PTEN enters the nucleus by diffusion

Abstract

Despite much evidence for phosphatidylinositol phosphate (PIP)-triggered signaling pathways in the nucleus, there is little understanding of how the levels and activities of these proteins are regulated. As a first step to elucidating this problem, we determined whether phosphatase and tensin homolog deleted on chromosome 10 (PTEN) enters the nucleus by passive diffusion or active transport. We expressed various PTEN fusion proteins in tsBN2, HeLa, LNCaP, and U87MG cells and determined that the largest PTEN fusion proteins showed little or no nuclear localization. Because diffusion through nuclear pores is limited to proteins of 60,000 Da or less, this suggests that nuclear translocation of PTEN occurs via diffusion. We examined PTEN mutants, seeking to identify a nuclear localization signal (NLS) for PTEN. Mutation of K13 and R14 decreased nuclear localization, but these amino acids do not appear to be part of an NLS. We used fluorescence recovery after photobleaching (FRAP) to demonstrate that GFP-PTEN can passively pass through nuclear pores. Diffusion in the cytoplasm is retarded for the PTEN mutants that show reduced nuclear localization. We conclude that PTEN enters the nucleus by diffusion. In addition, sequestration of PTEN in the cytoplasm likely limits PTEN nuclear translocation.

Nuclear Localization of PTEN Is Regulated by Ca2+ through a Tyrosil Phosphorylation–Independent Conformational Modification in Major Vault Protein

“…However, another group has recently reported that PTEN's nuclear entry is mediated by passive diffusion (21). To further confirm our conclusion, the present study examined the effect of siRNAmediated silencing of MVP on PTEN subcellular localization.…”

Nuclear PTEN: a tale of many tails

“…Interestingly, PTEN was found in this study to interact with importin a and b proteins, although such interaction was also observed in the NLS-like mutants that displayed defective nuclear accumulation. A second model of PTEN nuclear entry has been proposed by Liu et al 12 Using PTEN fusion proteins of variable size, the authors of this study noticed that large PTEN fusion proteins (4100 kDa) did not show nuclear localization, whereas PTEN alone (47 kDa) or a GFP-PTEN fusion protein (74 kDa) were present in both the cytoplasm and the nucleus. Also, nuclear localization of GFP-PTEN was not altered in tsBN2 cells, which show defective Ran-dependent nuclear transport at a nonpermissive temperature.…”

“…However, the N-terminal region of PTEN, when fused to chicken PK, did not facilitate the nuclear accumulation of this protein. Also of interest, Liu et al 12 found a fast mobility of GFP-PTEN into the nucleus, whereas in the cytoplasm the movement of GFP-PTEN was much more restricted, suggesting the tethering of PTEN to cytoplasmic structures which could prevent nuclear translocation. A third model to explain the nuclear accumulation of PTEN has been proposed more recently by us.…”

“…On the other hand, if proteolytic cleavage or mutation of key residues occurs, this transition would be irreversible. Alternative models of PTEN nuclear entry, as those proposed by Chung et al 11 and Liu et al, 12 could coexist that finely tune the amount of PTEN in the nucleus under particular cell growth conditions. Classical CRM1-dependent, leptomycin B-sensitive nuclear export, does not seem to be involved in the control of PTEN nuclear/cytoplasmic distribution.…”

Urocanic acid-modified chitosan-mediated PTEN delivery via aerosol suppressed lung tumorigenesis in K-rasLA1 mice

“…32 In the present study, we observed the decreased expressions of cyclin D3, CDK4 and PCNA, and increased expressions of cell cycle inhibitor p27 and p21 in the PTEN delivery lungs (Figure 4). Several recent studies 33,34 have reported that PTEN entered into nucleus through passive diffusion is prominent in the G 0 /G 1 segment of cell cycle. According to Freeman et al 26 and Su et al 35 p53 in the complex with PTEN inhibits cell cycle through increasing the CDK inhibitors such as p21 and p27.…”