PLEKHA7 modulates epithelial tight junction barrier function

Abstract

PLEKHA7 is a recently identified protein of the epithelial zonula adhaerens (ZA), and is part of a protein complex that stabilizes the ZA, by linking it to microtubules. Since the ZA is important in the assembly and disassembly of tight junctions (TJ), we asked whether PLEKHA7 is involved in modulating epithelial TJ barrier function. We generated clonal MDCK cell lines in which one of four different constructs of PLEKHA7 was inducibly expressed. All constructs were localized at junctions, but constructs lacking the C-terminal region were also distributed diffusely in the cytoplasm. Inducible expression of PLEKHA7 constructs did not affect the expression and localization of TJ proteins, the steady-state value of transepithelial resistance (TER), the development of TER during the calcium switch, and the flux of large molecules across confluent monolayers. In contrast, expression of three out of four constructs resulted both in enhanced recruitment of E-cadherin and associated proteins at the apical ZA and at lateral puncta adherentia (PA), a decreased TER at 18 h after assembly at normal calcium, and an attenuation in the fall in TER after extracellular calcium removal. This latter effect was inhibited when cells were treated with nocodazole. Immunoprecipitation analysis showed that PLEKHA7 forms a complex with the cytoplasmic TJ proteins ZO-1 and cingulin, and this association does not depend on the integrity of microtubules. These results suggest that PLEKHA7 modulates the dynamics of assembly and disassembly of the TJ barrier, through E-cadherin protein complex- and microtubule-dependent mechanisms.

Cell‐specific diversity in the expression and organization of cytoplasmic plaque proteins of apical junctions

“…6C). The TJ markers ZO-1 and cingulin were detected in PLEKHA7 IPs-not only in mCCD cells, supporting our previous observations in MDCK cells 85 -but also in meEC cells (Fig. 6A).…”

Distinct E-cadherin-based complexes regulate cell behaviour through miRNA processing or Src and p120 catenin activity

“…Therefore, the growth-suppressing or growth-promoting functions of p120 and E-cadherin are fine-tuned by binding to PLEKHA7. Further interactions of PLEKHA7 with paracingulin 54 , afadin 55 , ZO-1 and cingulin 56 , may also play a role in PLEKHA7 function, although the interaction with p120 is essential for modulating cell behaviour by regulating miRNA processing.…”

The Expression of the Zonula Adhaerens Protein PLEKHA7 Is Strongly Decreased in High Grade Ductal and Lobular Breast Carcinomas

“…This may in turn be subjected to regulatory control mechanisms, for example through associations with other proteins, which may also control stability. With this in mind, we examined the relationships between the expression and localization of PLEKHA7 with that of the zonular tight junction proteins ZO-1 and cingulin, and the adherens junction proteins E-cadherin and p120ctn, with which PLEKHA7 forms complexes [ 13 , 17 ]. We found that when PLEKHA7 was expressed, its subcellular localization was very similar to, although not precisely overlapping with, that of ZO-1 and cingulin, at apical zonulae .…”

“…PLEKHA7 interacts not only with p120ctn and paracingulin, but also with the adherens junction protein afadin [ 16 ] and the microtubule minus-end capping protein nezha [ 13 ]. In addition, it forms a complex with the TJ proteins cingulin and ZO-1 [ 17 ]. Importantly, unlike E-cadherin and associated catenins (p120ctn, α-catenin and β-catenin), but similarly to paracingulin and afadin, PLEKHA7 is not distributed along lateral contacts ( puncta adhaerentia ) of polarized epithelial cells, but exclusively at circumferential apical zonulae adhaerentes (ZA) [ 14 ].…”