PHLPP2 (PH domain leucine-rich repeat protein phosphatase 2)

2009-06-01   Audrey K ONeill , Alexandra C Newton 

Department of Pharmacology, University of California San Diego, 9500 Gilman Dr., Mail Code 0721, La Jolla, CA 92093, USA

Identity

HGNC
LOCATION
16q22.2
LOCUSID
ALIAS
PHLPPL,PPM3B
FUSION GENES

DNA/RNA

Atlas Image
Genomic organization of the PHLPP2 transcripts. Exons are represented by boxes, and position along chromosome 16 is indicated by the scale bar at the top.

Description

The gene for PHLPP2 is located at 16q22.3 and spans approximately 70 kb. The most recent version of the Ensembl database predicts four splice variants of PHLPP2, whose sizes range from 69.8 to 73.9 kb (see diagram).

Transcription

The predicted PHLPP2 transcripts have between 2877 and 7919 bp. Three of these predicted variants have 18 exons; the 7718 bp variant has only 17 exons. All of the variants have similar exon structures; only exon 1 and exon 7 (which is missing in the 7718 bp variant) differ. Of these putative transcripts, only the largest of these transcripts (labeled "PHLPP2" in the diagram) has been cloned and characterized.

Proteins

Atlas Image
PHLPP2 protein structure.

Description

Like the related isoform PHLPP1beta, the PHLPP2 protein contains a Ras association (RA) domain, a pleckstrin homology (PH) domain, a series of leucine-rich repeats (LRR), a PP2C phosphatase domain, and a C-terminal PDZ (post synaptic density protein [PSD95], Drosophila disc large tumor suppressor [DlgA], and zonula occludens-1 protein [zo-1]) binding motif. The characterized PHLPP1 protein has 1323 amino acids and a predicted molecular weight of approximately 147 kDa. Of the uncharacterized shorter transcripts, the longer (1256 aa) variant has a similar structure, while the two shorter variants (792 and 956 amino acids respectively) lack the RA and PH domains.

Expression

PHLPP2 is expressed in many human cancer cell lines and in all mouse tissues examined so far.

Localisation

PHLPP2 appears to be predominantly expressed in the cytosolic and nuclear fractions.

Function

PHLPP2, like PHLPP1, dephosphorylates Akt and conventional/novel protein kinase C (PKC) isoforms at their hydrophobic motifs (HM). Both kinases are regulated by phosphorylation at this site, which corresponds to serine 473 in Akt1 and serine 660 in PKCbetaII. HM motif phosphorylation of Akt occurs under agonist-stimulated conditions and allows full activation of the kinase. Phosphorylation of PKCs HM motif, on the other hand, is constitutive and regulates PKC stability. HM dephosphorylation by PHLPP renders PKC susceptible to dephosphorylation at two other important regulatory sites on the kinase (the activation loop and the turn motif). The fully-dephosphorylated form of PKC is shunted to the detergent-insoluble pellet and degraded. Thus, PHLPP functions to decrease Akts activity and PKCs stability, effectively dowregulating both kinases.

While PHLPP2 and its family member PHLPP1 have similar functions, their specificity for Akt isoforms differs. PHLPP1 preferentially binds and dephosphorylates Akt2 and Akt3, resulting in decreased phosphorylation of a set of Akt targets that includes GSK-3beta, TSC2, and FoxO, as well as HDM2 and GSK3a. PHLPP2, on the other hand, binds and dephosphorylates Akt1 and Akt3, resulting in downregulation of an overlapping yet distinct set of downstream targets: GSK-3beta, TSC2, and FoxO, as well as TSC2 and p27.

PHLPP2 regulates cellular survival and proliferation, partially by regulating Akt. PHLPP2 overexpression increases apoptosis in cancer cell lines under low serum conditions; this effect is partially blocked by overexpressing an Akt mutant that is resistant to dephosphorylation by PHLPP. Conversely, siRNA-mediated knockdown of PHLPP2 decreases basal and etoposide-stimulated apoptosis and increases cellular proliferation.

PHLPP2 may also be involved in cAMP signaling to Akt. PHLPP2 binds adenylyl cyclase type 6 in cardiac myocytes, and treatments that raise cAMP levels decrease Akt HM phosphorylation, possibly through activation of PHLPP.

