Rat homolog of PinX1 is a nucleolar protein involved in the regulation of telomere length.
Human PinX1 involves in regulation of telomere length. Here, we describe the function of a rat homolog of PinX1. Rat PinX1 (rPinX1) was cloned from WB-F344, a rat hepatic stem-like epithelial cell. It encodes a protein of 331 amino acids with 70% homology to human PinX1 and 91% homology to mouse. Northern analysis revealed that rPinX1 is expressed in both somatic and germ tissues, most abundantly in heart, liver and testis. Co-localization with a nucleolar protein, fibrillarin, showed that rPinX1 resides in the nucleolus. Analysis of truncated mutants revealed that an internal K,E/D region seems to be important for nucleolar localization. A stable cell line expressing rPinX1 was established in NIH3T3, a mouse-transformed embryonic fibroblast cell line, and stable cells were subcultured for more than 150 population doublings. The growth of stable rPinX1 cells slowed down at late passages, and a fraction of these cells exhibited increased size and stained positively for senescence-associated beta-galactosidase. Overexpression of rPinX1 in NIH3T3 cells resulted in gradual telomere shortening over successive passages. However, the telomeric 3' overhang was not altered by PinX1 expression. This study demonstrates that a rat homolog of human PinX1 is a nucleolar protein, and that overexpression of rPinX1 induces cellular senescence and telomere shortening, but has no effect on 3' overhang length. The function of PinX1 in regulating telomere length is conserved in rodents, and this study may provide insight into the mechanism by which a nucleolar protein can regulate telomere length.
Oh
Bong-Kyeong
BK
Cancer Metastasis Research Center, Yonsei University College of Medicine, 120-752, Republic of Korea.
Yoon
So-Mi
SM
Lee
Chan-Hee
CH
Park
Young Nyun
YN
D000818:Animals; D018797:Cell Cycle Proteins; D002466:Cell Nucleolus / Q000378:metabolism; D002478:Cells, Cultured; D016922:Cellular Senescence; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D016615:Telomere / Q000648:ultrastructure*; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C440808:PINX1 protein, human; C523966:PinX1 protein, rat; D025521:Tumor Suppressor Proteins