The 58‐kDa microspherule protein (MSP58), a nucleolar protein, interacts with nucleolar protein p120

Abstract

Protein p120 is a proliferation-related nucleolar protein which is detectable early in the G1 phase of the cell cycle and peaks early in the S phase. Most human malignant tumors contain much higher levels of protein p120 than normal resting cells. To identify p120-associated protein(s), a yeast two-hybrid screen was carried out using protein p120 as the bait. Two positive clones encoded portions of a novel protein, designated microspherule protein 58 kDa (MSP58). MSP58 mRNA is 1.9 kb and encodes an approximately 58-kDa polypeptide of 462 amino acids as shown by Western blotting of HeLa nucleolar proteins. The mouse MSP58 homolog has 97% amino acid similarity to human MSP58, but no MSP58 homolog was found in the yeast genome. The MSP58 N-terminal region contains serine-rich clusters and its C-terminal region has a coiled-coil domain. In insect Sf9 cells, recombinant p120 and MSP58 proteins associated with each other, confirming the results of the yeast two-hybrid assay. Deletion mutations revealed that the binding of MSP58 to p120 required a previously unrecognized coiled-coil domain within the N-terminal region of p120 and the C-terminal region of MSP58 protein. Immunofluorescence indicated that the MSP58 protein is localized in microspherules in the nucleolus. Anti-MSP58 Ig labeled nucleolar 'caps' when HeLa cells were treated with actinomycin D. When the MSP58 protein was overexpressed in COS-7 cells, the nucleolus became irregularly enlarged, which suggests that MSP58 may affect the size and shape of the nucleolus.Keywords : 58-kDa microspherule protein; p120; protein-protein interaction ; nucleolar protein; nucleolus.Nucleolar pleomorphism and hyperactivity of nucleolar is a proliferation-associated antigen which is visualized early in the G1 phase of the cell cycle and peaks in early S phase [7, 8]. function are major characteristics of cancer cells [1]. Biochemical and immunological analyses have demonstrated multiple difTransformation of NIH/3T3 cells was induced by overexpression of human p120 and growth was inhibited by a p120 ferences between nuclear and nucleolar proteins of tumor and non-tumor tissues [2Ϫ4]. Nucleolar components in interphase antisense construct [9]. A clinical study showed that decreased survival of breast cancer patients correlated with increased cells include fibrillar centers (FC) which contain nucleolar-organizer regions and rDNA genes; the dense fibrillar components amounts of nucleolar p120 [10].Overexpression of the nucleolar protein (NOP2) in yeast, which contain newly assembled ribonucleoproteins and the granular components which are maturation sites for pre-ribosomal which is homologous to the human protein p120, resulted in the formation of a nucleolus that did not localize to the nuclear particles. During prophase, the nucleolus is disassembled and the nucleolar constituents are dispersed throughout the nucleus. envelope but had a spherical shape within the nucleoplasm typical of plant nucleoli [11]. A recent study showed that NOP2 is During telophase, prenucleolar bodie...

TOJ3, a target of the v-Jun transcription factor, encodes a protein with transforming activity related to human microspherule protein 1 (MCRS1)

“…Figure 2) revealed apparent similarities to human sequences corresponding to the microspherule protein 1 (MCRS1) p78 (Bruni and Roizman, 1998), also designated as 58-kDa microspherule protein MSP58 (Ren et al, 1998) (Table 1). The MCRS1 protein is located in cellular nucleoli where it interacts with the nuclear regulatory protein ICP22 from herpes simplex virus 1, and accumulates in a cell cycle-dependent manner (Bruni and Roizman, 1998).…”

“…Aberrant migration has been also observed for the 462-amino acid MSP58 protein migrating with an apparent size of 58 kDa (Ren et al, 1998), and for the 534-amino acid MCRS1 (p78) protein with migration sizes of 78, 62 and 55 kDa (Bruni and Roizman, 1998). Apart from the 84 amino terminal residues, TOJ3 is highly related to the mammalian MCRS1 proteins and thus may represent the MCRS1 quail ortholog (cf.…”

“…The cell cycle-regulated factor p78 possibly controls the herpes simplex virus 1 (HSV-1) protein ICP22 via proteinprotein interaction (Bruni and Roizman, 1998). The MSP58 protein was identi®ed as the interacting partner of p120, a proliferation-related nucleolar protein present at signi®cantly elevated levels in most human tumor cells (Ren et al, 1998;Freeman et al, 1988). Both p78 and MSP58 are localized as dense bodies or microspherules within the nucleoli, respectively (Bruni and Roizman, 1998;Ren et al, 1998) and may be involved in the formation of ribosomal particles (Hozak, 1995).…”

“…The MCRS1 protein is located in cellular nucleoli where it interacts with the nuclear regulatory protein ICP22 from herpes simplex virus 1, and accumulates in a cell cycle-dependent manner (Bruni and Roizman, 1998). MSP58 was identi®ed as an interaction partner of the proliferationrelated nucleolar protein p120 which reaches peak levels in early S phase of the cell cycle (Ren et al, 1998) and is expressed at high levels in a variety of human malignant tumor cells (Freeman et al, 1988). The alignment of the 530-amino acid quail protein with the 534-amino acid human MCRS1, the 462-amino acid human MSP58, and the 462-amino acid murine MCRS1 proteins ( Figure 3) shows that the predicted quail protein shares a high degree of sequence identity in the carboxyl terminal 448 residues with all compared mammalian sequences.…”

MSP58 Knockdown Inhibits the Proliferation of Esophageal Squamous Cell Carcinoma in Vitro and in Vivo

“…MSP58 was first identified as a nuclear protein that interacts with the proliferation-related nucleus protein p120 (Ren et al, 1998). Additional studies showed that, in the nucleus, MSP58 could function to regulate transcription through its interactions with the transcription factors Daxx, STRA13, and the RNA-binding protein FMR (Lin et al, 2002;Ivanova et al, 2005;Davidovic et al, 2006).…”