Homology

PHLPP is a highly conserved phosphatase; its earliest orthologue is the yeast protein CYR1. In addition to a PP2C phosphatase domain, a leucine-rich repeat, and a Ras association domain, CYR1 contains an adenylate cyclase domain near its C terminus. Though invertebrates have only one PHLPP gene, most vertebrates have genes for both PHLPP1 and PHLPP2.

Mutations

Somatic

A common single nucleotide polymorphism (SNP) in the PP2C phosphatase domain of PHLPP2 may be involved in breast cancer progression. This SNP, a T->C nucleotide change at base pair position 3047, results in a Leu->Ser amino acid change at position 1016 in the PHLPP2 protein. Heterozygosity at this position is present in approximately 30% of the population, although Ser/Ser homozygosity has not yet been observed.

The L1016S variant of PHLPP2 may be involved in breast cancer. Although most breast cancer cell lines are homozygous for the Leucine allele, some are homozygous for the Serine allele. In addition, the normal breast cell line Hs578Bst is heterozygous (Leu/Ser) at position 1016, while its pair-matched tumor cell line Hs578t has only the Serine allele, suggesting that the gene has undergone loss of heterozygosity in this tumor. Similar results were obtained upon comparing normal and tumor tissues from breast cancer patients who are heterozygous at position 1016. High-grade breast tumors from some of these patients exhibited loss of the Leucine allele, but no tumors exhibited loss of the Serine allele. Further characterization of the L1016S mutant has revealed that its phosphatase activity (as measured by activity toward Akt) and its ability to promote apoptosis are defective. Moreover, siRNA-mediated knockdown of PHLPP2 in Ser/Ser breast cancer cell lines has no effect on Akt phosphorylation or PKCalpha levels, while knocking down PHLPP2 in cell lines with at least one Leucine allele increases Akt phosphorylation and PKCalpha levels. All in all, the data indicate that the version of PHLPP2 with Serine at position 1016 is less functional towards Akt and PKC than the wildtype version, and that loss of the wildtype allele in heterozygous (Leu/Ser) breast cancer patients may be involved in the progression of breast cancer.

Implicated in

Entity name
Various cancer
Cytogenetics
16q22.3, the chromosomal locus containing PHLPP2, commonly undergoes loss of heterozygosity in breast and ovarian cancers, Wilms tumors, prostate cancer and hepatocellular carcinomas.
Oncogenesis
siRNA-mediated reduction of PHLPP2 in breast cancer cell lines results in decreased apoptosis and increased proliferation, suggesting that PHLPP2 may act as a tumor suppressor. In addition, wildtype PHLPP2 may be lost in breast tumors with a less-functional PHLPP2 (PHLPP2 L1016S; see "Mutations" section), resulting in impaired Akt dephosphorylation and accelerating tumor development.
Entity name
Colorectal cancer
Oncogenesis
Overexpression of PHLPP1 or PHLPP2 in the human colon cancer cell lines HCT-116 and HT29 causes decreased expression of PKC and decreased phosphorylation of Akt. Cells overexpressing PHLPP exhibit decreased proliferation and were less able to induce tumors in nude mice. Conversely, DLD1 cells, which express high levels of PHLPP, respond to PHLPP1 or PHLPP2 knockdown with increased Akt phosphorylation, PKC stability, and proliferation.
Oncogenesis
PHLPP mRNA levels may be decreased in chronic myelogenous leukemia (CML). Bcr-Abl, the fusion protein responsible for CML, downregulates PHLPP1 and PHLPP2 mRNA levels; decreasing PHLPP levels interferes with the efficacy of Bcr-Abl inihibitors, including Gleevec, in CML cell lines.

