Parafibromin is a nuclear protein with a functional monopartite nuclear localization signal

Abstract

Parafibromin is a nuclear protein with a tumour suppressor role in the development of non-hereditary and hereditary parathyroid carcinomas, and the hyperparathyroidism-jaw tumour (HPT-JT) syndrome, which is associated with renal and uterine tumours. Nuclear localization signal(s), (NLS(s)), of the 61 kDa parafibromin remain to be defined. Utilization of computer-prediction programmes, identified five NLSs (three bipartite (BP) and two monopartite (MP)). To investigate their functionality, wild-type (WT) and mutant parafibromin constructs tagged with enhanced green fluorescent protein or cMyc were transiently expressed in COS-7 cells, or human embryonic kidney 293 (HEK293) cells, and their subcellular locations determined by confocal fluorescence microscopy. Western blot analyses of nuclear and cytoplasmic fractions from the transfected cells were also performed. WT parafibromin localized to the nucleus and deletions or mutations of the three predicted BP and one of the predicted MP NLSs did not affect this localization. In contrast, deletions or mutations of a MP NLS, at residues 136-139, resulted in loss of nuclear localization. Furthermore, the critical basic residues, KKXR, of this MP NLS were found to be evolutionarily conserved, and over 60% of all parafibromin mutations lead to a loss of this NLS. Thus, an important functional domain of parafibromin, consisting of an evolutionarily conserved MP NLS, has been identified.

A Comprehensive Overview of Skeletal Phenotypes Associated with Alterations in Wnt/β-catenin Signaling in Humans and Mice

“…Binding of β-catenin/parafibromin may be mediated by protein tyrosine phosphatase, PTPN11 (Shp2), which dephosphoylates parafibromin and thus allows it to bind β-catenin, recruit the PAF complex, and activate transcription (13). Interestingly, loss-of-function mutations within the coding sequence of parafibromin lead to parathyroid adenomas and ossifying fibromas of the jaw (412)(413)(414). Further work using cell-specific knock-outs are needed to help determine how these regulators of β-catenin/TCF-mediated transcription govern bone formation.…”

Human RNA polymerase II-associated factor complex: dysregulation in cancer

“…A clear functional nuclear localization signal (NLS) was not identified until one study reported that parafibromin contains a functional bipartite (BP) NLS (Hahn and Marsh, 2005). However, a recent report reveals that it contains five putative NLSs, three BP and two monopartites (MP) (Figure 1b), and that only one of these is evolutionarily conserved and functions as MP NLS (Bradley et al, 2007). The behavior of parafibromin reported so far in cancers is its potential function as a tumor suppressor.…”

Should parafibromin staining replace HRTP2 gene analysis as an additional tool for histologic diagnosis of parathyroid carcinoma?

“…Parafibromin, the 531 amino acid protein encoded by the HRPT2 gene (15), is part of the human Paf1 complex and involved in transcription regulation, histone modification and cell proliferation (16)(17)(18)(19)(20)(21). It has been shown that parafibromin down-regulates the expression of cyclin D1 (16,20).…”

“…It has been shown that parafibromin down-regulates the expression of cyclin D1 (16,20). The protein is mostly located in the nucleus and the nuclear localization signal (NLS) was originally identified at residues 125-139 (19) and most recently at residues 136-139 (21). Inactivating mutations of parafibromin were reported in 77% of sporadic parathyroid carcinomas (11)(12)(13) and loss of immunoreactivity for parafibromin was shown in the majority of parathyroid carcinomas (22,23).…”