CSB428H1F Article #4: Martin-Belmonte et al. PTEN control PIP and Cdc42
PTEN localizes to apical PM to increase PI45P2 by decreasing levels of PI345P3. Ectopic PI45P2 at
basolateral surface cause apical proteins to relocate to basolateral side.
Annexin 2 (Anx2) binds PI45P2 and is recruited to apical surface to bind Cdc42, which recruits
aPKC. Loss of PTEN, Anx2, Cdc42 or aPKC prevents apical surface and lumen formation.
Madin-Darby-canine kidney (MDCK) cells embedded in gels for cysts with lumen.
PI45P2 and PTEN localize to AP PM
PH domain of PLC fused to GFP (PHD-GFP) detects PI45P2. PHD-GFP localized mainly to AP PM
and little bit in BL PM, similar to that of actin.
PH-Akt-GFP detects both PI34P2 and PI345P2 which are enriched at BL PM.
Before lumen formation, PI345P3 and PI45P2 localized to cell-cell and cell-ECM contacts. During
lumen formation, PI45P2 became confined to AP PM, but PI345P3 became exclusive to BL.
In early stages, GFP-PTEN is localized to the cytoplasm but later is localized to AP PM and
overlapped with PI45P2 and cell-cell junctions.
Loss of PTEN disrupts PI45P2
SiRNA treated cells formed multiple small lumen with decreased actin levels but BL marker -cat
PTEN inhibitor bpV(pic) also inhibited lumen formation and both PI345P3 and PI45P2 became
homogenous in PM resulting in cyst with no lumen.
Therefore PTEN is required for apical enrichment of PI45P2 and AP PM lumen formation.
Exogenous PI45P2 localize AP protein to BL
Exogenous PI45P2 to BL PM induced shrinkage of lumen and patchy redistribution of PHD-GFP to
BL surface. AP marker gp135, ezrin, ZO-1 also re-localized to BL PM.
Lateral markers p58 and PI345P3 ended up in puncta at periphery and disappeared from basal
region. This shows ectopic PI45P2 to BL PM is sufficient to relocalize AP and TJ to periphery.