Characterization and cell cycle regulation of the related human telomeric proteins Pin2 and TRF1 suggest a role in mitosis

Abstract

Telomeres are essential for preserving chromosome integrity during the cell cycle and have been specifically implicated in mitotic progression, but little is known about the signaling molecule(s) involved. The human telomeric repeat binding factor protein (TRF1) is shown to be important in regulating telomere length. However, nothing is known about its function and regulation during the cell cycle. The sequence of PIN2, one of three human genes (PIN1-3) we previously cloned whose products interact with the Aspergillus NIMA cell cycle regulatory protein kinase, reveals that it encodes a protein that is identical in sequence to TRF1 apart from an internal deletion of 20 amino acids; Pin2 and TRF1 may be derived from the same gene, PIN2͞TRF1. However, in the cell Pin2 was found to be the major expressed product and to form homo-and heterodimers with TRF1; both dimers were localized at telomeres. Pin2 directly bound the human telomeric repeat DNA in vitro, and was localized to all telomeres uniformly in telomerase-positive cells. In contrast, in several cell lines that contain barely detectable telomerase activity, Pin2 was highly concentrated at only a few telomeres. Interestingly, the protein level of Pin2 was highly regulated during the cell cycle, being strikingly increased in G2؉M and decreased in G1 cells. Moreover, overexpression of Pin2 resulted in an accumulation of HeLa cells in G2؉M. These results indicate that Pin2 is the major human telomeric protein and is highly regulated during the cell cycle, with a possible role in mitosis. The results also suggest that Pin2͞TRF1 may connect mitotic control to the telomere regulatory machinery whose deregulation has been implicated in cancer and aging.

Serine/threonine phosphorylation in cytokine signal transduction

“…[117][118][119][120][121][122] Dr Kun Ping Lu (Harvard University, Boston, MA, USA) described techniques to isolate the Pin genes encoding these proteins and discussed how these low molecular weight proteins belong to a large multi-gene family. Pin proteins are peptidyl-prolyl cis/trans isomerases (PPIase).…”

Telomeric protein Pin2/TRF1 induces mitotic entry and apoptosis in cells with short telomeres and is down-regulated in human breast tumors

“…Transfected living cells were monitored over time and ®xed at various time points. The indexes of interphase, mitotic and apoptotic cells were determined after staining the cells with the DNA-binding dye DAPI or the mitosis-speci®c monoclonal antibody MPM-2, as described (Lu and Hunter, 1995;Shen et al, 1997). The apoptosis rate was determined by counting about 300 ± 400 GFP-positive cells.…”

“…TRF1 and Pin2 are likely two alternatively spliced isoforms of the same gene PIN2/ TRF1, as suggested by Young et al (1997). For clarity, we will here use Pin2 for the 20 amino acid deletion isoform and TRF1 for the 20 amino acid containing isoform, as they were originally identi®ed (Chong et al, 1995;Shen et al 1997), and will refer to the endogenous Pin2 and TRF1 proteins as Pin2/TRF1 since it is di cult to physically or functionally separate these isoforms at the present time. However, we have shown that Pin2 is 5 ± 10-fold more abundant than TRF1 in the cells and the expression level of Pin2/ TRF1 is tightly regulated during the cell cycle .…”

Molecular cloning and chromosomal localization of Chinese hamster telomeric protein chTRF1. Its potential role in chromosomal instability

“…We were interested to determine if Chinese hamster cells have genes that express telomere repeat binding factors and whether they are seen at chromosome ends. Recently, human and mouse telomere binding proteins (TRF1, TRF2 and PIN2) have been identi®ed (Bilaud et al, 1996(Bilaud et al, , 1997Broccoli et al, 1997a,b;Shen et al, 1997;Chong et al, 1995). The TRF1 gene has been implicated in the regulation of telomere length (van Steensel and de Lange, 1997).…”

“…Mammalian telomeres contain long arrays of TTAGGG repeats that are bound with specialized protein complexes and have several functions (Moyzis et al, 1988;Meyne et al, 1989;Zakian, 1996;Greider, 1996). Three telomere binding proteins namely, TRF1, TRF2 and PIN2 have been identi®ed (Bilaud et al, 1996(Bilaud et al, , 1997Broccoli et al, 1997a,b;Shen et al, 1997;Chong et al, 1995, Zhong et al, 1992. They have DNA binding properties with TTAGGG repeats in vitro irrespective of the presence of a DNA terminus, properties which are consistent with its presence along the ends of chromosomes.…”