMT during metastasis in vivo, accompanied by the development of refractory disease in relapse. We propose that epigenetic regulation plays a key role during phenotypical and functional changes in tumor cells and might therefore provide new treatment options for SCLC patients.
Asunto(s)
Metilación de ADN , Transición Epitelial-Mesenquimal/genética , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patología , Carcinoma Pulmonar de Células Pequeñas/genética , Carcinoma Pulmonar de Células Pequeñas/patología , Biomarcadores/metabolismo , Cadherinas/genética , Cadherinas/metabolismo , Línea Celular Tumoral , Movimiento Celular/genética , Resistencia a Antineoplásicos/genética , Espacio Extracelular/metabolismo , Expresión Génica , Estudios de Asociación Genética , Humanos , Neoplasias Pulmonares/metabolismo , Metaloproteinasas de la Matriz/biosíntesis , Proteolisis , Carcinoma Pulmonar de Células Pequeñas/metabolismo , Vimentina/genética , Vimentina/metabolismoRESUMEN
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.
