Structure, Expression, and Function of Human Pituitary Tumor-Transforming Gene (PTTG)

Abstract

Despite advances in characterizing the pathophysiology and genetics of pituitary tumors, molecular mechanisms of their pathogenesis are poorly understood. Recently, we isolated a transforming gene [pituitary tumor-transforming gene (PTTG)] from rat pituitary tumor cells. Here we describe the cloning of human PTTG, which is located on chromosome 5q33 and shares striking sequence homology with its rat counterpart. Northern analysis revealed PTTG expression in normal adult testis, thymus, colon, small intestine, brain, lung, and fetal liver, but most abundant levels of PTTG mRNA were observed in several carcinoma cell lines. Stable transfection of NIH 3T3 cells with human PTTG cDNA caused anchorage-independent transformation in vitro and induced in vivo tumor formation when transfectants were injected into athymic mice. Overexpression of PTTG in transfected NIH 3T3 cells also stimulated expression and secretion of basic fibroblast growth factor, a human pituitary tumor growth-regulating factor. A proline-rich region, which contains two PXXP motifs for the SH3 domain-binding site, was detected in the PTTG protein sequence. When these proline residues were changed by site-directed mutagenesis, PTTG in vitro transforming and in vivo tumor-inducing activity, as well as stimulation of basic fibroblast growth factor, was abrogated. These results indicate that human PTTG, a novel oncogene, may function through SH3-mediated signal transduction pathways and activation of growth factor(s).

Cell cycle regulated expression and phosphorylation of hpttg proto-oncogene product

“…Mutation of prolines 163, 170, 172 and 173 abrogated the hPTTG in vitro transforming and in vivo tumor-inducing activity as well as stimulation of basic ®broblast growth factor, suggesting that hPTTG may function through SH3-mediated signal transduction pathways (Zhang et al, 1999b). Interestingly, the Cdc2 phosphorylation site in hPTTG is located in the middle of this important proline rich region ( Figure 6a).…”

“…This hypothesis arose from the observation that hpttg is expressed at high levels, not only in tumor cells but also in normal tissues that contain proliferating cells (DomõÂ nguez et al, 1998;Zhang et al, 1999b).…”

“…In addition we showed that the expression was elevated in Jurkat (a lymphoma T cell line) as well as in primary hematopoietic tumors. Examination of several different tumor cell lines by Northern blot indicates that these lines all contain high levels of hpttg mRNA (Zhang et al, 1999b;our unpublished results). These data suggest that hpttg is preferentially expressed in proliferating cells.…”

“…A ®rst indication of the potential function of hPTTG was our demonstration that the acidic carboxyl-terminal region of hPTTG acts as a transactivation domain when fused to a heterologous DNA binding domain (DomõÂ nguez et al, 1998). More recently, the transforming activity of human pttg has been shown in NIH3T3 cells: stable transfection of these cells with hpttg cDNA caused anchorageindependent transformation in vitro and induced in vivo tumor formation when transfectants were injected into athymic mice (Zhang et al, 1999b).…”

Expression and possible role of hPTTG1/securin in cutaneous malignant melanoma

“…2,3 hPTTG1 is a proto-oncogene encoding for securin, a protein involved in several metabolic reactions, cellcycle progression, appropriate cell division and chromosome stability; upon overexpression, securin is involved in malignant transformation and tumorigenesis. 4 In normal tissues, securin expression is limited, in contrast to many human tumours, including pituitary adenomas, 5 lung and breast cancer, [5][6][7] colorectal cancer, 8 oesophageal cancer 9 and some lymphoid neoplasms.…”