Protein phosphatase PP4 is overexpressed in human breast and lung tumors

Dear Editor, Reversible protein phosphorylation by kinases and phosphatases is one of the most common mechanisms in controlling most, if not all, cellular processes [ 1 ]. Dephos- phorylation of serine/threonine residues is regulated by two distinct groups of functionally diverse serine/threonine protein phosphatases, the PPM family （which includes PP2C） and the PPP family, which includes the type 1 （PP1） and the type 2A （PP2A, PP2B, PP3, PP4, PP5, PP6, and PP7） protein phosphatases. Members of the type 2A group ofphosphatases （PP2A, PP4, and PP6） are the most closely related in sequence. They are sensitive to inhibition by low doses of okadaic acid （OA） or fostriecin, which distinguishes them from PP 1 [ 1 ]. The regulation and function of PP2A have been thoroughly investigated. PP2A is composed of a core complex containing the catalytic subunit （C） and the scaffold subunit （A）, which interacts with a wide variety of regulatory subunits and interacting proteins that target the AC core dimer to specific substrates and subcellular locations [ 1 ]. The assembly of many different types of heterotrimeric holoenzymes accounts for the ability of PP2A, and, possibly, PP4 and PP6, to regulate a wide range of biological orocesses.

Role of Ppt1 in multiple stress responses in Candida albicans

To study the function of CaPpt1,we deleted PPT1 gene from the Candida albicans genome by sequentially replacing the entire coding region with the selectable markers ARG4 and HIS1.The results showed that the deletion of Ppt1 did not affect the hyphal formation of C.albicans under serum induction and caused enhanced sensitivity to DNA damage,Calcofluor white and saltinduced stress.We also found that Ppt1 was not required for the phenotypic response of cells treated with the genotoxins,methylmethane sulfonate and hydroxyurea.Flow cytometric analyses indicated that ppt1D cells and wild-type cells showed similar G2/M arrest profiles when exposed to DNA damage stress.Ppt1 was not required for the activation of the DNA damage response pathway,as indicated by normal phosphorylation of Rad53 and Rfa2 in ppt1D cells under DNA damage stress.We suggest that Ppt1 plays important roles in response to various stress conditions in C.albicans.

Subcellular localization of PS1 based on PS1/GFP fusing protein

Mutations in presenilin 1(PS1)gene are closely associated with the early onset of familial Alzheimer’s disease(EOFAD).The fusion genes,GFP-PS1(recombinant plasmid pEGFP-C1-PS1)and PS1-GFP(recombinant plasmid pEGFP-N2-PS1)were constructed to study the subcellular localization of PS1 holoprotein.Recombinant plasmids were transiently transfected into two cell lines,HEK293 and CHO,respectively,using the green fluorescence from GFP(green fluorescence protein)as the PS1 localization signal.Then,we observed green fluorescence with a SPOT II(Olympus,BH2)and CONFOCAL microscope(Olympus,FV300)under 488 nm.The results show that PS1 located on the nuclear envelope.A few can be found on the cellular membrane and in the cytosol in a non-homogeneous distribution.