Specific interaction between lens MIP/Aquaporin-0 and two members of the γ-crystallin family

Purpose: Major Intrinsic Protein (MIP)/Aquaporin 0 is required for lens transparency and is specifically expressed in lens fiber cell membranes. We have demonstrated previously that in the rat lens MIP interacts specifically with γE-crystallin, resulting in its recruitment to the plasma membrane. Our goal was to examine the interaction or lack of interaction between MIP and all members of the γ-crystallin family and to provide evidence for a physiological role these interactions may play in γ-crystallin or MIP function. Methods: Full length MIP was expressed as untagged, enhanced green fluorescent protein (EGFP) tagged, or myc tagged proteins. Members of the γ-crystallin family were expressed as red fluorescent protein (HcRed) tagged proteins in the rabbit kidney epithelial cell line RK13. Co-localization of tagged proteins was analyzed by confocal fluorescence microscopy. Results: Confocal fluorescence microscopy demonstrated that γE- and γF-crystallin co-localize specifically with full length MIP in mammalian cells while other γ-crystallins, including γA-, γB-, γC-, γD-, and γS-crystallin do not. As a result of this interaction, either γE- or γF-crystallin was recruited to the plasma membrane from the cytoplasm. MIP does not interact with the Elo mutant of γE-crystallin, which has been linked to a dominant cataract phenotype in mice. Conclusions: These experiments demonstrate that MIP interacts selectively with γE- and γF-crystallin, and not with other γ-crystallins. This raises the possibility of MIP playing a structural role in the organization of γ-crystallins in rodent lens fibers and/or that γE- and γF-crystallin may have a specific role in MIP function in the rodent lens.