Bibliography

Pubmed IDLast YearTitleAuthors
193248702009Common polymorphism in the phosphatase PHLPP2 results in reduced regulation of Akt and protein kinase C.Brognard J et al
185112902008PHLiPPing the switch on Akt and protein kinase C signaling.Brognard J et al
194507232009Activation of PH-domain leucine-rich protein phosphatase 2 (PHLPP2) by agonist stimulation in cardiac myocytes expressing adenylyl cyclase type 6.Gao MH et al
181624662008The phosphatase PHLPP controls the cellular levels of protein kinase C.Gao T et al
192616082009Depletion of Pleckstrin homology domain leucine-rich repeat protein phosphatases 1 and 2 by Bcr-Abl promotes chronic myelogenous leukemia cell proliferation through continuous phosphorylation of Akt isoforms.Hirano I et al
190793412009Loss of PHLPP expression in colon cancer: role in proliferation and tumorigenesis.Liu J et al
173862582007PHLPPing it off: phosphatases get in the Akt.Mendoza MC et al

Other Information

Locus ID:

NCBI: 23035
MIM: 611066
HGNC: 29149
Ensembl: ENSG00000040199

Variants:

dbSNP: 23035
ClinVar: 23035
TCGA: ENSG00000040199
COSMIC: PHLPP2

RNA/Proteins

Gene IDTranscript IDUniprot
ENSG00000040199ENST00000393524Q6ZVD8
ENSG00000040199ENST00000564884H3BS75
ENSG00000040199ENST00000567016H3BMS5
ENSG00000040199ENST00000568004I3L187
ENSG00000040199ENST00000568954Q6ZVD8

Expression (GTEx)

0
5
10
15
20

Pathways

PathwaySourceExternal ID
PI3K-Akt signaling pathwayKEGGhsa04151
PI3K-Akt signaling pathwayKEGGko04151
Immune SystemREACTOMER-HSA-168256
Adaptive Immune SystemREACTOMER-HSA-1280218
Signaling by the B Cell Receptor (BCR)REACTOMER-HSA-983705
Downstream signaling events of B Cell Receptor (BCR)REACTOMER-HSA-1168372
PIP3 activates AKT signalingREACTOMER-HSA-1257604
Negative regulation of the PI3K/AKT networkREACTOMER-HSA-199418
Innate Immune SystemREACTOMER-HSA-168249
DAP12 interactionsREACTOMER-HSA-2172127
DAP12 signalingREACTOMER-HSA-2424491
Fc epsilon receptor (FCERI) signalingREACTOMER-HSA-2454202
Role of LAT2/NTAL/LAB on calcium mobilizationREACTOMER-HSA-2730905
Signal TransductionREACTOMER-HSA-162582
Signaling by EGFRREACTOMER-HSA-177929
GAB1 signalosomeREACTOMER-HSA-180292
Signalling by NGFREACTOMER-HSA-166520
NGF signalling via TRKA from the plasma membraneREACTOMER-HSA-187037
PI3K/AKT activationREACTOMER-HSA-198203
Signaling by PDGFREACTOMER-HSA-186797
Downstream signal transductionREACTOMER-HSA-186763
Signaling by SCF-KITREACTOMER-HSA-1433557

Protein levels (Protein atlas)

Not detected
Low
Medium
High

References

Pubmed IDYearTitleCitations
238562472013miR-205 targets PTEN and PHLPP2 to augment AKT signaling and drive malignant phenotypes in non-small cell lung cancer.77
203796142010Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score.62
205134272010Mst1 is an interacting protein that mediates PHLPPs' induced apoptosis.54
238463362013microRNA-224 promotes cell proliferation and tumor growth in human colorectal cancer by repressing PHLPP1 and PHLPP2.49
219864992011PHLPP-mediated dephosphorylation of S6K1 inhibits protein translation and cell growth.32
249457312014MicroRNA-141 promotes the proliferation of non-small cell lung cancer cells by regulating expression of PHLPP1 and PHLPP2.29
279136772016PHLPPing through history: a decade in the life of PHLPP phosphatases.23
259773412015PHLPP2 Downregulation Contributes to Lung Carcinogenesis Following B[a]P/B[a]PDE Exposure.22
258889502015Mir-135a enhances cellular proliferation through post-transcriptionally regulating PHLPP2 and FOXO1 in human bladder cancer.21
193248702009Common polymorphism in the phosphatase PHLPP2 results in reduced regulation of Akt and protein kinase C.18

Citation

Audrey K ONeill ; Alexandra C Newton

PHLPP2 (PH domain leucine-rich repeat protein phosphatase 2)

Atlas Genet Cytogenet Oncol Haematol. 2009-06-01

Online version: http://atlasgeneticsoncology.org/gene/44546/phlpp2