Nucleostemin mRNA is expressed in both normal and malignant renal tissues

Abstract

Nucleostemin (NS), a p53-binding protein, has been shown essential for stem and cancer cell proliferation and implicated in oncogenesis. To explore potential contributions of NS to the development of clear cell renal cell carcinomas (ccRCCs), we determined NS expression in ccRCC cell lines, and in paired normal and malignant renal tissues from 31 patients with ccRCC. Nucleostemin mRNA and/or protein expression was observed in all four cell lines and 27 of 31 (87%) tumour specimens. Surprisingly, 16 of 31 (52%) adjacent normal renal samples also expressed NS mRNA and its levels in four of them were comparable with those in paired tumour tissues. Three of the patients had detectable NS mRNA in their normal renal tissues whereas lacked its expression in the matched tumours. Compared to the oncogene c-MYC expression in these same samples, NS expression showed a much less specificity for ccRCC. We further demonstrated that NS mRNA expression was closely associated with cellular proliferation in normal fibroblasts or T lymphocytes and renal cell carcinoma cell lines. Collectively, NS expression widely occurs in normal and malignant renal tissues, and is likely a proliferation marker rather than a unique regulator of cell proliferation and survival in stem and cancer cells.

Figure 1

Nucleostemin expression in normal and malignant renal tissues and other types of normal human cells. (A) Nucleostemin mRNA (left panel) and protein (right panel) expression in ccRCC cell lines. Lane 1: A498 cells; 2: TK10; 3: KRY/C, and 4: Caki2. (B) and (C) NS and c-MYC mRNA expression in ccRCC samples and their adjacent normal renal tissues. (D) Nucleostemin mRNA expression in normal human fibroblasts, T lymphocytes, and A498 cells and relationship with cell proliferation statuses. Lanes 1 and 2: normal fibroblasts at senescence and at early passage, respectively. Lanes 3 and 4: normal resting and activated T lymphocytes, respectively. Lane 5: ccRCC A498 cells with serum-starvation for 72 h. Lane 6: A498 cells undergoing 72 h serum-starvation were re-fed with 20% serum for 24 h.

Figure 2

Immunohistochemical analyses for NS protein expression in tumour specimens derived from patients with ccRCC. Representative positive (A) and negative (B) stainings are shown.