RESUMO
In this article, we report that cutaneous T cell lymphoma (CTCL) cells and tissues ubiquitously express the immunosuppressive cell surface protein CD80 (B7-1). CD80 expression in CTCL cells is strictly dependent on the expression of both members of the STAT5 family, STAT5a and STAT5b, as well as their joint ability to transcriptionally activate the CD80 gene. In IL-2-dependent CTCL cells, CD80 expression is induced by the cytokine in a Jak1/3- and STAT5a/b-dependent manner, whereas in the CTCL cells with constitutive STAT5 activation, CD80 expression is also STAT5a/b dependent but is independent of Jak activity. Although depletion of CD80 expression does not affect the proliferation rate and viability of CTCL cells, induced expression of the cell-inhibitory receptor of CD80, CD152 (CTLA-4), impairs growth of the cells. Coculture of CTCL cells with normal T lymphocytes consisting of both CD4(+) and CD8(+) populations or the CD4(+) subset alone, transfected with CD152 mRNA, inhibits proliferation of normal T cells in a CD152- and CD80-dependent manner. These data identify a new mechanism of immune evasion in CTCL and suggest that the CD80-CD152 axis may become a therapeutic target in this type of lymphoma.
Assuntos
Antígeno B7-1/imunologia , Linfoma Cutâneo de Células T/imunologia , Fator de Transcrição STAT5/imunologia , Proteínas Supressoras de Tumor/imunologia , Adulto , Antígeno B7-1/genética , Antígeno B7-1/metabolismo , Western Blotting , Antígeno CTLA-4/imunologia , Antígeno CTLA-4/metabolismo , Linhagem Celular Tumoral , Proliferação de Células , Células Cultivadas , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica/imunologia , Humanos , Imuno-Histoquímica , Interleucina-2/farmacologia , Janus Quinase 1/imunologia , Janus Quinase 1/metabolismo , Janus Quinase 3/imunologia , Janus Quinase 3/metabolismo , Linfoma Cutâneo de Células T/genética , Linfoma Cutâneo de Células T/metabolismo , Modelos Imunológicos , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fator de Transcrição STAT5/genética , Fator de Transcrição STAT5/metabolismo , Linfócitos T/imunologia , Linfócitos T/metabolismo , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismoRESUMO
RasGRP3, an activator for H-Ras, R-Ras and Ras-associated protein-1/2, has emerged as an important mediator of signaling downstream from receptor coupled phosphoinositide turnover in B and T cells. Here, we report that RasGRP3 showed a high level of expression in multiple human melanoma cell lines as well as in a subset of human melanoma tissue samples. Suppression of endogenous RasGRP3 expression in these melanoma cell lines reduced Ras-GTP formation as well as c-Met expression and Akt phosphorylation downstream from hepatocyte growth factor (HGF) or epidermal growth factor (EGF) stimulation. RasGRP3 suppression also inhibited cell proliferation and reduced both colony formation in soft agar and xenograft tumor growth in immunodeficient mice, demonstrating the importance of RasGRP3 for the transformed phenotype of the melanoma cells. Reciprocally, overexpression of RasGRP3 in human primary melanocytes altered cellular morphology, markedly enhanced cell proliferation and rendered the cells tumorigenic in a mouse xenograft model. Suppression of RasGRP3 expression in these cells inhibited downstream RasGRP3 responses and suppressed cell growth, confirming the functional role of RasGRP3 in the altered behavior of these cells. The identification of the role of RasGRP3 in melanoma highlights its importance, as a Ras activator, in the phosphoinositide signaling pathway in human melanoma and provides a new potential therapeutic target.