Ikeda K, Okazaki R, Inoue D, Ogata E, Matsumoto T
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
J Biol Chem. 1993 Jan 15;268(2):1174-9.
Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of adult T-cell leukemia (ATL), and hypercalcemia frequently associated with ATL is mediated by parathyroid hormone-related peptide (PTHRP). The present study was undertaken to clarify the role of cAMP second messenger system in the regulation of human PTHRP gene expression in ATL cells, using an HTLV-I-infected T-cell line, MT-2. Forskolin and dibutyryl cAMP (Bt2cAMP) caused a marked and transient increase in the steady-state level of PTHRP mRNA. The effects of these agents were dose-dependent, and the maximal effects were observed at 3 h. Nuclear runoff transcription assay showed that forskolin and Bt2cAMP caused an increase in the transcription rate of the human PTHRP gene. In contrast, the stability of PTHRP mRNA was only modestly increased by these agents. Forskolin and Bt2cAMP also increased the secretion of PTHRP by MT-2 cells, as determined by both a newly established immunoradiometric assay using two antibodies against human PTHRP-(1-34) and PTHRP-(50-83) and a radioimmunoassay using an antibody against human PTHRP-(109-141). Prostaglandin E1 (PGE1) caused a marked stimulation of intracellular cAMP production in MT-2 cells, whereas PGE2 and PGF2 alpha had only modest effects. The ability of these PGs to stimulate cAMP production correlated well with their ability to increase PTHRP mRNA level and the secretion of PTHRP. Indomethacin did not affect the basal level of cAMP production or PTHRP mRNA, suggesting that endogenous PG was not involved in the basal production of cAMP or PTHRP. When PGE1 was given to MT-2 cells together with interleukin 2, which is another stimulator of PTHRP gene expression, PTHRP secretion was synergistically stimulated. These results suggest that the transcription of the human PTHRP gene is enhanced through a cAMP-dependent pathway by PGE1 and that PGE1, as well as interleukin 2, plays an important role in the overexpression of the human PTHRP gene in HTLV-I-infected T cells leading to the development of hypercalcemia in ATL patients.
人类I型T细胞白血病病毒（HTLV-I）是成人T细胞白血病（ATL）的病原体，而常与ATL相关的高钙血症是由甲状旁腺激素相关肽（PTHRP）介导的。本研究旨在利用一株HTLV-I感染的T细胞系MT-2，阐明cAMP第二信使系统在调节ATL细胞中人PTHRP基因表达中的作用。福斯可林和二丁酰环磷腺苷（Bt2cAMP）使PTHRP mRNA的稳态水平显著且短暂升高。这些试剂的作用呈剂量依赖性，在3小时时观察到最大效应。核转录分析表明，福斯可林和Bt2cAMP导致人PTHRP基因的转录速率增加。相比之下，这些试剂仅适度增加了PTHRP mRNA的稳定性。福斯可林和Bt2cAMP还增加了MT-2细胞分泌PTHRP，这是通过一种新建立的使用两种抗人PTHRP-（1-34）和PTHRP-（50-83）抗体的免疫放射分析以及一种使用抗人PTHRP-（109-141）抗体的放射免疫分析来确定的。前列腺素E1（PGE1）在MT-2细胞中引起细胞内cAMP产生的显著刺激，而PGE2和PGF2α的作用较小。这些前列腺素刺激cAMP产生的能力与其增加PTHRP mRNA水平和PTHRP分泌的能力密切相关。吲哚美辛不影响cAMP产生或PTHRP mRNA水平的基础水平，表明内源性前列腺素不参与cAMP或PTHRP的基础产生。当将PGE1与白细胞介素2（PTHRP基因表达的另一种刺激物）一起给予MT-2细胞时，PTHRP分泌受到协同刺激。这些结果表明，PGE1通过cAMP依赖性途径增强人PTHRP基因的转录，并且PGE1以及白细胞介素2在HTLV-I感染的T细胞中人PTHRP基因的过度表达中起重要作用，导致ATL患者发生高钙血症。
